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  • 1.
    Arthington, Angela H
    et al.
    Australian Rivers Institute and eWater Co-operative Research Centre, Griffith University, Brisbane, Qld, Australia.
    Naiman, Robert J
    School of Aquatic & Fishery Sciences, University of Washington-355020, Seattle, WA, U.S.A..
    McClain, Michael E
    UNESCO-IHE Institute for Water Education, Delft, The Netherlands and Department of Earth and Environment, Florida International University, Miami, FL, U.S.A..
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Preserving the biodiversity and ecological services of rivers: new challenges and research opportunities2010In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 55, no 1, p. 1-16Article in journal (Refereed)
    Abstract [en]

    Natural biogeochemical processes and diverse communities of aquatic biota regulate freshwater quantity and quality in ways that are not sufficiently acknowledged nor appreciated by the water resources management community. The establishment and enforcement of environmental flow requirements offer promising means to improve and care for these critical environmental services. This Special Issue provides new insights and novel techniques to determine, protect and restore ecologically and socially sustainable flow regimes, and thereby help achieve the water-related goals of the Millennium Ecosystem Assessment.

    Whilst alteration of flow, sediment, organic matter and thermal regimes interact to reduce biological diversity and the ecological integrity of freshwater ecosystems - and thereby degrade the properties and ecological services most valued by humans - ‘environmental flows' left in rivers, or restored to developed rivers, will sustain many ecological and societal values. The success of river protection and rehabilitation ⁄ restoration depends upon understanding and accurately modelling relationships between hydrological patterns, fluvial disturbance and ecological responses in rivers and floodplains.

    This Special Issue presents new analytical and modelling approaches to support the development of hydro-ecological models and environmental flow standards at multiple spatial scales - applicable to all rivers in any economic and societal setting. Examples include the new framework Ecological Limits of Hydrologic Alteration (ELOHA) founded on hydrological classification and gradient analysis; ecological trait analysis; Bayesian hierarchical modelling; Bayesian Decision Networks; and Integrated Basin Flow Assessment (IBFA).

    Advances in the allocation of flood flows along the River Murray in Australia, an Ecosystems Function Model (HEC-EFM) for the Bill Williams River restoration programme in Arizona (U.S.A), the European Water Framework Directive, and improved management of hydroelectric dams demonstrate the potential for significant ecological recovery following partial restoration of natural river flow regimes.

    Based on contributions to this Special Issue, the action agenda of the 2007 Brisbane Declaration on environmental flows and the wider literature, we propose an invigorated global research programme to construct and calibrate hydro-ecological models and to quantify the ecological goods and services provided by rivers in contrasting hydro-climatic settings across the globe. A major challenge will be to find acceptable ways to manage rivers for multiple uses. Climate change intensifies the urgency. Environmental flows help to preserve the innate resilience of aquatic ecosystems, and thereby offer the promise of improved sustainability and wellbeing for people as well as for ecosystems.

  • 2. Bejarano, Maria Dolores
    et al.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gonzales del Tanago, Marta
    Marchamalo, Miguel
    Responses of riparian trees and shrubs to flow regulationalong a boreal stream in northern Sweden2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 56, no 5, p. 853-866Article in journal (Refereed)
    Abstract [en]

    1. Flow dynamics is a major determinant of riparian plant communities. Therefore, flowregulation may heavily affect riparian ecosystems. Despite the large number of damsworldwide, little specific information is available on the longitudinal impacts of dams onvegetation, for example how far downstream and at what degree of regulation a dam on ariver can influence riparian woodlands.

    2. We quantified the long-term responses of riparian trees and shrubs to flow regulation byidentifying their lateral distribution and habitat conditions along a boreal river in northernSweden that has been regulated by a single dam since 1948. The regulation has reducedannual flow fluctuations, this effect being largest at the dam, downstream from which itprogressively decreases following the entrance of free-flowing tributaries.

    3. We related changes in the distribution patterns, composition, abundance and richness oftree and shrub species to the degree of regulation along the river downstream from thedam. Regulation has triggered establishment of trees and shrubs closer to the channel,making it possible to measure ecological impacts of flow regulation as differences invegetation attributes relative to the positions of tree and shrub communities establishedbefore and after regulation.

    4. Trees and shrubs had migrated towards the mid-channel along the entire study reach,but the changes were largest immediately downstream of the dam. Shrubs were mostimpacted by flow regulation in terms of lateral movement, but the effect on trees extendedfurthest downstream.

    5. The species composition of trees progressively returned to its pre-regulation state withdistance downstream, but entrance of free-flowing tributaries and variation in channelmorphology and substratum caused local deviations. Species richness after regulationincreased for trees but decreased for shrubs. The changes in species composition andrichness of trees and shrubs showed no clear downstream patterns, suggesting that otherfactors than the degree of regulation were more important in governing life form.

  • 3.
    Berger, Stella A.
    et al.
    Univ Munich, Dept Biol 2, Planegg Martinsried, Germany; Univ Georgia, Skidaway Inst Oceanog, Savannah, GA USA.
    Diehl, Sebastian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Univ Munich, Dept Biol 2, Planegg Martinsried, Germany.
    Stibor, Herwig
    Univ Munich, Dept Biol 2, Planegg Martinsried, Germany.
    Sebastian, Patrizia
    Univ Munich, Dept Biol 2, Planegg Martinsried, Germany.
    Scherz, Antonia
    Univ Munich, Dept Biol 2, Planegg Martinsried, Germany.
    Separating effects of climatic drivers and biotic feedbacks on seasonal plankton dynamics: no sign of trophic mismatch2014In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 59, no 10, p. 2204-2220Article in journal (Refereed)
    Abstract [en]

