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  • 1.
    Bastias, Elliot
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bundschuh, Mirco
    iES Landau, Institute for Environmental Sciences, University of Koblenz-Landau, Landau, Germany; Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Seasonal variation in the coupling of microbial activity and leaf litter decomposition in a boreal stream network2022In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 67, no 5, p. 812-827Article in journal (Refereed)
    Abstract [en]
    1. Most stream networks are characterised by spatial and temporal variability in the physico-chemical conditions that regulate microbial processing of particulate organic matter. How these patterns control the turnover of particulate organic matter via altered activity of leaf-associated microbes has rarely been studied in high-latitude landscapes, particularly throughout long (i.e., up to 6 months) ice- and snow-covered periods.
    2. We investigated development of fungal biomass, enzyme activity, microbial respiration, and birch leaf litter decomposition from autumn to early summer in 11 nested streams in a boreal catchment that encompass a gradient in wetland (mire) cover.
    3. We observed relatively low variability in decomposition rates across the network, despite differences in key physical and chemical variables (e.g. temperature, pH, and dissolved organic carbon [DOC] concentrations) over time and space.
    4. Microbial enzymatic activity and respiration were positively related to leaf litter decomposition rates during early stages of decomposition (i.e., up to c. 30% loss of initial ash-free dry mass). Thereafter, variation in microbial activity and respiration was decoupled from leaf litter mass loss, as enzymatic activity and respiration instead became positively related to DOC concentrations and upstream mire (wetland) cover among streams.
    5. Our results suggest that leaf-associated microbes increase their reliance on external sources of energy over time. This switch in resource use was more evident in streams with higher DOC concentration, which in boreal landscapes is largely determined by mire cover. Hence, variation in DOC concentration, linked to landscape configuration, or from intensified land use and climate change, could affect how different carbon sources are used by stream microbial communities, with consequences for overall carbon cycling in boreal headwaters.
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  • 2. Berggren, Martin
    et al.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Soares, Ana R. Alves
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Toward an ecologically meaningful view of resource stoichiometry in DOM-dominated aquatic systems2015In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 37, no 3, p. 489-499Article in journal (Refereed)
    Abstract [en]

    Research on nutrient controls of planktonic productivity tends to focus on a few standard fractions of inorganic or total nitrogen (N) and phosphorus (P). However, there is a wide range in the degree to which land-derived dissolved organic nutrients can be assimilated by biota. Thus, in systems where such fractions form a majority of the macronutrient resource pool, including many boreal inland waters and estuaries, our understanding of bacterio-and phytoplankton production dynamics remains limited. To adequately predict aquatic productivity in a changing environment, improved standard methods are needed for determining the sizes of active (bioavailable) pools of N, P and organic carbon (C). A synthesis of current knowledge suggests that variation in the C:N:P stoichiometry of bioavailable resources is associated with diverse processes that differentially influence the individual elements across space and time. Due to a generally increasing organic nutrient bioavailability from C to N to P, we hypothesize that the C:N and N:P of bulk resources often vastly overestimates the corresponding ratios of bioavailable resources. It is further proposed that basal planktonic production is regulated by variation in the source, magnitude and timing of terrestrial runoff, through processes that have so far been poorly described.

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  • 3.
    Berggren, Martin
    et al.
    Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
    Ye, Linlin
    Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden; School of Geographic Sciences, Nantong University, Nantong, China.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Verheijen, Hendricus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hensgens, Geert
    Department of Earth Sciences, Vrije Universiteit, Amsterdam, Netherlands.
    Nutrient limitation masks the dissolved organic matter composition effects on bacterial metabolism in unproductive freshwaters2023In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 68, no 9, p. 2059-2069Article in journal (Refereed)
    Abstract [en]

    Aquatic microbial responses to changes in the amount and composition of dissolved organic carbon (DOC) are of fundamental ecological and biogeochemical importance. Parallel factor (PARAFAC) analysis of excitation–emission fluorescence spectra is a common tool to characterize DOC, yet its ability to predict bacterial production (BP), bacterial respiration (BR), and bacterial growth efficiency (BGE) vary widely, potentially because inorganic nutrient limitation decouples microbial processes from their dependence on DOC composition. We used 28-d bioassays with water from 19 lakes, streams, and rivers in northern Sweden to test how much the links between bacterial metabolism and fluorescence PARAFAC components depend on experimental additions of inorganic nutrients. We found a significant interaction effect between nutrient addition and fluorescence on carbon-specific BP, and weak evidence for influence on BGE by the same interaction (p = 0.1), but no corresponding interaction effect on BR. A practical implication of this interaction was that fluorescence components could explain more than twice as much of the variability in carbon-specific BP (R2 = 0.90) and BGE (R2 = 0.70) after nitrogen and phosphorus addition, compared with control incubations. Our results suggest that an increased supply of labile DOC relative to ambient phosphorus and nitrogen induces gradually larger degrees of nutrient limitation of BP, which in turn decouple BP and BGE from fluorescence signals. Thus, while fluorescence does contain precise information about the degree to which DOC can support microbial processes, this information may be hidden in field studies due to nutrient limitation of bacterial metabolism.

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  • 4. Blackburn, M.
    et al.
    Ledesma, Jose L. J.
    Näsholm, Torgny
    Laudon, Hjalmar
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Evaluating hillslope and riparian contributions to dissolved nitrogen (N) export from a boreal forest catchment2017In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, no 2, p. 324-339Article in journal (Refereed)
    Abstract [en]

    Catchment science has long held that the chemistry of small streams reflects the landscapes they drain. However, understanding the contribution of different landscape units to stream chemistry remains a challenge which frequently limits our understanding of export dynamics. For limiting nutrients such as nitrogen (N), an implicit assumption is that the most spatially extensive landscape units (e.g., uplands) act as the primary sources to surface waters, while near-stream zones function more often as sinks. These assumptions, based largely on studies in high-gradient systems or in regions with elevated inputs of anthropogenic N, may not apply to low-gradient, nutrient-poor, and peat-rich catchments characteristic of many northern ecosystems. We quantified patterns of N mobilization along a hillslope transect in a northern boreal catchment to assess the extent to which organic matter-rich riparian soils regulate the flux of N to streams. Contrary to the prevailing view of riparian functioning, we found that near-stream, organic soils supported concentrations and fluxes of ammonium (NH4+) and dissolved organic nitrogen that were much higher than the contributing upslope forest soils. These results suggest that stream N chemistry is connected to N mobilization and mineralization within the riparian zone rather than the wider landscape. Results further suggest that water table fluctuation in near-surface riparian soils may promote elevated rates of net N mineralization in these landscapes.

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  • 5. Burrows, Ryan M.
    et al.
    Hotchkiss, Erin R.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    McKie, Brendan G.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nitrogen limitation of heterotrophic biofilms in boreal streams2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 7, p. 1237-1251Article in journal (Refereed)
    Abstract [en]

    Nutrient limitation of the biofilm is fundamental to stream ecosystem processes, as microbial activity shapes the biological availability and biogeochemical cycling of carbon and nutrients. We used nutrient-diffusing substrata (NDS) to investigate heterotrophic nutrient limitation of microbial respiration (MR) across 20 streams draining boreal landscapes in northern Sweden. We also explored variation in microbial biomass and community structure of biofilms that developed on NDS using phospholipid fatty acid (PLFA) biomarkers. Limitation was determined as a significant response of MR and biomass production on cellulose surfaces to enrichment with nitrogen (N), phosphorus (P) or N+P, relative to controls. Microbial respiration was N-limited, with an average 3.3-fold increase on N-amended NDS. Nitrogen limitation decreased, and control rates of MR increased, with greater background concentrations of inorganic N across the sites. In contrast to MR, microbial biomass was primarily N-limited but was greatest for the N+P NDS. Accordingly, differences in respiratory versus biomass responses to nutrient addition resulted in significantly greater biomass-specific MR on N-amended NDS compared to all other treatments. In addition, PLFA biomarkers indicated distinct microbial communities on N and N+P NDS compared to controls and/or P NDS. Greater MR and biomass, and the development of distinct microbial communities, when supplied with inorganic N suggest that factors which alter aquatic N loading during autumn may have important implications for ecosystem processes and the biogeochemistry of boreal streams and rivers. Our findings add to a growing body of evidence that the productivity of Fennoscandian boreal landscapes is constrained by N availability.

  • 6.
    Burrows, Ryan M.
    et al.
    School of Ecosystem and Forest Sciences, The University of Melbourne, Burnley Campus, Victoria, Richmond, Australia; Australian Rivers Institute, Griffith University, Brisbane, Australia.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fältström, Emma
    Environmental Technology and Management, Department of Management and Engineering, Linköping University, Sweden; Sweden Water Research AB, Lund, Sweden.
    Andersson, Jannika
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Interactive effects of light and nutrients on stream algal growth modified by forest management in boreal landscapes2021In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 492, article id 119212Article in journal (Refereed)
    Abstract [en]

    Boreal forests account for 30% of the world's total forest cover and in many places are subject to intensive forest management, which often involves complete removal of overstory vegetation by clear-cutting. However, we still do not fully understand how forest management affects aquatic ecosystems in these landscapes. Here we asked how forest management-induced changes in environmental conditions, such as incident light and nutrient availability, affect benthic algal growth and nutrient limitation in boreal headwater streams of northern Sweden. We answered this question using a combination of correlative and experimental approaches across a range of forested streams spanning a gradient of site (e.g. canopy openness and water chemistry) and catchment-level (e.g. age of forest regrowth) parameters, with variation among the study streams influenced by different forest management histories and underlying natural variation. We found that benthic algal growth in these forested streams was largely driven by local interactions between dissolved inorganic nitrogen (N) availability and incident light reaching benthic surfaces. Greater water temperature and shallower depths were also associated with greater algal growth. Although high dissolved organic carbon (DOC) concentrations often play a role in reducing light availability to autotrophs in boreal aquatic systems, it was not an important predictor of algal growth in small forested streams despite a large DOC concentration gradient (5 – 32 mg/L). Results from experimental nutrient additions supported the role of N as a key limiting nutrient, but also revealed both spatial and seasonal factors that modulate the effects of altered nutrient availability. Overall, our results suggest that differences in how light regimes and nutrient loading respond to forest management generate small-scale variation in the controls over stream primary productivity, which likely shift in relative importance at the time scale of a forest rotation (60 to 100 years).

