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  • 1. Bravo, Andrea G.
    et al.
    Kothawala, Dolly N.
    Attermeyer, Katrin
    Tessier, Emmanuel
    Bodmer, Pascal
    Ledesma, Jose U.
    Audet, Joachim
    Pere Casas-Ruiz, Joan
    Catalan, Nuria
    Cauvy-Fraunie, Sophie
    Colls, Miriam
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Evtimova, Vesela V.
    Fonvielle, Jeremy A.
    Fuss, Thomas
    Gilbert, Peter
    Ortega, Sonia Herrero
    Liu, Liu
    Mendoza-Lera, Clara
    Monteiro, Juliana
    Mor, Jordi-Rene
    Nagler, Magdalena
    Niedrist, Georg H.
    Nydahl, Anna C.
    Pastor, Ada
    Pegg, Josephine
    Roberts, Catherine Gutmann
    Pilotto, Francesca
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Portela, Ana Paula
    Gonzalez-Quijano, Clara Romero
    Romero, Ferran
    Rulik, Martin
    Amouroux, David
    The interplay between total mercury, methylmercury and dissolved organic matter in fluvial systems: A latitudinal study across Europe2018In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 144, p. 172-182Article in journal (Refereed)
    Abstract [en]

    Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concentrations in aquatic ecosystems. Studies attempting to link dissolved organic matter (DOM) to levels of THg or MeHg are few and geographically constrained. Additionally, stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concentration and composition, morphological descriptors, land uses and water chemistry on THg and MeHg concentrations and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64°N. THg concentrations (0.06–2.78 ng L−1) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concentrations (7.8–159 pg L−1) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concentrations, autochthonous DOM (aquatically produced) and the availability of electron acceptors for Hg methylating microorganisms (e.g. sulfate) drive %MeHg and potentially MeHg concentration. Overall, these results highlight the large spatial variability in THg and MeHg concentrations at the European scale, and underscore the importance of DOM composition on mercury cycling in fluvial systems.

  • 2.
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of inorganic nitrogen and organic carbon on pelagic food webs in boreal lakes2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Anthropogenic activities are increasing inorganic nitrogen (N) loadings to lakes in the northern hemisphere. In many boreal lakes phytoplankton are N limited, wherefore enhanced N input may affect the productivity of pelagic food webs. Simultaneously, global change causes increased inflows of terrestrial dissolved organic carbon (DOC) to boreal lakes. Between clear and humic lakes, whole lake primary and consumer production naturally differs. However, research is inconclusive as to what controls pelagic production in these lakes. Further, it is unclear how DOC affects the response of the pelagic food web to enhanced inorganic N availability. The overarching goal of this thesis was to study the effects of inorganic N and organic C for pelagic food webs in boreal lakes. In the thesis, I first identified the main drivers of pelagic production during summer in eight non-manipulated Swedish boreal lakes with naturally low or high DOC. Then I investigated how increased N availability affects the pelagic food chain, and how the response differs with DOC. Therefore, whole lake inorganic N fertilization experiments were conducted in six Swedish boreal lakes across a DOC gradient (low, medium, high) divided into three lake pairs (control, N enriched) with one reference and two impact years. In each lake, I also investigated the response of zooplankton growth using in situ mesocosm experiments excluding planktivores. I found that humic boreal lakes had lower phytoplankton production and biomass than clear water lakes. Further, phytoplankton community composition and food quality differed with DOC. However, high DOC did not reduce pelagic energy mobilization or zooplankton biomass, but promoted a higher dominance of cladoceran relative to copepod species. N addition clearly enhanced phytoplankton biomass and production in the experimental lakes. However, this stimulating N effect decreased with DOC as caused by light limitation. Further, the newly available phytoplankton energy derived from N addition was not efficiently transferred to zooplankton, which indicates a mismatch between producer energy supply and consumer energy use. Indeed, the mesocosm experiment revealed that decreased food quality of phytoplankton in response to N addition resulted in reduced food web performance, especially in clearer lakes. In humic lakes, zooplankton production and food web efficiency were clearly more resilient to N addition. In summary, my thesis suggests that any change in the landscape that enhances inorganic N availability will especially affect pelagic food webs in clear water lakes. In contrast, brownification will result in more lakes being resilient to eutrophication caused by enhanced N deposition.