    Climate change may impact most strongly on temperate lake plankton communities in spring, when light availability and water temperature change rapidly due to thermal stratification. Effects of changing light and temperature on one food-web component transfer to other components, producing a complex interplay between physical drivers and biotic feedbacks. Understanding this interplay is important, because altered climate regimes could result in phenological mismatch between the phytoplankton spring bloom and the timing of maximum food requirements of grazers. To separate direct effects of light and temperature on spring plankton dynamics from effects mediated through micro- and mesograzer feedbacks, we manipulated water temperature, stratification depth and presence/absence of the mesograzer Daphnia in lake mesocosms. In early spring, stratification depth and water temperature directly influenced the light supply to phytoplankton and the growth rates of all plankton groups. Subsequently, indirect effects, including light-dependent food supply to grazers and temperature-dependent grazing pressure, became increasingly important. Phytoplankton and Daphnia peaked earlier in warmer treatments and reached higher peaks when stratification depth was shallower. Ciliates responded positively to increased food density and higher temperature and subsequently affected the taxonomic composition, but not the total biomass, of phytoplankton. In the absence of Daphnia, phytoplankton did not enter a distinct clear water phase. When present, Daphnia caused an extended clear water phase, maintaining phytoplankton and ciliates at low levels throughout early summer and suppressing all direct effects of physical drivers on these plankton groups. Our Daphnia treatments mimicked the high and low fish predation settings of the largely descriptive, recently revised Plankton Ecology Group (PEG) model of seasonal plankton succession and explored their responses to climate change scenarios. The results largely support the PEG model, but attribute greater importance to early season temperature effects and later season grazing effects of Daphnia. In warmer treatments, the timing of phytoplankton and zooplankton peaks tended to be more closely coupled, and temperature did not affect the height of zooplankton peaks. In line with other experiments, these results do not support the widely held concern that warming may create a trophic mismatch between phytoplankton and zooplankton and reduce spring zooplankton production.

  • 4.
    Bergström, Ann-Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Drakare, Stina
    Blomqvist, Peter
    Occurrence of mixotrophic flagellates in relation to bacterioplankton production, light regime and availability of inorganic nutrients in unproductive lakes with differing humic contents2003In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 48, no 5, p. 868-877Article in journal (Refereed)
    Abstract [en]

    1. Field data from five unproductive Swedish lakes were used to investigate the occurrence of mixotrophic flagellates in relation to bacterioplankton, autotrophic phytoplankton, heterotrophic flagellates and abiotic environmental factors. Three different sources of data were used: (i) a 3-year study (1995-97) of the humic Lake Örträsket, (ii) seasonal measurements from five lakes with widely varying dissolved organic carbon (DOC) concentrations, and (iii) whole lake enrichment experiments with inorganic nutrients and organic carbon. 2. Mixotrophic flagellates usually dominated over autotrophic phytoplankton in Lake Örträsket in early summer, when both bacterial production and light levels were high. Comparative data from the five lakes demonstrated that the ratio between the biomasses of mixotrophic flagellates and autotrophic phytoplankton (the M/A-ratio) was positively correlated to bacterioplankton production, but not to the light regime. Whole lake carbon addition (white sugar) increased bacterial biomass, and production, reduced the biomass of autotrophs by a factor of 16, and increased the M/A-ratio from 0.03 to 3.4. Collectively, the results indicate that the dominance of mixotrophs among phytoplankton was positively related to bacterioplankton production. 3. Whole lake fertilisation with nitrogen (N) and phosphorus (P) demonstrated that the obligate autotrophic phytoplankton was limited by N. N-addition increased the biomass of the autotrophic phytoplankton but had no effect on mixotrophic flagellates or bacteria, and the M/A-ratio decreased from 1.2 to 0.6 after N-enrichment. Therefore, we suggest that bacteria under natural conditions, by utilising allochthonous DOC as an energy and carbon source, are able to outcompete autotrophs for available inorganic nutrients. Consequently, mixotrophic flagellates can become the dominant phytoplankters when phagotrophy permits them to use nutrients stored in bacterial biomass. 4. In Lake Ortrasket, the biomass of mixotrophs was usually higher than the biomass of heterotrophs during the summer. This dominance could not be explained by higher grazing rates among the mixotrophs. Instead, ratios between mixotrophic and heterotrophic biomass (the M/H-ratio) were positively related to light availability. Therefore, we suggest that photosynthesis can enable mixotrophic flagellates to outcompete heterotrophic flagellates.

  • 5. Brett, Michael T.
    et al.
    Bunn, Stuart E.
    Chandra, Sudeep
    Galloway, Aaron W. E.
    Guo, Fen
    Kainz, Martin J.
    Kankaala, Paula
    Lau, Danny C. P.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Moulton, Timothy P.
    Power, Mary E.
    Rasmussen, Joseph B.
    Taipale, Sami J.
    Thorp, James H.
    Wehr, John D.
    How important are terrestrial organic carbon inputs for secondary production in freshwater ecosystems?2017In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 62, no 5, p. 833-853Article, review/survey (Refereed)
    Abstract [en]

    1. Many freshwater systems receive substantial inputs of terrestrial organic matter. Terrestrially derived dissolved organic carbon (t-DOC) inputs can modify light availability, the spatial distribution of primary production, heat, and oxygen in aquatic systems, as well as inorganic nutrient bioavailability. It is also well-established that some terrestrial inputs (such as invertebrates and fruits) provide high-quality food resources for consumers in some systems. 2. In small to moderate-sized streams, leaf litter inputs average approximately three times greater than the autochthonous production. Conversely, in oligo/mesotrophic lakes algal production is typically five times greater than the available flux of allochthonous basal resources. 3. Terrestrial particulate organic carbon (t-POC) inputs to lakes and rivers are comprised of 80%-90% biochemically recalcitrant lignocellulose, which is highly resistant to enzymatic breakdown by animal consumers. Further, t-POC and heterotrophic bacteria lack essential biochemical compounds that are critical for rapid growth and reproduction in aquatic invertebrates and fishes. Several studies have directly shown that these resources have very low food quality for herbivorous zooplankton and benthic invertebrates 4. Much of the nitrogen assimilated by stream consumers is probably of algal origin, even in systems where there appears to be a significant terrestrial carbon contribution. Amino acid stable isotope analyses for large river food webs indicate that most upper trophic level essential amino acids are derived from algae. Similarly, profiles of essential fatty acids in consumers show a strong dependence on the algal food resources. 5. Primary production to respiration ratios are not a meaningful index to assess consumer allochthony because respiration represents an oxidised carbon flux that cannot be utilised by animal consumers. Rather, the relative importance of allochthonous subsidies for upper trophic level production should be addressed by considering the rates at which terrestrial and autochthonous resources are consumed and the growth efficiency supported by this food. 6. Ultimately, the biochemical composition of a particular basal resource, and not just its quantity or origin, determines how readily this material is incorporated into upper trophic level consumers. Because of its highly favourable biochemical composition and greater availability, we conclude that microalgal production supports most animal production in freshwater ecosystems.

