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  • 1.
    Blenckner, T.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Models as tools for understanding past, recent and future changes in large lakes.2008In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 599, p. 177-182Article in journal (Refereed)
    Abstract [en]

    Large lakes currently exhibit ecosystem responses to environmental changes such as climate and land use changes, nutrient loading, toxic contaminants, hydrological modifications and invasive species. These sources have impacted lake ecosystems over a number of years in various combinations and often in a spatially heterogeneous pattern. At the same time, many different kinds of mathematical models have been developed to help to understand ecosystem processes and improve cost-effective management. Here, the advantages and limitations of models and sources of uncertainty will be discussed. From these considerations and in view of the multiple environmental pressures, the following emerging issues still have to be met in order to improve the understanding of ecosystem function and management of large lakes: (1) the inclusion of thresholds and points-of-no-return; (2) construction of general models to simulate biogeochemical processes for a large number of lakes rather than for individual systems; (3) improvement of the understanding of spatio-temporal variability to quantify biogeochemical fluxes accurately; and (4) inclusion of biogeochemical linkages between terrestrial and aquatic ecosystems in model approaches to assess the effects of external environmental pressures such as land-use changes. The inclusion of the above-mentioned issues would substantially improve models as tools for the scientific understanding and cost-effective management of large lakes that are subject to multiple environmental pressures in a changing future.

  • 2.
    Bryhn, Andreas Christoffer
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    A morphometrically based method for predicting water layer boundaries in meromictic lakes2009In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 636, no 1, p. 413-419Article in journal (Refereed)
    Abstract [en]

    Many general mass-balance models that simulate processes in one or two water layers have been successfully constructed, tested and used to predict effects from remediating lake pollution and other environmental disturbances. However, these models are poorly suited for meromictic lakes which consist of yet another water layer. In order to determine a cross-systems based algorithm for the depth of the boundary between the two lowest layers (D crit2; in m), data from 24 three-layer lakes were analysed, and this depth could be predicted from the maximum depth and the lake surface area. The resulting model was tested with good results against independent data from 6 lakes which were not used for model development. Furthermore, D crit2 was predicted at a considerably lower depth than the theoretical wave base (a previously defined functional separator between the two top layers) in 110 out of 113 meromictic lakes. This indicates that the equation for D crit2 estimated in this study may be used for developing general mass-balance models for a large number of lakes which contain three stable water layers.

  • 3.
    Catalán, Núria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Herrero Ortega, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Gröntoft, H.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Hilmarsson, T. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Bertilsson, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Wu, Pianpian
    Levanoni, Oded
    Bishop, K.
    Garcia Bravo, Andrea
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Effects of beaver impoundments on dissolved organic matter quality and biodegradability in boreal riverine systems2016In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 793, no 1, p. 135-148Article in journal (Refereed)
    Abstract [en]

    Beaver impoundments modify the structure of river reaches and lead to changes in ecosystem function and biogeochemical processes. Here, we assessed the changes in dissolved organic matter (DOM) quality and the biodegradation patterns in a set of beaver systems across Sweden. As the effect of beaver impoundments might be transient and local, we compared DOM quality and biodegradability of both pond and upstream sections of differentially aged beaver systems. Newly established dams shifted the sources and DOM biodegradability patterns. In particular, humic-like DOM, most likely leached from surrounding soils, characterized upstream sections of new beaver impoundments. In contrast, autochthonous and processed compounds, with both higher biodegradation rates and a broader spectrum of reactivities, differentiated DOM in ponds. DOM in recently established ponds seemed to be more humic and less processed compared to older ponds, but system idiosyncrasies determined by catchment particularities influenced this ageing effect.