  • 3.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn
    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.
    Nitrogen effects on the pelagic food web are modified by dissolved organic carbon2017In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 184, no 4, p. 901-916Article in journal (Refereed)
    Abstract [en]

    Global environmental change has altered the nitrogen (N) cycle and enhanced terrestrial dissolved organic carbon (DOC) loadings to northern boreal lakes. However, it is still unclear how enhanced N availability affects pelagic food web efficiency (FWE) and crustacean zooplankton growth in N limited boreal lakes. Here, we performed in situ mesocosm experiments in six unproductive boreal Swedish lakes, paired across a DOC gradient, with one lake in each pair fertilized with N (2011: reference year; 2012, 2013: impact years). We assessed how zooplankton growth and FWE were affected by changes in pelagic energy mobilization (PEM), food chain length (phytoplankton versus bacterial production based food chain, i.e. PP:BP), and food quality (seston stoichiometry) in response to N fertilization. Although PP, PEM and PP:BP increased in low and medium DOC lakes after N fertilization, consumer growth and FWE were reduced, especially at low DOC-potentially due to reduced phytoplankton food quality [increased C: phosphorus (P); N:P]. At high DOC, N fertilization caused modest increases in PP and PEM, with marginal changes in PP:BP and phytoplankton food quality, which, combined, led to a slight increase in zooplankton growth and FWE. Consequently, at low DOC (<12 mg L-1), increased N availability lowers FWE due to mismatches in food quality demand and supply, whereas at high DOC this mismatch does not occur, and zooplankton production and FWE may increase. We conclude that the lake DOC level is critical for predicting the effects of enhanced inorganic N availability on pelagic productivity in boreal lakes.

  • 4.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    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.
    Nitrogen effects on aquatic food web efficiency in the pelagic zone of unproductive lakes along a gradient of dissolved organic carbonManuscript (preprint) (Other academic)
    Abstract [en]

    Atmospheric nitrogen (N) deposition and terrestrial dissolved organic carbon (DOC) loadings are increasing in northern boreal lakes. However, consequences of increased N availability on food web efficiency (FWE) and consumer growth in N limited unproductive boreal lakes are unclear. Here, we performed in situ mesocosm experiments in late summer (2011; 2013) in six unproductive boreal Swedish lakes, paired across a DOC gradient, with one lake in each pair fertilized with N (2011: reference year; 2012, 2013: impact years). We assessed how zooplankton growth and FWE were affected by changes in pelagic energy mobilization (PEM), food chain length (PP:BP, i.e. phytoplankton: bacterial production ratio), and food quality (seston stoichiometry) in response to N fertilization. Although PP, PEM and PP:BP increased in low and medium DOC lakes after N fertilization, consumer growth and FWE in the low DOC lake were reduced, potentially due to a reduction in phytoplankton food quality (increased C:P; N:P). At high DOC, N fertilization caused modest increases in PP and PEM, with marginal changes in PP:BP and phytoplankton food quality, which combined led to a slight increase in zooplankton growth and FWE. We conclude that the background lake DOC level is critical in order to infer effects of enhanced inorganic N availability on pelagic productivity and FWE. In clear lakes increased N deposition will decrease FWE due to mismatches in food quality demand and supply. In humic lakes this mismatch will not occur, wherefore and zooplankton production and FWE will increase slightly following enhanced N deposition.

