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  • 1. Ahlgren, Joakim
    et al.
    Reitzel, Kasper
    Tranvik, Lars
    Gogoll, Adolf
    Rydin, Emil
    Degradation of organic phosphorus compounds in anoxic Baltic Sea sediments: A P-31 nuclear magnetic resonance study2006Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 51, nr 5, s. 2341-2348Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The composition and abundance of phosphorus extracted by NaOH-ethylenediaminetetraacetic acid from anoxic Northwest Baltic Sea sediment was characterized and quantified using solution P-31 nuclear magnetic resonance. Extracts from sediment depths down to 55 cm, representing 85 yr of deposition, contained 18.5 g m(-2) orthophosphate. Orthophosphate monoesters, teichoic acid P, microbial P lipids, DNA P, and pyrophosphate corresponded to 6.7, 0.3, 1.1, 3.0, and 0.03 g P m(-2), respectively. The degradability of these compound groups was estimated by their decline in concentration with sediment depth. Pyrophosphate had the shortest half-life (3 yr), followed by microbial P lipids with a half-life of 5 yr, DNA P (8 yr), and orthophosphate monoesters (16 yr). No decline in concentration with sediment depth was observed for orthophosphate or teichoic acid P.

  • 2.
    Ask, Jenny
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ask, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Terrestrial organic matter and light penetration: Effects on bacterial and primary production in lakes2009Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, nr 6, s. 2034-2040Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden. Primary production and bacterial production in benthic and pelagic habitats were measured to estimate the variation in energy mobilization from external energy sources (primary production plus bacterial production on allochthonous organic carbon) along the gradient. Clear-water lakes were dominated by autotrophic energy mobilization in the benthic habitat, whereas humic lakes were dominated by heterotrophic energy mobilization in the pelagic habitat. Whole-lake (benthic + pelagic) energy mobilization was negatively correlated to the light-extinction coefficient, which was determined by colored terrestrial organic matter in the lake water. Thus, variation in the concentration of terrestrial organic matter and its light-absorbing characteristics exerts strong control on the magnitude, as well as on the processes and pathways, of energy mobilization in unproductive lakes. We suggest that unproductive lakes in general are sensitive to input of terrestrial organic matter because of its effects on basal energy mobilization in both benthic and pelagic habitats.

  • 3. Berggren, M.
    et al.
    Bengtson, P.
    Soares, A. R. A.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Climate Impacts Research Centre (CIRC).
    Terrestrial support of zooplankton biomass in northern rivers2018Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, nr 6, s. 2479-2492Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The contribution of terrestrially derived carbon to micro-crustacean zooplankton biomass (i.e., allochthony) has been previously studied in lakes, reservoirs, and estuaries, but little is known about zooplankton allochthony in rivers. In lacustrine environments, allochthony is regulated by distinct selective feeding behavior of different taxa. However, we hypothesized that restricted possibility for selective grazing in turbulent environments such as rivers would decouple zooplankton from specific microbial and algal food resources, such that their allochthony would mirror the terrestrial contribution to the surrounding bulk particle pool. We tested this idea by analyzing allochthony in 13 widely distributed Swedish rivers, using a dual-isotope mixing model. Zooplankton biomasses were generally low, and allochthony in different micro-crustacean groups (Cladocera, Cyclopoida, Calanoida) varied from 2% to 77%. As predicted, there were no correlations between allochthony and variables indicating the supply of algal and microbial food resources, such as chlorophyll a and bacterial production. Instead, the allochthony was generally similar to the share allochthonous contribution in bulk particulate organic matter, with relationships close to the 1 : 1 line. The zooplankton community allochthony was strongly regulated by the ecosystem metabolic balance between production and respiration, which in turn was dependent upon the ratio between total autochthonous organic carbon concentrations and water color. Our study for the first time shows that micro-crustacean allochthony is regulated differently in rivers compared to in lacustrine systems, and points to inefficient support of zooplankton biomass by algal resources in turbulent waters.

  • 4.
    Berggren, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Hjalmar, Laudon
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Aging of allochthonous organic carbon regulates bacterial production in unproductive boreal lakes2009Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, nr 4, s. 1333-1342Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We calculated average aquatic dissolved organic carbon (DOC) age (the time span from soil discharge to observation) in water from the inlets and outlets of two unproductive Swedish lakes at different times during an annual cycle. Bacterial production (BP) and bacterial growth efficiency (BGE) determined during 7-d bioassays decreased with increasing average aquatic DOC age. Parallel to the declines in BP and BGE there was a rise in specific ultraviolet absorbance at the wavelength of 254 nm (SUVA254), which indicates that decreasing BP and BGE were connected to a shift to a more aromatic and recalcitrant DOC pool. The relationships between bacterial metabolism and DOC age were stronger after a Q10 correction of the DOC age, showing that temperature affected rates of DOC quality changes over time and should be taken into account when relating lake bacterial growth to substrate aging in natural environments. We propose that hydrological variability in combination with lake size (water renewal time) have a large influence on pelagic BP in lakes with high input of terrigenous DOC.

  • 5. Burrows, Ryan M.
    et al.
    Laudon, Hjalmar
    McKie, Brendan G.
    Sponseller, Ryan A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Seasonal resource limitation of heterotrophic biofilms in boreal streams2017Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, nr 1, s. 164-176Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 6.
    Deininger, Anne
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Faithfull, Carolyn L.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Oceanography, University of Hawai'i, Honolulu, USA.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Klaus, Marcus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Pelagic food web response to whole lake N fertilization2017Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, nr 4, s. 1498-1511Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Anthropogenic activities are increasing inorganic nitrogen (N) loadings to unproductive boreal lakes. In many of these lakes phytoplankton are N limited, consequently N fertilization may affect ecosystem productivity and consumer resource use. Here, we conducted whole lake inorganic N fertilization experiments with six small N limited unproductive boreal lakes (three control and three N enriched) in an area receiving low N deposition with one reference and two impact years. Our aim was to assess the effects of N fertilization on pelagic biomass production and consumer resource use. We found that phytoplankton primary production (PP) and biomass, and the PP: bacterioplankton production ratio increased after fertilization. As expected, the relative contribution of phytoplankton derived resources (autochthony) that supported the crustacean zooplankton community increased. Yet, the response in the consumer community was modest with autochthony only increasing in one of the three major zooplankton groups and with no effect on zooplankton biomass. In conclusion, our findings imply that newly available phytoplankton energy derived from N fertilization was not efficiently transferred up to zooplankton, indicating a mismatch between producer energy supply and consumer energy use with potential accumulation of phytoplankton biomass as the result.