  • 6.
    Brodin, Tomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Johansson, Frank
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergsten, Johannes
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Predator related oviposition site selection of aquatic beetles (Hydroporus spp.) and effects on offspring life-history2006In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 51, no 7, p. 1277-1285Article in journal (Refereed)
    Abstract [en]

    1. Theory predicts that natural selection should favour females that are able to correctly assess the risk of predation and then use that information to avoid high-risk oviposition sites to reduce the risk of offspring predation. Despite the potential significance of such behaviour on individual fitness, population dynamics and community structure, relatively few studies of oviposition behaviour connected to the risk of predation have been carried out.

    2. However, some recent studies suggest that oviposition site selection in response to risk of predation may be a common phenomenon, at least among amphibians and mosquitoes. A vast majority of previous studies have, however, neglected to investigate how the offspring are affected, in terms of fitness related parameters, by the maternal oviposition site choice.

    3. In an outdoor artificial pond experiment we tested the oviposition site selection of female aquatic beetles (Hydroporus spp.) in relation to the presence or absence of a predatory fish (Perca fluviatilis). In addition, we monitored how the oviposition site selection affected the behaviour, growth and food resource of the progeny.

    4. We show that free-flying females of the aquatic beetles Hydroporus incognitus and H. nigrita prefer to oviposit in waters without fish compared with waters with fish. Larval activity of Hydroporus spp. was unaffected by fish presence. Our results indicate that beetle larvae from females that do lay eggs in waters with fish show increased growth compared with larvae in waters without fish. We explain this difference in growth by a higher per-capita food supply in the presence of a fish predator. This finding may have important implications for our understanding of how the variance of oviposition site selection in a population is sustained.

  • 7. Burrows, Ryan M.
    et al.
    Hotchkiss, Erin R.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    McKie, Brendan G.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nitrogen limitation of heterotrophic biofilms in boreal streams2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 7, p. 1237-1251Article in journal (Refereed)
    Abstract [en]

    Nutrient limitation of the biofilm is fundamental to stream ecosystem processes, as microbial activity shapes the biological availability and biogeochemical cycling of carbon and nutrients. We used nutrient-diffusing substrata (NDS) to investigate heterotrophic nutrient limitation of microbial respiration (MR) across 20 streams draining boreal landscapes in northern Sweden. We also explored variation in microbial biomass and community structure of biofilms that developed on NDS using phospholipid fatty acid (PLFA) biomarkers. Limitation was determined as a significant response of MR and biomass production on cellulose surfaces to enrichment with nitrogen (N), phosphorus (P) or N+P, relative to controls. Microbial respiration was N-limited, with an average 3.3-fold increase on N-amended NDS. Nitrogen limitation decreased, and control rates of MR increased, with greater background concentrations of inorganic N across the sites. In contrast to MR, microbial biomass was primarily N-limited but was greatest for the N+P NDS. Accordingly, differences in respiratory versus biomass responses to nutrient addition resulted in significantly greater biomass-specific MR on N-amended NDS compared to all other treatments. In addition, PLFA biomarkers indicated distinct microbial communities on N and N+P NDS compared to controls and/or P NDS. Greater MR and biomass, and the development of distinct microbial communities, when supplied with inorganic N suggest that factors which alter aquatic N loading during autumn may have important implications for ecosystem processes and the biogeochemistry of boreal streams and rivers. Our findings add to a growing body of evidence that the productivity of Fennoscandian boreal landscapes is constrained by N availability.

  • 8.
    Byström, Pär
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Huss, Magnus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ontogenetic constraints and diet shifts in Perch (Perca fluviatilis): mechanisms and consequences for intra-cohort cannibalism2012In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, no 4, p. 847-857Article in journal (Refereed)
    Abstract [en]

    1. In many populations, sufficient size variation to allow for cannibalism may develop not only among age cohorts but also within them. Here, we used data on resource dynamics, consumer body size distribution and gape size limitation to unravel mechanisms promoting cannibalism within cohorts of young-of-the-year (YOY) perch (Perca fluviatilis). 2. Perch are strongly gape limited when feeding on large zooplankton during early ontogeny. As a consequence, only initially large fish were able to shift to feeding on abundant large invertebrates, necessary to sustain fast growth. 3. We suggest that a combination of high initial size variation and exclusive access to resources for individuals with an initial size advantage is a prerequisite for the development of a size distribution sufficient for intra-cohort cannibalism to occur. 4. During the time when cannibalism was observed, growth of the largest individuals in YOY perch cohorts was faster than that of smaller individuals. However, the energy gain from cannibalism did not increase growth rate enough to reach a size necessary to feed on more abundant size classes of victims, and therefore, the effect of cannibalism on overall cohort density was minor. 5. In addition to a high energy gain from cannibalism allowing for fast growth, strong resource limitation and slow growth rates of small individuals (i.e. potential victims) are a prerequisite not only for the development of intra-cohort cannibalism but also for its persistence.

  • 9.
    Byström, Pär
    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.
    Nilsson, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Van Kooten, Tobias
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Frans
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Substitution of top predators: effects of pike invasion in a subarctic lake2007In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 52, no 7, p. 1271–1280-Article in journal (Refereed)
    Abstract [en]

    1. Invasions of top predators may have strong cascading effects in ecosystems affecting both prey species abundance and lower trophic levels. A recently discussed factor that may enhance species invasion is climate change and in this context, we studied the effects of an invasion of northern pike into a subarctic lake ecosystem formerly inhabited by the native top predator Arctic char and its prey fish, ninespined stickleback.

