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  • 1.
    Bergfur, Jenny
    et al.
    Department of Aquatic Sciences and Assessment, Swedish Agricultural University, Uppsala, Sweden; The Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, UK .
    Johnson, Richard K
    Department of Aquatic Sciences and Assessment, Swedish Agricultural University, Uppsala, Sweden.
    Sandin, Leonard
    Department of Aquatic Sciences and Assessment, Swedish Agricultural University, Uppsala, Sweden.
    Goedkoop, Willem
    Department of Aquatic Sciences and Assessment, Swedish Agricultural University, Uppsala, Sweden.
    Effects of nutrient enrichment on C and N stable isotope ratios of invertebrates, fish and their food resources in boreal streams2009In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 628, p. 67-79Article in journal (Refereed)
    Abstract [en]

    Carbon and nitrogen stable isotopes are frequently used to study energy sources and food web structure in ecosystems, and more recently, to study the effects of anthropogenic stress on aquatic ecosystems. We investigated the effect of nutrient enrichment on  d13C and d15N in fine (FPOM), coarse (CPOM) particulate organic matter, periphyton, invertebrates and fish in nine boreal streams in south-central Sweden. In addition, we analysed the diet of benthic consumers using stable isotope data. Increases in d15N of periphyton (R2 = 0.88), CPOM (0.78), invertebrates (0.92) and fish (0.89) were related to nutrient enrichment. In contrast, d13C signatures did not change along the nutrient gradient. Our results show that d15N has potential as a sensitive indicator of nutrient enrichment in boreal streams. Carbon and nitrogen isotopes failed to elucidate putative diets of selected aquatic consumers. Indeed, comparison of low- and high-impact sites showed that d13C of many consumers were found outside the ranges of basal resource d13C. Moreover, ranges of basal resource d13C and d15N overlapped at both low and high sites, making discrimination between the importance of allochthonous and autochthonous production difficult. Our findings show that a fractionation rate of 3.4% is not always be appropriate to assess trophic interactions, suggesting that more studies are needed on fractionation rates along gradients of impairment.

  • 2.
    Blindow, Irmgard
    et al.
    Ernst Moritz Arndt University of Greifswald, Germany .
    Hargeby, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Hilt, Sabine
    Leibniz Institute Freshwater Ecol and Inland Fisheries, Germany .
    Facilitation of clear-water conditions in shallow lakes by macrophytes: differences between charophyte and angiosperm dominance2014In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 737, no 1, p. 99-110Article in journal (Refereed)
    Abstract [en]

    A number of mechanisms result in a feedback between water clarity and macrophytes and, consequently, the occurrence of alternative stable states in shallow lakes. We hypothesize that bottom-up mechanisms and interactions within the benthic food web are more important in a charophyte-dominated clear-water state, while top-down mechanism and interactions in the planktonic food web prevail at angiosperm dominance. Charophytes, which dominate at lower nutrient concentrations and develop higher densities than most angiosperms, can have a higher influence on sedimentation, resuspension, and water column nutrients. During dominance of dense submerged vegetation like charophytes, zooplankton can be hampered by low food quality and quantity and by high predation pressure from juvenile fish, which in turn are favoured by the high refuge potential of this vegetation. Grazing pressure from zooplankton on phytoplankton can therefore be low in charophytes, but the main feedback in angiosperm-dominated ecosystems. Charophytes offer a higher surface than most angiosperms to periphyton, which favors benthic invertebrates. These support macrophytes by grazing periphyton and constitute a central link in a trophic cascade from fish to periphyton and macrophytes. To test these hypotheses, more experiments and field measurements comparing the effect of charophytes and angiosperms on water clarity are needed.

  • 3.
    Das, Supriyo Kumar
    et al.
    Department of Geology and Geochemistry, Stockholm University, Stockholm, Sweden.
    Routh, Joyanto
    Department of Geology and Geochemistry, Stockholm University, Stockholm, Sweden.
    Roychoudhury, Alakendra N.
    Department of Geological Sciences, University of Cape Town, Rondebosch, South Africa.
    Val Klump, J.
    Department of Biological Sciences and Department of Geosciences, Great Lakes WATER Institute, University of Wisconsin-Milwaukee, Milwaukee, USA.
    Ranjan, Rajesh Kumar
    School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India.
    Phosphorus dynamics in shallow eutrophic lakes: an example from Zeekoevlei, South Africa2009In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 619, p. 55-66Article in journal (Refereed)
    Abstract [en]

    Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO4 (3-)), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO3 and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column.

  • 4.
    Hansson, Lars-Anders
    et al.
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Nicolle, Alice
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Bronmark, Christer
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Hargeby, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Lindstrom, Ake
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Andersson, Gunnar
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Waterfowl, macrophytes, and the clear water state of shallow lakes2010In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 646, no 1, p. 101-109Article in journal (Refereed)
    Abstract [en]

    The importance of lake ecosystems for waterfowl remains a topic of debate. In order to assess how temporal variations in lake features, specifically shifts between alternative stable states, may interact with the waterfowl fauna, we performed a long-term (22 years) study of the shallow Lake Krankesjon, southern Sweden. Lower total numbers of waterfowl occurred during periods with low macrophyte cover and turbid water, than when submersed macrophytes flourished and the water was clear. Some specific functional groups of waterfowl, such as herbivores, invertebrate, and fish feeders, showed a positive relation to clear water and high macrophyte cover. Hence, our data suggest that some migratory waterfowl may select lakes based on water quality, thereby adjusting their large-scale migratory routes. On the other hand, omnivorous waterfowl exhibited their highest abundances during turbid conditions. Furthermore, waterfowl not primarily relying on food from the lake showed no response to fluctuations in turbidity or macrophyte cover, but followed regional trends in population dynamics. In our study lake, L. Krankesjon, we estimated that waterfowl remove less than 3% of the macrophyte biomass during a stable clear-water state with lush macrophyte beds. However, during transition periods between alternative stable states, when macrophyte biomass is lower and the plants already stressed, the consumption rate of waterfowl may have a stronger effect on lake ecosystem functioning.