  • 7.
    Faithfull, Carolyn
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Vrede, Tobias
    Swedish University of Agricultural Sciences, Uppsala.
    Effects of nutrients and physical lake characteristics on bacterial and phytoplankton production: A meta-analysis2011Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 56, nr 5, s. 1703-1713Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We performed a meta-analysis comprising field (300 studies) and experimental data (249 studies) from a widerange of lake trophic states and locations. We examined the effects of nitrogen (N), phosphorus (P), carbon(dissolved organic matter [DOM]), temperature, latitude, and lake morphometry on the absolute and relative ratesof phytoplankton primary production (PPr) and secondary bacterial production (BP). Areal and volumetric rates ofPPr, BP, and BP : PPr were compared, and we analyzed differences between experimental and natural systems. Bothfield studies and experimental results showed agreement with regard to N and P as predictors of volumetric PPr andBP, respectively, despite the large variation in study duration, size, and nutrient addition rates in experimentalsystems. This indicates that bacteria and phytoplankton do not seem to be competing for the same nutrients. Arealmeasurements were more difficult to predict and were more dependent on physical lake characteristics thannutrients. Temperature was positively correlated with PPr, but not with BP. BP: PPr was stable across experimentsregardless of N, P, DOM, or glucose additions. In contrast, BP : PPr ratios varied greatly in the field data set andwere highest in systems with low total N and at high latitudes. This pattern was driven by reduced PPr, not BP;therefore, experimenters may need to manipulate PPr to change BP: PPr. Collectively, our results indicate thatincreased temperatures and N availability will lead to higher PPr and lower BP : PPr, potentially decreasing theimportance of energy mobilized through the microbial food web on a global scale.

  • 8. Fridolfsson, Emil
    et al.
    Lindehoff, Elin
    Legrand, Catherine
    Hylander, Samuel
    Thiamin (vitamin B1) content in phytoplankton and zooplankton in the presence of filamentous cyanobacteria2018Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, nr 6, s. 2423-2435Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Top predators in several aquatic food webs regularly display elevated reproductive failure, caused by thiamin(vitamin B1)deficiency. The reasons for these low-thiamin levels are not understood and information about the transfer of thiamin from the producers (bacteria and phytoplankton) to higher trophic levels is limited. One main concern is whether cyanobacterial blooms could negatively affect thiamin transfer in aquatic systems. Laboratory experiments with Baltic Sea plankton communities and single phytoplankton species were used to study the effect of filamentous cyanobacteria on the transfer of thiamin from phytoplankton to zooplankton. Experiments showed that the thiamin content in copepods was reduced when exposed to elevated levels of cyanobacteria, although filamentous cyanobacteria had higher levels of thiamin than any other analyzed phytoplankton species. Filamentous cyanobacteria also had a negative effect on copepod egg production despite high concentrations of non-cyanobacterial food. Phytoplankton species composition affected overall thiamin concentration with relatively more thiamin available for transfer when the relative abundance of Dinophyceae was higher. Finally, phytoplankton thiamin levels were lower when copepods were abundant, indicating that grazers affect thiamin levels in phytoplankton community, likely by selective feeding. Overall, high levels of thiamin in phytoplankton communities are not reflected in the copepod community. We conclude that presence of filamentous cyanobacteria during summer potentially reduces the transfer of thiamin to higher trophic levels by negatively affecting phytoplankton and copepod thiamin content as well as copepod reproduction, thereby lowering the absolute capacity of the food web to transfer thiamin through copepods to higher trophic levels.

  • 9.
    Gälman, Veronika
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rydberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Decadal diagenetic effects on d13C and d15N studied in varved lake sediment2009Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, nr 3, s. 917-924Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To assess the long-term (27 yr) effects of sediment aging on stable carbon and nitrogen isotope values (δ13C and δ15N), we used a collection of eight freeze cores of annually laminated (varved) lake sediment collected from 1979 to 2007 in Nylandssjon (northern Sweden). Previous research has shown that 20–23% of carbon and 35% of nitrogen is lost in 27 yr. Material from specific years was compared in the cores, e.g., δ13C and δ15N of the surface varve of the 1979 core was followed in cores retrieved in 1980, 1989, 1993, 2002, 2004, and 2006. δ13C increased by 0.4–1.5% during the first 5 yr. After this initial increase, only minor fluctuations were recorded. There is a good correlation between the magnitude in δ13C changes and the initial carbon and nitrogen concentrations, indicating that the initial sediment composition is important for the 13C fractionation. δ15N gradually decreased by 0.3–0.7% over the entire 27-yr period. The lack of correlation with the initial sediment composition and the gradual decrease in δ15N indicates a microbial control on δ15N change. The diagenetic changes in the stable isotope values that occur in Nylandssjon are small, but of the same magnitude as the down-core variation in the varves deposited 1950–2006. Diagenetic effects should be considered when δ13C and δ15N are used to study organic matter sources or paleoproductivity, especially when dealing with recent trends or small changes. Based on our findings, diagenetic effects for δ13C are observed during the first 5–10 yr, whereas no delimitation can be recommended for δ15N.

  • 10.
    Gälman, Veronika
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rydberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Decadal diagenetic effects on δ13C and δ15N studied in varved lake sediment2009Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, nr 3, s. 905-916Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Livingstone and Imboden (1996) model for the oxygen depletion rate in lake hypolimnia was evaluated with field results in 32 lakes. The volumetric oxygen consumption rate (JV) was strongly related to lake trophic state, as represented by the growing season mean chlorophyll a (Chl a) and annual mean total phosphorus concentration, and might reach a maximum of 0.23–0.24 g O2 m-3 d-1 in eutrophic lakes. The areal oxygen consumption rate (JA) was not related to trophic state and was lower than the value estimated by the sediment core method, particularly in eutrophic lakes; the mean was 0.0816 6 0.0150 g O2 m-2 whole sediment d-1. We modified the model and it was used to confirm that the field JA, the average for the hypolimnion for the deoxygenation period, is influenced by JV and the range of sediment area to water volume ratio, (Z) (Z is water depth), in the hypolimnion, as well as the oxygen consumption rate in whole sediment (R). It was suggested that this is the reason for the difference between field and sediment core JA values. The R in 10 lakes varied from 7 to 460 g O2 m-3 whole sediment d-1. Overall, the Livingstone and Imboden model with constant JA and with a JV value derived from an empirical relationship with either measure of trophic state was considered to be a suitable condensed model for oxygen depletion in lake hypolimnia.

  • 11.
    Gälman, Veronika
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rydberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Sjöstedt-de Luna, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Renberg, Ingemar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Carbon and nitrogen loss rates during aging of lake sediment: Changes over 27 years studied in varved lake sediment2008Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, nr 3, s. 1076-1082Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We used a collection of ten freeze cores of annually laminated (varved) lake sediment from Nylandssjön in northern Sweden collected from 1979 to 2007 to follow the long-term loss of carbon (C) and nitrogen (N) due to processes that occur in the lake bottom as sediment ages. We compared specific years in the different cores. For example, the loss of C from the surface varve of the 1979 core (sediment deposited during 1978) was followed in the cores from 1980, 1985, 1989, and so on until 2006. The C concentration of the sediment decreased by 20% and N decreased by 30% within the first five years after deposition, and after 27 yr in the sediment, there was a 23% loss of C and 35% loss of N. Because the relative loss of C with time was smaller than loss of N, the C:N ratio increased with increasing age of the sediment; the surface varves start with a ratio of ~10, which then increases to ~12.