    2. Our study demonstrated a strong change in fish community composition from a system with Arctic char as top predator and high densities of sticklebacks to a system with northern pike as top predator and very low densities of sticklebacks. A combination of both predation and competition from pike is the likely cause of the extinction of char.

    3. The change in top predator species also cascaded down to primary consumers as both zooplankton and predator-sensitive macroinvertebrates increased in abundance.

    4. Although the pike invasion coincided with increasing summer temperatures in the study area we have no conclusive evidence that the temperature increase is the causal mechanism behind the pike invasion. But still, our study provides possible effects of future pike invasions in mountain lakes related to climate change. We suggest that future pike invasions will have strong effects in lake ecosystems, both by replacing native top consumers and through cascading effects on lower trophic levels.

  • 10. Dessborn, Lisa
    et al.
    Elmberg, Johan
    Englund, Göran
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Pike predation affects breeding success and habitat selection of ducks2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 56, no 3, p. 579-589Article in journal (Refereed)
    Abstract [en]

    1. Fish and ducks often belong to the same local food web, and several studies indicate that there is a general negative effect of fish on breeding ducks. This pattern has so far been addressed mainly within the framework of competition for common invertebrate prey, while predation by large fish as a force behind settlement and abundance patterns in ducks remains largely unknown. This is the first study to address the effect of fish predation on breeding ducks, isolated from that of competition, and the first experiment to explore the ability of ducks to identify and avoid lakes with high risk of fish predation.

    2. We used a before–after control–impact design and 11 naturally fishless lakes. Waterfowl on the lakes were surveyed during the breeding season of 2005. Large adult pike (Esox lucius) were added to two lakes in early spring 2008, and waterfowl surveys were repeated on all 11 lakes.

    3. Pike introduction did not affect the number of pairs on lakes during the nesting season in any of three focal duck species (mallard Anas platyrhynchos, teal Anas crecca, and goldeneye Bucephala clangula). During the brood-rearing season, however, there was a decrease in duck days in teal and goldeneye in lakes with pike, with similar trends observed in mallard. The number of goldeneye ducklings was also significantly lower in lakes with pike. We were unable to determine whether the response was attributable to direct pike predation or to broods leaving experimental lakes, but in either case, our study demonstrates high fitness costs for ducks breeding on lakes with pike.

    4. The apparent inability of nesting ducks to detect pike and the clear fitness implications may influence the annual recruitment of ducks on a larger scale as pike are both common and widespread. Vegetation complexity and food abundance are likely to be of overriding importance when breeding ducks are choosing a nesting site. As pike have a strong influence on breeding birds, relying on vegetation and cues of food abundance, while ignoring indicators of predation risk from fish, could lead to lakes with pike acting as an ecological trap.

  • 11.
    Diehl, Sebastian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Integrated Science Lab (IceLab), Umeå University, Sweden.
    Thomsson, Gustaf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kahlert, Maria
    Guo, Junwen
    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.
    Liess, Antonia
    Inverse relationship of epilithic algae and pelagic phosphorus in unproductive lakes: Roles of N-2 fixers and light2018In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 63, no 7, p. 662-675Article in journal (Refereed)
    Abstract [en]

    Phosphorus (P) often limits the biomass of primary producers in freshwater lakes. However, in unproductive northern lakes, where anthropogenic nitrogen (N) deposition is low, N instead of P can limit primary producers. In addition, light can be limiting to primary producers at high concentrations of coloured dissolved organic matter (cDOM), as cDOM is the major determinant of light penetration in these lakes.

    To address resource limitation of epilithic algal biomass, we repeatedly sampled epilithon (periphyton on stony substrata) in 20 lakes covering a large, correlated cDOM and N‐deposition gradient across boreal and subarctic Sweden. Across these lakes, pelagic total N (TN) and total P (TP) were positively correlated, and benthic light supply was negatively correlated, with cDOM. Microscopically determined algal biovolume and epilithic carbon (C), N and P were subsequently regressed against benthic light supply and pelagic TN and TP.

    Patterns in epilithic biovolume were driven by N2‐fixing cyanobacteria, which accounted for 2%–90% of total epilithic biovolume. Averaged over the growing season, epilithic algal biovolume, C and N were negatively related to TP and positively to TN, and were highest in the clearest, most phosphorus‐poor lakes, where epilithon was heavily dominated by potentially N2‐fixing cyanobacteria.

    A structural equation model supports the hypothesis that cDOM had two counteracting effects on total epilithic algal biovolume: a positive one by providing N to algae that depend on dissolved N for growth, and a negative one by shading N2‐fixing cyanobacteria, with the negative effect being somewhat stronger.

    Together, these findings suggest that (1) light and N are the main resources limiting epilithic algal biomass in boreal to subarctic Swedish lakes, (2) epilithic cyanobacteria are more competitive in high‐light and low‐nitrogen environments, where their N2‐fixing ability allows them to reach high biomass, and (3) epilithic N increases with N2 fixer biomass and is—seemingly paradoxically—highest in the most oligotrophic lakes.

  • 12. Drakare, Stina
    et al.
    Blomqvist, Peter
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Primary production and phytoplankton composition in relation to DOC input and bacterioplankton production in humic Lake Örträsket2002In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 47, no 1, p. 41-52Article in journal (Refereed)
    Abstract [en]

    1. The biomass and production of picophytoplankton, large phytoplankton and heterotrophic bacterioplankton were measured in humic Lake Örträsket, northern Sweden during four consecutive summers. 2. High flow episodes, carrying fresh dissolved organic carbon (DOC) into the lake, always stimulated heterotrophic bacterial production at the expense of primary production. Primary production never exceeded bacterial production for approximately 20 days after such an episode had replenished epilimnial DOC. We suggest that allochthonous DOC is an energy source that stimulates bacterioplankton that, because of their efficient uptake of inorganic nutrients, are then able to outcompete phytoplankton. After the exhaustion of readily available DOC, phytoplankton were able to dominate epilimnion production in Lake Örträsket. 3. Biomass production was higher when dominated by phytoplankton than by bacterioplankton, despite a similar utilization of nutrients in the epilimnion throughout the summer. We propose that different C : N : P ratios of bacterioplankton and phytoplankton permit the latter to produce more carbon (C) biomass per unit of available inorganic nutrients than bacterioplankton.