  • 7. Burrows, Ryan M.
    et al.
    Laudon, Hjalmar
    McKie, Brendan G.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Seasonal resource limitation of heterotrophic biofilms in boreal streams2017In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, no 1, p. 164-176Article in journal (Refereed)
    Abstract [en]

    Unraveling the potentially shifting controls over microbial activity among habitats and across seasonal transitions is critical for understanding how freshwater ecosystems influence broader elemental cycles, and how these systems may respond to global changes. We used nutrient-diffusing substrates to investigate seasonal patterns and constraints on microbial activity of biofilms in streams draining distinct landscape features of the boreal biome (forests, mires, and lakes). Microbial respiration (MR) largely mirrored spatial and temporal variation in water temperature. However, limitation by labile carbon (C) was a constraint to microbial activity during ice-covered periods, when MR of control nutrient-diffusing substrates fell below rates predicted from stream temperature alone. Variation in C limitation among the study streams was reflective of putative organic C availability, with C limitation of biofilms weakest in the dissolved organic C (DOC)-rich, mire-outlet stream and greatest in the relatively DOC-poor, forest stream. Incidences of nutrient limitation were only observed during warmer months. Our study illustrates how variation in processes mediated by heterotrophic biofilms and seasonal shifts in resource limitation can emerge in a stream network draining a heterogeneous landscape. In addition, our results show that, for a large portion of the year, heterotrophic processes in boreal streams can be strongly limited by the availability of labile C, despite high DOC concentrations. Metabolic constraints to dissolved organic matter processing at near-freezing temperatures, coupled with hydrological controls over the delivery of more labile organic resources to streams (e.g., soil freezing and flooding), have potentially strong influences on the productivity of boreal streams.

  • 8.
    Cook, Elizabeth M.
    et al.
    School of Life Sciences, Arizona State University, AZ, Tempe, United States; Urban Systems Lab, Environmental Studies Department, The New School, NY, New York, United States.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Grimm, Nancy B.
    School of Life Sciences, Arizona State University, AZ, Tempe, United States; Julie Ann Wrigley Global Institute of Sustainability, Arizona State University, AZ, Tempe, United States.
    Hall, Sharon J.
    School of Life Sciences, Arizona State University, AZ, Tempe, United States; Julie Ann Wrigley Global Institute of Sustainability, Arizona State University, AZ, Tempe, United States.
    Mixed method approach to assess atmospheric nitrogen deposition in arid and semi-arid ecosystems2018In: Environmental Pollution, ISSN 0269-7491, E-ISSN 1873-6424, Vol. 239, p. 617-630Article in journal (Refereed)
    Abstract [en]

    Arid and semi-arid ecosystems (aridlands) cover a third of Earth's terrestrial surface and contain organisms that are sensitive to low level atmospheric pollutants. Atmospheric nitrogen (N) inputs to aridlands are likely to cause changes in plant community composition, fire frequency, and carbon cycling and storage. However, few studies have documented long-term rates of atmospheric N inputs in aridlands because dry deposition is technically difficult to quantify, and extensive sampling is needed to capture fluxes with spatially and temporally heterogeneous rainfall patterns. Here, we quantified long-term spatial and temporal patterns of inorganic N deposition in protected aridland ecosystems across an extensive urban-rural gradient using multiple sampling methods. We compared long-term rates of N deposition from ion-exchange resin (IER) collectors (bulk and throughfall, 2006-2015), wet-dry bucket collectors (2006-2015), and dry deposition from the inferential method using passive samplers (2010-2012). From mixed approaches with IER collectors and inferential methods, we determined that 7.2 ± 0.4 kgNha−1y−1 is deposited to protected Sonoran Desert within metropolitan Phoenix, Arizona and 6.1 ± 0.3 kgNha−1y−1 in nearby desert ecosystems. Regional scale models overestimated deposition rates for our sampling period by 60% and misidentified hot spots of deposition across the airshed. By contrast, the easy-deployment IER throughfall collectors showed minimal spatial variation across the urban-rural gradient and underestimated deposition fluxes by 54%, largely because of underestimated dry deposition in throughfall. However, seasonal sampling of the IER collectors over 10 years allowed us to capture significant seasonal variation in N deposition and the importance of precipitation timing. These results, derived from the longest, spatially and temporally explicit dataset in drylands, highlight the need for long-term, mixed methods to estimate atmospheric nutrient enrichment to aridlands in a rapidly changing world. Our findings highlight low rates of inorganic nitrogen deposition to protected Sonoran Desert ecosystems, the need for mixed methods, and the importance of season and timing of precipitation as primary drivers of atmospheric nutrient enrichment to aridland systems.

  • 9.
    Costello, David M.
    et al.
    Department of Biological Sciences, Kent State University, OH, Kent, United States; Environmental Science and Design Research Institute, Kent State University, OH, Kent, United States.
    Tiegs, Scott D.
    Department of Biological Sciences, Oakland University, MI, Rochester, United States.
    Boyero, Luz
    Department of Plant Biology and Ecology, University of the Basque Country, Bilbao, Spain; Ikerbasque, Bilbao, Spain.
    Canhoto, Cristina
    Department of Life Sciences, Centre for Functional Ecology, University of Coimbra, Coimbra, Portugal.
    Capps, Krista A.
    Odum School of Ecology, University of Georgia, GA, Athens, United States; Savannah River Ecology Laboratory, University of Georgia, GA, Athens, United States.
    Danger, Michael
    LIEC-CNRS, University of Lorraine, Metz, France.
    Frost, Paul C.
    Department of Biology, Trent University, ON, Peterborough, Canada.
    Gessner, Mark O.
    Department of Experimental Limnology, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Stechlin, Germany; Department of Ecology, Berlin Institute of Technology (TU Berlin), Berlin, Germany.
    Griffiths, Natalie A.
    Climate Change Science Institute and Environmental Sciences Division, Oak Ridge National Laboratory, TN, Oak Ridge, United States.
    Halvorson, Halvor M.
    Department of Biology, University of Central Arkansas, AR, Conway, United States.
    Kuehn, Kevin A.
    School of Biological, Environmental and Earth Sciences, University of Southern Mississippi, MS, Hattiesburg, United States.
    Marcarelli, Amy M.
    Department of Biological Sciences, Michigan Technological University, MI, Houghton, United States.
    Royer, Todd V.
    O'Neill School of Public and Environmental Affairs, Indiana University, IN, Bloomington, United States.
    Mathie, Devan M.
    Department of Biological Sciences, Kent State University, OH, Kent, United States.
    Albariño, Ricardo J.
    INIBIOMA, Universidad Nacional Comahue (CONICET), San Carlos de Bariloche, Argentina.
    Arango, Clay P.
    Department of Biological Sciences, Central Washington University, WA, Ellensburg, United States.
    Aroviita, Jukka
    Freshwater Centre, Finnish Environment Institute (SYKE), Helsinki, Finland.
    Baxter, Colden V.
    Department of Biological Sciences, Stream Ecology Center, Idaho State University, ID, Pocatello, United States.
    Bellinger, Brent J.
    Watershed Protection Department, City of Austin, TX, Austin, United States.
    Bruder, Andreas
    Institute of Microbiology, University of Applied Sciences and Arts of Southern Switzerland, Canobbio, Switzerland.
    Burdon, Francis J.
    Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
    Callisto, Marcos
    Genetics, Ecology and Evolution Department of Institute of Biological Sciences, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
    Camacho, Antonio
    Cavanilles Institute for Biodiversity and Evolutionary Biology, University of Valencia, Paterna, Spain.
    Colas, Fanny
    ENTPE, Université Claude Bernard Lyon 1, Lyon, France.
    Cornut, Julien
    Institute of Earth Sciences, University of Applied Sciences and Arts of Southern Switzerland, Manno, Switzerland.
    Crespo-Pérez, Verónica
    Limnology Laboratory, Zoology Museum QCAZ-I, Quito, Ecuador; School of Biological Sciences, Pontifical Catholic University of Ecuador, Quito, Ecuador.
    Cross, Wyatt F.
    Department of Ecology, Montana State University, MT, Bozeman, United States.
    Derry, Alison M.
    Department of Biological Sciences, Université Du Québec à Montréal, QC, Montreal, Canada.
    Douglas, Michael M.
    School of Biological Sciences, University of Western Australia, WA, Perth, Australia.
    Elosegi, Arturo
    Department of Plant Biology and Ecology, University of the Basque Country, Bilbao, Spain.
    de Eyto, Elvira
    Marine Institute, Galway, Ireland.
    Ferreira, Verónica
    Department of Life Sciences, Marine and Environmental Sciences Centre (MARE), University of Coimbra, Coimbra, Portugal.
    Ferriol, Carmen
    Department of Microbiology and Ecology, University of Valencia, Valencia, Spain.
    Fleituch, Tadeusz
    Institute of Nature Conservation, Polish Academy of Sciences, Kraków, Poland.
    Follstad Shah, Jennifer J.
    Department of Geography, University of Utah, UT, Salt Lake City, United States.
    Frainer, André
    Department of Arctic and Marine Biology, UiT the Arctic University of Norway, Tromsø, Norway; Norwegian Institute for Nature Research (NINA), University of Tromsø, Tromsø, Norway.
    Garcia, Erica A.
    Research Institute for the Environment and Livelihoods, Charles Darwin University, NT, Casuarina, Australia.
    García, Liliana
    Department of Ecology and Animal Biology, University of Vigo, Vigo, Spain.
    García, Pavel E.
    Escuela de Biología, Universidad de San Carlos de Guatemala, Guatamala City, Guatemala; Ecology and Evolution Program, University of Montana, MT, Missoula, United States.
    Giling, Darren P.
    Department of Experimental Limnology, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Stechlin, Germany; Centre for Applied Water Science, Institute for Applied Ecology, University of Canberra, ACT, Canberra, Australia; CSIRO Land and Water, ACT, Canberra, Australia.
    Gonzales-Pomar, R. Karina
    Instituto de Ecología, Univerdiad Mayor de San Andrés, La Paz, Bolivia.
    Graça, Manuel A. S.
    Department of Life Sciences, Marine and Environmental Sciences Centre (MARE), University of Coimbra, Coimbra, Portugal.
    Grossart, Hans-Peter
    Department of Experimental Limnology, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Stechlin, Germany; Institute for Biochemistry and Biology, Potsdam University, Potsdam, Germany.
    Guérold, François
    LIEC-CNRS, University of Lorraine, Metz, France.
    Hepp, Luiz U.
    Universidade Federal de Mato Grosso do Sul, Campus Três Lagoas, Campo Grande, Brazil.
    Higgins, Scott N.
    International Institute for Sustainable Development, MB, Winnipeg, Canada.
    Hishi, Takuo
    Shiiba Research Forest, Kyushu University, Kyushu, Japan.
    Iñiguez-Armijos, Carlos
    Departamento de Ciencias Biológicas, Universidad Técnica Particular de Loja, Loja, Ecuador.
    Iwata, Tomoya
    Department of Environmental Sciences, University of Yamanashi, Kofu, Japan.
    Kirkwood, Andrea E.
    Faculty of Science, Ontario Tech University, ON, Oshawa, Canada.
    Koning, Aaron A.
    Global Water Center, University of Nevada, NV, Reno, United States.
    Kosten, Sarian
    Department of Aquatic Ecology and Environmental Biology, Radboud University, Nijmegen, Netherlands; Institute for Water and Wetland Research, Radboud University, Nijmegen, Netherlands.
    Laudon, Hjalmar
    Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Leavitt, Peter R.
    Department of Biology, University of Regina, SK, Regina, Canada.
    Lemes da Silva, Aurea L.
    Department of Ecology and Zoology, Federal University of Santa Catarina, Santa Catarina, Brazil.
    Leroux, Shawn J.
    Department of Biology, Memorial University of Newfoundland, NL, St. Johns, Canada.
    LeRoy, Carri J.
    Environmental Studies Program, The Evergreen State College, WA, Olympia, United States.
    Lisi, Peter J.
    Center for Limnology, University of Wisconsin, WI, Madison, United States.
    Masese, Frank O.
    Department of Fisheries & Aquatic Science, University of Eldoret, Eldoret, Kenya.
    McIntyre, Peter B.
    Department of Natural Resources and the Environment, Cornell University, NY, Ithaca, United States.
    McKie, Brendan G.
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Medeiros, Adriana O.
    Institute of Biology, Federal University of Bahia (UFBA), Salvador, Brazil.
    Miliša, Marko
    Department of Biology, Faculty of Science, University of Zagreb, Zagreb, Croatia.
    Miyake, Yo
    Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan.
    Mooney, Robert J.
    Center for Limnology, University of Wisconsin, WI, Madison, United States.
    Muotka, Timo
    Department of Ecology & Genetics, University of Oulu, Oulu, Finland.
    Nimptsch, Jorge
    Instituto de Ciencias Marinas y Limnologicas, Universidad Austral de Chile, Valdivia, Chile.
    Paavola, Riku
    Oulanka Research Station, University of Oulu, Oulu, Finland.
    Pardo, Isabel
    Department of Ecology and Animal Biology, University of Vigo, Vigo, Spain.
    Parnikoza, Ivan Y.
    National Antarctic Scientific Center of Ukraine, Kiev, Ukraine; Institute of Molecular Biology and Genetics, National Institute of Science of Ukraine, Kiev, Ukraine.
    Patrick, Christopher J.
    Department of Biological Science, Virginia Institute of Marine Science, College of William and Mary, VA, Gloucester Point, United States.
    Peeters, Edwin T. H. M.
    Aquatic Ecology and Water Quality Management Group, Wageningen University, Wageningen, Netherlands.
    Pozo, Jesus
    Department of Plant Biology and Ecology, University of the Basque Country, Bilbao, Spain.
    Reid, Brian
    Research Center on Ecosystems of Patagonia, Centro de Investigacion en Ecosistemas de La Patagonia, Valdivia, Chile.
    Richardson, John S.
    Department of Forest & Conservation Sciences, University of British Columbia, BC, Vancouver, Canada.
    Rincón, José
    Departamento de Biología, Universidad Del Zulia, Maracaibo, Venezuela.
    Risnoveanu, Geta
    Department of Systems Ecology and Sustainability, University of Bucharest, Bucharest, Romania.
    Robinson, Christopher T.
    Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
    Santamans, Anna C.
    Cavanilles Institute for Biodiversity and Evolutionary Biology, University of Valencia, Paterna, Spain.
    Simiyu, Gelas M.
    School of Environmental Studies, University of Eldoret, Eldoret, Kenya.
    Skuja, Agnija
    Institute of Biology, University of Latvia, Riga, Latvia.
    Smykla, Jerzy
    Institute of Nature Conservation, Polish Academy of Sciences, Kraków, Poland.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Teixeira-de Mello, Franco
    Department de Ecología y Gestión Ambiental, Universidad de La República (CURE), Maldonado, Uruguay.
    Vilbaste, Sirje
    Institute of Agricultural and Environmental Science, Estonian University of Life Sciences, Tartu, Estonia.
    Villanueva, Verónica D.
    INIBIOMA, Universidad Nacional Comahue (CONICET), San Carlos de Bariloche, Argentina.
    Webster, Jackson R.
    Department of Biological Sciences, Virginia Tech, VA, Blacksburg, United States.
    Woelfl, Stefan
    Instituto de Ciencias Marinas y Limnologicas, Universidad Austral de Chile, Valdivia, Chile.
    Xenopoulos, Marguerite A.
    Department of Biology, Trent University, ON, Peterborough, Canada.
    Yates, Adam G.
    Department of Biology, University of Waterloo, ON, Waterloo, Canada; Canadian Rivers Institute, NB, Saint John, Canada.
    Yule, Catherine M.
    School of Science, Technology and Engineering, University of the Sunshine Coast, QLD, Maroochydore, Australia.
    Zhang, Yixin
    Department of Landscape Architecture, Soochow University, Suzhou, China; Zhejiang Institute of Research and Innovation, The University of Hong Kong, Kowloon, Hong Kong.
    Zwart, Jacob A.
    U.S. Geological Survey Integrated Information Dissemination Division, VA, Reston, United States.
    Global patterns and controls of nutrient immobilization on decomposing cellulose in riverine ecosystems2022In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 36, no 3, article id e2021GB007163Article in journal (Refereed)
    Abstract [en]

    Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature. Collectively, we demonstrated that exogenous nutrient supply and immobilization are critical control points for decomposition of organic matter.

  • 10.
    Denfeld, Blaize A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaus, Marcus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Swedish University of Agricultural Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Carbon Dioxide and Methane Dynamics in a Small Boreal Lake During Winter and Spring Melt Events2018In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 123, no 8, p. 2527-2540Article in journal (Refereed)
    Abstract [en]

    In seasonally ice‐covered lakes, carbon dioxide (CO2) and methane (CH4) emission at ice‐off can account for a significant fraction of the annual budget. Yet knowledge of the mechanisms controlling below lake‐ice carbon (C) dynamics and subsequent CO2 and CH4 emissions at ice‐off is limited. To understand the control of below ice C dynamics, and C emissions in spring, we measured spatial variation in CO2, CH4, and dissolved inorganic and organic carbon from ice‐on to ice‐off, in a small boreal lake during a winter with sporadic melting events. Winter melt events were associated with decreased surface water DOC in the forest‐dominated basin and increased surface water CH4 in the mire‐dominated basin. At the whole‐lake scale, CH4 accumulated below ice throughout the winter, whereas CO2 accumulation was greatest in early winter. Mass‐balance estimates suggest that, in addition to the CO2 and CH4 accumulated during winter, external inputs of CO2 and CH4 and internal processing during ice‐melt could represent significant sources of C gas emissions during ice‐off. Moreover, internal processing of CO2 and CH4 worked in opposition, with production of CO2 and oxidation of CH4 dominating at ice‐off. These findings have important implications for how small boreal lakes will respond to warmer winters in the future; increased winter melt events will likely increase external inputs below ice and thus alter the extent and timing of CO2 and CH4 emissions to the atmosphere at ice‐off.

  • 11.
    Denfeld, Blaize A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lupon, Anna
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Heterogeneous CO2 and CH4 patterns across space and time in a small boreal lake2020In: Inland Waters, ISSN 2044-2041, E-ISSN 2044-205X, Vol. 10, no 3, p. 348-359Article in journal (Refereed)
    Abstract [en]

    Small boreal lakes emit large amounts of carbon dioxide (CO2) and methane (CH4) to the atmosphere. Yet emissions of these greenhouse gases are variable in space and time, in part due to variable within-lake CO2 and CH4 concentrations. To determine the extent and the underlying drivers of this variation, we measured lake water CO2 and CH4 concentrations and estimated associated emissions using spatially discrete water samples collected every 2 weeks from a small boreal lake. On select dates, we also collected groundwater samples from the surrounding catchment. On average, groundwater draining a connected peat mire complex had significantly higher CO2 and CH4 concentrations compared to waters draining forest on mineral soils. However, within the lake, only CH4 concentrations nearshore from the mire complex were significantly elevated. We observed little spatial variability in surface water CO2; however, bottom water CO2 in the pelagic zone was significantly higher than bottom waters at nearshore locations. Overall, temperature, precipitation, and thermal stratification explained temporal patterns of CO2 concentration, whereas hydrology (discharge and precipitation) best predicted the variation in CH4 concentration. Consistent with these different controls, the highest CO2 emission was related to lake turnover at the end of August while the highest CH4 emission was associated with precipitation events at the end of June. These results suggest that annual carbon emissions from small boreal lakes are influenced by temporal variation in weather conditions that regulate thermal stratification and trigger hydrologic land-water connections that supply gases from catchment soils to the lake.

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  • 12.
    Ehnvall, B.
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ratcliffe, J.L.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden; North Highland College, Environmental Research Institute, University of the Highlands and Islands, Thurso, United Kingdom; Unit for Field-Based Forest Research, Swedish University of Agricultural Sciences, Vindeln, Sweden.
    Nilsson, M.B.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Öquist, M.G.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Grabs, T.
    Department of Earth Sciences, Geocentrum, Uppsala University, Uppsala, Sweden.
    Topography and time shape mire morphometry and large-scale mire distribution patterns in the northern boreal landscape2024In: Journal of Geophysical Research - Earth Surface, ISSN 2169-9003, E-ISSN 2169-9011, Vol. 129, no 2, article id e2023JF007324Article in journal (Refereed)
    Abstract [en]

    Peatlands are major terrestrial soil carbon stores, and open mires in boreal landscapes hold a considerable fraction of the global peat carbon. Despite decades of study, large-scale spatiotemporal analyses of mire arrangement have been scarce, which has limited our ability to scale-up mire properties, such as carbon accumulation to the landscape level. Here, we use a land-uplift mire chronosequence in northern Sweden spanning 9,000 years to quantify controls on mire distribution patterns. Our objectives include assessing changes in the spatial arrangement of mires with land surface age, and understanding modifications by upland hydrotopography. Characterizing over 3,000 mires along a 30 km transect, we found that the time since land emergence from the sea was the dominant control over mire coverage, especially for the establishment of large mire complexes. Mires at the youngest end of the chronosequence were small with heterogenous morphometry (shape, slope, and catchment-to-mire areal ratios), while mires on the oldest surfaces were variable in size, but included larger mires with more complex shapes and smaller catchment-to-mire ratios. In general, complex topography fragmented mires by constraining the lateral expansion, resulting in a greater number of mires, but reduced total mire area regardless of landscape age. Mires in this study area occurred on slopes up to 4%, indicating a hydrological boundary to peatland expansion under local climatic conditions. The consistency in mire responses to spatiotemporal controls illustrates how temporal limitation in peat initiation and accumulation, and topographic constraints to mire expansion together have shaped present day mire distribution patterns.

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  • 13.
    Ehnvall, Betty
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Ratcliffe, Joshua L.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Bohlin, Elisabet
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Nilsson, Mats B.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Öquist, Mats G.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Grabs, Thomas
    Department of Earth Sciences, Geocentrum, Uppsala University, Villavägen 16, Uppsala, Sweden.
    Landscape constraints on mire lateral expansion2023In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 302, article id 107961Article in journal (Refereed)
    Abstract [en]

    Little is known about the long-term expansion of mire ecosystems, despite their importance in the global carbon and hydrogeochemical cycles. It has been firmly established that mires do not expand linearly over time. Despite this, mires are often assumed to have expanded at a constant rate after initiation simply for lack of a better understanding. There has not yet been a serious attempt to determine the rate and drivers of mire expansion at the regional, or larger spatial scales. Here we make use of a natural chronosequence, spanning the Holocene, which is provided by the retreating coastline of Northern Sweden. By studying an isostatic rebound area we can infer mire expansion dynamics by looking at the portion of the landscape where mires become progressively scarce as the land becomes younger. Our results confirms that mires expanded non-linearly across the landscape and that their expansion is related to the availability of suitably wet areas, which, in our case, depends primarily on the hydro-edaphic properties of the landscape. Importantly, we found that mires occupied the wettest locations in the landscape within only one to two thousand years, while it took mires three to four thousand years to expand into slightly drier areas. Our results imply that the lateral expansion of mires, and thus peat accumulation is a non-linear process, occurring at different rates depending, above all else, on the wetness of the landscape.