  • 12. Herrero Ortega, Sonia
    et al.
    Catalan, Núria
    Björn, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Gröntoft, Hannes
    Hilmarsson, Torfi Geir
    Bertilsson, Stefan
    Wu, Pianpian
    Bishop, Kevin
    Levanoni, Oded
    Bravo, Andrea G.
    High methylmercury formation in ponds fueled by fresh humic and algal derived organic matter2018Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, s. S44-S53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Neurotoxic methylmercury causes adverse effects to ecosystem viability and human health. Previous studies have revealed that ponding alters natural organic matter (NOM) composition and increase methylmercury concentrations in rivers, especially in the first years after flooding. Here, we investigate the influence of NOM composition (i.e., sources and degradation status) on mercury methylation rate constants in nine boreal beaver ponds of different ages across Sweden. We show that increased methylmercury concentrations in surface waters is a consequence of enhanced mercury methylation in the pond sediments. Moreover, our results reveal that during the first years after the initial flooding, mercury methylation rates are fueled by the amount of fresh humic substances released from the flooded soils and by an increased production of algal-derived NOM triggered by enhanced nutrient availability. Our findings indicate that impoundment-induced changes in NOM composition control mercury methylation processes, causing the raise in MeHg levels in ponds.

  • 13.
    Hotchkiss, Erin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Hall, Robert
    High rates of daytime respiration in three streams: Use of delta O-18(O2) and O-2 to model diel ecosystem metabolism2014Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, nr 3, s. 798-810Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photosynthesis and respiration determine the carbon and oxygen (O-2) balance of ecosystems. Current methods used to estimate ecosystem respiration (ER) do not include diel ER fluctuations, which limit testing predictions about short-term drivers of ecosystem metabolism. Diel changes in delta O-18(O2) can be used to estimate diel ER due to discrimination against O-18(O2) during respiration. We monitored diel delta O-18(O2), O-2, light, and water temperature in three Wyoming streams and measured respiration fractionation (alpha(R)) against O-18(O2) in dark benthic flow chambers in two streams. The ranges of measured and literature alpha(R) values were used to estimate uncertainty in metabolism parameters associated with not measuring alpha(R) directly. Daytime ER was 54-340% higher than nighttime ER using delta O-18(O2), but diel ER parameter estimates were highly uncertain relative to traditional estimates of ecosystem metabolism. Diel variations in water temperature only accounted for 4-55% of the range of diel ER calculated using diel delta O-18(O2). Measured benthic flow chamber alpha(R) varied within the range of literature values: from 0.9755 to 0.9954. Metabolism parameter estimates were very sensitive to choice of alpha(R) within the measured and published range of values. The mean and uncertainty of diel ER estimates increased with decreasing alpha(R), with daily ER more than ten times higher given an alpha(R) of 0.975 vs. 0.999. Diel changes in ER can be modeled using delta O-18(O2) and O-2, but diel ER estimates depend on the choice of alpha(R), suggesting the need to better understand how alpha(R) may vary within spatial and temporal scales appropriate for delta O-18(O2) metabolism models.

  • 14. Hylander S, S
    et al.
    Boeing, WJ
    Granéli, W
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    von Einem, J
    Gutseit, K
    Hansson, L-H
    Complementary UV protective compounds in zooplankton2009Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, s. 1883-1893Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zooplankton accumulate several groups of photoprotective compounds to shield against damaging ultraviolet radiation (UV). One of these groups, the carotenoids, makes the animals more conspicuous to visually hunting predators, whereas others, such as the mycosporine-like amino acids (MAAs) may not. The blend of photoprotective compounds is therefore important for the UV defense but also for the ability to escape predation through crypsis. Here we assess laboratory and field data from different latitudes to examine how UV, predation threat, and pigment availability (in food) affects the mixture of UV-protective compounds in copepods. Overall, the blend of MAAs and carotenoids was partly explained by the availability of MAAs in the food, the UV-threat, and the presence of predators. Copepods upregulated their MAA content when UV threat was increasing (i.e., if MAAs were abundant in food), and in field data this accumulation only occurred at high levels of predation threat. If MAAs were scarce, copepods instead compensated with higher carotenoid accumulation. However, when there was a high predation threat this carotenoid compensatory effect was disadvantageous, and low concentrations of both MAAs and carotenoids at high UV-threat resulted in lower reproduction. In all, these results showed that carotenoids and MAAs are complementary substances, i.e., one is high when the other is low, and copepods are, hence, able to adjust their blend of different UV-protective compounds to optimize their defenses to the threats of UV and predation. These defense systems may buffer against direct food-web interactions and help the zooplankton to survive in environments with high UV threat.

  • 15.
    Jansson, Mats
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Berggren, Martin
    Laudon, Hjalmar
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bioavailable phosphorus in humic headwater streams in boreal Sweden2012Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, nr 4, s. 1161-1170Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bioavailable phosphorus (BAP) concentrations were determined nine times between April and October 2010 in two humic boreal headwater streams draining forest-and mire-dominated catchments. BAP was analyzed in a bioassay in which natural P-limited bacterioplankton grew with natural P as the sole P source. In both streams, approximately 90% of the BAP occurred as dissolved species (passing a 0.2-mu m filter), consisting partly of low-molecular-weight forms (passing a filter with nominal cutoff at 1 kDa) and partly of high-molecular-weight forms (passing a 0.2-mu m filter but not a 1-kDa filter). Concentrations of total dissolved BAP varied between 1 mu g L-1 and 14 mu g L-1, with the highest values in the middle of the summer. Compared to the forest stream, BAP concentrations were generally higher in the mire stream, where it occasionally amounted to nearly 50% of total P. Molybdate reactive phosphorus overestimated BAP considerably. Most of the BAP was in forms other than free orthophosphate. Temporal BAP variations showed no relationships with dissolved organic carbon (C) or iron but were positively related to air temperature and negatively related to the absorbance ratio (a254 : a365) of organic compounds in the water, indicating connections between terrestrial export of BAP and temperature-dependent terrestrial C metabolism. Concentrations of BAP can relieve stream bacteria from P limitation, and a significant share of BAP exported to streams can reach and be used in downstream lakes.