  • 13. Drakare, Stina
    et al.
    Blomqvist, Peter
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Relationships between picophytoplankton and environmental variables in lakes along a gradient of water colour and nutrient content2003In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 48, no 4, p. 729-740Article in journal (Refereed)
    Abstract [en]

    1. Biomass and production of picophytoplankton, phytoplankton and heterotrophic bacterioplankton were measured in seven lakes, exhibiting a broad range in water colour because of humic substances. The aim of the study was to identify environmental variables explaining the absolute and relative importance of picophytoplankton. In addition, two dystrophic lakes were fertilised with inorganic phosphorus and nitrogen, to test eventual nutrient limitation of picophytoplankton in these systems. 2. Picophytoplankton biomass and production were highest in lakes with low concentrations of dissolved organic carbon (DOC), and DOC proved the factor explaining most variation in picophytoplankton biomass and production. The relationship between picophytoplankton and lake trophy was negative, most likely because much P was bound in humic complexes. Picophytoplankton biomass decreased after the additions of P and N. 3. Compared with heterotrophic bacterioplankton, picophytoplankton were most successful at the clearwater end of the lake water colour gradient. Phytoplankton dominated over heterotrophic bacteria in the clearwater systems possibly because heterotrophic bacteria in such lakes are dependent on organic carbon produced by phytoplankton. 4. Compared with other phytoplankton, picophytoplankton did best at intermediate DOC concentrations; flagellates dominated in the humic lakes and large autotrophic phytoplankton in the clearwater lakes. 5. Picophytoplankton were not better competitors than large phytoplankton in situations when heterotrophic bacteria had access to a non-algal carbon source. Neither did their small size lead to picophytoplankton dominance over large phytoplankton in the clearwater lakes. Possible reasons include the ability of larger phytoplankton to float or swim to reduce sedimentation losses and to acquire nutrients by phagotrophy.

  • 14. Drakare, Stina
    et al.
    Liess, Antonia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Local factors control the community composition ofcyanobacteria in lakes while heterotrophic bacteriafollow a neutral model2010In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 55, no 12, p. 2447-2457Article in journal (Refereed)
    Abstract [en]

    1. Neutral community models are derived from the proposition that basic probabilities ofspecies loss (extinction, emigration) and gain (immigration, speciation) explain biologicalcommunity structure, such that species with many individuals are very likely to bewidespread. Niche models on the other hand assume that interactions between species anddifferential resource use mediate species coexistence, thus invoking environmental factorsto explain community patterns.2. In this study, we compared neutral and niche models to test how much of the spatialvariability of assemblages of heterotrophic bacteria and phytoplankton in 13 lakes theycould explain. Analysis of phytoplankton was restricted to cyanobacteria, so that theycould be studied with the same molecular fingerprinting method, automated ribosomalintergenic spaces analysis (ARISA), as heterotrophic bacteria. We determined local bioticand abiotic lake variables as well as lake age, glacial history and distance between sites.3. The neutral community model had a good fit to the community composition ofheterotrophic bacteria (R2 = 0.69), whereas it could not produce a significant model for thecommunity composition of cyanobacteria.4. The community composition of cyanobacteria was instead correlated to environmentalvariables. The best model, a combination of total organic carbon, biomass of eukaryoticphytoplankton, pH and conductivity, could explain 8% of the variation. In contrast,variation in the community composition of heterotrophic bacteria was not predicted byany of the environmental variables. Historical and spatial variables were not correlated tothe community composition of either group.5. The pattern found for heterotrophic bacteria suggests that stochastic processes areimportant. The correlation of cyanobacteria with local environmental variables alone isconsistent with the niche model. We suggest that cyanobacteria, a group of organismscontaining bloom-forming species, may be less likely to fit a neutral community model,since these blooms are usually triggered by a particular combination of environmentalconditions.Keywords: automated

  • 15.
    Engström, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Weber, Christine
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of river ice on riparian vegetation2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 56, no 6, p. 1095-1105Article in journal (Refereed)
    Abstract [en]

    1.  Many rivers and streams experience pronounced ice dynamics caused by the formation of anchor and frazil ice, leading to flooding and disturbance of riparian and aquatic communities.  The effects of dynamic ice conditions on riverine biota are little known.

    2.  We studied the formation of anchor ice in natural streams over 2 years, and assessed the effects of anchor ice on riparian vegetation by comparing sites with frequent or abundant and little or no anchor ice formation. We also studied the direct impact of ice on riparian plants by experimentally creating ice in the riparian zone over three winters, and by exposing plants of different life-forms to ‑18oC cold ice in the laboratory.

    3.  Riparian species richness per 1-m2 plot was higher at sites affected by anchor ice than at sites where anchor ice was absent or rare. Dominance was lower at anchor ice sites, suggesting that ice disturbance enhanced species richness. Species composition was more homogenous among plots at anchor ice sites. Experimentally creating riparian ice corroborated the comparative results, with species richness increasing in ice-treated plots compared to controls, irrespective of whether the sites showed natural anchor ice.

    4.  Because of human alterations of running waters, the natural effects of river ice on stream hydrology, geomorphology and ecology are little known.  Global warming in northern streams will lead to more dynamic ice conditions, offering new challenges for aquatic organisms and river management.  We expect that the results discussed here can stimulate new research, contributing to a better understanding of ecosystem function during winter.

  • 16.
    Faithfull Mathisen, Carolyn
    et al.
    Otago University, Dunedin, New Zealand.
    Burns, Carolyn
    Otago University, Dunedin, New Zealand.
    Effects of salinity and source of inocula on germination of Anabaena akinetes from a tidally influenced lake2006In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 51, no 4, p. 705-716Article in journal (Refereed)
    Abstract [en]

    1. Sedimentary akinetes (resting stages) may represent significant potential inocula for nuisance blooms of cyanobacteria. We studied the effects of salinity and sediment source on the germination and subsequent growth of Anabaena flos-aquae akinetes from a shallow, tidally influenced lake.

