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  • 1.
    Almeida, Rafael M.
    et al.
    Cornell University, USA.
    Paranaíba, José R.
    Federal University of Juiz de Fora, Brazil.
    Barbosa, Ícaro
    Federal University of Juiz de Fora, Brazil.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kosten, Sarian
    University Nijmegen, The Netherlands.
    Linkhorst, Annika
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Mendonça, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Federal University of Juiz de Fora, Brazil.
    Quadra, Gabrielle
    Federal University of Juiz de Fora, Brazil.
    Roland, Fábio
    Federal University of Juiz de Fora, Brazil.
    Barros, Nathan
    Federal University of Juiz de Fora, Brazil.
    Carbon dioxide emission from drawdown areas of a Brazilian reservoir is linked to surrounding land cover2019In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 81, article id 68Article in journal (Refereed)
    Abstract [en]

    Reservoir sediments exposed to air due to water level fluctuations are strong sources of atmospheric carbon dioxide (CO2). The spatial variability of CO2 fluxes from these drawdown areas are still poorly understood. In a reservoir in southeastern Brazil, we investigated whether CO2 emissions from drawdown areas vary as a function of neighboring land cover types and assessed the magnitude of CO2 fluxes from drawdown areas in relation to nearby water surface. Exposed sediments near forestland (average = 2733 mg C m−2 day−1) emitted more CO2 than exposed sediments near grassland (average = 1261 mg C m−2 day−1), congruent with a difference in organic matter content between areas adjacent to forestland (average = 12.2%) and grassland (average = 10.9%). Moisture also had a significant effect on CO2 emission, with dry exposed sediments (average water content: 13.7%) emitting on average 2.5 times more CO2 than wet exposed sediments (average water content: 23.5%). We carried out a systematic comparison with data from the literature, which indicates that CO2 efflux from drawdown areas globally is about an order of magnitude higher than CO2 efflux from adjacent water surfaces, and within the range of CO2 efflux from terrestrial soils. Our findings suggest that emissions from exposed sediments may vary substantially in space, possibly related to organic matter supply from uphill vegetation, and that drawdown areas play a disproportionately important role in total reservoir CO2 emissions with respect to the area they cover.

  • 2.
    Andersson, Eva
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology. Swedish Nuclear Fuel and Waste Management.
    Brunberg, Anna-Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Inorganic nutrient acquisition in a shallow clearwater lake: dominance of benthic microbiota2006In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 68, no 2, p. 172-180Article in journal (Refereed)
    Abstract [en]

    This mesocosm study from the oligotrophic Lake Eckarfjärden in Sweden shows, in contrast to many previous studies, that benthic microbiota dominated production following elevated nutrient concentrations in the water. Increased nutrient concentrations favoured microphytobenthos, whereas phytoplankton biomass remained roughly the same. Microphytobenthos biomass and production were clearly stimulated by nitrogen addition, while phytoplankton showed signs of phosphorus limitation. There were tight interactions between pelagic and benthic habitats and between organisms, and pelagic as well as benthic heterotrophic bacteria were disfavoured when microphytobenthos had access to nitrogen.

    We conclude that increased nutrient concentrations in the water column may trigger immediate responses in both habitats, altering the tight interactions between microbiota, but not necessarily resulting in a shift towards pelagic production.

  • 3.
    Andersson, Eva
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Kumblad, Linda
    A carbon budget for an oligotrophic clearwater lake in mid-Sweden2006In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 68, no 1, p. 52-64Article in journal (Refereed)
    Abstract [en]

    In this study, a whole-lake carbon budget for the oligotrophic, clearwater Lake Eckarfjärden was established both on an annual and seasonal basis. For budget calculations, the lake was divided into three habitats (pelagial, littoral and benthic) and the biota into 19 functional groups. In the lake, major parts of biomass (97%) and primary production (91%) are concentrated in benthic and littoral habitats and to a few functional groups. Respiration on the other hand, is focused on benthic and pelagial habitats where 60% and 39%, respectively, of the respiration took place. Our conceptual model indicates strong interactions between habitats. For instance, the pelagial is fed with carbon fixed by primary producers in the benthic and littoral zones. On an annual basis, total primary production exceeds total respiration and the lake is net autotrophic. However, there are clear differences between habitats and between seasons. For instance, the littoral is net autotrophic during spring, summer and autumn, the benthic habitat is net autotrophic only during summer, and the pelagial is always net heterotrophic. Our results demonstrate clear couplings between habitats and organisms and the importance of a holistic view when studying lake ecosystems.

  • 4.
    Attermeyer, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Chemical Analytics and Biogeochemistry, Germany.
    Grossart, Hans-Peter
    Leibniz-Institute of Freshwater Ecology and InlandFisheries, Experimental Limnology, Germany; Institute for Biochemistry and Biology, Potsdam University, Germany.
    Flury, Sabine
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Chemical Analytics and Biogeochemistry, Germany; Faculty of Science, University of Geneva, Switzerland.
    Premke, Katrin
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Chemical Analytics and Biogeochemistry, Germany; Leibniz Centre for Agricultural Landscape Research (ZALF), Institute for Landscape Biogeochemistry, Germany.
    Bacterial processes and biogeochemical changes in the water body of kettle holes: mainly driven by autochthonous organic matter?2017In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 79, no 3, p. 675-687Article in journal (Refereed)
    Abstract [en]

    Kettle holes are small inland waters formed from glacially-created depressions often situated in agricultural landscapes. Due to their high perimeter-to-area ratio facilitating a high aquatic-terrestrial coupling, kettle holes can accumulate high concentrations of organic carbon and nutrients, fueling microbial activities and turnover rates. Thus, they represent hotspots of carbon turnover in the landscape, but their bacterial activities and controlling factors have not been well investigated. Therefore, we aimed to assess the relative importance of various environmental factors on bacterial and biogeochemical processes in the water column of kettle holes and to disentangle their variations. In the water body of ten kettle holes in north-eastern Germany, we measured several physico-chemical and biological parameters such as carbon quantity and quality, as well as bacterial protein production (BP) and community respiration (CR) in spring, early summer and autumn 2014. Particulate organic matter served as an indicator of autochthonous production and represented an important parameter to explain variations in BP and CR. This notion is supported by qualitative absorbance indices of dissolved molecules in water samples and C:N ratios of the sediments, which demonstrate high fractions of autochthonous organic matter (OM) in the studied kettle holes. In contrast, dissolved chemical parameters were less important for bacterial activities although they revealed strong differences throughout the growing season. Pelagic bacterial activities and dynamics might thus be regulated by autochthonous OM in kettle holes implying a control of important biogeochemical processes by internal primary production rather than facilitated exchange with the terrestrial surrounding due to a high perimeter-to-area ratio.