  • 16.
    Jansson, Mats
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Blomqvist, Peter
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nutrient limitation of bacterioplankton, autotrophic and mixotrophic phytoplankton, and heterotrophic nanoflagellates in Lake Örträsket1996Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 41, nr 7, s. 1552-1559Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Enrichment experiments with P and N were conducted in humic Lake Örträsket in northern Sweden. The composition of the microplankton community showed a dominance by bacterioplankton, followed by mixotrophic sind potentially mixotrophic phytoplankton, heterotrophic nanoflagellates, and autotrophic phytoplankton. Bacterioplankton was P limited for most of the ice-free period, and phytoplankton biomass and primary production mostly increased after enrichment with N, but not with P. The dominant group of phytoplankton, the mixotrophic flagellates, was stimulated by N bur not by P, while obligate autotrophic species were stimulated only by P+N. It is suggested that N limitation in mixotrophic species is induced by grazing of P-rich bacteria. The results suggest that primary productivity in humic lakes can be limited by N and indicate the importance of phagocytosis as a means of nutrition in phytoplankton. A link is suggested to exist in humic lakes whereby heterotrophic bacterioplankton, which use humic compounds as their principal energy source, can transfer energy and nutrients to potentially autotrophic organisms, with subsequent utilization by other components of the food web.

  • 17.
    Jansson, Mats
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Blomqvist, P
    Allochthonous organic carbon decreases pelagic energy mobilization in lakes2003Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 48, nr 4, s. 1711-1716Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Over the past decade, it has been Shown that unproductive lakes worldwide are net heterotrophic because bacterial respiration of allochthonous. organic carbon (AOC) makes community respiration exceed primary production. Net heterotrophy means that aquatic systems are net sources of CO2 to the atmosphere but also that bacterial utilization of AOC increases bacterioplankton production (BP) and bacterial uptake of limiting inorganic nutrients at the expense of phytoplankton production (PP). We studied 15 unproductive lakes in northern Sweden with dissolved organic carbon concentrations between 3 and 22 mg L-1. We found a highly significant negative relationship between the degree of heterotrophy and total pelagic energy mobilization (PP + BP based on AOC) per unit of limiting nutrient. We suggest that this is because the high cell phosphorous (P) requirement of bacteria makes energy mobilization per P unit considerably lower in bacterioplankton than in phytoplankton. We also suggest that the productivity of the entire pelagic ecosystem is determined by the availability of inorganic nutrients and AOC and by whether nutrients are allocated to BP or PP.

  • 18.
    Jonsson, Anders
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Meili, Markus
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Whole-lake mineralization of allochthonous and autochthonous organic carbon in a large humic lake (Örträsket, N. Sweden)2001Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 46, nr 7, s. 1691-1700Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Organic carbon mineralization was studied. in a large humic lake (Lake Örträsket) in northern Sweden during a well-defined summer stratification period following high water flow during snowmelt. Several independent methods including plankton counts, measurements of bacterioplankton and phytoplankton production, stable isotope monitoring, sediment trapping, and mass balance calculations were used. Total organic carbon mineralization showed a summer mean of 0.3 g C m(-2) d(-1) and was partitioned about equally between water and sediment. In the water column, organic matter was mineralized by bacteria (60%) and protozoan and metazoan zooplankton (30%), as well as by photooxidation (10%). Most of the mineralized organic carbon was of allochthonous origin. Primary production in the lake contributed at most 5% of the total organic carbon input and about 20% of the total organic carbon mineralization. Total carbon mineralization in. the epilimnion and metalimnion agreed well with an estimate of CO2 evasion from the stratified lake, while CO2 accumulation in the hypolimnion matched the O-2 consumption and resulted in a very negative delta C-13 of DIC before autumn overturn (-23 parts per thousand). Isotopic compositions of DIC and POC confirmed the dominant influence of terrestrial organic input on the cycling of both organic and inorganic carbon in the lake.

  • 19.
    Jäger, Christoph G.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Diehl, Sebastian
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Schmidt, Gertraud M.
    Influence of water-column depth and mixing on phytoplankton biomass, community composition, and nutrients2008Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, nr 6, s. 2361-2373Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We independently manipulated mixing intensity (strong artificial mixing vs. background turbulence) andwater-column depth (2 m, 4 m, 8 m, and 12 m) in order to explore their separate and combined effects in a fieldenclosure experiment. To accentuate the vertical light gradient, enclosures had black walls, resulting in a euphoticdepth of only 3.7 m. All enclosures were placed in a well-mixed water bath to equalize temperature acrosstreatments. Phytoplankton responded to an initial phosphorus pulse with a transient increase in biomass, whichwas highest in the shallowest, least light-limited water columns where dissolved mineral phosphorus subsequentlybecame strongly limiting. As a consequence, the depth-averaged mineral phosphorus concentration increased andthe seston carbon (C) : phosphorous (P) ratio decreased with increasing water-column depth. Low turbulenceenclosures became quickly dominated by motile taxa (flagellates) in the upper water column, whereas mixedenclosures became gradually dominated by pennate diatoms, which resulted in higher average sedimentation ratesin the mixed enclosures over the 35-d experimental period. Low turbulence enclosures showed pronouncedvertical structure in water columns .4 m, where diversity was higher than in mixed enclosures, suggesting verticalniche partitioning. This interpretation is supported by a primary production assay, where phytoplanktonoriginating from different water depths in low-turbulence treatments had the relatively highest primaryproductivity when incubated at their respective depths of origin.

  • 20.
    Karlsson, Jan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ask, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Winter respiration of allochthonous and autochthonous organic carbon in a subarctic clear-water lake2008Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, nr 3, s. 948-954Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We studied a small subarctic lake to assess the magnitude of winter respiration and the organic carbon (OC) source for this respiration. The concentration and stable isotopic composition (d13C) of dissolved inorganic carbon (DIC) accumulating in the lake water under ice was analyzed over one winter (7 months). The DIC concentration increased and the d13C of DIC decreased over time, with the greatest changes at the lake bottom. Winter respiration was 26% of annual respiration in the lake. Keeling plot analysis demonstrated that the d13C of respired DIC varied spatially, high d13C values occurring at shallow (2.5 m, 21.7‰) compared with intermediate (4 m, 25.1‰) and deep (6 m, 27.8‰) locations in the lake. The variation in the d13C of respired DIC was related to the variation in the d13C of the sediments between locations, suggesting that sediment OC supported much of the winter respiration and that the dominant OC source for respiration was OC from benthic algae at shallow locations and settled OC, of predominately terrestrial origin, at deep locations. The respiration of OC from benthic algae constituted 55% of the winter respiration, equaling 54% of the primary production by benthic algae the previous summer. The study indicates the importance of temporal and spatial variation in respiration for the metabolism and net DIC production in unproductive high-latitude lakes; both allochthonous and autochthonous carbon can contribute to winter DIC accumulation and, consequently, to spring CO2 emissions from lakes.