  • 5.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    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.
    Phytoplankton response to whole lake inorganic N fertilization along a gradient in dissolved organic carbon2017In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 98, no 4, p. 982-994Article in journal (Refereed)
    Abstract [en]

    Global change has increased inorganic nitrogen (N) and dissolved organic carbon (DOC; i.e. ‘browning’) inputs to northern hemisphere boreal lakes. However, we do not know how phytoplankton in nutrient poor lake ecosystems of different DOC concentration respond to increased N availability. Here, we monitored changes in phytoplankton production, biomass and community composition in response to whole lake inorganic N fertilization in six boreal unproductive Swedish lakes divided into three lake pairs (control, N enriched) at three DOC levels (low, medium, high), with one reference year (2011) and two impact years (2012, 2013). We found that phytoplankton biomass and production decreased with DOC concentration before N fertilization. Further, phytoplankton community composition also differed with respect to DOC, with a dominance of non-flagellated autotrophs at low DOC towards an increasing dominance of flagellated autotrophs with increased lake DOC concentration. The N fertilization increased phytoplankton biomass and production in all lakes, but did not affect phytoplankton community composition. However, the net response in biomass and production to N fertilization declined with increasing DOC, implying that the lake DOC concentration is critical in order to infer phytoplankton responses to N fertilization, and that the system switches from being primarily nutrient limited to becoming increasingly light limited with increased DOC concentration. In conclusion, our results show that browning will reduce phytoplankton production and biomass and influence phytoplankton community composition, whereas increased inorganic N loadings from deposition, forestry or other land use will primarily enhance phytoplankton biomass and production. Together, any change in the landscape that enhances inorganic N availability will increase phytoplankton production and biomass, but the positive effects of N will be much weaker or even neutralized in browner lakes as caused by light limitation.

  • 6.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Oceanography, University of Hawai'i, Honolulu, USA.
    Karlsson, Jan
    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.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Pelagic food web response to whole lake N fertilization2017In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, no 4, p. 1498-1511Article in journal (Refereed)
    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.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lange, K.
    Bayer, T.
    Vidussi, F.
    Liess, Antonia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Simulated terrestrial runoff triggered a phytoplankton succession and changed seston stoichiometry in coastal lagoon mesocosms2016In: Marine Environmental Research, ISSN 0141-1136, E-ISSN 1879-0291, Vol. 119, p. 40-50Article in journal (Refereed)
    Abstract [en]

    Climate change scenarios predict intensified terrestrial storm runoff, providing coastal ecosystems with large nutrient pulses and increased turbidity, with unknown consequences for the phytoplankton community. We conducted a 12-day mesocosm experiment in the Mediterranean Thau Lagoon (France), adding soil (simulated runoff) and fish (different food webs) in a 2 x 2 full factorial design and monitored phytoplankton composition, shade adaptation and stoichiometry. Diatoms (Chaetoceros) increased fourfold immediately after soil addition, prymnesiophytes and dinoflagellates peaked after six- and 12 days, respectively. Soil induced no phytoplanlcton shade adaptation. Fish reduced the positive soil effect on dinoflagellates (Scripsiella, Glenodinium), and diatom abundance in general. Phytoplankton community composition drove seston stoichiometry. In conclusion, pulsed terrestrial runoff can cause rapid, low quality (high carbon: nutrient) diatom blooms. However, bloom duration may be short and reduced in magnitude by fish. Thus, climate change may shift shallow coastal ecosystems towards famine or feast dynamics.

  • 8.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Norwegian Institute for Water Research (NIVA), Oslo, Norway; Department of Natural Sciences, University of Agder, Kristiansand, Norway.
    Jonsson, A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, J.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, A-K.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Pelagic food webs of humic lakes show low short-term response to forest harvesting2019In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 29, no 1, article id UNSP e01813Article in journal (Refereed)
    Abstract [en]