  • 4. Catalán, Núria
    et al.
    Obrador, Biel
    Pretus, Joan Lluís
    Ecosystem processes drive dissolved organic matter quality in a highly dynamic water body2014In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117Article in journal (Refereed)
  • 5. Hilt, Sabine
    et al.
    Wanke, Thomas
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Brauns, Mario
    Syväranta, Jari
    Brothers, Soren
    Gaedke, Ursula
    Köhler, Jan
    Lischke, Betty
    Mehner, Thomas
    Contrasting response of two shallow eutrophic cold temperate lakes to a partial winterkill of fish2015In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 749, no 1, p. 31-42Article in journal (Refereed)
    Abstract [en]

    Food-web effects of winterkill are difficult to predict as the enhanced mortality of planktivorous fish may be counterbalanced by an even higher mortality of piscivores. We hypothesised that a winterkill in a clear and a turbid shallow lake would equalise their fish community composition, but seasonal plankton successions would differ between lakes. After a partial winterkill, we observed a reduction of fish biomass by 16 and 43% in a clear-water and a turbid small temperate lake, respectively. Fish biomass and piscivore shares (5% of fish biomass) were similar in both lakes after this winterkill, but young-of-the-year (YOY) abundances were higher in the turbid lake. Top-down control by crustaceans was only partly responsible for low phytoplankton biomass at the end of May following the winterkill in both lakes. Summer phytoplankton biomass remained low in the clear-water lake despite high abundances of YOY fish (mainly roach). In contrast, the crustacean biomass of the turbid lake was reduced in summer by a high YOY abundance (sunbleak and roach), leading to a strong increase in phytoplankton biomass. The YOY abundance of fish in shallow eutrophic lakes may thus be more important for their summer phytoplankton development after winterkill than the relative abundance of piscivores.

  • 6. Hooge, Matthew
    et al.
    Wallberg, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Systematic Zoology.
    Todt, Christiane
    Maloy, Aaron
    Jondelius, Ulf
    Tyler, Seth
    A revision of the systematics of panther worms (Hofstenia spp., Acoela), with notes on color variation and genetic variation within the genus2007In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 592, p. 439-454Article in journal (Refereed)
    Abstract [en]

    Species of the genus Hofstenia are voracious predators and among the largest and most colorful of the Acoela. They are known from Japan, the Red Sea, the North Atlantic islands of Bermuda and the Bahamas, and the Caribbean and in a variety of habitats including the rocky intertidal, among Thalassia sea grass, on filamentous algae and decaying mangrove leaves. Certain color morphs associated with each of these habitats seem to have confused the taxonomy of the group. While brown-and-white banding and spotting patterns of Hofstenia miamia and Hofstenia giselae are distinctive for species associated with mangrove leaves and Thallasia sp. and are likely to be cryptic for these specific environments, we find some evidence to suggest that the coloration is mimicry of a nudibranch with aposematic coloration. The common plan in these patterns is one with three variously solid or spotted lighter cross bands on a dark background. Our examination of museum type material and live specimens of Hofstenia collected from Bahamas, Belize, Bermuda, and Panama revealed no internal morphological differences between the Hofstenia species occurring in the Caribbean. Similarly, our analyses of 18S and 28S molecular sequence data revealed no significant differences among specimens. Accordingly, we declare that Hofstenia giselae is a junior synonym of Hofstenia miamia, the three- banded panther worm.

  • 7. Jonsson, Mikael
    et al.
    Ranaker, Lynn
    Nicolle, Alice
    Ljungberg, Peter
    Fagerberg, Tony
    Hylander, Samuel
    Jephson, Therese
    Lebret, Karen
    von Einem, Jessica
    Hansson, Lars-Anders
    Nilsson, P. Anders
    Balseiro, Esteban
    Modenutti, Beatriz
    Glacial clay affects foraging performance in a Patagonian fish and cladoceran2011In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 663, no 1, p. 101-108Article in journal (Refereed)
    Abstract [en]

    Climate change is altering temperatures and precipitation patterns all over the world. In Patagonia, Argentina, predicted increase in precipitation together with rapidly melting glaciers increase the surface runoff, and thereby the transport of suspended solids to recipient lakes. Suspended solids affect the visual conditions in the water which in turn restricts visual foraging. The native fish Aplochiton zebra Jenyns, and its filter-feeding cladoceran prey, Daphnia commutata Ekman, were subjected to foraging experiments at three turbidity levels. A. zebra foraging rate was substantially reduced at naturally occurring turbidity levels and the filtering rate of D. commutata was reduced at the highest turbidity level. This indicates that Daphnia may be partly released from predation from A. zebra at the same time as it can maintain relatively high feeding rates as turbidity increases. Lower foraging rates at the same time as the metabolic demand increases, through increased temperatures, may result in larger effects on A. zebra than could be expected from increases in turbidity or temperature alone. Turbidity may, as an indirect effect of climate change, decrease planktivore foraging rates and thereby alter the interaction strength between trophic levels.