  • 21.
    Karlsson, Jan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Berggren, M.
    Ask, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Laudon, H.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Response to Comment: Terrestrial support of pelagic consumers in unproductive lakes- Uncertainty and potential in assessments using stable isotopes2014Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, nr 5, s. 1800-1803Artikkel i tidsskrift (Fagfellevurdert)
  • 22.
    Karlsson, Jan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Berggren, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ask, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Terrestrial organic matter support of lake food webs: Evidence from lake metabolism and stable hydrogen isotopes of consumers2012Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, nr 4, s. 1042-1048Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We quantified the utilization of terrestrial organic matter (OM) in the food web of a humic lake by analyzing the metabolism and the consumers' stable isotopic (C, H, N) composition in benthic and pelagic habitats. Terrestrial OM inputs (3 g C m(-2) d(-1)) to the lake greatly exceeded autochthonous OM production (3 mg C m(-2) d(-1)) in the lake. Heterotrophic bacterial growth (19 mg C m(-2) d(-1)) and community respiration (115 mg C m(-2) d(-1)) were high relative to algal photosynthesis and were predominantly (> 85%) supported by terrestrial OM in both habitats. Consequently, terrestrial OM fueled most (85%) of the total production at the base of the lake's food web (i.e., the sum of primary and bacterial production). Despite the uncertainties of quantitatively estimating resource use based on stable isotopes, terrestrial OM clearly also supported around half the zooplankton (47%), macrozoobenthos (63%), and fish (57%) biomass. These results indicate that, although rates of terrestrial OM inputs were around three orders of magnitude greater than that of autochthonous OM production, the use of the two resources by higher trophic levels was roughly equal. The disproportionally low reliance on terrestrial OM at higher trophic levels, compared with its high rates of input and high support of basic biomass production in the lake, suggests that autochthonous resources could not be completely replaced by terrestrial resources and indicates an upper limit to terrestrial support of lake food webs.

  • 23.
    Karlsson, Jan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Meili, M
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Control of zooplankton dependence on allochthonous organic carbon in humic and clear-water lakes in northern Sweden2003Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 48, nr 1, s. 269-276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We compared the stable carbon isotopic composition (delta(13)C) of crustacean zooplankton with that of potential carbon sources in 15 lakes in northern Sweden with different dissolved organic carbon (DOC) concentrations (2-9 mg L-1) to test the hypothesis that zooplankton depended more on allochthonous carbon in humic lakes than in clear-water lakes. Based on delta(13)C signature, we found that the pool of organic matter in the lakes was dominated by carbon of allochthonous origin over the whole DOC gradient. Zooplankton were generally depleted in C-13 compared to organic matter in the catchment, particulate organic matter in the lake water, and shallow surface sediment. However, the isotopic composition of zooplankton could not be explained without a significant contribution from both allochthonous and autochthonous carbon sources in all lakes. The relative importance of these two carbon sources did not relate to the concentration of, or proportion between, allochthonous and autochthonous organic carbon in the water. Instead, the proportion between allochthonous and autochthonous carbon in the crustacean zooplankton was consistent with a rather conservative use of the energy mobilized by bacterioplankton and phytoplankton in the lakes.

  • 24.
    Kisand, Veljo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Andersson, Nina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Wikner, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet).
    Bacterial freshwater species successfully immigrate to the brackish water environment in the northern Baltic2005Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 50, nr 3, s. 945-956Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We studied the distribution and seasonal dynamics of five species from the genus Flavobacterium and one species from the genus Marinomonas over the course of a year along a northern Baltic Sea river-marine transect. All of the species had been previously demonstrated as important consumers of riverine dissolved organic carbon. Quantitative DNA-DNA hybridization data showed that two of the Flavobacterium spp. and the Marinomonas sp. had highest abundance in the river water (maximum 20,000 cells ml-1), with maximum relative abundance of 0.5-2.5% of the bacterial community. These species declined in abundance from the river to the estuary and the offshore site. Abundance and dynamics in the estuarine environment suggested successful immigration of freshwater bacteria, accompanied by growth in the brackish water environment. Two of the three abundant species showed high cell numbers also during late autumn to early spring in the estuary, indicating a selective advantage when riverine dissolved organic carbon was the main carbon source. The remaining three species showed more episodic abundance close to the detection limit of the method, providing weaker evidence of occurrence in the freshwater environment. Some bacterioplankton consuming riverine organic carbon in the brackish water environment in the northern Baltic are therefore freshwater species, with a selective advantage during winter.

  • 25.
    Klaus, Marcus
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Deininger, Anne
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Geibrink, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Weak response of greenhouse gas emissions to whole lake N enrichment2018Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, s. S340-S353Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Global warming and land use scenarios suggest increased 21st century nitrogen (N) inputs to aquatic systems. Nitrogen affects in-lake processing and, potentially, atmospheric exchange of greenhouse gases, probably being most relevant in unproductive systems. Here, we test for the first time the effect of a whole-lake experimental increase (threefold) in external nitrate loads on the atmospheric exchange of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from N-limited unproductive boreal lakes. Nitrate enrichment effects were assessed within a paired Before/After-Control/Impact framework based on 2-hourly to biweekly surface-water sampling of dissolved gas concentrations, and monthly whole-lake inventory surveys, carried out over 4 yrs in six lakes. Nitrate enrichment did not affect gas exchange during summer stratification and whole-lake gas inventories during summer and winter stratification. This finding specifically emphasizes the modest role of internal carbon fixation for the CO2 dynamics of unproductive boreal lakes. A global synthesis of 52 published studies revealed a wide range of nutrient fertilization effects, both in systems similar to our experimental lakes, and other more productive systems. Effects depended mainly on the spatiotemporal scale of the study and became more pronounced when N enrichment was combined with phosphorous. Conclusively, although short-term and habitat-specific effects can occur, changes in N supply have only weak whole-ecosystem effects on greenhouse gas emissions from unproductive boreal lakes.

  • 26. Lupon, Anna
    et al.
    Denfeld, Blaize A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Leach, Jason
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Sponseller, Ryan A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Groundwater inflows control patterns and sources of greenhouse gas emissions from streams2019Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 64, nr 4, s. 1545-1557Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 27.
    Maier, Dominique B.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Diehl, Sebastian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Interannual variation in seasonal diatom sedimentation reveals the importance of late winter processes and their timing for sediment signal formation2019Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 64, nr 3, s. 1186-1199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Disentangling the process information contained in a diatom sediment signature is crucial for reliable future predictions based on paleolimnological records. In this study, we combine limnological and paleolimnological monitoring to address the fundamental question: Which environmental information is contained in a diatom sediment signal? We compared annual diatom sequential sediment trap records with the diatom record of the annually varved lake sediment of Nylandssjon (northern Sweden) from three meteorologically different years (2012-2014). The seasonal patterns in diatom sedimentation were strikingly different in varve years 2012 and 2014 compared to varve year 2013. In 2012 and 2014, up to 70% of the annual flux occurred in a single spring month and was dominated by Cyclotella glomerata. In contrast, in 2013, peak fluxes were much lower and more annually integrated. Next, we compared the full-year diatom trap results with year round in-lake physical, chemical, and biological monitored parameters, as well as meteorological variables. Annual averages of environmental conditions did not explain the interannual variability in diatom sedimentation. Instead, the seasonality of diatom sedimentation was determined by the timing of the spring diatom bloom relative to lake over-turn in winters with warm vs. cold air temperature. With our combined limnological and paleolimnological monitoring approach, we find that an annual diatom signal can either contain primarily seasonal climate information from a short time period or be annually integrated. We synthesize our results in a novel conceptual model, which describes the response of sediment diatom signals to two distinct sequences of late-winter conditions.