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  • 14. Einarsdottir, Karolina
    et al.
    Attermeyer, Katrin
    Hawkes, Jeffrey A.
    Kothawala, Dolly
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Tranvik, Lars J.
    Particles and Aeration at Mire-Stream Interfaces Cause Selective Removal and Modification of Dissolved Organic Matter2020In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 125, no 12, article id e2020JG005654Article in journal (Refereed)
    Abstract [en]

    Peatlands are dominant sources of dissolved organic matter (DOM) to boreal inland waters and play important roles in the aquatic carbon cycle. Yet before peat-derived DOM enters aquatic networks, it needs to pass through peat-stream interfaces that are often characterized by transitions from anoxic or hypoxic to oxic conditions. Aeration at these interfaces may trigger processes that impact the DOM pool, and its fate downstream. Here we experimentally assessed how the aeration of iron- and organic-rich mire-waters influences biodegradation, particle-formation, and modification of DOM. In addition, we investigated how suspended peat-derived particles from mires may influence these processes. We found that within 5 days of aeration, 20% of the DOM transformed into particulate organic matter (POM). This removal was likely due to combination of mechanisms including coprecipitation with oxidized iron, aggregation, and DOM-adsorption onto peat-derived particles. Peat-derived particles promoted microbial activity, but biodegradation was a minor loss mechanism of DOM removal. Interestingly, microbial respiration accounted for only half of the oxygen loss, suggesting substantial nonrespiratory oxygen consumption. The differences observed in DOM characteristics between anoxic and aerated treatments suggest that hydrophilic, aromatic DOM coprecipitated with iron oxides in aerated samples, and the corresponding C:N analysis of generated POM revealed that these organic species were nitrogen-poor. Meanwhile, POM formed via adsorption onto peat-derived particles generated from nonaromatic DOM and more nitrogen-rich species. Hence, selective removal of DOM, dissolved iron, and thus oxygen may be important and overlooked processes in mire-dominated headwater systems.

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  • 15.
    Fork, Megan L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Cary Institute of Ecosystem Studies, Millbrook, New York.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dissolved organic matter regulates nutrient limitation and growth of benthic algae in northern lakes through interacting effects on nutrient and light availability2020In: Limnology and Oceanography Letters, E-ISSN 2378-2242, Vol. 5, no 6, p. 417-424Article in journal (Refereed)
    Abstract [en]

    Widespread increases in dissolved organic matter (DOM) concentration across northern lakes can alter rates of primary production by increasing nutrient availability and decreasing light availability. These dual effects of DOM generate a unimodal relationship in pelagic primary production and primary producer biomass among lakes over a gradient of DOM concentration. However, the responses of benthic algae to variation in DOM loading are less clear because of their potential to access sediment nutrients. We tested algal production and nutrient limitation along a DOM gradient in northern Sweden. Without added nutrients, benthic algal production showed a unimodal relationship with DOM, similar to reported pelagic responses. Nutrient addition revealed widespread nitrogen limitation, with decreasing severity in lakes with higher DOM. Because the majority of northern Swedish lakes currently fall below the inflection point in this unimodal relationship, moderate increases in DOM have the potential to increase benthic primary production, particularly for epilithic algae.

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  • 16.
    Fork, Megan L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Changing Source-Transport Dynamics Drive Differential Browning Trends in a Boreal Stream Network2020In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 56, no 2, article id e2019WR026336Article in journal (Refereed)
    Abstract [en]

    Dissolved organic carbon (DOC) concentrations are increasing in freshwaters worldwide, with important implications for aquatic ecology, biogeochemistry, and ecosystem services. While multiple environmental changes may be responsible for these trends, predicting the occurrence and magnitude of "browning" and relating such trends to changes in DOC sources versus hydrologic transport remain key challenges. We analyzed long-term trends in DOC concentration from the two dominant landscape sources (riparian soils and mire peats) and receiving streams in a boreal catchment to evaluate how browning patterns relate to land cover and hydrology. Increases in stream DOC were widespread but not universal. Browning was most pronounced in small, forested streams, where trends corresponded to twofold to threefold increases in DOC production in riparian soils and increases in annual DOC export from a forested headwater. By contrast, DOC did not change in mire peats or streams draining catchments with high lake or mire cover, nor did we observe trends in DOC export from a mire-dominated headwater. The distinct long-term trends in DOC sources also altered concentration-discharge relationships, with a forested headwater shifting from transport-limited toward chemostasis, and a mire outlet stream shifting from chemostasis to source-limitated. Modified DOC supply to headwaters, together with altered seasonal hydrology and differences in the dominant water source along the stream network gave rise to predictable browning trends and consistent concentration-discharge relationships. Overall, our results show that the sources of DOC to boreal aquatic ecosystems are responding to environmental change in fundamentally different ways, with important consequences for browning along boreal stream networks.

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  • 17. Futter, Martyn N.
    et al.
    Högbom, Lars
    Valinia, Salar
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Conceptualizing and communicating management effects on forest water quality2016In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 45, p. S188-S202Article in journal (Refereed)
    Abstract [en]

    We present a framework for evaluating and communicating effects of human activity on water quality in managed forests. The framework is based on the following processes: atmospheric deposition, weathering, accumulation, recirculation and flux. Impairments to water quality are characterized in terms of their extent, longevity and frequency. Impacts are communicated using a "traffic lights" metaphor for characterizing severity of water quality impairments arising from forestry and other anthropogenic pressures. The most serious impairments to water quality in managed boreal forests include (i) forestry activities causing excessive sediment mobilization and extirpation of aquatic species and (ii) other anthropogenic pressures caused by long-range transport of mercury and acidifying pollutants. The framework and tool presented here can help evaluate, summarize and communicate the most important issues in circumstances where land management and other anthropogenic pressures combine to impair water quality and may also assist in implementing the "polluter pays" principle.

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  • 18.
    Gómez-Gener, Lluís
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Institute of Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Centre for Advanced Studies of Blanes, Spanish National Research Council (CEAB-CSIC), Blanes, Spain.
    Hotchkiss, Erin R.
    Department of Biological Sciences, Virginia Polytechnic Institute and State University, VA, Blacksburg, United States.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Integrating Discharge-Concentration Dynamics Across Carbon Forms in a Boreal Landscape2021In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 57, no 8, article id e2020WR028806Article in journal (Refereed)
    Abstract [en]

    The flux of terrestrial carbon across land-water boundaries influences the overall carbon balance of landscapes and the ecology and biogeochemistry of aquatic ecosystems. The local consequences and broader fate of carbon delivered to streams is determined by the overall composition of carbon inputs, including the balance of organic and inorganic forms. Yet, our understanding of how hydrologic fluxes across different land-water interfaces regulate carbon supply remains poor. We used 7 years of data from three boreal catchments to test how different land-water interfaces (i.e., forest, wetland, and lake) modulate concentration-discharge (C-Q) relationships for dissolved organic carbon (DOC), carbon dioxide (CO2), and methane, as well as the balance among forms (e.g., DOC:CO2). Seasonal patterns in concentrations and C-Q relationships for individual carbon forms differed across catchments. DOC varied between chemostasis and transport limitation in the forest catchment, between supply limitation and chemostasis in the wetland catchment, and was persistently chemostatic in the lake outlet stream. Carbon gases were supply limited overall, but exhibited chemostasis or transport limitation in the forest and wetland catchments linked to elevated flow in summer and autumn. Unique C-Q relationships for individual forms reflected the properties of different interfaces and underpinned changes in the composition of lateral carbon supply. Accordingly, DOC dominated the carbon flux during snowmelt, whereas gas evasion increased in relative importance during other times of the year. Integrating the C-Q dynamics of individual carbon forms provides insight into the shifting composition of lateral export, and thus helps to predict how hydrologic changes may alter the fate of carbon supplied to streams.

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  • 19.
    Gómez-Gener, Lluís
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, GR A0 412 (Bâtiment GR), CH-1015 Lausanne, Switzerland.
    Lupon, Anna
    Laudon, Hjalmar
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Drought alters the biogeochemistry of boreal stream networks2020In: Nature Communications, E-ISSN 2041-1723, Vol. 11, no 1, article id 1795Article in journal (Refereed)
    Abstract [en]

    Drought is a global phenomenon, with widespread implications for freshwater ecosystems. While droughts receive much attention at lower latitudes, their effects on northern river networks remain unstudied. We combine a reach-scale manipulation experiment, observations during the extreme 2018 drought, and historical monitoring data to examine the impact of drought in northern boreal streams. Increased water residence time during drought promoted reductions in aerobic metabolism and increased concentrations of reduced solutes in both stream and hyporheic water. Likewise, data during the 2018 drought revealed widespread hypoxic conditions and shifts towards anaerobic metabolism, especially in headwaters. Finally, long-term data confirmed that past summer droughts have led to similar metabolic alterations. Our results highlight the potential for drought to promote biogeochemical shifts that trigger poor water quality conditions in boreal streams. Given projected increases in hydrological extremes at northern latitudes, the consequences of drought for the health of running waters warrant attention. High latitude droughts are increasing, but their effects on freshwater systems are poorly understood. Here the authors investigate Sweden's most severe drought in the last century and show that these dry conditions induce hypoxia and elevated methane production from streams.

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  • 20.
    Hasselquist, Eliza Maher
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Kuglerová, Lenka
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Sjögren, Jörgen
    Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Hjältén, Joakim
    Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ring, Eva
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Elisabet
    Lundström, Johanna
    Department of Forest Resource Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Mancheva, Irina
    Umeå University, Faculty of Social Sciences, Department of Political Science.
    Nordin, Annika
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology Swedish University of Agricultural Sciences, Umeå, Sweden.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Moving towards multi-layered, mixed-species forests in riparian buffers will enhance their long-term function in boreal landscapes2021In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 493, article id 119254Article in journal (Refereed)
    Abstract [en]

    Riparian buffers are the primary tool in forest management for protecting the habitat structure and function of streams. They help protect against biogeochemical perturbation, filter sediments and nutrients, prevent erosion, contribute food to aquatic organisms, regulate light and hence water temperature, contribute deadwood, and preserve biodiversity. However, in production forests of Sweden and Finland, many headwater streams have been straightened, ditched, and/or channelized, resulting in altered hydrology and reduced natural disturbance by floods, which in turn affects important riparian functions. Furthermore, in even-aged management systems as practiced in much of Fennoscandia, understory trees have usually been cleared right up to the stream’s edge during thinning operations, especially around small, headwater streams. Fire suppression has further favored succession towards shade tolerant species. In the regions within Fennoscandia that have experienced this combination of intensive management and lack of natural disturbance, riparian zones are now dominated by single-storied, native Norway spruce. When the adjacent forest is cut, thin (5 - 15m) conifer-dominated riparian buffers are typically left. These buffers do not provide the protection and subsidies, in terms of leaf litter quality, needed to maintain water quality or support riparian or aquatic biodiversity. Based on a literature review, we found compelling evidence that the ecological benefits of multi-layered, mixed-species riparian forest with a large component of broadleaved species are higher than what is now commonly found in the managed stands of Fennoscandia. To improve the functionality of riparian zones, and hence the protection of streams in managed forest landscapes, we present some basic principles that could be used to enhance the ecological function of these interfaces. These management actions should be prioritized on streams and streamside stands that have been affected by simplification either through forest management or hydrological modification. Key to these principles is the planning and managing of buffer zones as early as possible in the rotation to ensure improved function throughout the rotation cycle and not only at final felling. This is well in line with EU and national legislation which can be interpreted as requiring landscape planning at all forest ages to meet biodiversity and other environmental goals. However, it is still rare that planning for conservation is done other than at the final felling stage. Implementing this new strategy is likely to have long-term positive effects and improve the protection of surface waters from negative forestry effects and a history of fire suppression. By following these suggested management principles, there will be a longer time period with high function and greater future management flexibility in addition to the benefits provided by leaving riparian buffers at the final felling stage.