  • 5.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The use of TN:TP and DIN:TP ratios as indicators for phytoplankton nutrient limitation in oligotrophic lakes affected by N deposition2010In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 72, no 3, p. 277-281Article in journal (Refereed)
    Abstract [en]

    The stoichiometric composition of lake water chemistry affects nutrient limitation among phytoplankton. I show how TN:TP and DIN:TP ratios vary in oligotrophic lakes of Europe and the USA affected by different amounts of N deposition, and evaluate whether the DIN:TP ratio is a better indicator than the TN:TP ratio for discriminating between N and P limitation of phytoplankton. Data were compiled from boreal and low to high alpine lakes, and comprise epilimnetic lake water chemistry data (106 lakes) and results from short-term nutrient bioassay experiments (28 lakes). A large share (54%) of the oligotrophic lakes in the study had low TN:TP mass ratios (<25). DIN:TP ratios showed higher variability than TN:TP ratios. Variability in DIN:TP ratios was related to N deposition, but also to catchment characteristics. Data from short-term bioassay experiments with separate addition of N and P showed that the DIN:TP ratio was a better indicator than the TN:TP ratio for N and P limitation of phytoplankton. Phytoplankton shift from N to P limitation when DIN:TP mass ratios increase from 1.5 to 3.4. High DIN:TP ratios, indicating P limitation of phytoplankton, were generally found in alpine lakes with low to moderate N deposition and in boreal lakes with high to very high amounts of N deposition.

  • 6.
    Bergström, Ann-Kristin
    et al.
    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.
    Karlsson, Daniel
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vrede, Tobias
    Contrasting plankton stoichiometry and nutrient regeneration in northern arctic and boreal lakes2018In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 80, no 2, article id UNSP 24Article in journal (Refereed)
    Abstract [en]

    Contrasting carbon: nitrogen: phosphorus (C: N: P) stoichiometry between phytoplankton and zooplankton affect consumer growth and phytoplankton nutrient limitation via nutrient recycling by zooplankton. However, no study has assessed how regional differences in terrestrial loadings of organic matter affect plankton N: P stoichiometry and recycling in systems with low N deposition and N-limited phytoplankton. We address this question by using data from 14 unproductive headwater arctic and boreal lakes. We found that boreal lakes had higher lake water-and seston C, N and P concentrations than arctic lakes, whereas seston C: N, C: P and N: P ratios did not differ among regions. Boreal zooplankton were also richer in N and P relative to C, with lower somatic N: P ratios, compared to arctic lakes. Consequently, the estimated N: P imbalances between seston and zooplankton were negative in arctic lakes, indicating zooplankton feeding on phytoplankton of suboptimal N content, resulting in low consumer driven N: P recycling (medians arctic sub-mid and high altitude lakes: 11 and 13). In boreal lakes, estimated N: P imbalance did not differ from zero, with a seston N: P stoichiometry matching the N: P requirements of zooplankton, which resulted in higher consumer driven N: P recycling (median 18). Our results imply that regional climate induced catchment differences, through enhanced terrestrial nutrient inputs, affect plankton stoichiometry by raising consumer N: P recycling ratio and changing zooplankton from being mainly N-(arctic) to NP co-limited (boreal). Browning of lakes, in regions with low N deposition, may therefore promote large-scale regional changes in plankton nutrient limitation with potential feedbacks on pelagic food webs.

  • 7. Bergström, Ann-Kristin
    et al.
    Karlsson, Jan
    Karlsson, Daniel
    Vrede, Tobias
    Contrasting plankton stoichiometry and nutrient regeneration in northern arctic and boreal lakes2018In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 80, no 24Article in journal (Refereed)
    Abstract [en]

    Contrasting carbon: nitrogen: phosphorus (C: N: P) stoichiometry between phytoplankton and zooplankton affect consumer growth and phytoplankton nutrient limitation via nutrient recycling by zooplankton. However, no study has assessed how regional differences in terrestrial loadings of organic matter affect plankton N: P stoichiometry and recycling in systems with low N deposition and N-limited phytoplankton. We address this question by using data from 14 unproductive headwater arctic and boreal lakes. We found that boreal lakes had higher lake water- and seston C, N and P concentrations than arctic lakes, whereas seston C: N, C: P and N: P ratios did not differ among regions. Boreal zooplankton were also richer in N and P relative to C, with lower somatic N: P ratios, compared to arctic lakes. Consequently, the estimated N: P imbalances between seston and zooplankton were negative in arctic lakes, indicating zooplankton feeding on phytoplankton of suboptimal N content, resulting in low consumer driven N: P recycling (medians arctic sub-mid and high altitude lakes: 11 and 13). In boreal lakes, estimated N: P imbalance did not differ from zero, with a seston N: P stoichiometry matching the N:P requirements of zooplankton, which resulted in higher consumer driven N: P recycling (median 18). Our results imply that regional climate induced catchment differences, through enhanced terrestrial nutrient inputs, affect plankton stoichiometry by raising consumer N: P recycling ratio and changing zooplankton from being mainly N- (arctic) to NP co-limited (boreal). Browning of lakes, in regions with low N deposition, may therefore promote large-scale regional changes in plankton nutrient limitation with potential feedbacks on pelagic food webs.

  • 8. Blenckner, T
    et al.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Rummukainen, Markku
    SMHI, Research Department, Climate research - Rossby Centre.
    A Swedish case study of contemporary and possible future consequences of climate change on lake function2002In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 64, no 2, p. 171-184Article in journal (Refereed)
    Abstract [en]

    A physical lake model was employed to obtain a basis of discussing the impact of climate variability and climate change on the ecology of Lake Erken, Sweden. The validity of this approach was tested by running the PROBE-lake model for a 30-year period (STD) with observed meteorological data. The lake is adequately modelled, as seen in the comparison with actual lake observations. The validated lake model was then forced with meteorological data obtained from a regional climate model (RCM) with a horizontal resolution of 44 km for present (CLTR) and 2 x CO(2) (SCEN) climate conditions. The CUR lake simulation compares reasonably with the STD. Applying the SCEN simulation leads to a climate change scenario for the lake. The physical changes include elevated temperatures, shorter periods of ice cover combined with two of ten years being totally ice-free, and changes in the mixing regime. The ecological consequences of the physical simulation results are derived from the historical dataset of Lake Erken. Consequences of a warmer climate could imply increased nutrient cycling and lake productivity. The results suggest that an application of RCMs with a suitable resolution for lakes in combination with physical lake models allows projection of the responses of lakes to a future climate.

  • 9. Bloch, Ina
    et al.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Long-term changes in physical and chemical conditions of nutrient-poor lakes along a latitudinal gradient: is there a coherent phytoplankton community response?2012In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 74, no 1, p. 77-85Article in journal (Refereed)
    Abstract [en]

    To evaluate climate and atmospheric deposition induced physical and water chemical changes and their effects on phytoplankton communities, we used complete time series (14 years, monthly measurements during the growing season) of 18 physical and chemical variables and phytoplankton data from 13 nutrient-poor Swedish reference lakes along a latitudinal gradient. We found numerous strong significant changes over time that were most coherent among lakes for sulfate concentrations, conductivity, calcium, magnesium, chloride, potassium, water color, surface water temperature and the intensity of thermal stratification. Despite these pronounced coherent physical and water chemical changes over Sweden, the phytoplankton biomass and species richness of six phytoplankton groups, measured at the same time as the water chemical variables, showed only few and weak significant changes over time. The only coherent significant change over Sweden, occurring in seven lakes, was observed in the species richness of chlorophytes. The number of chlorophyte taxa significantly declined over Sweden. Using a partial least square model for each lake, we attributed the decline primarily to an increase in water temperatures and water color, which were among the most important variables for the model performance of each lake. All other taxonomic groups were driven primarily by non-coherent changes in nutrient concentrations, pH and probably also non-coherent grazing pressure. We concluded that coherent phytoplankton responses can only be achieved for taxonomic groups that are driven primarily by coherent physical/chemical changes. According to our study, chlorophytes belong to such a group, making them possible global change indicators. Our findings give new insights into global change effects on different phytoplankton taxonomic groups in nutrient-poor lakes.