  • 28.
    Rosén, Peter
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Cunningham, Laura
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Vonk, Jorien
    Department of Applied Environmental Science (ITM), Stockholm University, Stockholm, Sweden.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Effects of climate on organic carbon and the ratio of planktonic to benthic primary producers in a subarctic lake during the past 45 years2009Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, nr 5, s. 1723-1732Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of climatic variables on lake-water total organic carbon (TOC) concentrations and benthic and pelagic primary producers during the past 45 yr were assessed using the sediment records of two subarctic lakes, one with mires and one without mires connected to the lake. The lake with a mire showed large and synchronous changes in the planktonic to benthic (P : B) ratio of diatoms and concentrations of TOC inferred from nearinfrared spectroscopy. During periods of warm temperatures, high precipitation, and long ice-free conditions, we inferred high TOC in the lake, and the diatom community was dominated by planktonic species. The stable carbon isotopic (d13C) values of sediment organic matter were negatively correlated with inferred TOC concentration and P :B ratio. We suggest that the changes in TOC and P : B ratio were a result of changing climate, permafrost degradation, and related changes in the catchment. Terrestrial organic matter, by its strong effect on the penetration of light through the lake water, possibly affected the habitats available for benthic photosynthesis and thus the d13C of the sediment organic matter. The large changes in recent times may also be because of unusually long ice-free periods, warmer temperatures, and other associated limnological changes. The lake with no mire next to the lake showed only minor changes in lake-water TOC during the same period and P :B ratio remained almost constant until the past 5 yr, when the P :B ratio increased rapidly. The observed changes in P :B ratio within this lake may be because of complex interactions of several climate-related variables.

  • 29. Sarmento, Hugo
    et al.
    Romera-Castillo, Cristina
    Lindh, Markus V.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Pinhassi, Jarone
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Sala, M. Montserrat
    Gasol, Josep M.
    Marrase, Celia
    Taylor, Gordon T.
    Phytoplankton species-specific release of dissolved free amino acids and their selective consumption by bacteria2013Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 58, nr 3, s. 1123-1135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite representing only a small fraction of the ocean's dissolved organic matter pool, dissolved free amino acids (DFAA) have high turnover rates and are major nitrogen and carbon sources for bacterioplankton. Both phytoplankton and bacterioplankton assimilate and release DFAA, but their consumption and production are difficult to quantify in nature due to their short residence times (min) as dissolved monomers. We segregated DFAA production by phytoplankton and bacterial consumption by measuring individual DFAA concentrations in four axenic phytoplankton cultures during the exponential growth phase, and also after 4 d incubations in the presence of a natural bacterioplankton community. The amounts and composition of the DFAA pool varied widely among phytoplankton species. The proportion of dissolved organic carbon attributed to DFAA varied among cultures. The picoeukaryotic prasinophyte, Micromonas pusilla, released higher amounts of DFAA than the other species tested (diatoms and dinoflagellate), especially alanine, which has been reported as the dominant individual DFAA in some oligotrophic environments. Community structure of heterotrophic prokaryotes responded to differences in the quality of organic matter released among microalgal species, with Roseobacter-related bacteria responding strongly to exudate composition. Our results demonstrate the specificity of DFAA extracellular release among several algal species and their preferential uptake by members of bacterial communities.

  • 30.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lake morphometry moderates the relationship between water color and fish biomass in small boreal lakes2018Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, nr 5, s. 2171-2178Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lake morphometry may moderate the effects of water color on fish biomass in boreal lakes, but empirical evidence is scarce because there are a limited number of lakes for which both water color and bathymetry have been measured. We evaluated variations in catch-per-unit-effort (CPUE), an indicator of fish biomass, across orthogonal gradients of light extinction and mean depth in 16 small Swedish lakes (mean depth 1.7-4.8 m, surface area 1-10 ha). Multiple regression coefficients indicated that the effect of light extinction on CPUE was negative, and that the relationship was more negative for deeper lakes than it was for shallower lakes. The pattern was strongest for lakes with mean depths between 2.1 m and 3.5 m. We estimated that 26% of small lakes in boreal Sweden fall within this mean depth range. These results contribute to the growing understanding of how variations in water color and lake morphometry influence patterns of fish biomass across the boreal landscape.

  • 31.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lapierre, Jean-Francois
    East Lansing, Michigan.
    Ask, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Deininger, Anne
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rodriguez, Patricia
    Tierra del Fuego, Argentina.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    The influence of dissolved organic carbon on primary production in northern lakes2015Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, nr 4, s. 1276-1285Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dissolved organic carbon (DOC) concentrations in lakes are changing globally, but little is known about potential ecosystem impacts.We evaluated the relationship between DOC and whole-lake primary production in arctic and boreal lakes. Both light extinction (inhibits primary production) and nutrient availability (stimulates primary production) are positively and nonlinearly related to DOC concentration. These nonlinearities create a threshold DOC concentration (4.8mg L-1), below which the DOC-primary production relationship is positive, and above which the relationship is negative. DOC concentration varies maximally between regions, creating a unimodal relationship between primary production and DOC that emerges at broader scales because arctic lakes largely fall below the threshold DOC concentration, but boreal lakes fall above it. Our analysis suggests that the impact of DOC trends on lake primary production will vary across lakes and regions as a result of contrasting baseline conditions relative to the DOC threshold.

  • 32.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia.
    Lapierre, Jean-Francois
    Pace, Michael L.
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey.
    Sobek, Sebastian
    Tranvik, Lars J.
    Regional-scale variation of dissolved organic carbon concentrations in Swedish lakes2014Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, nr 5, s. 1612-1620Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We assessed spatial variability in dissolved organic carbon (DOC) concentrations measured in nearly 2000 Swedish lakes. Inter-lake variance peaked at two different scales, representing within-region and between-region variability. The variation between regions was greater than the variation among lakes within regions. We tested relationships between DOC and runoff, drainage ratio, and altitude for spatial heterogeneity using geographically weighted regression. Relationships varied geographically, but cluster analysis delineated two contiguous regions of similar relationships. Altitude had a significant inverse relationship with DOC in the highlands, and drainage ratio had a significant positive relationship with DOC in the lowlands. These heterogeneous relationships explained regional patterns in DOC concentrations. We conclude that regions, rather than individual lakes, are a key, emergent scale of spatial variability for DOC concentrations. This scale of variability reflects the intersection of environmental gradients (e.g., altitude) with spatially heterogeneous relationships (e.g., DOC-drainage ratio relationship). Regional-scale structure in limnological patterns indicates that individual lakes are not independent from one another, but are emergent groups where DOC concentrations are a function of similar environmental patterns and processes.