  • 21. Hasselquist, Eliza Maher
    et al.
    Lidberg, William
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Agren, Anneli
    Laudon, Hjalmar
    Identifying and assessing the potential hydrological function of past artificial forest drainage2018In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 47, no 5, p. 546-556Article in journal (Refereed)
    Abstract [en]

    Drainage of forested wetlands for increased timber production has profoundly altered the hydrology and water quality of their downstream waterways. Some ditches need network maintenance (DNM), but potential positive effects on tree productivity must be balanced against environmental impacts. Currently, no clear guidelines exist for DNM that strike this balance. Our study helps begin to prioritise DNM by: (1) quantifying ditches by soil type in the 68 km(2) Krycklan Catchment Study in northern Sweden and (2) using upslope catchment area algorithms on new high-resolution digital elevation models to determine their likelihood to drain water. Ditches nearly doubled the size of the stream network (178-327 km) and 17% of ditches occurred on well-draining sedimentary soils, presumably making DNM unwarranted. Modelling results suggest that 25-50% of ditches may never support flow. With new laser scanning technology, simple mapping and modelling methods can locate ditches and model their function, facilitating efforts to balance DNM with environmental impacts.

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  • 22.
    Hotchkiss, E. R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hall, R. O., Jr.
    Sponseller, R. A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Butman, D.
    Klaminder, J.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, H.
    Rosvall, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Karlsson, J.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sources of and processes controlling CO2 emissions change with the size of streams and rivers2015In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 8, no 9, p. 696-699Article in journal (Refereed)
    Abstract [en]

    Carbon dioxide (CO2) evasion from streams and rivers to the atmosphere represents a substantial flux in the global carbon cycle(1-3). The proportions of CO2 emitted from streams and rivers that come from terrestrially derived CO2 or from CO2 produced within freshwater ecosystems through aquatic metabolism are not well quantified. Here we estimated CO2 emissions from running waters in the contiguous United States, based on freshwater chemical and physical characteristics and modelled gas transfer velocities at 1463 United States Geological Survey monitoring sites. We then assessed CO2 production from aquatic metabolism, compiled from previously published measurements of net ecosystem production from 187 streams and rivers across the contiguous United States. We find that CO2 produced by aquatic metabolism contributes about 28% of CO2 evasion from streams and rivers with flows between 0.0001 and 19,000 m(3) s(-1). We mathematically modelled CO2 flux from groundwater into running waters along a stream-river continuum to evaluate the relationship between stream size and CO2 source. Terrestrially derived CO2 dominates emissions from small streams, and the percentage of CO2 emissions from aquatic metabolism increases with stream size. We suggest that the relative role of rivers as conduits for terrestrial CO2 efflux and as reactors mineralizing terrestrial organic carbon is a function of their size and connectivity with landscapes.

  • 23.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Burrows, Ryan M.
    Lidman, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fältström, Emma
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Land use influences macroinvertebrate community composition in boreal headwaters through altered stream conditions2017In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 46, no 3, p. 311-323Article in journal (Refereed)
    Abstract [en]

    Land use is known to alter the nature of land-water interactions, but the potential effects of widespread forest management on headwaters in boreal regions remain poorly understood. We evaluated the importance of catchment land use, land cover, and local stream variables for macroinvertebrate community and functional trait diversity in 18 boreal headwater streams. Variation in macroinvertebrate metrics was often best explained by in-stream variables, primarily water chemistry (e.g. pH). However, variation in stream variables was, in turn, significantly associated with catchment-scale forestry land use. More specifically, streams running through catchments that were dominated by young (11-50 years) forests had higher pH, greater organic matter standing stock, higher abundance of aquatic moss, and the highest macroinvertebrate diversity, compared to streams running through recently clear-cut and old forests. This indicates that catchment-scale forest management can modify in-stream habitat conditions with effects on stream macroinvertebrate communities and that characteristics of younger forests may promote conditions that benefit headwater biodiversity.

  • 24.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Polvi, Lina E.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stenroth, Karolina
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Catchment properties predict autochthony in stream filter feeders2018In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 815, no 1, p. 83-95Article in journal (Refereed)
    Abstract [en]

    Stream ecological theory predicts that the use of allochthonous resources declines with increasing channel width, while at the same time primary production and autochthonous carbon use by consumers increase. Although these expectations have found support in several studies, it is not well known how terrestrial runoff and/or inputs of primary production from lakes alter these longitudinal patterns. To investigate this, we analyzed the diet of filter-feeding black fly and caddisfly larvae from 23 boreal streams, encompassing gradients in drainage area, land cover and land use, and distance to nearest upstream lake outlet. In five of these streams, we also sampled repeatedly during autumn to test if allochthony of filter feeders increases over time as new litter inputs are processed. Across sites, filter-feeder autochthony was 21.1-75.1%, did not differ between black fly and caddisfly larvae, was not positively related to drainage area, and did not decrease with distance from lakes. Instead, lake and wetland cover promoted filter-feeder autochthony independently of stream size, whereas catchment-scale forest cover and forestry reduced autochthony. Further, we found no seasonal increase in allochthony, indicating low assimilation of particles derived from autumn litter fall. Hence, catchment properties, rather than local conditions, can influence levels of autochthony in boreal streams.

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  • 25.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The role of macroinvertebrates on plant litter decomposition in streams2021In: The ecology of plant litter decomposition in stream ecosystems / [ed] Christopher M. Swan; Luz Boyero; Cristina Canhoto, Springer, 2021, p. 193-216Chapter in book (Refereed)
    Abstract [en]

    Macroinvertebrate detritivores (i.e., shredders) in freshwaters are often a main driver of decomposition rates of terrestrial plant litter. Yet, the extent to which shredders drive this process depends on the specific functional traits and species present in the shredder community, which in turn are determined by the broader species pool, as well as a range of local environmental conditions, such as pH, substrate characteristics, water chemistry, water temperature, and current velocity. Projected global change will modify several of these environmental conditions, with potential consequences for litter decomposition rates and overall carbon cycling in freshwaters. In this chapter, we describe how a range of freshwater environmental conditions determines the presence of certain species (i.e., functional traits) and the characteristics of shredder communities (i.e., species composition and richness). We then discuss how these characteristics in turn may influence interactions among shredders, and between shredders and other freshwater organisms, to determine their influence on litter decomposition in streams.

  • 26.
    Koizumi, Shuntaro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Warming and browning alters aquatic insect biomass and emergence dynamicsManuscript (preprint) (Other academic)
  • 27. Kuglerova, Lenka
    et al.
    Hasselquist, Eliza Maher
    Richardson, John S.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kreutzweiser, David P.
    Laudon, Hjalmar
    Management perspectives on Aqua incognita: Connectivity and cumulative effects of small natural and artificial streams in boreal forests2017In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 31, no 23, p. 4238-4244Article in journal (Other academic)
  • 28. Kuglerova, Lenka
    et al.
    Hasselquist, Eliza Maher
    Sponseller, Ryan Allen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Muotka, Timo
    Hallsby, Goran
    Laudon, Hjalmar
    Multiple stressors in small streams in the forestry context of Fennoscandia: The effects in time and space2021In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 756, article id 143521Article in journal (Refereed)
    Abstract [en]

    In this paper we describe how forest management practices in Fennoscandian countries, namely Sweden and Finland, expose streams to multiple stressors over space and time. In this region, forestry includes several different management actions and we explore how these may successively disturb the same location over 60-100 year long rotation periods. Of these actions, final harvest and associated road construction, soil scarification, and/or ditch network maintenance are the most obvious sources of stressors to aquatic ecosystems. Yet, more subtle actions such as planting, thinning of competing saplings and trees, and removing logging residues also represent disturbances around waterways in these landscapes. We review literature about how these different forestry practices may introduce a combination of physicochemical stressors, including hydrological change, increased sediment transport, altered thermal and light regimes, and water quality deterioration. We further elaborate on how the single stressors may combine and interact and we consequently hypothesise how these interactions may affect aquatic communities and processes. Because production forestry is practiced on a large area in both countries, the various stressors appear multiple times during the rotation cycles and potentially affect the majority of the stream network length within most catchments. We concluded that forestry practices have traditionally not been the focus of multiple stressor studies and should be investigated further in both observational and experimental fashion. Stressors accumulate across time and space in forestry dominated landscapes, and may interact in unpredictable ways, limiting our current understanding of what forested stream networks are exposed to and how we can design and apply best management practices.

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  • 29.
    Kuglerová, Lenka
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Sveriges lantbruksuniversitet.
    Malm-Renöfält, Birgitta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Local and regional processes determine plant species richness in a river-network metacommunity2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 2, p. 381-391Article in journal (Refereed)
    Abstract [en]

    River systems form dendritic ecological networks that influence the spatial structure of riverine communities. Few empirical studies have evaluated how regional, dispersal-related processes and local habitat factors interact to govern network patterns of species composition. We explore such interactions in a boreal watershed and show that riparian plant species richness increases strongly with drainage size, i.e., with downstream position in the network. Assemblage composition was nested, with new species successively added downstream. These spatial patterns in species composition were related to a combination of local and regional processes. Breadth in local habitat conditions increased downstream in the network, resulting in higher habitat heterogeneity and reduced niche overlap among species, which together with similar trends in disturbance, allows more species to coexist. Riparian edaphic conditions were also increasingly favorable to more species within the regional pool along larger streams, with greater nitrogen availability (manifested as lower C:N) and more rapid mineralization of C and N (as indicated by ratios of stable isotopes) observed with downstream position in the network. The number of species with capacity for water dispersal increased with stream size providing a mechanistic link between plant traits and the downstream accumulation of species as more propagules arrive from upstream sites. Similarity in species composition between sites was related to both geographical and environmental distance. Our results provide the first empirical evidence that position in the river network drives spatial patterns in riparian plant diversity and composition by the joint influence of local (disturbance, habitat conditions, and breadth) and regional (dispersal) forces.