  • 10.
    Bryhn, Andreas Christoffer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Hessen, Dag O
    Blenckner, Thorsten
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Predicting particulate pools of nitrogen, phosphorus and organic carbon in lakes2007In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 69, no 4, p. 484-494Article in journal (Refereed)
    Abstract [en]

    The variation between lakes with respect to concentrations of particulate nutrient pools was studied in 126 Norwegian lakes covering a wide range in lake-specific properties. Particulate phosphorus (P) always constituted close to 60% of total P (TP) concentrations. Particulate nitrogen (N) and organic carbon (C) concentrations, on the other hand, were sensitive to several lake characteristics, particularly to TP concentrations. Through optimisation procedures and multivariate regression, the present study presents general empirical models for predicting particulate nutrient concentrations. Furthermore, significant trend shifts in the relationships between TP vs. particulate N and TP vs. particulate organic C were observed at TP = 6 mu g l(-1) and TP = 80 mu g l(-1), suggesting non-linearities in these relationships along the TP gradient. A trend shift in the TP vs. chlorophyll relationship was observed at TP = 90. Taking such non-linearities into account may decrease the uncertainty in predicting particulate N, particulate organic C and chlorophyll.

  • 11. Catalán, Núria
    et al.
    Obrador, Biel
    Felip, Marisol
    Pretus, Joan Lluís
    Higher reactivity of allochthonous vs. autochthonous DOC sources in a shallow lake2013In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 75, no 4, p. 581-593Article in journal (Refereed)
  • 12.
    Deutsch, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Voss, M.
    Fischer, H.
    Nitrogen transformation processes in the Elbe River: Distinguishing between assimilation and denitrification by means of stable isotope ratios in nitrate2009In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 71, no 2, p. 228-237Article in journal (Refereed)
    Abstract [en]

    During a 9-day Lagrangian sampling campaign along the free-flowing section of the Elbe River in July 2005, water from the river as well as from major tributaries and sewage treatment plants was sampled to investigate major nitrogen transformation processes, focussing on denitrification and N-assimilation by phytoplankton. Samples were analysed for delta N-15 - NO3-, delta O-18 - NO3-, delta N-15 - NH4+, nutrient concentrations, chlorophyll a (Chl a), and particulate organic matter. A strong decrease in nitrate concentration accompanied by strong increases in Chl a, particulate organic carbon (POC) and delta N-15- and delta O-18 - NO3- values were measured along the river. The ratio of the increase in delta N-15 vs. delta O-18 of the river nitrate samples was 0.89:1. Together with the observed decrease in nitrate and the increase in Chl a and POC, this indicates a major role of nitrogen assimilation by phytoplankton. This finding is supported by budget calculations, while nitrate inputs from the sampled tributaries and from sewage treatment plants were of minor importance for the nitrogen budget of the Elbe River. The stable isotope analysis of nitrogen and oxygen in nitrate is shown to be a powerful tool for the identification of N transformation processes along large rivers, particularly if combined with Lagrangian measurements of algal biomass, and dissolved and particulate nutrient concentrations.

  • 13.
    Ekelund, Nils
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Danilov, Roman
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    The influence of selenium on photosynthesis and light-enhanced dark respiration (LEDR) in the flagellate Euglena gracilis after exposure to ultraviolet radiation2001In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 63, no 4, p. 457-465Article in journal (Refereed)
    Abstract [en]

    Photodamage of photosynthesis arises from oxidative damage. One of the protective mechanisms is to convert excessive absorbed energy into thermal radiation. Another mechanism could be to strengthen the antioxidative capacity of plants and algae. Selenium is important in antioxidation in humans and may play a role in antioxidative mechanisms in plants. The aim of this investigation was to study the role of selenium in "light-enhanced dark respiration" (LEDR) and photosynthesis in the flagellate Euglena gracilis, after exposure to ultraviolet radiation (UV-radiation). Selenium was added into the growth medium at different concentrations of selenite (10-7, 10-8, 10-9 and 10-10 M, Na2SeO3 · 5H2O). E. gracilis were given six different light pulses with a photon fluence rate of 59, 163, 600, 1180, 2080 and 3340 μmol m-2 s-1 and periods of darkness between the light pulses. Photosynthetic saturation occurred at irradiances higher than 600 μmol m-2 s-1 and at the highest irradiance the photosynthetic rate decreased due to photoinhibition. Without any exposure to UV-radiation (UV-A, 320-400 nm, of 1.02 W m-2 plus UV-B, 280-320 nm, of 0.73 W m-2) LEDR increased with increasing photon fluence rate. After 40 min exposure to UV-radiation, photosynthetic rate and LEDR as functions of photon fluence rate were reduced. Neither in control (no UV-radiation) or when measured immediately after exposure to UV-radiation selenium had no stimulating effects on photosynthesis and LEDR. However, after UV-treatment and 24 h of recovery the presence of selenium led to an increase in photosynthesis and LEDR at higher irradiances. The results indicates that selenium might play a role in the repair mechanisms in E. gracilis after UV treatments.

  • 14.
    Ekström, Sara M.
    et al.
    Lund University.
    Sandahl, Margareta
    Lund University.
    Nilsson, Per Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences. Lund University.
    Kleja, Dan B.
    Swedish University of Agricultural Sciences.
    Kritzberg, Emma S.
    Lund University.
    Reactivity of dissolved organic matter in response to acid deposition2016In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 78, no 3, p. 463-475Article in journal (Refereed)
    Abstract [en]

    Fluvial export of organic matter from the terrestrial catchment to the aquatic system is a large and increasing carbon flux. The successful reduction in sulfuric acid deposition since the 1980s has been shown to enhance the mobility of organic matter in the soil, with more terrestrially derived dissolved organic matter (DOM) reaching aquatic systems. Changes in soil acidity also affect the quality of the DOM. In this study we explore the consequences this may have on the reactivity and turnover of the terrestrially derived DOM as it reaches the aquatic system. DOM of different quality (estimated by absorbance, fluorescence and size exclusion chromatography) was produced through extraction of boreal forest O-horizon soils from podzol at two sulfuric acid concentrations corresponding to natural throughfall in spruce forest in Southern Sweden around 1980 and today. Extraction was done using two different methods, i.e. field leaching and laboratory extraction. The DOM extracts were used to assess if differences in acidity generate DOM of different reactivity. Three reactivity experiments were performed: photodegradation by UV exposure, biodegradation by bacteria, and biodegradation after UV exposure. Reactivity was assessed by measuring loss of dissolved organic carbon and absorbance, change in fluorescence and molecular weight, and bacterial production. DOM extracted at lower sulfuric acid concentration was more susceptible to photooxidation, and less susceptible to bacterial degradation, than DOM extracted at a higher sulfuric acid concentration. Thus the relative importance of these two turnover processes may be altered with changes in acid deposition.