  • 5.
    Johannesson, Karin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Andersson, Jonas
    WRS Uppsala AB, Sweden.
    Sundblad-Tonderski, Karin
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Efficiency of a constructed wetland for retention of sediment associated phosphorus2011In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 674, no 1, p. 179-190Article in journal (Refereed)
    Abstract [en]

    A constructed wetland (2.1 ha; 2% of catchment area) in southeast Sweden, in a catchment with 35% arable land on clay soils, was investigated with respect to phosphorus (P) retention, focusing on particulate P (PP) and sediment accretion. The aims were to i) estimate P retention and identify the dominating retention processes; ii) investigate how well estimates of P retention based on inflow-outflow measurements compared with the amount of P accumulated in the sediment. In- and outflow of P was measured during four years with continuous flow measurements and flow proportional weekly composite samples. P in the accumulated sediment was estimated based on core samples and analyzed using sequential fractionation. Total P load during four years was 65 kg/ha and intensive sampling events detected 69% as PP. Based on inflow-outflow estimates the mean P retention was 2.8 kg/ha/yr, or 17%, but the amount of P accumulated in the inlet zone  equated 78% of the TP load. This discrepancy showed the need to add studies of sediment accumulation to inflow-outflow estimates for an improved understanding of the P retention. The dominating P forms in the sediment were organic P (38%) and P associated with iron or aluminum (39%), i.e. potentially mobile forms. In areas colonized by Typha latifolia, the amount of P in the upper sediment layer (390 kg) was more than double the total P load of 136 kg. Cycling and release in those areas is a potential source of P that deserves further attention.

  • 6.
    Müren, U
    et al.
    Umeå University.
    Berglund, J
    Umeå University.
    Samuelsson, Kristina
    Umeå University.
    Andersson, A
    Umeå University.
    Potential effects of elevated sea-water temperature on pelagic food webs.2005In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 545, no 1, p. 153-166Article in journal (Refereed)
    Abstract [en]

    The effect of temperature changes on the marine pelagic food web was studied in three successive mesocosm experiments, performed during the spring bloom 2001 in the northern Baltic Sea. The temperature was varied from 5 to 20 °C in each experiment, running over a 3-week period. The experiments included food webs of at least four trophic levels: (1) phytoplankton-bacteria, (2) flagellates, (3) ciliates and (4) metazooplankton. The results showed that heterotrophic to autotrophic biomass ratio (H/A) increased 5 times when temperature was raised from 5 to 10 °C. In agreement, the carbon fixation to respiration ratio indicated a decrease of six times over the same temperature range. Furthermore, the sedimentation decreased by 45% when the temperature was elevated from 5 to 10 °C, probably as a consequence of the increased respiration losses and bacterial biodegradation of settling material. Analyzed parameters, thus, indicated that the degree of heterotrophy increased in the temperature interval of 5–10 °C. Above 10 °C, the analyzed parameters in general were more stable. Our results indicate that moderately elevated seawater temperatures, due to climate change or weather alterations, may affect the entire ecosystem function in temperate sea areas by altering the balance between autotrophy and heterotrophy.

  • 7.
    Persson Vinnersten, Thomas Z.
    et al.
    Department of Ecology and EVolution/Population Biology.
    Lundström, Jan O.
    Department of Ecology and EVolution/ Animal Ecology.
    Petersson, Erik
    Institute of Freshwater Research.
    Landin, Jan
    Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
    Diving beetle assemblages of flooded wetlands in relation to time, wetland type and Bti-based mosquito control2009In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, no 635, p. 189-203Article in journal (Refereed)
    Abstract [en]

    We investigated the abundance and taxonomic composition of the aquatic predatory insect fauna, with focus on adult diving beetles (Coleoptera: Dytiscidae), in eight temporary flooded wet meadows and two alder swamps in the River Dalälven floodplains, central Sweden from 2002 to 2006. Diving beetles are generalist predators and often abundant in various waters, including temporary wetlands. In the River Dalälven floodplains, recurrent floods induce massive hatching of flood-water mosquitoes (Diptera: Culicidae), which constitute a superabundant patchy and irregular food resource for aquatic predatory insects. Our aims were (1) to characterize the assemblage of adult diving beetles occurring in the wetlands during floods in relation to time and wetland type and (2) to evaluate the effect on the aquatic predator assemblage of strongly reducing the abundance of a potential prey, flood-water mosquito larvae with Bacillus thuringiensis var. israelensis (Bti) during floods. We found diving beetles to be the dominating aquatic predatory insect taxa in all 10 wetlands. There was a difference in Dytiscidae species richness but not in diversity between wet meadows and alder swamps after rarefaction. The cluster analysis based on dytiscid species and abundances showed very high similarities between the wetlands. The variance component analysis was unable to distinguish any factor that could explain more than 7.4% of the variation in the dytiscid species assemblages. The only effect of Bti-treatment against flood-water mosquito larvae, potential food for the predatory dytiscids, was a slight increase in abundance of the medium-sized dytiscid species. Our results are in accordance with previous studies, suggesting that irregular and recurrent flood dynamic structure the dytiscid fauna more than food limitations and environmental factors.

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