  • 30.
    Kupryianchyk, Darya
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bidleman, Terry F.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Liljelind, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lau, Danny Chun Pong
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Patrik L.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Industrial and natural compounds in filter-feeding black fly larvae and water in 3 tundra streams2018In: Environmental Toxicology and Chemistry, ISSN 0730-7268, E-ISSN 1552-8618, Vol. 37, no 12, p. 3011-3017Article in journal (Refereed)
    Abstract [en]

    We report concentrations of polychlorinated biphenyls, polybrominated diphenyl ethers, novel flame retardants, and naturally occurring bromoanisoles in water and filter-feeding black fly (Simuliidae) larvae in 3 tundra streams in northern Sweden. The results demonstrate that black fly larvae accumulate a wide range of organic contaminants and can be used as bioindicators of water pollution in Arctic streams.

  • 31.
    Laudon, Hjalmar
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Hasselquist, Eliza Maher
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Peichl, Matthias
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Lindgren, Kim
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lidman, Fredrik
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Kuglerová, Lenka
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Hasselquist, Niles J.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Bishop, Kevin
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Nilsson, Mats B.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ågren, Anneli M.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Northern landscapes in transition: Evidence, approach and ways forward using the Krycklan Catchment Study2021In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 35, no 4, article id e14170Article in journal (Refereed)
    Abstract [en]

    Improving our ability to detect changes in terrestrial and aquatic systems is a grand challenge in the environmental sciences. In a world experiencing increasingly rapid rates of climate change and ecosystem transformation, our ability to understand and predict how, when, where, and why changes occur is essential for adapting and mitigating human behaviours. In this context, long-term field research infrastructures have a fundamentally important role to play. For northern boreal landscapes, the Krycklan Catchment Study (KCS) has supported monitoring and research aimed at revealing these changes since it was initiated in 1980. Early studies focused on forest regeneration and microclimatic conditions, nutrient balances and forest hydrology, which included monitoring climate variables, water balance components, and stream water chemistry. The research infrastructure has expanded over the years to encompass a 6790 ha catchment, which currently includes 11 gauged streams, ca. 1000 soil lysimeters, 150 groundwater wells, >500 permanent forest inventory plots, and a 150 m tall tower (a combined ecosystem-atmosphere station of the ICOS, Integrated Carbon Observation System) for measurements of atmospheric gas concentrations and biosphere-atmosphere exchanges of carbon, water, and energy. In addition, the KCS has also been the focus of numerous high resolution multi-spectral LiDAR measurements and large scale experiments. This large collection of equipment and data generation supports a range of disciplinary studies, but more importantly fosters multi-, trans-, and interdisciplinary research opportunities. The KCS attracts a broad collection of scientists, including biogeochemists, ecologists, foresters, geologists, hydrologists, limnologists, soil scientists, and social scientists, all of whom bring their knowledge and experience to the site. The combination of long-term monitoring, shorter-term research projects, and large-scale experiments, including manipulations of climate and various forest management practices, has contributed much to our understanding of boreal landscape functioning, while also supporting the development of models and guidelines for research, policy, and management.

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  • 32. Laudon, Hjalmar
    et al.
    Kuglerova, Lenka
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Futter, Martyn
    Nordin, Annika
    Bishop, Kevin
    Lundmark, Tomas
    Egnell, Gustaf
    Agren, Anneli M.
    The role of biogeochemical hotspots, landscape heterogeneity, and hydrological connectivity for minimizing forestry effects on water quality2016In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 45, p. S152-S162Article in journal (Refereed)
    Abstract [en]

    Protecting water quality in forested regions is increasingly important as pressures from land-use, long-range transport of air pollutants, and climate change intensify. Maintaining forest industry without jeopardizing sustainability of surface water quality therefore requires new tools and approaches. Here, we show how forest management can be optimized by incorporating landscape sensitivity and hydrological connectivity into a framework that promotes the protection of water quality. We discuss how this approach can be operationalized into a hydromapping tool to support forestry operations that minimize water quality impacts. We specifically focus on how hydromapping can be used to support three fundamental aspects of land management planning including how to (i) locate areas where different forestry practices can be conducted with minimal water quality impact; (ii) guide the off-road driving of forestry machines to minimize soil damage; and (iii) optimize the design of riparian buffer zones. While this work has a boreal perspective, these concepts and approaches have broad-scale applicability.

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  • 33.
    Laudon, Hjalmar
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Lidberg, William
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Maher Hasselquist, Eliza
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Westphal, Florian
    Department of Computing, Jönköping University, Jönköping, Sweden.
    Östlund, Lars
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Sandström, Camilla
    Umeå University, Faculty of Social Sciences, Department of Political Science.
    Järveoja, Järvi
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Peichl, Matthias
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ågren, Anneli M.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Emerging technology can guide ecosystem restoration for future water security2022In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 36, no 10, article id e14729Article in journal (Refereed)
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  • 34. Laudon, Hjalmar
    et al.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    How landscape organization and scale shape catchment hydrology and biogeochemistry: insights from a long-term catchment study2018In: WIREs Water, E-ISSN 2049-1948, Vol. 5, no 2, article id e1265Article, review/survey (Refereed)
    Abstract [en]

    Catchment science plays a critical role in the protection of water resources in the face of ongoing changes in climate, long-range transport of air pollutants, and land use. Addressing these challenges, however, requires improved understanding of how, when, and where changes in water quantity and quality occur within river networks. To reach these goals, we must recognize how different catchment features are organized to regulate surface chemistry at multiple scales, from processes controlling headwaters, to the downstream mixing of water from multiple landscape sources and deep aquifers. Here we synthesize 30-years of hydrological and biogeochemical research from the Krycklan catchment study (KCS) in northern Sweden to demonstrate the benefits of coupling long-term monitoring with multi-scale research to advance our understanding of catchment functioning across space and time. We show that the regulation of hydrological and biogeochemical patterns in the KCS can be decomposed into four, hierarchically structured landscape features that include: (1) transmissivity and reactivity of dominant source layers within riparian soils, (2) spatial arrangement of groundwater input zones that govern water and solute fluxes at reach- to segment-scales, (3) landscape scale heterogeneity (forests, mires, and lakes) that generates unique biogeochemical signals downstream, and (4) broad-scale mixing of surface streams with deep groundwater contributions. While this set of features are perhaps specific to the study region, analogous hierarchical controls are likely to be widespread. Resolving these scale dependent processes is important for predicting how, when, and where different environmental changes may influence patterns of surface water chemistry within river networks. (C) 2017 Wiley Periodicals, Inc.

  • 35. Laudon, Hjalmar
    et al.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bishop, Kevin
    From legacy effects of acid deposition in boreal streams to future environmental threats2021In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 16, no 1, article id 015007Article in journal (Refereed)
    Abstract [en]

    Few environmental issues have resulted in such a heated policy-science controversy in Sweden as the 1990s acidification debate in the north of the country. The belief that exceptionally high stream acidity levels during hydrological events was caused by anthropogenic deposition resulted in a governmentally funded, multi-million dollar surface-water liming program. This program was heavily criticized by a large part of the scientific community arguing that the acidity of northern streams was primarily caused by naturally occurring organic acids. Here, we revisit the acid deposition legacy in northern Sweden two decades after the culmination of the controversy by examining the long-term water chemistry trends in the Svartberget/Krycklan research catchment that became a nexus for the Swedish debate. In this reference stream, trends in acidic episodes do show a modest recovery that matches declines in acid deposition to pre-industrial levels, although stream acidity continues to be overwhelmingly driven by organic acidity. Yet there are legacies of acid deposition related to calcium losses from soils, which are more pronounced than anticipated. Finally, assessment of these trends are becoming increasingly complicated by new changes and threats to water resources that must be recognized to avoid unnecessary, expensive, and potentially counterproductive measures to adapt and mitigate human influences. Here we make the argument that while the acidification era is ending, climate change, land-use transitions, and long-range transport of other contaminants warrant close monitoring in the decades to come.

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  • 36. Ledesma, José L. J.
    et al.
    Futter, Martyn N.
    Blackburn, M.
    Lidman, Fredrik
    Grabs, Thomas
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Bishop, Kevin H.
    Köhler, Stephan J.
    Towards an Improved Conceptualization of Riparian Zones in Boreal Forest Headwaters2018In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 21, no 2, p. 297-315Article in journal (Refereed)
    Abstract [en]

    The boreal ecoregion supports about one-third of the world's forest. Over 90% of boreal forest streams are found in headwaters, where terrestrial-aquatic interfaces are dominated by organic matter (OM)-rich riparian zones (RZs). Because these transition zones are key features controlling catchment biogeochemistry, appropriate RZ conceptualizations are needed to sustainably manage surface water quality in the face of a changing climate and increased demands for forest biomass. Here we present a simple, yet comprehensive, conceptualization of RZ function based on hydrological connectivity, biogeochemical processes, and spatial heterogeneity. We consider four dimensions of hydrological connectivity: (1) laterally along hillslopes, (2) longitudinally along the stream, (3) vertically down the riparian profile, and (4) temporally through event-based and seasonal changes in hydrology. Of particular importance is the vertical dimension, characterized by a 'Dominant Source Layer' that has the highest contribution to solute and water fluxes to streams. In addition to serving as the primary source of OM to boreal streams, RZs shape water chemistry through two sets of OM-dependent biogeochemical processes: (1) transport and retention of OM-associated material and (2) redox-mediated transformations controlled by RZ water residence time and availability of labile OM. These processes can lead to both retention and release of pollutants. Variations in width, hydrological connectivity, and OM storage drive spatial heterogeneity in RZ biogeochemical function. This conceptualization provides a useful theoretical framework for environmental scientists and ecologically sustainable and economically effective forest management in the boreal region and elsewhere, where forest headwaters are dominated by low-gradient, OM-rich RZs.

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  • 37.
    Lidman, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Burrows, Ryan M.
    Bundschuh, Mirco
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Composition of riparian litter input regulates organic matter decomposition: Implications for headwater stream functioning in a managed forest landscape2017In: Ecology and Evolution, E-ISSN 2045-7758, Vol. 7, no 4, p. 1068-1077Article in journal (Refereed)
    Abstract [en]

    Although the importance of stream condition for leaf litter decomposition has been extensively studied, little is known about how processing rates change in response to altered riparian vegetation community composition. We investigated patterns of plant litter input and decomposition across 20 boreal headwater streams that varied in proportions of riparian deciduous and coniferous trees. We measured a suite of in-stream physical and chemical characteristics, as well as the amount and type of litter inputs from riparian vegetation, and related these to decomposition rates of native (alder, birch, and spruce) and introduced (lodgepole pine) litter species incubated in coarse- and fine-mesh bags. Total litter inputs ranged more than fivefold among sites and increased with the proportion of deciduous vegetation in the riparian zone. In line with differences in initial litter quality, mean decomposition rate was highest for alder, followed by birch, spruce, and lodgepole pine (12, 55, and 68% lower rates, respectively). Further, these rates were greater in coarse-mesh bags that allow colonization by macroinvertebrates. Variance in decomposition rate among sites for different species was best explained by different sets of environmental conditions, but litter-input composition (i.e., quality) was overall highly important. On average, native litter decomposed faster in sites with higher-quality litter input and (with the exception of spruce) higher concentrations of dissolved nutrients and open canopies. By contrast, lodgepole pine decomposed more rapidly in sites receiving lower-quality litter inputs. Birch litter decomposition rate in coarse-mesh bags was best predicted by the same environmental variables as in fine-mesh bags, with additional positive influences of macroinvertebrate species richness. Hence, to facilitate energy turnover in boreal headwaters, forest management with focus on conifer production should aim at increasing the presence of native deciduous trees along streams, as they promote conditions that favor higher decomposition rates of terrestrial plant litter.