  • 15.
    Engel, Fabian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Drakare, Stina
    Swedish Univ Agr Sci SLU, Dept Aquat Sci & Assessment, POB 7050, S-75007 Uppsala, Sweden.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Environmental conditions for phytoplankton influenced carbon dynamics in boreal lakes2019In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 81, no 2, article id 35Article in journal (Refereed)
    Abstract [en]

    The partial pressure of CO2 (pCO(2)) in lake water, and thus CO2 emissions from lakes are controlled by hydrologic inorganic carbon inputs into lakes, and in-lake carbon transformation (mainly organic carbon mineralization and CO2 uptake by primary producers). In boreal lakes, CO2 uptake by phytoplankton is often considered to be of minor importance. At present, however, it is not known in which and how many boreal lakes phytoplankton CO2 uptake has a sizeable influence on the lake water pCO(2). Using water physico-chemical and phytoplankton data from 126 widely spread Swedish lakes from 1992 to 2012, we found that pCO(2) was negatively related to phytoplankton carbon in lakes in which the phytoplankton share in TOC (C-phyto:TOC ratio) exceeded 5%. Total phosphorus concentration (TP) was the strongest predictor of spatial variation in the C-phyto:TOC ratio, where C-phyto:TOC ratios>5% occurred in lakes with TP>30 mu gl(-1). These lakes were located in the hemi-boreal zone of central and southern Sweden. We conclude that during summer, phytoplankton CO2 uptake can reduce the pCO(2) not only in warm eutrophic lakes, but also in relatively nutrient poor hemi-boreal lakes.

  • 16. Galik, Alfred
    et al.
    Haidvogl, Gertrud
    Bartosiewicz, László
    Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies, Osteoarchaeological Research Laboratory.
    Guti, Gabor
    Fish remains as a source to reconstruct long-term changes of fish communities in the Austrian and Hungarian Danube2015In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 77, no 3, p. 337-354Article in journal (Refereed)
  • 17. Gascon Diez, Elena
    et al.
    Garcia Bravo, Andrea
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    à Porta, Natacha
    Masson, Matthieu
    Graham, Neil D.
    Stoll, Serge
    Akhtman, Yosef
    Amouroux, David
    Loizeau, Jean-Luc
    Influence of a wastewater treatment plant on mercury contamination and sediment characteristics in Vidy Bay (Lake Geneva, Switzerland)2014In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 76, no S1, p. S21-S32Article in journal (Refereed)
    Abstract [en]

    Previous direct observations of the sediment surface in Vidy Bay, Lake Geneva (Switzerland), revealed a range of sediment characteristics in terms of colour, texture and morphology. Dives with the MIR submersibles during the éLEMO project permitted the exploration of a large portion of Vidy Bay. It is the most contaminated part of Lake Geneva, due to inputs of treated and untreated waters from a large wastewater treatment plant (WWTP). To evaluate the influence of WWTP effluent on mercury contamination and sediment characteristics, 14 sediment cores were retrieved in the vicinity of the wastewater treatment plant effluent. Total mercury concentrations in sediments ranged between 0.32 and 10.1 mg/kg. Inorganic mercury and monomethylmercury concentrations in overlying and pore waters were also measured. The total partition coefficients of mercury (logK d) ranged from 3.6 to 5.8. The monomethylmercury concentration in pore waters of surface sediments was a large proportion of the total mercury concentration (44 ± 25 %). A Spearman test showed a negative correlation between the distance to the wastewater treatment plant outlet and the concentrations of total mercury in sediments and pore waters. Visual observations from the submersible allowed recognizing six different types of sediment. The areal distribution of these different sediment types clearly showed the influence of the wastewater treatment plant outlet on the sediment surface patterns. However, no relationship with mercury concentrations could be established.

  • 18. Karlsson, Jan
    et al.
    Lymer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Vrede, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Jansson, Mats
    Differences in efficiency of carbon transfer from dissolved organic carbon to two zooplankton groups: An enclosure experiment in an oligotrophic lake2007In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 69, no 1, p. 108-114Article in journal (Refereed)
    Abstract [en]

    We added dissolved organic carbon (C) in various amounts to 6 enclosures in an oligotrophic subarctic lake to assess how bacterioplankton growth on dissolved organic C affects the growth of calanoid copepod (Eudiaptomus graciloides) and cladoceran (Daphnia longispina) zooplankton. Organic C was added as glucose (12.5 to 400 µgC L−1d−1) and was isotopically distinct (−11.7 ‰) from lakewater organic C (<−27.2‰). All enclosures were also enriched with the same amounts of inorganic nitrogen (30 µgN L−1d−1 as NH4NO3) and inorganic phosphorus (2 µgP L−1d−1 as Na3PO4). The results showed a direct relationship between bacterial growth on dissolved organic C and incorporation of bacterial biomass into crustacean zooplankton. After 9 days, D. longispina and E. graciloides contained glucose-C in all treatments and the incorporation of glucose-C by zooplankton was strongly correlated with bacterial growth on glucose-C.δ15N data revealed different trophic positions of the two crustaceans, suggesting that D. longispina fed directly on bacteria while E. graciloides incorporated bacterial C by consumption of bacterivorus protozoans. Greater incorporation of glucose-C in D. longispina than in E. graciloides was explained by higher individual growth rates in D. longispina, and this difference between the two zooplankters increased as the bacterial production increased. Thus, the results show that the transfer of dissolved organic C through the food web can be more efficient via cladocerans than via calanoid copepods and that the effect becomes more pronounced as bacterial energy mobilization increases.

  • 19. Khalili, Maria I.
    et al.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Growing season variability of nitrate along a trophic gradient: contrasting patterns between lakes and streams2009In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 71, no 1, p. 25-33Article in journal (Refereed)
    Abstract [en]

    We studied the growing season (May to October) variability of NO3-N across Swedish lakes and streams. We found that NO3-N concentrations showed the highest growing season variability among all water chemical variables tested, both in lakes and in streams. However, the growing season variability of NO3-N increased with increasing trophic status in lakes while it decreased in streams. We attributed the contrasting pattern between lakes and streams to the relative importance of biological uptake and denitrification with increasing trophic status. Our results highlight the relation between growing season NO3-N variability and trophic status, which is positive in lakes but negative in streams. The findings of this study have important ramifications for ecosystem studies as well as water management. We suggest that the assessment of growing season variability of NO3-N in aquatic systems can be improved by considering the effect of trophic status.