  • 8.
    Karlsson, Irene
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Limnology.
    Benthic growth of Gloeotrichia echinulata2003In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 506, no 1, p. 189-193Article in journal (Refereed)
    Abstract [en]

    Gloeotrichia echinulata is an akinete forming cyanobacterium with both a pelagic and a benthic phase. After germination of the akinete there is a short phase of growth on the sediment before the filaments develop gas vacuoles and migrate up into the water. It has been indicated that during the time of growth on the sediment surface the germlings take up nutrients. Those nutrients would be used during the pelagic phase as the pelagic colonies do not have a very efficient nutrient uptake. To test the length of the initial growth period `akinete colonies' were picked out of sediment samples from Lake Erken, Sweden, and placed on a thin layer of sediment in wellplates (Nunclon multidish, 48 wells) in an incubator with 17 °C and a light:dark cycle of 16:8 h. The plates were then studied under a stereomicroscope and pictures were taken one or two times per day for 20 days. Germination occurred in one third of the wells and the growth was recorded. The germlings formed bundles on the surface of the old akinete colony during the experiment. Several bundles were found on the same akinete colony. In the migration traps colonies and filament bundles were found. The morphology of filament bundles found in the migration traps was similar to the filament bundles found in the germination experiment which had reached a stage of development where they would soon be considered colonies.

  • 9.
    Koblmueller, Stephan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics.
    Sefc, Kristina M.
    Sturmbauer, Christian
    The Lake Tanganyika cichlid species assemblage: recent advances in molecular phylogenetics2008In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 615, p. 5-20Article in journal (Refereed)
    Abstract [en]

    Lake Tanganyika is not the most species-rich of the Great East African Lakes, but comprises the greatest diversity of cichlid fishes in terms of morphology, ecology, and breeding styles. The lake contains a polyphyletic assemblage of cichlid lineages, which evolved from several ancient species that colonized the emerging lake some 9-12 million years ago. Based on morphological characteristics, the Tanganyikan cichlids have been classified into 12, or, more recently, 16 tribes, which are largely supported by molecular data. The radiations of East African cichlids are believed to be driven by complex interactions between extrinsic factors, such as climatic changes and geological processes, and intrinsic biological characteristics of the involved organisms. Diversification within different lineages occurred simultaneously in response to drastic habitat changes such as the establishment of lacustrine deep-water conditions 5-6 MYA and subsequent major lake-level fluctuations. This seems particularly true for the mouthbrooding lineages whereas the substrate breeders underwent a more gradual process of diversification. This review presents an account of the taxonomy and phylogeny of the Lake Tanganyika cichlid species assemblage, its relationship to the African cichlid fauna, key factors leading to the astonishing diversity and discusses recently proposed alternative age estimates for the Lake Tanganyika cichlid species assemblage.

  • 10.
    Kruitbos, L. M.
    et al.
    Northern Rivers Institute, School of Geosciences, University of Aberdeen, Aberdeen, UK.
    Tetzlaff, D.
    Northern Rivers Institute, School of Geosciences, University of Aberdeen, Aberdeen, UK.
    Soulsby, C.
    Northern Rivers Institute, School of Geosciences, University of Aberdeen, Aberdeen, UK.
    Buttle, J.
    Department of Geography, Trent University, Peterborough, ON, Canada.
    Carey, S. K.
    School of Geography and Earth Sciences, McMaster University, Hamilton, ON, Canada.
    Laudon, H.
    Forest Ecology and Management, SLU, Umeå, Sweden.
    McDonnell, J. J.
    Department of Forest Engineering, Resources and Management, Oregon State University, Corvallis, OR, USA.
    McGuire, K.
    Department of Forest Resources and Environmental Conservation, Virginia Water Resources Research Center, Virginia Tech, Blacksburg, VA, USA.
    Seibert, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Cunjak, R.
    Canadian Rivers Institute, Department of Biology and the Faculty of Forestry and Environmental Management, University of New Brunswick, Fredericton, NB, Canada.
    Shanley, J.
    US Geological Survey, Reston, VT, USA.
    Hydroclimatic and hydrochemical controls on Plecoptera diversity and distribution in northern freshwater ecosystems2012In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 693, no 1, p. 39-53Article in journal (Refereed)
    Abstract [en]