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  • 38. Lucas, Richard W.
    et al.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gundale, Michael J.
    Stendahl, Johan
    Fridman, Jonas
    Hogberg, Peter
    Laudon, Hjalmar
    Long-term declines in stream and river inorganic nitrogen (N) export correspond to forest change2016In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 26, no 2, p. 545-556Article in journal (Refereed)
    Abstract [en]

    Human activities have exerted a powerful influence on the biogeochemical cycles of nitrogen (N) and carbon (C) and drive changes that can be a challenge to predict given the influence of multiple environmental stressors. This study focused on understanding how land management and climate change have together influenced terrestrial N storage and watershed inorganic N export across boreal and sub-arctic landscapes in northern Sweden. Using long-term discharge and nutrient concentration data that have been collected continuously for over three decades, we calculated the hydrologic inorganic N export from nine watersheds in this region. We found a consistent decline in inorganic N export from 1985 to 2011 over the entire region from both small and large watersheds, despite the absence of any long-term trend in river discharge during this period. The steepest declines in inorganic N export were observed during the growing season, consistent with the hypothesis that observed changes are biologically mediated and are not the result of changes in long-term hydrology. Concurrent with the decrease in inorganic N export, we report sustained increases in terrestrial N accumulation in forest biomass and soils across northern Sweden. Given the close communication of nutrient and energy stores between plants, soils, and waters, our results indicate a regional tightening of the N cycle in an already N-limited environment as a result of changes in forest management and climate-mediated growth increases. Our results are consistent with declining inorganic N efflux previously reported from small headwater streams in other ecosystems and shed new light on the mechanisms controlling these patterns by identifying corresponding shifts in the terrestrial N balance, which have been altered by a combination of management activities and climate change.

  • 39. Lupon, Anna
    et al.
    Denfeld, Blaize A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Leach, Jason
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Groundwater inflows control patterns and sources of greenhouse gas emissions from streams2019In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 64, no 4, p. 1545-1557Article in journal (Refereed)
    Abstract [en]

    Headwater streams can be important sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere. However, the influence of groundwater-stream connectivity on the patterns and sources of carbon (C) gas evasion is still poorly understood. We explored these connections in the boreal landscape through a detailed study of a 1.4 km lake outlet stream that is hydrologically fed by multiple topographically driven groundwater input zones. We measured stream and groundwater dissolved organic C (DOC), CO2, and CH4 concentrations every 50 m biweekly during the ice-free period and estimated in-stream C gas production through a mass balance model and independent estimates of aquatic metabolism. The spatial pattern of C gas concentrations was consistent over time, with peaks of both CH4 and CO2 concentrations occurring after each groundwater input zone. Moreover, lateral C gas inputs from riparian soils were the major source of CO2 and CH4 to the stream. DOC mineralization and CH4 oxidation within the stream accounted for 17-51% of stream CO2 emissions, and this contribution was the greatest during relatively higher flows. Overall, our results illustrate how the nature and arrangement of groundwater flowpaths can organize patterns of stream C concentrations, transformations, and emissions by acting as a direct source of gases and by supplying organic substrates that fuel aquatic metabolism. Hence, refined assessments of how catchment structure influences the timing and magnitude of groundwater-stream connections are crucial for mechanistically understanding and scaling C evasion rates from headwaters.

  • 40. Lupon, Anna
    et al.
    Denfeld, Blaize A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Leach, Jason
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Discrete groundwater inflows influence patterns of nitrogen uptake in a boreal headwater stream2020In: Freshwater Science, ISSN 2161-9549, E-ISSN 2161-9565, Vol. 39, no 2, p. 228-240Article in journal (Refereed)
    Abstract [en]

    Dissolved organic carbon (DOC) influences stream nitrogen (N) dynamics by regulating the nutrient demand of heterotrophic microbes and mediating their interactions with nitrifiers. However, DOC supply to streams is dynamic in space and time, which may create variability in N dynamics as a result of shifts between heterotrophic and chemoautotrophic influences. To test this, we measured spatial and temporal variation in concentrations and net uptake of dissolved organic nitrogen (DON), ammonium (NH4+), and nitrate (NO3−) along a 1.4-km boreal stream fed by 4 discrete groundwater inflow zones. We also performed constant rate additions of NH4+, with and without acetate, to test the influence of labile DOC availability on N cycling. Groundwater N supply did not drive spatial patterns in N concentrations. However, we observed high rates of net NH4+ uptake at the sub-reach with the greatest groundwater DOC inputs, whereas net nitrification occurred where such inputs were negligible. At the reach scale, net DON and NH4+ uptake increased with greater groundwater discharge, DOC∶DIN, and ecosystem respiration, whereas net nitrification increased with greater DOC aromaticity. Finally, constant rate additions showed that, under increased DOC availability, NH4+ uptake increased 2×, whereas the proportion of NH4+ nitrified decreased from 42 to 15%. Together, these observations suggest that nitrification rivals heterotrophic uptake when aromatic DOC promotes heterotrophic carbon limitation. Discrete groundwater inflows and periods of elevated discharge can partially alleviate this limitation by supplying labile DOC from riparian soils. Hence, accounting for these land–water connections, over both time and space, is critical for understanding N dynamics in boreal streams.

  • 41.
    Lupon, Anna
    et al.
    Integrative Freshwater Ecology Group, Centre for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Spain.
    Gómez-Gener, Lluís
    Centre for Research on Ecology and Forestry Applications (CREAF), Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Barcelona, Spain.
    Fork, Megan L.
    Department of Biology, West Chester University, PA, West Chester, United States.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Martí, Eugènia
    Integrative Freshwater Ecology Group, Centre for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Spain.
    Lidberg, William
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Groundwater-stream connections shape the spatial pattern and rates of aquatic metabolism2023In: Limnology and Oceanography Letters, E-ISSN 2378-2242, Vol. 8, no 2, p. 350-358Article in journal (Refereed)
    Abstract [en]

    A longstanding challenge in stream ecology is to understand how landscape configuration organizes spatial patterns of ecosystem function via lateral groundwater connections. We combined laboratory bioassays and field additions of a metabolic tracer (resazurin) to test how groundwater-stream confluences, or “discrete riparian inflow points” (DRIPs), regulate heterotrophic microbial activity along a boreal stream. We hypothesized that DRIPs shape spatial patterns and rates of aquatic heterotrophic microbial activity by supplying labile dissolved organic matter (DOM) to streams. Laboratory bioassays showed that the potential influence of DRIPs on heterotrophic activity varied spatially and temporally, and was related to their DOM content and composition. At the reach scale, DRIP-stream confluences elevated the spatial heterogeneity and whole-reach rates of heterotrophic activity, especially during periods of high land–water hydrological connectivity. Collectively, our results show how the arrangement of lateral groundwater connections influence heterotrophic activity in streams with implications for watershed biogeochemical cycles.

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  • 42.
    McKie, Brendan G.
    et al.
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Tattersdill, Kristina
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ecke, Frauke
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden; Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, Sweden; Organismal and Evolutionary Biology Research Programme, FIN-00014 University of Helsinki, Helsinki, Finland.
    Frainer, André
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden; Department of Norwegian College of Fishery Science, The Arctic University of Norway, Tromsø, Norway; Norwegian Institute for Nature Research (NINA), Tromsø, Norway.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A long-established invasive species alters the functioning of benthic biofilms in lakes2023In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 68, no 12, p. 2068-2083Article in journal (Refereed)
    Abstract [en]

    Invasive species often transform environmental conditions, exclude native species and alter ecosystem functioning, including key ecosystem processes underpinning nutrient and energy cycles. However, such impacts have been most documented during periods of invasive species dominance; their influences on functioning at lower relative abundances and after long-term establishment are less well-known. We investigated the effects of Elodea canadensis, a macrophyte native to North America with a long invasion history in many regions of the world, on the biomass accrual and metabolism of littoral zone biofilms growing on organic and inorganic substrates. We deployed nutrient diffusing substrates (NDS) in 18 replicate transects distributed across six lakes, comprising three invaded by E. canadensis and three uninvaded reference lakes. NDS were amended with nitrogen (N), phosphorus (P) or N + P together, or were deployed as unamended controls. E. canadensis relative abundance varied widely in the invaded transects, ranging from 13% to 93% of all macrophyte cover. On control substrates, algal biomass, quantified as Chlorophyll-a, and gross primary production (GPP) were 42% and 78% greater in the invaded compared to uninvaded lakes, respectively. Respiration rates, attributable to responses of both autotrophs and heterotrophs, were 45% greater on control substrates in invaded lakes. By contrast, N-limitation of both biofilm GPP and respiration was 25% and 35% greater in uninvaded compared with invaded lakes. There was no evidence for differences in nutrients, light availability or grazing pressure between invaded and uninvaded transects. Rather, the observed differences in metabolism suggest that the presence of E. canadensis increases availability of N at local scales, reducing N-limitation of biofilms and resulting in elevated rates of biofilm productivity. Our results demonstrate that invasive elodeids might have significant impacts on biofilms and processes associated with the cycling of nutrients, even when long-established and present at lower relative abundances.

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  • 43.
    Menden-Deuer, Susanne
    et al.
    University of Rhode Island, Graduate School of Oceanography, RI, United States.
    Mullarney, Julia C.
    Coastal Marine Group, Te Aka Mātuatua-School of Science, University of Waikato, Waikato, Hamilton, New Zealand.
    Boersma, Maarten
    Alfred-Wegener-Institut Helmholtz-Zentrum für Polar-und Meeresforschung, Biologische Anstalt Helgoland, Helgoland, Germany.
    Grossart, Hans-Peter
    Department of Plankton and Microbial Ecology, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany; Institute of Biochemistry and Biology, Potsdam University, Potsdam, Germany.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Woodin, Sarah Ann
    Department of Biological Sciences, University of South Carolina, SC, Columbia, United States.
    Cascading, interactive, and indirect effects of climate change on aquatic communities, habitats, and ecosystems2023In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 68, no S1, p. S1-S7Article in journal (Refereed)
    Abstract [en]

    Climate-change is rapidly and intensively altering aquatic communities and habitats. While previous work has focused on direct effects of potential drivers, indirect and interactive effects on organisms and ecosystems have received less attention. Here, we give an overview of contributions to a special issue in Limnology and Oceanography that addresses this knowledge gap. Contributions covered diverse habitats, from polar to tropical regions, alpine streams to coral reefs. Several studies relied on time-series to identify indirect effects, thus emphasizing our need to maintain high-quality time-series data. Time-series are particularly crucial now that the pace of climate-change on aquatic-ecosystems is accelerating. Another common theme is the role of species-specific characteristics in physiology, behavior or genetics in aquatic ecosystem function. The addition of inter- and intra-specific variability to investigations of climate-change may be challenging particularly since ecosystem studies typically involve a large parameter space of environmental and biological variables across spatial and temporal scales. However, the results demonstrate that inclusion of species-specific dynamics, although challenging, can deliver mechanistic insights into aquatic ecosystem patterns and processes. Some contributions leverage habitat changes from disturbances or climate shifts to document capacity for resilience or recovery of pelagic and benthic communities. Jointly, the results in this special issue document fruitful approaches and provide urgent information needed for deciphering aquatic ecosystem responses to climate forcings. This information is foundational if we wish to tackle the combined effects of climate change and other human impacts with maximum efficacy and minimize unintended consequences for biodiversity and ecosystem functioning.