  • 20. Kohler, S
    et al.
    Buffam, I
    Jonsson, A
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bishop, K
    Photochemical and microbial processing of stream and soilwater dissolved organic matter in a boreal forested catchment in northern Sweden2002In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 64, no 3, p. 269-281Article in journal (Refereed)
    Abstract [en]

    Natural organic matter (NOM) from stream and soil water in a humic-rich headwater catchment in northern Sweden (initial total organic carbon (TOC) concentrations 10-40 mg C L-1) was rapidly degraded by light and microbial activity in an incubation experiment. Concentration losses were 33-50% after 12 days of exposure to 69 W m(-2) artificial PAR and 16 W m(-2) UV radiation. Natural, unshaded mid-day solar radiation in the region (68degreesN 18degreesE) during the month of june is 159 W m(-2) for PAR. In contrast to microbial organic carbon removal, TOC exponentially decreased upon radiation, which suggests that TOC is more rapidly oxidized by light than by ambient microbes. Further, rapid decline in TOC concentration implies the presence of a dominant pool of photo-labile compounds (p > 95%). A measured mass balance for carbon identified 50-75% of the degraded TOC as carbon dioxide after 12 days of exposure to light. The observed conversion of organic to inorganic carbon was accompanied by increases in pH and alkalinity, suggesting that photo-degradation of NOM potentially contributes to in-stream buffering capacity. The remaining refractory TOC changed in chemical character, including an altered molecular weight distribution with decreased average weight and a change in the proportions of humics as evidenced by absorbance ratios (A(254)/A(420)). Extrapolation of the experiment to natural headwater conditions show that photo-degradation is an important in-stream process that should be considered in calculations of carbon turnover in surface waters because of its influence on both TOC amount and character.

  • 21.
    Müller, Roger A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Futter, Martyn N.
    Swedish University of Agricultural Sciences (SLU).
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Nisell, J.
    Swedish University of Agricultural Sciences (SLU).
    Bishop, Kevin
    Swedish University of Agricultural Sciences (SLU).
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Water renewal along the aquatic continuum offsets cumulative retention by lakes: implications for the character of organic carbon in boreal lakes2013In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 75, no 4, p. 535-545Article in journal (Refereed)
    Abstract [en]

    The character of organic carbon (OC) in lake waters is strongly dependent on the time water has spent in the landscape as well as in the lake itself due to continuous biogeochemical OC transformation processes. A common view is that upstream lakes might prolong the water retention in the landscape, resulting in an altered OC character downstream. We calculated the number of lakes upstream for 24,742 Swedish lakes in seven river basins spanning from 56º to 68º N. For each of these lakes, we used a lake volume to discharge comparison on a landscape scale to account for upstream water retention by lakes (Tn tot). We found a surprisingly weak relationship between the number of lakes upstream and Tn tot. Accordingly, we found that the coloured fraction of organic carbon was not related to lake landscape position but significantly related to Tn tot when we analysed lake water chemical data from 1,559 lakes in the studied river basins. Thus, we conclude that water renewal along the aquatic continuum by lateral water inputs offsets cumulative retention by lakes. Based on our findings, we suggest integrating Tn tot in studies that address lake landscape position in the boreal zone to better understand variations in the character of organic carbon across lake districts.

  • 22.
    Persson, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Vrede, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Holmgren, Staffan
    Responses in zooplankton populations to food quality and quantity changes after whole lake nutrient enrichment of an oligotrophic sub-alpine reservoir2008In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 70, no 2, p. 142-155Article in journal (Refereed)
    Abstract [en]

    To sustain production of higher trophic levels in oligotrophic systems it is important that the trophic transfer of energy and nutrients is efficient. The phytoplankton-zooplankton interface is of specific interest since nutritional constraints can decouple energy flow in this step. Increased nutrient loading to oligotrophic systems with initially low abundance of high quality phytoplankton could induce changes in seston composition that reduces the nutritional value for zooplankton. We carried out a whole lake enrichment experiment for five years in two ultraoligotrophic subalpine hydroelectric power reservoirs in Sweden. The first year was an untreated reference year. Phosphorus and nitrogen were added to Lake Stora Mjolkvattnet during the following four years, and upstream Lake Burvattnet was used as an untreated reference lake. The phosphorus content of seston in the experimental lake increased in the years of fertilization and seston phosphorus to carbon ratios (atomic) were non-limiting for zooplankton growth. Decreasing concentrations of phosphorus in the reference lake lead to low phosphorus to carbon ratios that probably affected zooplankton growth negatively. The seston fatty acid concentrations and phytoplankton composition indicated good food quality in both lakes. The phytoplankton increased in the experimental lake despite an increase in zooplankton biomass. Some changes in the relative contributions of plankton species occurred but the same species were present. The crustacean zooplankton community composition shifted towards smaller species during the latter years in the experimental lake, indicating increased predation pressure from fish. A major result of this whole-lake ecosystem fertilization experiment is that gentle fertilization can significantly boost phytoplankton production while food quality remains high, and plankton community composition is not substantially altered.

  • 23. Persson, Jonas
    et al.
    Vrede, Tobias
    Holmgren, Staffan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development.
    Responses in zooplankton populations to food quality and quantity changes after whole lake nutrient enrichment of an oligotrophic sub-alpine reservoir2008In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 70, no 2, p. 142-155Article in journal (Refereed)
    Abstract [en]

    To sustain production of higher trophic levels in oligotrophic systems it is important that the trophic transfer of energy and nutrients is efficient. The phytoplankton-zooplankton interface is of specific interest since nutritional constraints can decouple energy flow in this step. Increased nutrient loading to oligotrophic systems with initially low abundance of high quality phytoplankton could induce changes in seston composition that reduces the nutritional value for zooplankton. We carried out a whole lake enrichment experiment for five years in two ultraoligotrophic subalpine hydroelectric power reservoirs in Sweden. The first year was an untreated reference year. Phosphorus and nitrogen were added to Lake Stora Mjölkvattnet during the following four years, and upstream Lake Burvattnet was used as an untreated reference lake. The phosphorus content of seston in the experimental lake increased in the years of fertilization and seston phosphorus to carbon ratios (atomic) were non-limiting for zooplankton growth. Decreasing concentrations of phosphorus in the reference lake lead to low phosphorus to carbon ratios that probably affected zooplankton growth negatively. The seston fatty acid concentrations and phytoplankton composition indicated good food quality in both lakes. The phytoplankton increased in the experimental lake despite an increase in zooplankton biomass. Some changes in the relative contributions of plankton species occurred but the same species were present. The crustacean zooplankton community composition shifted towards smaller species during the latter years in the experimental lake, indicating increased predation pressure from fish. A major result of this whole-lake ecosystem fertilization experiment is that gentle fertilization can significantly boost phytoplankton production while food quality remains high, and plankton community composition is not substantially altered.

  • 24.
    Pilotto, Francesca
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany; Institute of Biology, Freie Universität Berlin, Berlin; School of Geography, Queen Mary University of London, London, UK.
    Harvey, Gemma L.
    Wharton, Geraldene
    Pusch, Martin T.
    Simple large wood structures promote hydromorphological heterogeneity and benthic macroinvertebrate diversity in low-gradient rivers2016In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 78, no 4, p. 755-766Article in journal (Refereed)
    Abstract [en]

    The presence of large wood (LW) in river channels adds an important habitat feature for benthic macroinvertebrates. However, there has been a lack of studies focusing on the effects of simple wood structures on hydromorphology and macroinvertebrate diversity in surrounding channel areas. This study explores whether consistent patterns in LW-related benthic habitat complexity and macroinvertebrate diversity can be identified across a set of low-gradient streams dominated by fine sediments. While the presence of LW did not change the average values of standard hydromorphological variables (flow velocity, turbulence, median sediment grain size and sorting index), the coefficients of variation of such variables for wood rich sites were consistently higher than those for wood poor sites (velocity: 85 % higher, turbulence: 89 %, grain size: 126 %, sorting index: 67 % higher). In parallel, beta diversity was on average 31 % higher in the wood rich sites, and positively correlated with the amount of LW at the site. The hotspots of local (alpha) diversity were located in the river-bed areas surrounding the LW, where taxonomic richness was 83 % higher and Shannon-Wiener diversity 39 % higher compared to the sites with less wood. These results demonstrate that the presence of LW in sandy lowland rivers induces consistent patterns of increased spatial variability of benthic habitats in the surrounding channel areas and this significantly enhances alpha and beta diversity of macroinvertebrate communities. Therefore, LW should be conserved in river channels wherever possible, and its potential for introduction into degraded systems should be explored further because even simple pieces of LW introduced to lowland streams can deliver benefits.