    2. Surface sediments collected from littoral and open-water sites were used as inocula to culture A. flos-aquae akinetes in four salinities (0.1, 2.2, 4.4 and 6.5) over 22 days. Akinete germination and development was followed by counting developmental stages every second day.

    3. Filament growth, but not akinete germination, was inhibited by salinity and there were significantly fewer filaments at 6.5 than at 0.1 and 2.2. Cultures inoculated with littoral sediment had more akinetes, germlings and filaments than those inoculated with open-water sediment.

    4. Sediment is a potential source of inocula for Anabaena blooms in the lake, which potentially could develop solely from this source because germination and subsequent filament growth do not depend on the existence of an initial pelagic Anabaena population.

  • 17.
    Gardeström, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Aquatic Sciences & Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ermold, Matti
    Goedkoop, Willem
    McKie, Brendan G.
    Disturbance history influences stressor impacts: effects of a fungicide and nutrients on microbial diversity and litter decomposition2016In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 61, no 12, p. 2171-2184Article in journal (Refereed)
    Abstract [en]

    Streams draining agricultural catchments are severely degraded by multiple stressors, including nutrient enrichment and pesticides. The understanding of how such stressors interact to alter ecosystem structure and function, and how responses of biota reflect their longer-term disturbance history, remains limited. We conducted a multifactorial stream microcosm experiment to investigate how elevated nutrients and a fungicide (azoxystrobin) interact to affect multiple variables associated with leaf decomposition: the biomass, sporulation rate and diversity of aquatic hyphomycete decomposers, litter decomposition rates and detritivore growth. We further manipulated decomposer species composition by using three distinct fungal assemblages drawn from streams with contrasting histories of agricultural disturbance: a forest stream, a mixed land-use stream subject to nutrient enrichment but little pesticide use, and an agricultural stream subjected to both intensive nutrient and pesticide use. We also varied the presence of the detritivorous isopod Asellus aquaticus. The fungicide azoxystrobin reduced both biomass and diversity of aquatic hyphomycetes and growth of A.aquaticus, and had negative knock-on effects on leaf decomposition and fungal sporulation. These impacts further varied with nutrient concentration. Impacts of the fungicide differed markedly among the three fungal assemblages. The agricultural assemblages were dominated by tolerant species and showed some capacity for maintaining processes under pesticide exposure, whereas diversity and functioning were strongly suppressed in the forest stream assemblage, which was dominated by stress-intolerant species. Pesticides, in interaction with other agricultural stressors, can impact microbial diversity and key ecosystem processes underlying the delivery of ecosystem services from streams. The extent of such impacts vary according to the longer-term disturbance history of the biota, and might be most acute when agricultural activity expands into previously uncultivated catchments, as is currently occurring in many regions of the world.

  • 18.
    Huss, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Borcherding, Jost
    Heermann, Lisa
    Timing of the diet shift from zooplankton to macroinvertebrates and size at maturity determine whether normally piscivorous fish can persist in otherwise fishless lakes2013In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 58, no 7, p. 1416-1424Article in journal (Refereed)
    Abstract [en]

    Using a size-structured population model, life-history information and records of piscivores in systems without prey fish, we analysed the role of the timing of shifting from small-to-large invertebrate prey types in regulating piscivore performance, especially under conditions of low availability of prey fish. Large invertebrate prey are generally absent or at low densities in pelagic habitats; consequently, pelagic piscivorous fish species with a poor ability to exploit zooplankton depend on prey fish in order to persist. In contrast, our model shows that abundant large invertebrate prey in the littoral habitat may allow littoral piscivores to persist in the absence of prey fish if they can shift diet from zooplankton to macroinvertebrates early in life. However, if the diet shift from zooplankton to macroinvertebrates is delayed, or density dependence reduces growth rate, the persistence of even littoral piscivorous fish species in the absence of other prey fish is severely constrained. Our results suggest that undergoing an early diet shift from zooplankton to macroinvertebrates may be necessary to reach sizes large enough to enable successful exploitation of the piscivorous niche. These insights can help to understand the persistence of piscivorous fish species, or their absence, in otherwise fishless lakes.

  • 19.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Drakare, Stina
    Blomqvist, Peter
    Nutrient limitation of bacterioplankton and phytoplankton in humic lakes in northern Sweden2001In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 46, no 5, p. 653-666Article in journal (Refereed)
    Abstract [en]

    1. Two small humic lakes in northern Sweden with concentrations of dissolved organic carbon (DOC) between 15 and 20 mg L-1 were fertilized with inorganic phosphorus (P) and inorganic nitrogen (N), respectively. A third lake was unfertilized and served as a control. In addition to this lake fertilization experiment, data from different regional surveys were used to assess the role of different limiting factors. 2. The P fertilization had no effects on bacterioplankton or phytoplankton, while phytoplankton were significantly stimulated by N fertilization. Inorganic nutrient limitation of bacterioplankton was a function of DOC concentration in water of the investigated region and nutrient-limited bacteria were found only in lakes with DOC concentrations less than around 15 mg L-1 3. The fertilization experiments demonstrated that the DOC-rich experimental lakes contained a bioavailable pool of P that was not utilized to its full potential under natural conditions. The overall mobilization of energy (bacterioplankton plus phytoplankton) in the experimental lakes was restricted by lack of inorganic N.

  • 20.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Biomass and structure of planktonic communities along an air temperature gradient in subarctic Sweden2010In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 55, no 3, p. 691-700Article in journal (Refereed)
    Abstract [en]

    1. Air temperature will probably have pronounced effects on the composition of plankton communities in northern lake ecosystems, either via indirect effects on the export of essential elements from catchments or through direct effects of water temperature and the ice-free period on the behaviour of planktonic organisms.

    2. We assessed the role of temperature by comparing planktonic communities in 15 lakes along a 6 °C air temperature gradient in subarctic Sweden.

    3. We found that the biomass of phytoplankton, bacterioplankton and the total planktonic biomass were positively related to air temperature, probably as a result of climatic controls on the export of nitrogen from the catchment (which affects phytoplankton biomass) and dissolved organic carbon (affecting bacterioplankton biomass).