    Freshwater ecosystems in the mid- to upper-latitudes of the northern hemisphere are particularly vulnerable to the impact of climate change as slight changes in air temperature can alter the form, timing, and magnitude of precipitation and consequent influence of snowmelt on streamflow dynamics. Here, we examine the effects of hydro-climate, flow regime, and hydrochemistry on Plecoptera (stonefly) alpha (alpha) diversity and distribution in northern freshwater ecosystems. We characterized the hydroclimatic regime of seven catchments spanning a climatic gradient across the northern temperate region and compared them with estimates of Plecoptera genera richness. By a space-for-time substitution, we assessed how warmer temperatures and altered flow regimes may influence Plecoptera alpha diversity and composition at the genus level. Our results show wide hydroclimatic variability among sites, including differences in temporal streamflow dynamics and temperature response. Principal component analysis showed that Plecoptera genera richness was positively correlated with catchment relief (m), mean and median annual air temperature (A degrees C), and streamflow. These results provide a preliminary insight into how hydroclimatic change, particularly in terms of increased air temperature and altered streamflow regimes, may create future conditions more favorable to some Plecopteras in northern catchments.

  • 11.
    Liao, Yi-Fan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Faulks, Leanne K.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Östman, Örjan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Stress tolerance and population stability of rock pool Daphnia in relation to local conditions and population isolation2015In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 742, no 1, p. 267-278Article in journal (Refereed)
    Abstract [en]

    Small fragmented populations can lose genetic variability, which reduces population viability through inbreeding and loss of adaptability. Current and previous environmental conditions can also alter the viability of populations, by creating local adaptations that determine responses to stress. Yet, most studies on stress tolerance usually consider either the effect of genetic diversity or the local environment, missing a more holistic perspective of the factors contributing to stress tolerance among natural populations. Here, we studied how salinity stress affects population growth of Daphnia longispina, Daphnia magna, and Daphnia pulex from rock pools with varying degrees of population isolation and salinity conditions. Standing variation of in situ rock pool salinity conditions explained more variation in salt tolerance than the standing variation of population isolation or genetic diversity, in both a pulse and a press disturbance experiment. This indicates that the level of stress, which these natural populations experience, influences their response to that stress, which may have important consequences for the conservation of fragmented populations. However, long-term population stability in the field decreased with population isolation, indicating that natural populations experience a variety of stresses; thus, population isolation and genetic diversity may stabilize population dynamics over larger spatiotemporal scales.

  • 12.
    Markensten, Hampus
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Climate effects on early phytoplankton biomass over three decades modified by the morphometry in connected lake basins2006In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 559, no 1, p. 319-329Article in journal (Refereed)
    Abstract [en]

    A 30-year continuous record of chlorophyll a samples in May from six locations in the Swedish Lake Mälaren was tested for the correlation to air temperature, water temperature, precipitation, discharge, nutrients, yellow substance, dissolved phosphorous load, ice cover and NAO (North Atlantic Oscillation) index. In the deep basins subjected to stratification chlorophyll a concentration correlated with air temperature with equal or shorter delay than it did in the shallow basins. Both precipitation and discharge were significant negatively correlated with chlorophyll a concentration in many of the basins with varying retention times. However, discharge into flushed basins had a more immediate influence on chlorophyll a concentration, and precipitation was earlier correlated with chlorophyll a concentration in basins fed from the smaller and closer situated catchment.

  • 13.
    Mendonca, Raquel
    et al.
    Department of Ecology, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; Department of Aquatic Ecology and Water Quality Management, University of Wageningen, Wageningen, The Netherlands..
    Sarian, Kosten
    Lacerot, Gissell
    Mazzeo, Nestor
    Roland, Fábio
    Ometto, Jean
    Bove, Cláudia
    Bueno, Norma
    Alonso Paz, Eduardo
    Scheffer, Marten
    Bimodality in stable isotope composition facilitates the tracing of carbon transfer from macrophytes to highertrophic levels2013In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 710, no 1, p. 205-218Article in journal (Refereed)
    Abstract [en]