  • 25.
    Rinta, Paeivi
    et al.
    University of Bern, Switzerland; University of Bern, Switzerland.
    Bastviken, David
    Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    van Hardenbroek, Maarten
    University of Bern, Switzerland; University of Bern, Switzerland; University of Southampton, England.
    Kankaala, Paula
    University of Eastern Finland, Finland.
    Leuenberger, Markus
    University of Bern, Switzerland; University of Bern, Switzerland.
    Schilder, Jos
    University of Bern, Switzerland; University of Bern, Switzerland.
    Stoetter, Tabea
    University of Bern, Switzerland; University of Bern, Switzerland.
    Heiri, Oliver
    University of Bern, Switzerland; University of Bern, Switzerland.
    An inter-regional assessment of concentrations and delta C-13 values of methane and dissolved inorganic carbon in small European lakes2015In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 77, no 4, p. 667-680Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) and carbon dioxide emissions from lakes are relevant for assessing the greenhouse gas output of wetlands. However, only few standardized datasets describe concentrations of these gases in lakes across different geographical regions. We studied concentrations and stable carbon isotopic composition (delta C-13) of CH4 and dissolved inorganic carbon (DIC) in 32 small lakes from Finland, Sweden, Germany, the Netherlands, and Switzerland in late summer. Higher concentrations and delta C-13 values of DIC were observed in calcareous lakes than in lakes on non-calcareous areas. In stratified lakes, delta C-13 values of DIC were generally lower in the hypolimnion due to the degradation of organic matter (OM). Unexpectedly, increased delta C-13 values of DIC were registered above the sediment in several lakes. This may reflect carbonate dissolution in calcareous lakes or methanogenesis in deepwater layers or in the sediments. Surface water CH4 concentrations were generally higher in western and central European lakes than in Fennoscandian lakes, possibly due to higher CH4 production in the littoral sediments and lateral transport, whereas CH4 concentrations in the hypolimnion did not differ significantly between the regions. The delta C-13 values of CH4 in the sediment suggest that delta C-13 values of biogenic CH4 are not necessarily linked to delta C-13 values of sedimentary OM but may be strongly influenced by OM quality and methanogenic pathway. Our study suggests that CH4 and DIC cycling in small lakes differ between geographical regions and that this should be taken into account when regional studies on greenhouse gas emissions are upscaled to inter-regional scales.

  • 26.
    Rodriguez, Patricia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Geibrink, Erik
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hedström, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vasconcelos, Francisco Rivera
    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.
    Do warming and humic river runoff alter the metabolic balance of lake ecosystems?2016In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 78, no 4, p. 717-725Article in journal (Refereed)
    Abstract [en]

    Global warming is expected to influence lake gross primary production (GPP) and ecosystem respiration (R) by increasing water temperature and terrestrial export of organic material and inorganic nutrients from the catchment. We experimentally tested the effects of warming (3 A degrees C) and natural humic river runoff, separately and in combination, on habitat-specific and whole ecosystem net ecosystem production (NEP = GPP - R) in replicated large scale (136 m(3)) experimental pond ecosystems over one open water season. Pelagic NEP was reduced by warming and increased with humic river water addition. Littoral NEP (benthos, macrophytes, periphyton) showed an opposite pattern with increasing NEP following warming and decreasing NEP following humic river water addition. These changes were a result of changes in GPP with warming (negative in pelagic, positive in littoral) and with humic water addition (positive in pelagic, negative in littoral), while no effects were observed on pelagic respiration. As a result of the counteracting effects on NEP in pelagic and littoral habitats, whole ecosystem NEP was not affected by the treatments. The study suggests that climate mediated changes in temperature and river runoff have relatively small effects on the overall metabolic balance of shallow aquatic ecosystems but there may be large habitat-specific effects.

  • 27.
    Rydin, E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Vrede, T.
    Persson, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Holmgren, S.
    Jansson, M.
    Tranvik, L.J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Milbrink, G.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Compensatory nutrient enrichment in an oligotrophic mountain reservoir: effects and fate of added nutrients2008In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 70, no 3, p. 323-336Article in journal (Refereed)
    Abstract [en]

    Most Scandinavian rivers are impounded for power production. High altitude reservoirs retain water during summer and fall for power production during winter and spring. The oligotrophic lakes Mjölkvattnet and Burvattnet were impounded in 1942. Annual water level fluctuations caused by regulation have resulted in a loss of littoral habitat, and Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) populations have declined. To assess compensatory nutrient enrichment as a remedy against declining fish populations, we added dissolved phosphate and nitrate to Mjölkvattnet in June and July in 2002 and 2003, and used the upstream lake Burvattnet as a reference system. Nutrient addition doubled water column total phosphorus concentration, from 3 to 6 μg P/L and increased nitrogen concentration by about 20 μg/L. Half of the added phosphorus settled out as organic matter, and about one third was lost downstream. Phytoplankton production and biomass increased, but species composition remained principally unchanged. Rotifers and cladocerans responded rapidly, as did the condition of fish. After two years of nutrient addition, five year old Arctic char had doubled in weight and increased significantly in length, reaching pre-impoundment conditions.

  • 28. Rydin, E
    et al.
    Vrede, T
    Persson, J
    Holmgren, Staffan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development.
    Jansson, M
    Tranvik, L
    Milbrink, G
    Compensatory nutrient enrichment in an oligotrophicated mountain reservoir - effects and fate of added nutrients2008In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 70, no 3, p. 323-336Article in journal (Refereed)
    Abstract [en]

    Most Scandinavian rivers are impounded for power production. High altitude reservoirs retain water during summer and fall for power production during winter and spring. The oligotrophic lakes Mjolkvattnet and Burvattnet were impounded in 1942. Annual water level fluctuations caused by regulation have resulted in a loss of littoral habitat, and Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) populations have declined. To assess compensatory nutrient enrichment as a remedy against declining fish populations, we added dissolved phosphate and nitrate to Mjolkvattnet in June and July in 2002 and 2003, and used the upstream lake Burvattnet as a reference system. Nutrient addition doubled water column total phosphorus concentration, from 3 to 6 mu g P/L and increased nitrogen concentration by about 20 mu g/L. Half of the added phosphorus settled out as organic matter, and about one third was lost downstream. Phytoplankton production and biomass increased, but species composition remained principally unchanged. Rotifers and cladocerans responded rapidly, as did the condition of fish. After two years of nutrient addition, five year old Arctic char had doubled in weight and increased significantly in length, reaching pre-impoundment conditions.