  • 33. Steger, Kristin
    et al.
    Premke, Katrin
    Gudasz, Cristian
    Department of Ecology and Genetics/Limnology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Sundh, Ingvar
    Tranvik, Lars J.
    Microbial biomass and community composition in boreal lake sediments2011Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 56, nr 2, s. 725-733Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We used phospholipid fatty acids (PLFA) to determine microbial biomass and community structure in the sediments of eight boreal lakes with different loadings of allochthonous organic carbon and total phosphorus (TP) in the water during the course of a year. The total concentration of PLFA, an estimate of the microbial biomass, depended more on TP, a proxy for pelagic primary production, but not on dissolved organic carbon, a proxy for terrestrial organic carbon input. The composition of PLFAs varied considerably over time, demonstrating seasonal dynamics in microbial community composition. When PLFA profiles in all lakes and seasons are compared, community composition is more similar within season than within lakes.

  • 34. Stolpe, Bjorn
    et al.
    Hassellov, Martin
    Nanofibrils and other colloidal biopolymers binding trace elements in coastal seawater: Significance for variations in element size distributions2010Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 55, nr 1, s. 187-202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Colloidal size spectra of Fe, Cu, Ag, La, and Pb were determined by asymmetrical flow field-flow fractionation coupled to high-resolution inductively coupled plasma mass spectrometry, in samples from 0.5-40-m depth profiles from the Gullmarsfjord on the Swedish west coast, at nine occasions between February 2004 and July 2005. Trace elements were quantified in unfiltered and 0.45-mm filtered samples, and total organic carbon and transparent exopolymer particles were measured. Atomic force microscopy was used to determine sizes and shapes of colloids. Most Fe was associated with Al-rich particles that were resuspended from the sediment or derived from a local river. Dissolved Fe and Cu had depth profiles similar to total organic carbon and transparent exopolymer particles, and highest concentrations occurred in the surface and the upper mixed-water layer, where the in situ biological production and the inputs of water from the Baltic Sea and a local river were high. The colloidal size spectra of the elements, and the atomic force microscopy images, revealed that three to four classes of colloids were present in the samples, differing in size, shape, and element-binding properties. Small (0.5-3 nm) spherical macromolecules of chromophoric dissolved organic matter, binding most elements, occurred at all depths and on all sampling occasions. Populations of 3-7-nm globular or slightly elongated colloids, binding Cu, Ag, and Pb, and 7-40-nm fibrillar colloids, binding Fe and Pb, appeared in the upper mixed-water layer during late spring and summer, thereby changing the colloidal size spectra of associated elements in June-July.

  • 35.
    Thorlacius, Magnus
    et al.
    Marine and Freshwater Research Institute, Reykjavik, Iceland.
    Brodin, Tomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Investigating large-scale invasion patterns using-small scale invasion successions-phenotypic differentiation of the invasive round goby (Neogobius melanostomus) at invasion fronts2018Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, nr 2, s. 702-713Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Species invasions are an ever-growing problem that increases with globalization through increased frequency of unintentional introductions. Between establishment and spread, a lag phase often occurs in which population growth is exponential and dispersal frequency low. Individual variation in behavioral traits, consistent through time and context, have been found crucial for understanding ecological processes such as density dependent dispersal during species invasions. In a previous study of the invasive round goby (Neogobius melanostomus), we found population differentiation between old and new populations in the Baltic Sea with individuals in new populations being more asocial, bold, and active. Here, we investigate if behavioral differentiations are created already during the initial spread from newly established populations. Hence, we monitored population growth and subsequent small-scale spread (< 800 m) in two newly invaded areas, as well as the behavioral traits previously connected to dispersal, over two successional seasons. We found phenotypic differentiation between dispersing and resident individuals with small-scale dispersers being smaller and more asocial. In addition, our catch-per-unit-effort data suggest a lag-phase of 3-5 yr, following initial colonization, before the round goby start spreading into the surrounding environment. This suggests that, at least in species that grow to high densities fast, sociability is more important than boldness and activity for triggering density-dependent dispersal.

  • 36. Tiwari, Tejshree
    et al.
    Buffam, Ishi
    Sponseller, Ryan A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Inferring scale-dependent processes influencing stream water biogeochemistry from headwater to sea2017Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, s. S58-S70Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding how scale-dependent processes regulate patterns of water chemistry remains a challenge in aquatic biogeochemistry. This study evaluated how chemical properties of streams and rivers vary with drainage size and explored mechanisms that may underlie nonlinear changes with increasing scale. To do this, we contrasted concentrations of total organic carbon (TOC) with pH and cations (Ca and Mg) from 69 catchments in northern Sweden, spanning a size gradient from headwaters (<0.01 km(2)) to major rivers and estuaries (>100,000 km(2)). Across this gradient, we evaluated (1) changes in average concentrations and temporal variation, (2) scale breaks in catchment area-concentration relationships, and (3) the potential importance of groundwater inputs and instream processes as drivers of change. Results indicated that spatial and temporal signals converge at approximate to 2-10 km(2) as streams draining distinct headwater catchments coalesce and mix. Beyond 10 km(2), streams tended to lose headwater signatures, reflecting a transition from shallow to deep groundwater influence. This was accompanied by a second break at approximate to 70-500 km(2) corresponding to reduced spatial variability and a convergence of the response to snowmelt, as the dominance of deep groundwater influence increased with catchment scale. Larger catchments showed greater effect of instream processing on TOC, as concentrations predicted from the conservative mixing of upstream signals and dilution with deep groundwater were lower than measured. This study improves the understanding of scaling biogeochemical patterns and processes in stream networks, highlighting thresholds that imply shifts in the factors that shape variation in chemistry from headwaters to the sea.

  • 37. Weyhenmeyer, Gesa A
    et al.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nonlinear response of dissolved organic carbon concentrations in boreal lakes to increasing temperatures2009Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, nr 6 part 2, s. 2513-2519Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent increases in concentrations of dissolved organic carbon (DOC) in lakes and rivers over large regionshave been related to both changes in the climate and in atmospheric deposition chemistry. Using a data set of1041 boreal lakes along a 13u latitudinal gradient, sampled in 1995, 2000, and 2005, and an additional data set of90 lakes along a 1000-m altitudinal gradient at 68uN, we show that DOC concentrations increase in a nonlinearway along a latitudinal and altitudinal temperature gradient. The nonlinear relation of DOC to increasingtemperatures was consistent over space and time. Out of 14 meteorological, catchment, morphometric, andatmospheric deposition variables tested, the variable best explaining this kind of nonlinear pattern was thenumber of days when air temperatures exceeded 0uC, i.e., the duration of the main growing and runoff season(DT.0). Using DT.0 as an input variable, we were able to predict the nonlinear temperature response of DOCconcentrations, both spatially (R2 5 0.90, p , 0.0001) and temporally (R2 5 0.90, p , 0.0001). DT.0 has anadvantage over other variables because it includes the time factor, which is decisive for the duration thatbiogeochemical processes can take place. We suggest that DOC concentrations in lakes are influenced by climatechange and that present temperature increases over Sweden result in an accelerated DOC increase toward warmergeographical regions.