    Even though the suitability of macrophytesto act as a carbon source to food webs hasbeen questioned by some studies, some others indicate that macrophyte-derived carbon may play an importantrole in the trophic transfer of organic matter in thefood web of shallow lakes. To evaluate the importanceof macrophytes to food webs, we collected primaryproducers—macrophytes and periphyton—and consumersfrom 19 South American shallow lakes andanalyzed their carbon stable isotopes composition(d13C). Despite the diversity of inorganic carbonsources available in our study lakes, the macrophytes’d13C signatures showed a clear bimodal distribution:13C-depleted and 13C-enriched, averaging at -27.2 and -13.5%, respectively. We argue that the use ofeither CO2 or HCO3- by the macrophytes largelycaused the bimodal pattern in d13C signals. Thecontribution of carbon from macrophytes to the lake’sfood webs was not straightforward in most of the lakesbecause the macrophytes’ isotopic composition wasquite similar to the isotopic composition of periphyton,phytoplankton, and terrestrial carbon. However,in some lakes where the macrophytes had a distinctisotopic signature, our data suggest that macrophytescan represent an important carbon source to shallowlake food webs.

  • 14.
    Moore, Karen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Pierson, Donald
    Pettersson, Kurt
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Schneiderman, Elliot
    Samuelsson, Patrick
    Effects of Warmer World Scenarios on Hydrologic Inputs to Lake Mälaren, Sweden and Implications for Nutrient Loads2008In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 599, p. 191-199Article in journal (Refereed)
    Abstract [en]

    A simple, rapid, and flexible modelling approach was applied to explore the impacts of climate change on hydrologic inputs and consequent implications for nutrient loading to Lake Malaren, Sweden using a loading function model (GWLF). The first step in the process was to adapt the model for use in a large and complex Swedish catchment. We focused on the Galten basin with four rivers draining into the western region of Malaren. The catchment model was calibrated and tested using long-term historical data for river discharge and dissolved nutrients (N, P). Then multiple regional climate model simulation results were downscaled to the local catchment level, and used to simulate possible hydrological and nutrient loading responses to warmer world scenarios. Climate change projections for the rivers of Galten basin show profound changes in the timing of discharge and nutrient delivery due to increased winter precipitation and earlier snow melt. Impacts on total annual discharge and load are minimal, but the alteration in river flow regime and the timing of nutrient delivery for future climate scenarios is strikingly different from historical conditions.

  • 15.
    Naddafi, Rahmat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Blenckner, Thorsten
    Eklöv, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Pettersson, Kurt
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Physical and chemical properties determine zebra mussel invasion success in lakes2011In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 669, no 1, p. 227-236Article in journal (Refereed)
    Abstract [en]

    To address the question whether the abundance of an invasive species can be explained by physical and chemical properties of the invaded ecosystems, we gathered density data of invasive zebra mussels and the physical and chemical data of ecosystems they invaded. We assembled published data from 55 European and 13 North American lakes and developed a model for zebra mussel density using a generalized additive model (GAM) approach. Our model revealed that the joint effect of surface area, total phosphorus and calcium concentrations explained 62% of the variation in Dreissena density. Our study indicates that large and less productive North American lakes can support larger local populations of zebra mussels. Our results suggest that the proliferation of an exotic species in an area can partially be explained by physical and chemical properties of the recipient environment.

  • 16.
    Nissling, Anders
    Gotland University, Department of Biology.
    Effects of temperature on egg and larval survival of cod (Gadus morhua) and sprat (Sprattus sprattus) in the Baltic Sea – implications for stock development2004In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 514, no 1-3, p. 115-123Article in journal (Refereed)
    Abstract [en]