  • 29. Schoelynck, Jonas
    et al.
    Schaller, Jörg
    Murray-Hudson, Mike
    Frings, Patrick J
    Swedish Museum of Natural History, Department of Geology.
    Conley, Daniel
    van Pelt, Dimitri
    Mosimane, Keotshephile
    Gondwe, Mangaliso
    Wolski, Piotr
    Meire, Patrick
    Struyf, Eric
    The trapping of organic matter within plant patches in the channels of the Okavango Delta: a matter of quality2017In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 79, no 3, p. 661-674Article in journal (Refereed)
    Abstract [en]

    The role of in-stream aquatic vegetation as ecosystem engineers in the distribution of organic matter was investigated in the Okavango Delta, one of the world’s largest oligotrophic wetlands. The Okavango channel beds are covered up to 50% with submerged macrophyte patches. By accumulating and concentrating organic matter in the sediments below the patches, macrophytes are likely able to locally forestall a deficiency of nutrients. Up to 21 times more N, 18 times more C, 13 times more P and 6 times more Si can be found in vegetated sediments compared to non-vegetated sediments. Nutrient specific accumulation relates to its relative scarcity in the overlaying water. There is a depletion of dissolved N relative to P, whereas Si is relatively abundant. The Okavango Delta water can generally be characterised as oligotrophic based on plant species composition (e.g. presence of carnivorous plants and absence of floating plants), low plant N:P ratios, and low nutrient- and element-concentrations. Local mineralization and intensified nutrient cycling in the sediments is hypothesized to be crucial for the macrophytes’ survival because it provides a key source of the essential nutrients which plants otherwise cannot obtain in sufficient quantities from the nutrient poor water. By engineering the ecosystem as such, channel vegetation also retards the loss of elements and nutrients to island groundwater flow, contributing to one of the key processes driving the high productivity of the Okavango Delta, making it unique among its kind.

  • 30. Selvam, Balathandayuthabani Panneer
    et al.
    Lapierre, Jean-Francois
    Soares, Ana R. A.
    Bastviken, David
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berggren, Martin
    Photo-reactivity of dissolved organic carbon in the freshwater continuum2019In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 81, no 4, article id UNSP 57Article in journal (Refereed)
    Abstract [en]

    The patterns in dissolved organic carbon (DOC) photo-mineralization along the freshwater continuum from land to sea are poorly known. Specifically, it has not been resolved how the photo-degradation ofDOC into CO2 (PD)depends on the combination of intrinsic properties of DOC and extrinsic variables that affect the photo-reactions. We measured PD per unit of absorbed ultraviolet light energy (PD-E-w) in headwater streams, lakes, intermediate rivers and river mouths in Sweden. Surprisingly, no trend of decreasing PD-E-w was found with decreases in colored DOC. However, there was a relationship between PD-E-w and pH, best described by a quadratic (U-shaped) curve, indicating environmental control of photo-reactivity. Interestingly, the highest values for both of these variables were recorded for river mouths. Moreover, PD-E-w increased with proxy variables for the amount of autochthonous DOC in the water. Thus, changes in pH and autochthonous DOC input along the continuum may sustain high DOC photo-mineralization throughout continental aquatic networks.

  • 31.
    Selvam, Balathandayuthabani Panneer
    et al.
    Lund Univ, Sweden.
    Lapierre, Jean-Francois
    Univ Montreal, Canada.
    Soares, Ana R. A.
    Lund Univ, Sweden.
    Bastviken, David
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Karlsson, Jan
    Umea Univ, Sweden.
    Berggren, Martin
    Lund Univ, Sweden.
    Photo-reactivity of dissolved organic carbon in the freshwater continuum2019In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 81, no 4, article id UNSP 57Article in journal (Refereed)
    Abstract [en]

    The patterns in dissolved organic carbon (DOC) photo-mineralization along the freshwater continuum from land to sea are poorly known. Specifically, it has not been resolved how the photo-degradation ofDOC into CO2 (PD)depends on the combination of intrinsic properties of DOC and extrinsic variables that affect the photo-reactions. We measured PD per unit of absorbed ultraviolet light energy (PD-E-w) in headwater streams, lakes, intermediate rivers and river mouths in Sweden. Surprisingly, no trend of decreasing PD-E-w was found with decreases in colored DOC. However, there was a relationship between PD-E-w and pH, best described by a quadratic (U-shaped) curve, indicating environmental control of photo-reactivity. Interestingly, the highest values for both of these variables were recorded for river mouths. Moreover, PD-E-w increased with proxy variables for the amount of autochthonous DOC in the water. Thus, changes in pH and autochthonous DOC input along the continuum may sustain high DOC photo-mineralization throughout continental aquatic networks.

  • 32.
    Sobek, Sebastian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Zurbruegg, Roland
    Eawag, Swiss Federal Institute of Aquatic Science and Technology.
    Ostrovsky, Ilia
    Israel Oceanographic and Limnological Research, Yigal Allon Kinneret Limnological Laboratory.
    The burial efficiency of organic carbon in the sediments of Lake Kinneret2011In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 73, no 3, p. 355-364Article in journal (Refereed)
    Abstract [en]

    Even though lake sediments constitute a significant long-term carbon sink, studies on the regulation of carbon burial in lakes sediments have, to date, been surprisingly few. We investigated to what degree the organic carbon (OC) being deposited onto the bottom of Lake Kinneret (Israel) is buried in the sediment at four different sites with varying degrees of oxygenation and varying supply of allochthonous particles from the River Jordan. For estimation of the OC burial efficiency (OC BE), i.e., the ratio between buried and deposited OC, we calculated OC burial from dated sediment cores, and calculated OC deposition using three different approaches. Calculation of OC deposition from sediment trap-derived mass deposition rates multiplied with the OC content of surface sediment yielded OC BE values that were at odds with published values for sediments dominated by autochthonous OC sources. Calculation via sediment trap data on organic matter flux collected within the Lake Kinneret monitoring program, as well as calculation of OC deposition as the sum of OC burial plus OC mineralization, returned fairly congruent estimates of OC BE (range 10-41%), but only if the sediment trap data were corrected for the proportion of resuspended particles in the traps. Differences in OC BE between sites were small, indicating that OC source (common to all sites) was a more important regulator of OC BE in Lake Kinneret than oxygen exposure or mineral particles characteristics.