    4. The structure of the zooplankton community, and top down effects on phytoplankton, were apparently not related to temperature but mainly to trophic interactions ultimately dependent on the presence of fish in the lakes.

    5. Our results suggest that air temperature regimes and long-term warming can have strong effects on the planktonic biomass in high latitude lakes. Effects of temperature on the structure of the planktonic community might be less evident unless warming permits the invasion of fish into previous fishless lakes.

  • 21.
    Jansson, Roland
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Malmqvist, Björn
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Restoring freshwater ecosystems in riverine landscapes: the roles of connectivity and recovery processes2007In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 52, no 4, p. 589-596Article in journal (Refereed)
    Abstract [en]

    1. This paper introduces key messages from a number of papers emanating from the Second International Symposium on Riverine Landscapes held in August 2004 in Sweden, focusing on river restoration. Together these papers provide an overview of the science of river restoration, and point out future research needs.

    2. Restoration tests the feasibility of recreating complex ecosystems from more simple and degraded states, thereby presenting a major challenge to ecological science. Therefore, close cooperation between practitioners and scientists would be beneficial, but most river restoration projects are currently performed with little or no scientific involvement.

    3. Key messages emanating from this series of papers are: The scope, i.e. the maximum and minimum spatial extent and temporal duration of habitat use, of species targeted for restoration should be acknowledged, so that all relevant stages in their life cycles are considered. Species that have been lost from a stream cannot be assumed to recolonise spontaneously, calling for strategies to ensure the return of target species to be integrated into projects. Possible effects of invasive exotic species also need to be incorporated into project plans, either to minimise the impact of exotics, or to modify the expected outcome of restoration in cases where extirpation of exotics is impractical.

    4. Restoration of important ecological processes often implies improving connectivity of the stream. For example, longitudinal and lateral connectivity can be enhanced by restoring fluvial dynamics on flood-suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal, thereby increasing habitat and species diversity. Restoring links between surface and ground water flow enhances vertical connectivity and communities associated with the hyporheic zone.

    5. Future restoration schemes should consider where in the catchment to locate projects to make restoration most effective, consider the cumulative effects of many small projects, and evaluate the potential to restore ecosystem processes under highly constrained conditions such as in urban areas. Moreover, restoration projects should be properly monitored to assess whether restoration has been successful, thus enabling adaptive management and learning for the future from both successful and unsuccessful restorations.

  • 22.
    Jonsson, Micael
    et al.
    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.
    Stenroth, Karolina
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hotchkiss, Erin R
    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.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Climate change modifies the size structure of assemblages of emerging aquatic insects2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 1, p. 78-88Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to not only raise water temperatures, but also to cause brownification of aquatic ecosystems via increased inputs of terrestrial dissolved organic matter. While efforts have been made to understand how increased temperature and brownification separately influence aquatic food webs, their interactive effects have been less investigated. Further, although climate change effects on aquatic ecosystems likely will propagate to terrestrial consumers via changes in aquatic insect emergence, this has rarely been studied. We investigated the effect of climate change on aquatic insect emergence, in a large-scale outdoor pond facility where 16 sections - each containing natural food webs including a fish top-consumer population - were subjected to warming (3 degrees C above ambient temperatures) and/or brownification (by adding naturally humic stream water). Aquatic insect emergence was measured biweekly over 18weeks. We found no effect of warming or brownification on total emergent insect dry mass. However, warming significantly reduced the number of emergent Chironomidae, while numbers of larger taxa, Trichoptera and Ephemeroptera, remained unchanged. On average, 57% and 58% fewer Chironomidae emerged from the warmed clear and humic pond sections, respectively. This substantial decrease in emergent Chironomidae resulted in a changed community structure and on average larger individuals emerging from warm sections as well as from humic sections under ambient conditions. There was also a weak influence of fish biomass on the size structure of emergent aquatic insects, with a positive relationship between individual insect size and total fish biomass, but effects of fish were clearly subordinate to those of warming. Climate change impacts on aquatic systems can have widespread consequences also for terrestrial systems, as aquatic insects are ubiquitous and their emergence represents an important resource flow from aquatic to terrestrial environments. While we found that neither warming nor brownification quantitatively changed total aquatic insect emergence biomass, the warming-induced decrease in number of emergent Chironomidae and the subsequent increase in average body size will likely impact terrestrial consumers relying on emergent aquatic insect as prey.

  • 23.
    Jäger, Christoph G.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Aquatic Ecosystems Analysis and Management, Helmholtz Centre for Environmental Research – UFZ, Magdeburg, Germany.
    Vrede, Tobias
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Persson, Lennart
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Interactions between metazoans, autotrophs, mixotrophs and bacterioplankton in nutrient-depleted high DOC environments: a long-term experiment2014In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 59, no 8, p. 1596-1607Article in journal (Refereed)
    Abstract [en]

    1. Humic lakes with a high external supply of DOC and low input of nutrients can often support a high biomass of metazoan zooplankton. In such lakes, autotrophic algae compete with bacteria for inorganic nutrients, but bacteria support mixotrophic growth. Consequently, planktonic communities are often dominated by mixotrophic flagellates, while obligate autotrophic phytoplankton occurs in low numbers for extended periods.

    2. To test the importance of autotrophic phytoplankton and mixotrophic flagellates as food resources for metazoan grazers and, in turn, the feedback effects of grazers on basal food-web interactions, we conducted a long-term experiment where we simulated abiotic resource relationships of humic lakes (high DOC [glucose] and low P input). We examined the population dynamics of Daphnia galeata when inoculated in systems with autotrophic algae only, mixotrophic algae only and a mixture of autotrophic and mixotrophic algae, and how the systems changed after the inoculation of Daphnia. All combinations were run at high-and low-light conditions to analyse the effects of light on food quantity and quality.

    3. Daphnia grew to high densities only when mixotrophs were present at high-light conditions and showed no or only weak growth at low-light conditions or with autotrophs as the only food source.