    Stock development of cod and sprat, two major fish species in the Baltic Sea, is linked by trophic interactions. Depending on recruitment success the Baltic may be pushed towards either a cod- or a clupeid dominated system. Both cod and sprat spawn in the Baltic deep basins at strongly varying hydrographical conditions with survival during the egg and early larval stages regarded as a major bottleneck. Due to differences in egg specific gravity, cod and sprat eggs occur at different depths and are thus subject to different hydrographical conditions. For sprat, weak year-classes have been associated with low water temperatures during peak spawning. For cod the shift in peak spawning from spring to summer during the 1990s has been discussed as a reason for the poor recruitment at present as delayed spawning may involve egg development at too high temperatures. In the present study cod and sprat eggs and yolk sac larvae were incubated at different temperatures, 1–11thinsp°C for cod and 1–13thinsp°C for sprat. No difference in viable hatch occurred in the range 3–9thinsp°C for cod and in the range 5–13thinsp°C for sprat. Larval viability decreased at 11thinsp°C for cod and at le5thinsp°C for sprat. Comparing the results with vertical egg distribution and temperature profiles from field studies suggested no major influence of temperature on cod reproduction, but a considerable effect on sprat. The results imply that different environmental conditions; frequency of major saline water inflows into the Baltic Sea for cod, and water temperature in the upper layers, e.g. following severe/mild winters, for sprat, involve different opportunities for egg and larval survival and may thus cause a displacement in the balance between cod and sprat.

  • 17. Noges, Peeter
    et al.
    Noges, Tiina
    Adrian, Rita
    Weyhenmeyer, Gesa A.
    Silicon load and the development of diatoms in three river-lake systems in countries surrounding the Baltic Sea2008In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 599, p. 67-76Article in journal (Refereed)
  • 18. Palm, Fredrik
    et al.
    El-Daoushy, Farid
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Svensson, Jan-Erik
    Development of subfossil Daphnia and Chaoborus assemblages in relation to progressive acidification and fish community alterations in SW Sweden2012In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 684, no 1, p. 83-95Article in journal (Refereed)
    Abstract [en]

    Dated sediment cores from acidified and fishless Lake Gaffeln and Lake Harsvatten, SW Sweden, were analyzed for Daphnia ephippia and Chaoborus mandibles to test whether acidification history and fish extirpations could be reconstructed in a paleo-study using these easily identifiable animal remains. According to monitoring data fish were lost in both lakes from the 1950s to the 1970s. Progressive acidification prior to monitoring was confirmed by a gradual decrease and eventual loss of Daphnia ephippia in both study lakes during the first half of the twentieth century. In Lake Gaffeln mandibles of C. obscuripes appeared immediately after fish loss in 1973, and the regular presence of this species confirmed the succeeding fishless state of this lake. In Lake Harsvatten sediments C. obscuripes appeared only recently, i.e. three decades after fish extirpation, showing that the absence of C. obscuripes mandibles is not a trustworthy indicator of fish presence. Hence, the appearance of C. obscuripes was not temporally related to fish loss but confirmed the present fishless condition. Known historical presence of cyprinid fish in Lake Gaffeln was confirmed by a significantly higher proportion of fragmented mandibles of C. flavicans compared to the historically cyprinid-free Lake Harsvatten. In addition, both lake profiles displayed zero-proportions of fragmented mandibles during fishless periods. We conclude that acidification history and fish extirpations can be inferred by integrated studies on subfossil Daphnia ephippia and Chaoborus mandibles. However, during extreme ultra-oligotrophic conditions in acidified clear-water lakes subfossil Chaoborus mandibles may be too scarce to infer fish absence/presence.

  • 19. Pettersson, K
    et al.
    Grust, K
    Weyhenmeyer, G
    Blenckner, T
    Seasonality of chlorophyll and nutrients in Lake Erken - effects of weather conditions2003In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 506, no 1-3, p. 75-81Article in journal (Refereed)
  • 20. PIERSON, DC
    et al.
    WEYHENMEYER, GA
    HIGH-RESOLUTION MEASUREMENTS OF SEDIMENT RESUSPENSION ABOVE AN ACCUMULATION BOTTOM IN A STRATIFIED LAKE1994In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 284, no 1, p. 43-57Article in journal (Refereed)
    Abstract [en]