  • 33. Tranvik, L J
    et al.
    van Hees, P A W
    Lundstrom, Ulla S
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Abundance and functions of natural organic matter species in soil and water2004In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 66, no 2, p. 149-150Article in journal (Refereed)
  • 34.
    Trinh, Duc Anh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Vietnam Acad Sci & Technol, Inst Chem ICH, A18,18 Hoang Quoc Viet, Hanoi, Vietnam.
    Luu, Thi Nguyet Minh
    Trinh, Quan Hong
    Tran, Hai Sy
    Tran, Tien Minh
    Le, Thi Phuong Quynh
    Duong, Thuy Thi
    Orange, Didier
    SFRI, IRD, iEES Paris UMR 242, Hanoi, Vietnam.;Inst Rech Dve IRD Eco & Sols, UMR 210, Pl Viala, Montpellier, France..
    Janeau, Jean Louis
    SFRI, IRD, iEES Paris UMR 242, Hanoi, Vietnam..
    Pommier, Thomas
    Univ Lyon 1, UMR CNRS 5557, Lab Ecol Microbienne, USC INRA 1364, Bat G Mendel,43 Blvd 11 Novembre 1918, F-69622 Villeurbanne, France..
    Rochelle-Newall, Emma
    SFRI, IRD, iEES Paris UMR 242, Hanoi, Vietnam.;IRD, iEES Paris, UMR 242, 32 Ave Henri Varagnat, Bondy, France..
    Impact of terrestrial runoff on organic matter, trophic state, and phytoplankton in a tropical, upland reservoir2016In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 78, no 2, p. 367-379Article in journal (Refereed)
    Abstract [en]

    The impact of organic matter inputs from agricultural, forest and domestic sources on aquatic processes has been considerably less studied in tropical reservoirs relative to temperate systems despite the high number of these small aquatic systems in the tropics. Here we present the results of an in situ mesocosm study that examined the impact of allochthonous organic matter on a headwater reservoir in Northern Vietnam. We examined the impact of wastewater and soils from floodplain paddies, Acacia mangium plantations and from upland slopes on the metabolic status of the reservoir. The addition of floodplain paddy soils to the reservoir water led to a rapid switch in metabolic status from net autotrophic to net heterotrophic. In contrast, the addition of wastewater in low concentrations had less impact on the metabolic status of the reservoir, reflecting the low population density in the area. The addition of floodplain paddy soils also increased phytoplankton diversity and evenness relative to the control. In summary, soils from floodplain paddies and from A. mangium plantations had the highest impact on the reservoir, with upland soils and wastewater having less of an impact. We also found that primary production in this reservoir was nitrogen limited. In order to avoid accelerating the impact of runoff on the reservoir, future management options should perhaps focus on minimizing water and sediment runoff from upstream paddy fields and from A. mangium plantations. These results also underline the importance of studying these upland tropical water bodies that can contribute an important but, on the whole, ignored part of the global carbon balance.

  • 35.
    Vezza, Paolo
    et al.
    Institut d’Investigació per a la Gestió Integrada de Zones Costaneres, Universitat Politècnica de València, Spain.
    Parasiewicz, P.
    Rushing Rivers Institute, Amherst, MA, USA .
    Calles, Olle
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Spairani, M.
    FLUME s.r.l, Aosta, Italy .
    Comoglio, Claudio
    Department of Environment, Land and Infrastructure Engineering, Politecnico di Torino, Turin, Italy .
    Modelling habitat requirements of bullhead (Cottus gobio)in Alpine streams2014In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 76, no 1, p. 1-15Article in journal (Refereed)
    Abstract [en]

    In the context of water resources planning andmanagement, the prediction of fish distribution related tohabitat characteristics is fundamental for the definition ofenvironmental flows and habitat restoration measures. Inparticular, threatened and endemic fish species should bethe targets of biodiversity safeguard and wildlife conservationactions. The recently developed meso-scale habitatmodel (MesoHABSIM) can provide solutions in this senseby using multivariate statistical techniques to predict fishspecies distribution and to define habitat suitability criteria.In this research, Random Forests (RF) and LogisticRegressions (LR) models were used to predict the distributionof bullhead (Cottus gobio) as a function of habitatconditions. In ten reference streams of the Alps (NW Italy),95 mesohabitats were sampled for hydro-morphologic andbiological parameters, and RF and LR were used todistinguish between absence/presence and presence/abundanceof fish. The obtained models were compared on thebasis of their performances (model accuracy, sensitivity,specificity, Cohen’s kappa and area under ROC curve).Results indicate that RF outperformed LR, for bothabsence/presence (RF: 84 % accuracy, k = 0.58 andAUC = 0.88; LR: 78 % accuracy, k = 0.54 and AUC =0.85) and presence/abundance models (RF: 79 % accuracy,k = 0.57 and AUC = 0.87; LR: 69 % accuracy, k = 0.43and AUC = 0.81). The most important variables, selectedin each model, are discussed and compared to the availableliterature. Lastly, results from models’ application in regulatedsites are presented to show the possible use of RF inpredicting habitat availability for fish in Alpine streams.

  • 36.
    Wu, Liuming
    et al.
    Luleå tekniska universitet.
    Forsling, Willis
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Surface complexation at hydrous fluorapatite1993In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 55, no 4, p. 336-346Article in journal (Refereed)
    Abstract [en]

    The adsorption of H+, OH- and ARS (Alizarin Red S) onto hydrous fluorapatite surfaces and Ca2+-ARS complexation in solution were studied by means of combined potentiometric and spectrophotometric titrations, as well as zeta potential and FT-IR measurements. Corresponding equilibrium constants of surface and solution reactions are determined. The application in flotation processes is discussed.

  • 37. Ågren, Anneli
    et al.
    Jansson, Mats
    Ivarsson, Hans
    Bishop, Kevin
    Seibert, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Seasonal and runoff-related changes in total organic carbon concentrations in the River Öre, Northern Sweden2008In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 70, no 1, p. 21-29Article in journal (Refereed)
    Abstract [en]

    The impact of runoff on allochthonous organic carbon was studied in the River Ore, Northern Sweden, using extensive TOC (total organic carbon) and runoff measurements. No relationship existed between TOC concentration and runoff on an annual basis. However, positive correlations between TOC concentration and runoff were found when observations were divided into three different seasons (winter, spring and summer/autumn). During these seasons runoff explained 62-70% of the TOC variation. Differences in these seasonal relationships indicated that the TOC concentration was restricted by the soil TOC pool during snowmelt, while the pool of TOC in the soil or its availability never limited the TOC export during the rest of the year. Two sets of data were used, a detailed study over 2 years and a long-term study over 14 years. Both showed similar results which indicated that the seasonal variation in the relationship between TOC and runoff is similar from year to year. The chemical variation usually decreases downstream in large rivers due to mixing of water from different sources. Our study, however, showed a strong correlation between TOC and runoff even in a large river like the River Ore. This result indicated that the general pattern of the TOC concentrations was to a large extent determined by the hydrology and climate conditions.

  • 38.
    Österling, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Timing, growth and proportion of spawners of the threatened unionoid mussel Margaritifera margaritifera: Influence of water temperature, turbidity and mussel density2015In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 77, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Anthropogenic disturbances often cause decline and extinction of threatened species. The present study investigated how gravid freshwater mussels, Margaritifera margaritifera, were affected by turbidity and water temperature, and by mussel density. At an early date of mussel spawning, there were lower proportions of gravid mussels in streams with evidence of mussel recruitment than in streams without mussel recruitment. At a late spawning date, this pattern was reversed. Higher water temperature in streams without recruitment was probably responsible for this difference. The combination of high water temperature and turbidity may be one reason for reduced growth of gravid mussels in streams without recruitment. There was a positive relationship between adult mussel density and the proportions of gravid mussels. Early gravidity may lead to early release of larvae, early infestation on the host fish and an earlier start of the benthic phase, which may reduce survival rates. Clear-cutting of forests and global warming are factors that are likely to cause increased turbidity/sedimentation and water temperatures in streams. One restoration measure that reduces sediment input and water temperatures is maintaining or restoring riparian zones, but these are long-term measures that require many years before they have an effect in streams.

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