    Forest harvest in the boreal zone can increase the input of terrestrial materials such as dissolved organic carbon (DOC) and nitrate (NO3-) into nearby aquatic ecosystems, with potential effects on phytoplankton growth through enhanced nutrient (i.e., positive) or reduced light availability (i.e., negative), which may affect ecosystem productivity and consumer resource use. Here, we conducted forest clear-cutting experiments in the catchments of four small, humic, and nitrogen-limited unproductive boreal lakes (two controls and two clear-cut, 18% and 44% of area cut) with one reference and two impact years. Our aim was to assess the effects of forest clear-cutting on pelagic biomass production and consumer resource use. We found that pelagic biomass production did not change after two years of forest clear-cutting: Pelagic primary and bacterial production (PP, BP), PP:BP ratio, chl a, and seston carbon (seston C) were unaffected by clear-cutting; neither did tree harvest affect seston stoichiometry (i.e., N:phosphorus [P], C:P) nor induce changes in zooplankton resource use, biomass, or community composition. In conclusion, our findings suggest that pelagic food webs of humic lakes (DOC > 15 mg/L) might be resilient to a moderate form of forest clear-cutting, at least two years after tree removal, before mechanical site preparation (e.g., mounding, plowing) and when leaving buffer strips along lakes and incoming streams. Thus, pelagic food web responses to forest clear-cutting might not be universal, but could depend on factors such as the time scale, share of catchment logged, and the forest practices involved, including the application of buffer strips and site preparation.

  • 9.
    Faithfull, Carolyn L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Deininger, Anne
    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.
    Food quantity and quality in unproductive clear water and humic lakes and consequences for pelagic mesozooplanktonManuscript (preprint) (Other academic)
    Abstract [en]

    1. Small oligotrophic humic lakes are the most common type of lake in the boreal zone and are predicted to become more abundant with climate change. Humic lakes generally have lower whole lake primary and consumer production than clear water lakes, but research is inconclusive as to what controls pelagic production in these lakes.

    2. We compared food quantity (primary production (PP) and phytoplankton biomass, pelagic energy mobilization, seston carbon (C)) and food quality (phytoplankton edibility, seston stoichiometry) for crustacean mesozooplankton in four humic (> 15 mg L-1 DOC) and four clear water lakes.

    3. We found that PP was over three times higher in clear water lakes, and was controlled by nutrient concentrations and temperature, whereas in humic lakes PP was dependant on light availability. Nevertheless, total food quantity (i.e. pelagic energy mobilization, seston C concentrations) was similar between lake types, even though food composition differed. In humic lakes bacterial production based on allochthonous C contributed three times more to total pelagic energy mobilization and seston C consisted of 20% less phytoplankton biomass.

    4. Food composition did not have any effect on total zooplankton biomass, however, cladoceran: copepod biomass ratios increased with DOC concentration, both in our lakes and in a subset of northern lakes from the Swedish lake monitoring program.

    5. Our results imply that increased DOC concentrations in boreal lakes will reduce PP and phytoplankton biomass and can alter food composition. However, browning of boreal lakes is unlikely to reduce pelagic energy mobilization or total zooplankton biomass, but can promote a higher dominance of cladocerans relative to copepods, which may have consequences for pelagic planktivorous predators.

  • 10. Furey, Paula C
    et al.
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Liess, Antonia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Substratum-Associated Microbiota2016In: Water environment research, ISSN 1061-4303, E-ISSN 1554-7531, Vol. 88, no 10, p. 1638-1672Article in journal (Refereed)
    Abstract [en]

    This survey of literature on substratum associated microbiota from 2015 highlights research findings associated with benthic algae and bacteria from a variety of aquatic environments, but primarily freshwaters. It focuses on topics of interest to the Water Environment Federation along with those of current emerging interest such as global change, oil spills, and environmental contaminants like pharmaceutical compounds, microplastics, nanoparticles and organic pollutants. Other interesting findings briefly covered include areas of general ecology, nutrient cycling, trophic interactions, water quality, nuisance and invasive species, bioindicators, and bioremediation.

  • 11.
    Klaus, Marcus
    et al.
    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.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Geibrink, Erik
    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.
    Weak response of greenhouse gas emissions to whole lake N enrichment2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, p. S340-S353Article in journal (Refereed)
    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.