    A detailed record of suspended particulate matter (SPM) concentrations in the benthic boundary layer (BBL) 1.5 m above an accumulation bottom and 13.5 m below the surface was obtained from frequent (30 min interval) beam attenuation measurements made with a Sea Tech transmissometer in the main basin of Lake Erken, a moderately deep (mean depth 9 m, maximum depth 21 m) dimictic lake in central Sweden. Concentrations of SPM (g m-3) were not as strongly correlated to the beam attenuation coefficient (c, [m-1]), as were concentrations of the inorganic SPM fraction. Apparently, this was caused by large optically inactive organic particles which significantly affected the measurements of SPM, but had little effect on the attenuation of light. When the water column was thermally stratified, SPM concentrations in the BBL showed a seasonal increase which was related to an increase in the thermocline depth. As the epilimnion deepened, there was also a marked increase in the occurrence of rapid and large changes in SPM concentration. After the loss of stratification, the amount of SPM and the temporal variability in its concentration was reduced. Since surface waves could not influence sediment resuspension at the depth of measurement, these data show the importance of internal waves in promoting sediment resuspension in areas of sediment accumulation. The relatively short period in each summer, when the thermocline reaches a sufficient depth to allow for resuspension over accumulation bottoms, can have important consequences for both the redistribution of lake sediments and the internal loading of phosphorus.

  • 21.
    Van Nieuwerburgh, Lies
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Evolutionary Biology.
    Wänstrand, Ingrid
    Snoeijs, Pauli
    Growth and C:N:P ratios in copepods grazing on N- or Si-limited phytoplankton blooms2004In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 514, no 1-3, p. 57-72Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate how nutrient limitation in phytoplankton blooms affects growth and C:N:Pratios in marine pelagic copepods.We performed two mesocosm experiments on the Atlantic coast near Trondhjem(Norway). Si-limitation in a phytoplankton bloom was triggered by N and P additions (NP treatment) and Nlimitationwas triggered by N, P and Si additions (NPSi treatment). Both nutrient treatments stimulated microalgalgrowth and increased the biomass of the phytoplankton manifold. The initial phytoplankton community consistedof flagellates and diatoms. Throughout both experiments, community composition stayed relatively stable anddiverse in the NP treatments, but in the NPSi treatments large and heavily silicified diatoms came to dominatecompletely. Phytoplankton C:N ratios in the Si-limited blooms were close to the Redfield ratio of 6.6 (on a molarbasis), but they were higher in the Control treatment without nutrient additions (ca. 8.6) and up to 14 in heavily Nlimitedblooms. When phytoplankton blooms (chlorophyll a > 25 nmol l−1) had established, wild copepods wereadded to the mesocosms. During Si-limitation the copepod density increased by ca. 40% in one of the experiments,while the C:N ratio was 5.5–6 in the copepods. During N-limitation, the copepod density stayed stable, while theC:N ratio increased to ca. 7 in the course of the experiment. In the other experiment the copepod density decreasedby ca. 25%, irrespective of nutrient treatment (C:N ratio ca. 9). The N:P ratios in the copepods varied between 16and 22 and were not different in the NP and NPSi treatments. Our study shows that N-limitation in phytoplanktoncells can increase the C:N ratio of their grazers, which has a reportedly negative effect on copepod growth andreproduction. Our study also shows that copepod populations can be regulated by seawater Si:N ratios via diatoms:at high ratios the growth from eggs/nauplii to copepodites was hampered. High Si:N ratios provide diatoms withpossibilities to escape from grazing (large species, heavy silicification, excretion of secondary metabolites), leadingto the accumulation of algal biomass without transfer to higher trophic levels.

  • 22.
    Vinnersten, Thomas Z. Persson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution.
    Lundström, Jan O.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution.
    Petersson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution.
    Landin, Jan
    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, Vol. 635, no 1, 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 Dalalven flood-plains, central Sweden from 2002 to 2006. Diving beetles are generalist predators and often abundant in various waters, including temporary wetlands. In the River Dalalven 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.

  • 23. Weyhenmeyer, Gesa A.
    Rates of change in physical and chemical lake variables - are they comparable between large and small lakes?2008In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 599, p. 105-110Article in journal (Refereed)
  • 24. Weyhenmeyer, Gesa A.
    et al.
    Westoeoe, Anna-Karin
    Willen, Eva
    Increasingly ice-free winters and their effects on water quality in Sweden's largest lakes2008In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 599, p. 111-118Article in journal (Refereed)
  • 25. Yang, Yang
    et al.
    Pettersson, Kurt
    Effects of physical factors on spring phytoplankton in a temperate lake (Lake Erken, Sweden)In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117Article in journal (Other academic)
  • 26.
    Yang, Yang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Pettersson, Kurt
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Padisák, Judit
    Repetitive baselines of phytoplankton succession in an unstably stratified temperate lake (Lake Erken, Sweden): a long-term analysis2016In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 764, no 1, p. 211-227Article in journal (Refereed)
    Abstract [en]