  • 38.
    Wikner, Johan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet).
    Hagström, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    ANNUAL STUDY OF BACTERIOPLANKTON COMMUNITY DYNAMICS1991Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 36, nr 7, s. 1313-1324Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bacterial growth, abundance, and grazing were measured simultaneously during a full seasonal cycle in a temperate brackish water estuary, covering diel and seasonal variability. Growth of bacteria was balanced by bacterivory on an annual basis, and observed net change in bacterial numbers matched the net change calculated by a simple Lotka-Volterra equation lacking immigration or emigration terms. Bacterial growth was dependent on water temperature below 6-degrees-C, but other factors dominated at higher temperatures. The community clearance rate of the bacterivores was stringently regulated at 0.6 d-1, showing a linear functional response within the range of natural bacterial abundances recorded. Furthermore, bacterivores showed a threshold at 7 x 10(5) bacteria ml-1 when grazing ceased, suggesting that pelagic bacteria have a numerical refuge promoting coexistence with bacterivores in aquatic environments. The observed lack of timing between bacterial growth and grazing in spring allowed accumulation of bacterial cells, but grazing exceeded growth in winter. We inferred that the specific growth rate of the bacterial community and the community clearance rate of bacterivores together determined change in and abundance of bacterioplankton in the waters examined.

  • 39.
    Wikner, Johan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet).
    Rassoulzadegan, Fereidoun
    Hagström, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Periodic bacterivore activity balances bacterial-growth in the marine-environment1990Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 35, nr 2, s. 313-324Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The grazing rate of pelagic bacteria was repeatedly determined during 36-h time-course experiments with the minicell recapture technique. Die1 variation in the rate of grazing occurred in all water masses investigated. Maximal rates reached 2 x lo5 cells ml-’ h-r, whereas minimal values were 20 times lower. Highest grazing rates were found during the day in most cases, but grazing could also dominate at night as found in one study. Die1 periodicity was mainly due to variation in the per-cell feeding rate of bacterivorous flagellates. Accumulation of the bacterial biomass into the l-3-pm size fraction was positively correlated with changes in bacterial grazing. The transfer efficiency to organisms z 10 pm was low. On average, the daily grazing rate equaled 60% of the bacterial standing stock, exceeding bacterial growth by a factor of 2.6, as estimated from [3H]thymidine incorporation.

  • 40. Winder, Monika
    et al.
    Bouquet, Jean-Marie
    Bermudez, J. Rafael
    Berger, Stella A.
    Hansen, Thomas
    Brandes, Jay
    Sazhin, Andrey F.
    Nejstgaard, Jens C.
    Båmstedt, Ulf
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jakobsen, Hans H.
    Dutz, Joerg
    Frischer, Marc E.
    Troedsson, Christofer
    Thompson, Eric M.
    Increased appendicularian zooplankton alter carbon cycling under warmer more acidified ocean conditions2017Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, nr 4, s. 1541-1551Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Anthropogenic atmospheric loading of CO2 raises concerns about combined effects of increasing ocean temperature and acidification, on biological processes. In particular, the response of appendicularian zooplankton to climate change may have significant ecosystem implications as they can alter biogeochemical cycling compared to classical copepod dominated food webs. However, the response of appendicularians to multiple climate drivers and effect on carbon cycling are still not well understood. Here, we investigated how gelatinous zooplankton (appendicularians) affect carbon cycling of marine food webs under conditions predicted by future climate scenarios. Appendicularians performed well in warmer conditions and benefited from low pH levels, which in turn altered the direction of carbon flow. Increased appendicularians removed particles from the water column that might otherwise nourish copepods by increasing carbon transport to depth from continuous discarding of filtration houses and fecal pellets. This helps to remove CO2 from the atmosphere, and may also have fisheries implications.

  • 41. Wollrab, Sabine
    et al.
    Diehl, Sebastian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Univ Munich, Dept Biol 2, Planegg Martinsried, Germany.
    Bottom-up responses of the lower oceanic food web are sensitive to copepod mortality and feeding behavior2015Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, nr 2, s. 641-656Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The functional response, describing consumption rate as a function of food abundance, critically links consumer-resource dynamics. Yet, little is known about how its shape affects communities of multiple, dynamically linked species. We theoretically investigated how the functional response of copepods (saturating type 2 vs. sigmoidal type 3, both of which have been observed) mediates bottom-up and top-down influences on the lower oceanic food web as described by five compartments (pentagon web): a shared limiting nutrient, small and large algae, ciliates feeding on small algae, and copepods feeding on ciliates and large algae. We compare system dynamics in response to nutrient enrichment and copepod mortality, the latter being varied first directly and then indirectly through inclusion of planktivores (fish or jellyfish). Regardless of functional response type, when planktivores are absent, equilibrium densities of all members of the even food chain (nutrients-small algae-ciliates-copepods) typically increase with nutrient enrichment whereas large algae decrease. In contrast, and congruent with conventional wisdom, large algae increase with nutrient enrichment when copepods are controlled by planktivores. A type 2 response in copepods strongly destabilizes the pentagon web, whereas stable equilibria are possible when copepods have a type 3 response. High copepod mortality (e.g., caused by increasing planktivore pressure under nutrient enrichment) destabilizes such systems, however. Moreover, because community feedbacks produce a negative correlation between the copepod's alternative prey, type 3 switching behavior is amplified in the pentagon web. This prevents extinctions but can give rise to an alternative state with small algal dominance at high enrichment.

  • 42.
    Zweifel, Ulla-Li
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Wikner, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Hagström, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Lundberg, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Norrman, Bo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för molekylärbiologi (Teknisk-naturvetenskaplig fakultet). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    DYNAMICS OF DISSOLVED ORGANIC-CARBON IN A COASTAL ECOSYSTEM1995Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 40, nr 2, s. 299-305Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the Bothnian Sea, there was a marked seasonal variation of dissolved organic C (DOC) in 1990-1992, with a large increase in DOC concentrations in summer at two stations. The accumulation of DOC at the coastal station persisted for 5 months, reaching peak values 24-31% above the mean winter value (288 mu M). At the offshore station DOC concentrations were elevated throughout the water column in July, reaching 14% above the mean winter value (291 mu M). The DOC concentration at the Coastal station was significantly correlated to water flow in an adjacent river, suggesting that the source of the summer DOC increase was largely explained by riverine input. Bioassays indicated that a large portion (22-99%) of the introduced DOC was degradable by bacteria after inorganic nutrients were added. A negative correlation between DOC and phosphate concentration was also found, suggesting that the system was P deficient in summer. The accumulation of DOC in summer was thus possibly caused by slow bacterial degradation due td phosphate deficiency and transient accumulation of refractory DOG. An annual C balance at the coastal station indicated an insufficient supply of C from phytoplankton production to support the C demand of the system; at the offshore station the budget was close to balanced. The results suggest that riverine DOC had a major impact on coastal DOC dynamics and that it was partly used in the microbial food web in the bay.

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