  • 12.
    Liess, Antonia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Laboratoire Ecosystémes Marins Côtiers, UMR5119 CNRS, Université Montpellier2, IRD, IFREMER, Paris, France.
    Rowe, Owen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Francoeur, S. N.
    Guo, Junwen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lange, K.
    Schroeder, A.
    Reichstein, Birte
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lefèbure, Robert
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Mathisen, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Terrestrial runoff boosts phytoplankton in a Mediterranean coastal lagoon, but these effects do not propagate to higher trophic levels2016In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 766, no 1, p. 275-291Article in journal (Refereed)
    Abstract [en]

    Heavy rainfall events causing significant terrestrial runoff into coastal marine ecosystems are predicted to become more frequent with climate change in the Mediterranean. To simulate the effects of soil runoff on the pelagic food web of an oligotrophic Mediterranean coastal lagoon, we crossed soil extract addition (increasing nutrient availability and turbidity) and fish presence in a full factorial design to coastal mesocosms containing a natural pelagic community. Soil extract addition increased both bacteria and phytoplankton biomass. Diatoms however profited most from soil extract addition, especially in the absence of fish. In contrast zooplankton and fish did not profit from soil extract addition. Furthermore, our data indicate that nutrients (instead of light or carbon) limited basal production. Presumed changes in carbon availability are relatively unimportant to primary and secondary production in strongly nutrient limited systems like the Thau Lagoon. We conclude that in shallow Mediterranean coastal ecosystems, heavy rainfall events causing soil runoff will (1) increase the relative abundance of phytoplankton in relation to bacteria and zooplankton, especially in the absence of fish (2) not lead to higher biomass of zooplankton and fish, possibly due to the brevity of the phytoplankton bloom and the slow biomass response of higher trophic levels.

  • 13.
    Seekell, David A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lapierre, Jean-Francois
    East Lansing, Michigan.
    Ask, Jenny
    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.
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rodriguez, Patricia
    Tierra del Fuego, Argentina.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The influence of dissolved organic carbon on primary production in northern lakes2015In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, no 4, p. 1276-1285Article in journal (Refereed)
    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.

  • 14. Wu, Pianpian
    et al.
    Kainz, Martin
    Akerblom, Staffan
    Garcia Bravo, Andrea
    Sonesten, Lars
    Branfireun, Brian
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Natural Sciences, University of Agder, Kristiansand, Norway; Norwegian Institute for Water Research (NIVA), Grimstad, Norway.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bishop, Kevin
    Terrestrial diet influences mercury bioaccumulation in zooplankton and macroinvertebrates in lakes with differing dissolved organic carbon concentrations2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 669, p. 821-832Article in journal (Refereed)
    Abstract [en]

    Dietary uptake is a key step in conveying both toxic mercury (Hg; particularly as highly bioavailable methylmercury, MeHg) and essential dietary biochemicals, such as polyunsaturated fatty acids (PUFA), across trophic levels within aquatic food webs. Using stable isotopes and fatty acids we evaluated the role of food sources in size-fractioned plankton and littoral macroinvertebrates for the bioaccumulation of total Hg and MeHg in six oligotrophic and one mesotrophic Swedish lakes with differing concentrations of dissolved organic carbon (DOC). We found that the consumption of both algal and terrestrial diets (assessed by PUFA and long-chain saturated fatty acids, respectively) predicted >66% of the Hg concentration variability in meso- (100-500 mu m) and macrozooplankton (>500 mu m) in oligotrophic lakes. In the mesotrophic lake, total Hg bioaccumulation in higher trophic level biota, carnivorous macroinvertebrates was also significantly related to terrestrial diet sources (R-2 = 0.65, p < 0.01). However, lake pH and DOC correlated to total Hg bioaccumulation and bioconcentration across all lakes, suggesting the consumption of different diet sources is mediated by the influence of lake characteristics. This field study reveals that using dietary biomarkers (stable isotopes and fatty acids) together with the physico-chemical lake parameters pH and nutrients together improve our ability to predict Hg bioaccumulation in aquatic food webs. Fatty acids used as dietary biomarkers provide correlative evidence of specific diet source retention in consumers and their effect on Hg bioaccumulation, while pH and nutrients are the underlying physico-chemical lake parameters controlling differences in Hg bioaccumulation between lakes. 

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