    The seasonal development of phytoplankton is a sequence of consecutive events with waxes and wanes of biomass and compositional shifts. This study analyzed 16 years data in Lake Erken, Sweden and revealed four baselines of phytoplankton succession with their underlying drivers. Results showed that there were two diatom-dominated phases annually. The vernal community was dominated by centric diatoms larger than 15 A mu m (functional groups B and C) which were fast-growing diatoms being highly efficient in the use of nutrients. The autumn community was comprised mainly meroplanktonic mixing-dependent Aulacoseira granulata and Fragilaria sp. (MP and P) or/and large centric diatoms (B). Between the two mixing-phases with diatoms, a Gloeotrichia echinulata (H 2) bloom occurred due to its preference for a stratified water column with elevated water temperatures and high light availability. The summer stratification in Lake Erken was weak and short, thus, favoring meroplanktonic diatoms to peak once the lake turned over in early autumn. Lake Erken represents an intermediate case between a highly mixed polymictic lake and a lake with strong summer stratification, where the observed stratification patterns allowed the development of an autumn diatom phase similar, by extent, to the vernal one and mainly dominated by meroplanktonic diatoms.

  • 27.
    Yang, Yang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Stenger-Kovacs, Csilla
    Univ Pannonia, Dept Limnol, Egyet U 10, H-8200 Veszprem, Hungary..
    Padisak, Judit
    Univ Pannonia, Dept Limnol, Egyet U 10, H-8200 Veszprem, Hungary.;MTA PE Limnoecol Res Grp, Egyet U 10, H-8200 Veszprem, Hungary..
    Pettersson, Kurt
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Effects of winter severity on spring phytoplankton development in a temperate lake (Lake Erken, Sweden)2016In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 780, no 1, p. 47-57Article in journal (Refereed)
    Abstract [en]

    Phytoplankton seasonal succession has been linked to a variety of serial environmental changes, especially weather- and climate-induced physical forcing. This study compared spring phytoplankton dynamics after winters of different severity (cold, normal, and warm) in Lake Erken, Sweden. The spring diatom bloom was dominated by different functional groups: group A (centric diatoms 5-10 mu m) after cold winters, B (centric diatoms > 15 mu m) after normal winters, and P (Aulacoseira granulata, Fragilaria crotonensis) after warm winters. Our results suggest that weather-related processes were the primary external drivers accounting for differences in spring phytoplankton dynamics in Lake Erken. Spring phytoplankton are influenced by overwintering species from the last autumn that can initiate the following spring bloom. Average taxonomic distinctness of the spring community was assessed using a new biodiversity measurement that incorporates taxonomic relatedness information. This value was lower than expected after warm and cold winters, which had winter air temperature 1A degrees C deviation from an average value calculated over 21 years. Such winters increased the level of disturbance or stress to the lake, resulting in a spring with less diverse phytoplankton by narrowing the niche for species with various ecological requirements.

  • 28.
    Östman, Örjan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Population and conservation biology.
    Lundström, Jan O.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Population and conservation biology.
    Vinnersten, Thomas Z. Persson
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Population and conservation biology.
    Effects of mosquito larvae removal with Bacillus thuringiensis israelensis (Bti) on natural protozoan communities2008In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 607, no 1, p. 231-235Article in journal (Refereed)
    Abstract [en]

    The protein crystals produced by Bacillus thuringiensis israelensis (Bti) are used against the larvae of pestiferous flood-water mosquitoes in ephemeral wetlands. Although mosquito larvae are considered important predators on protozoans and bacteria, it is not known how a distinct reduction of mosquito larvae density in natural wetlands caused by application of Bti may indirectly affect these microbial communities. Here we show, in a large scale experiment in six natural wetlands, that the densities of heterotrophic protozoans was on an average 4.5 times higher in wetland areas treated with Bti than in control areas. In addition, the taxonomic richness of heterotrophic protozoans increased on an average of 60% in areas with Bti application compared to control areas. The increase in protozoan density and richness was fairly consistent among sites of different wetland habitats. We discuss the potential implications of our results for other parts of the ecosystem.

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