  • 44. Metcalfe, Daniel B.
    et al.
    Hermans, Thirze D. G.
    Ahlstrand, Jenny
    Becker, Michael
    Berggren, Martin
    Bjork, Robert G.
    Björkman, Mats P.
    Blok, Daan
    Chaudhary, Nitin
    Chisholm, Chelsea
    Classen, Aimee T.
    Hasselquist, Niles J.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kristensen, Jeppe A.
    Kumordzi, Bright B.
    Lee, Hanna
    Mayor, Jordan R.
    Prevey, Janet
    Pantazatou, Karolina
    Rousk, Johannes
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sundqvist, Maja K.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Center for Macroecology, Evolution and Climate, Natural History Museum of Copenhagen, University of Copenhagen, Copenhagen, Denmark.
    Tang, Jing
    Uddling, Johan
    Wallin, Göran
    Zhang, Wenxin
    Ahlström, Anders
    Tenenbaum, David E.
    Abdi, Abdulhakim M.
    Patchy field sampling biases understanding of climate change impacts across the Arctic2018In: Nature Ecology & Evolution, E-ISSN 2397-334X, Vol. 2, no 9, p. 1443-1448Article in journal (Refereed)
    Abstract [en]

    Effective societal responses to rapid climate change in the Arctic rely on an accurate representation of region-specific ecosystem properties and processes. However, this is limited by the scarcity and patchy distribution of field measurements. Here, we use a comprehensive, geo-referenced database of primary field measurements in 1,840 published studies across the Arctic to identify statistically significant spatial biases in field sampling and study citation across this globally important region. We find that 31% of all study citations are derived from sites located within 50 km of just two research sites: Toolik Lake in the USA and Abisko in Sweden. Furthermore, relatively colder, more rapidly warming and sparsely vegetated sites are under-sampled and under-recognized in terms of citations, particularly among microbiology-related studies. The poorly sampled and cited areas, mainly in the Canadian high-Arctic archipelago and the Arctic coastline of Russia, constitute a large fraction of the Arctic ice-free land area. Our results suggest that the current pattern of sampling and citation may bias the scientific consensuses that underpin attempts to accurately predict and effectively mitigate climate change in the region. Further work is required to increase both the quality and quantity of sampling, and incorporate existing literature from poorly cited areas to generate a more representative picture of Arctic climate change and its environmental impacts.

  • 45.
    Mosquera, Virginia
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Blackburn, Meredith
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Hasselquist, Eliza Maher
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Concentration-discharge patterns reveal catchment controls over the stoichiometry of carbon and nutrient supply to boreal streams2023In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 128, no 8, article id e2022JG007179Article in journal (Refereed)
    Abstract [en]

    Carbon (C), nitrogen (N), and phosphorus (P) export from catchments is strongly regulated by interactions between hydrological flowpaths and their terrestrial use/storage. While concentration-discharge (c-Q) relationships have been widely used to understand this interplay for C, N, and P individually, how flow regulates the relative supply of these resources across spatial and temporal scales is not well documented. Here, we analyze c-Q relationships from 12 years of data to test how seasonal flow regulates the concentrations of inorganic N (Dissolved inorganic nitrogen [DIN]) and P (Dissolved inorganic phosphorus [DIP]), dissolved organic N (DON) and C (dissolved organic carbon [DOC]) and their respective ratios across 12 streams in a boreal landscape. We observed opposing c-Q relationships between organic and inorganic solutes. DOC and DON tended toward transport limitation with little year-to-year change, whereas ammonium (NH4) and DIP were increasingly source limited over time. These different c-Q relationships translated into large (up to three-fold) shifts in resource ratios (e.g., DOC:DIN) in response to changes in flow. Our results also highlight strong influences of catchment structure on c-Q patterns, regardless of solute, season, and longer-term directional changes. Here, the organic solute c-Q responses became less transport limited over time; while inorganic solute responses became less source limited with increasing mire/decreasing forest cover. Overall, differences in timing of catchment exports for C, N, and P, create dynamic variation in solute concentrations in streams with subsequent impacts on resource stoichiometry that is central to aquatic ecological processes.

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  • 46.
    Mosquera, Virginia
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Maher Hasselquist, Eliza
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Co-occurrence of browning and oligotrophication in a boreal stream network2022In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 67, no 10, p. 2325-2339Article in journal (Refereed)
    Abstract [en]

    The relative supply of carbon (C), nitrogen (N), and phosphorus (P) to freshwater ecosystems is of fundamental importance to aquatic productivity, nutrient cycling, and food web dynamics. In northern landscapes, ongoing climate change, as well as legacies from atmospheric deposition, have the potential to drive changes in how these elements are recycled on land and exported to streams. While it is well established that dissolved organic carbon (DOC) concentrations have increased in many high latitude streams, the simultaneous trends for N and P and the ratios among these resources, are not well documented. We used data from 13 sites in a boreal stream network to analyze decadal-scale changes in dissolved inorganic N (DIN), dissolved organic N (DON), and dissolved inorganic P (DIP) concentrations and partition these trends seasonally. We observed widespread declines for DIP and DIN in streams, regardless of catchment characteristics. DIN decline was strongest during the growing season, and together with increases in DOC/DON at several sites, suggests increasing N retention by plants and soil microbes across this landscape. By contrast, declines for DIP occurred primarily during late autumn and winter, indicating that key biogeochemical changes are also occurring during non-growing season. Linking these trends to increases in DOC concentration in streams revealed changes in the ratio of energy to nutrient supply for the majority of sites, becoming richer in carbon and poorer in limiting nutrients over time. Overall, our observations from this stream network point to ongoing oligotrophication, with possible consequences for aquatic ecosystems in boreal landscapes.

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  • 47.
    Myrstener, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Fork, Megan L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Biology, West Chester University, PA, West Chester, United States.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Puts, Isolde
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hauptmann, Demian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Isles, Peter D. F.
    Vermont Department of Environmental Conservation, 1 National Live Drive, VT, Montpelier, United States.
    Burrows, Ryan M.
    School of Ecosystem and Forest Sciences, The University of Melbourne, Burnley Campus, VIC, Burnley, Australia.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Resolving the Drivers of Algal Nutrient Limitation from Boreal to Arctic Lakes and Streams2022In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 25, p. 1682-1699Article in journal (Refereed)
    Abstract [en]

    Nutrient inputs to northern freshwaters are changing, potentially altering aquatic ecosystem functioning through effects on primary producers. Yet, while primary producer growth is sensitive to nutrient supply, it is also constrained by a suite of other factors, including light and temperature, which may play varying roles across stream and lake habitats. Here, we use bioassay results from 89 lakes and streams spanning northern boreal to Arctic Sweden to test for differences in nutrient limitation status of algal biomass along gradients in colored dissolved organic carbon (DOC), water temperature, and nutrient concentrations, and to ask whether there are distinct patterns and drivers between habitats. Single nitrogen (N) limitation or primary N-limitation with secondary phosphorus (P) limitation of algal biomass was the most common condition for streams and lakes. Average response to N-addition was a doubling in biomass; however, the degree of limitation was modulated by the distinct physical and chemical conditions in lakes versus streams and across boreal to Arctic regions. Overall, algal responses to N-addition were strongest at sites with low background concentrations of dissolved inorganic N. Low temperatures constrained biomass responses to added nutrients in lakes but had weaker effects on responses in streams. Further, DOC mediated the response of algal biomass to nutrient addition differently among lakes and streams. Stream responses were dampened at higher DOC, whereas lake responses to nutrient addition increased from low to moderate DOC but were depressed at high DOC. Our results suggest that future changes in nutrient availability, particularly N, will exert strong effects on the trophic state of northern freshwaters. However, we highlight important differences in the physical and chemical factors that shape algal responses to nutrient availability in different parts of aquatic networks, which will ultimately affect the integrated response of northern aquatic systems to ongoing environmental changes.

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  • 48.
    Myrstener, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fork, Megan L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Callisto Puts, Isolde
    Hauptmann, Demian
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Resolving the drivers of aquatic nutrient limitation along boreal to Arctic climate gradientsManuscript (preprint) (Other academic)
  • 49.
    Myrstener, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre, Umeå University, Umeå, Sweden.
    Gómez-Gener, Lluís
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre, Umeå University, Umeå, Sweden; Stream Biolm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, ÉcolePolytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Rocher-Ros, Gerard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre, Umeå University, Umeå, Sweden.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre, Umeå University, Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre, Umeå University, Umeå, Sweden.
    Nutrients influence seasonal metabolic patterns and total productivity of Arctic streams2021In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 66, no S1, p. S182-S196Article in journal (Refereed)
    Abstract [en]

    The seasonality of gross primary production (GPP) in streams is driven by multiple physical and chemical factors, yet incident light is often thought to be most important. In Arctic tundra streams, however, light is available in saturating amounts throughout the summer, but sharp declines in nutrient supply during the terrestrial growing season may constrain aquatic productivity. Given the opposing seasonality of these drivers, we hypothesized that "shoulder seasons"-spring and autumn-represent critical time windows when light and nutrients align to optimize rates of stream productivity in the Arctic. To test this, we measured annual patterns of GPP and biofilm accumulation in eight streams in Arctic Sweden. We found that the aquatic growing season length differed by 4 months across streams and was determined largely by the timing of ice-off in spring. During the growing season, temporal variability in GPP for nitrogen (N) poor streams was correlated with inorganic N concentration, while in more N-rich streams GPP was instead linked to changes in phosphorus and light. Annual GPP varied ninefold among streams and was enhanced by N availability, the length of ice-free period, and low flood frequency. Finally, network scale estimates of GPP highlight the overall significance of the shoulder seasons, which accounted for 48% of annual productivity. We suggest that the timing of ice off and nutrient supply from land interact to regulate the annual metabolic regimes of nutrient poor, Arctic streams, leading to unexpected peaks in productivity that are offset from the terrestrial growing season.

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  • 50.
    Myrstener, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rocher-Ros, Gerard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Burrows, Ryan M.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persistent nitrogen limitation of stream biofilm communities along climate gradients in the Arctic2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 8, p. 3680-3691Article in journal (Refereed)
    Abstract [en]

    Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll-a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.

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