    4. Autotrophic algae and bacteria showed a strong competition for nutrients. Autotrophic algae were released from competition for nutrients after Daphnia grazed on bacteria, which led to a probable change of the bacteria community to less edible but less competitive taxa. As a consequence, there was a mutualistic interaction between autotrophs and mixotrophs before Daphnia were introduced which turned into competition after Daphnia inoculation.

    5. We suggest that mixotrophic flagellates can be a critical resource for cladocerans and thereby also have a cascading effect on higher trophic levels, and cladocerans, in turn, have important indirect effects on basal planktonic food webs; hence, both might affect whole lake ecosystems.

  • 24. Lange, Katharina
    et al.
    Liess, Antonia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Piggott, Jeremy J.
    Townsend, Colin R.
    Matthaei, Christoph D.
    Light, nutrients and grazing interact to determine stream diatom community composition and functional group structure2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 56, no 2, p. 264-278Article in journal (Refereed)
    Abstract [en]

    P>1. Benthic algal communities are shaped by the availability of nutrients and light and by herbivore consumption. Many studies have examined how one of these factors affects algal communities, but studies simultaneously addressing all three are rare. 2. We investigated the effects of nutrients, light and a herbivore (the snail Potamopyrgus antipodarum) on benthic stream algae in a fully factorial experiment in 128 circular streamside channels. Four nutrient levels (none added to highly enriched), four snail grazing pressures (no snails to 777 individuals m-2) and two light levels (ambient and 65% reduced) were applied. Colonising algae were dominated by diatoms (Bacillariophyta), which were determined to species using acid-cleaned samples and assigned to functional groups according to their physiognomic growth form. 3. Diatom community structure changed considerably in response to our manipulations. Light had the strongest influence (as indicated by manova effect size), whereas nutrients had an intermediate effect and grazing was fairly weak. Relative abundances of six common diatom taxa decreased under reduced light, whereas five others became more prevalent. Eight taxa benefitted from nutrient enrichment, while three became rarer. Grazing affected the relative density of only one common taxon, which increased at higher grazing pressure. 4. Diatom functional groups also responded strongly. 'Low profile' taxa dominated at low resource levels (nutrients and especially light), whereas 'high profile' and 'motile' taxa became markedly more prevalent at higher resource levels. 5. Two-way interactions between experimental factors were quite common. For example, Planothidium lanceolatum and Rossithidium petersenii responded more strongly to nutrient enrichment at reduced than at ambient light, whereas Cocconeis placentula responded more strongly at ambient light. For diatom functional groups, the benefit of nutrient enrichment for 'motile' diatoms was greater at ambient than at reduced light. 6. Our results imply that multifactor experiments are required to determine the main forces driving the composition of benthic algal communities. Further, our findings highlight the considerable potential of using functional algal groups as indicators of changing environmental conditions to complement the traditional taxonomic approach.

  • 25.
    Lau, Danny C. P.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Vrede, Tobias
    Goedkoop, Willem
    Lake responses to long-term disturbances and management practices2017In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 62, no 4, p. 792-806Article in journal (Refereed)
    Abstract [en]

    1. Long-term human-induced disturbances such as acidification and algal invasions, and management practices such as liming, are known to alter community structure and biodiversity of north temperate lakes. We assessed if they impacted on the trophic ecology and production of apex consumers (i.e. fish) and the overall food-chain length (FCL) of boreal lake ecosystems, and if these functional responses were consistent with the biodiversity changes. We hypothesise that fish production and FCL decrease with decreasing species biodiversity of lake communities, and that long-term environmental perturbations will alter the relative reliance of fish on littoral versus pelagic trophic pathways and their ontogenetic changes in trophic position (TP). 2. We analysed long-term data and stable isotopes of multiple organismal groups - phytoplankton, zooplankton, littoral and sub-littoral/profundal macroinvertebrates, and fish - collected from small boreal lakes that have been subjected to acidification, lime application and/or algal invasion by Gonyostomum semen. Species biodiversity, FCL and fish production (i.e. growth and catch-per-uniteffort) were compared among three lake categories, i.e. acidic, limed and circumneutral (reference) lakes, within each three lakes were selected. Fish TP and their relative littoral versus pelagic reliance were estimated based on stable nitrogen and carbon isotopes respectively. 3. Gonyostomum contributed to 77-98% phytoplankton biovolume in acidic lakes, <1-79% in limed lakes and 0-30% in circumneutral lakes. Its prevalence was correlated with total organic carbon concentration but not with lake pH, alkalinity or any other environmental variable. Diversity and evenness of phytoplankton, macroinvertebrates and fish generally decreased with increasing Gonyostomum biovolume, such that biodiversity was higher in circumneutral and limed lakes than in acidic lakes. 4. Isotopic data revealed that FCL was shortest in limed lakes (3.94 +/- 0.08; least- squares mean +/- SE), intermediate in acidic lakes (4.19 +/- 0.07) and longest in circumneutral lakes (4.38 +/- 0.08). Limed lakes also had the lowest fish growth and CPUE. Overall littoral reliance of fish was higher in acidic lakes (0.53 +/- 0.03) than in limed lakes (0.42 +/- 0.02) and circumneutral lakes (0.30 +/- 0.02), suggesting that fish production and FCL there could have been sustained by the increased littoral reliance when pelagic trophic pathways were hindered by Gonyostomum invasion. European perch (Perca fluviatilis), the most common fish in the lakes, showed faster TP increases in acidic and limed lakes, likely due to their earlier ontogenetic shift from zooplanktivory to zoobenthivory and/or piscivory. 5. Overall, our findings indicate that long-term disturbances (i.e. acidification and algal invasions) and management practices (i.e. liming) can (i) induce contrasting responses in biodiversity, FCL and fish production of boreal lakes; (ii) be the primary driver of FCL variation among small and similar-size ecosystems; and (iii) alter the trophic ecology (i.e. TP change during ontogeny and littoral reliance) of key fish species. The trophic ecology and production of apex consumers and FCL together can provide useful integrated proxies for ecosystem functioning, which can supplement traditional biodiversity measurements for more robust environmental assessments.

  • 26.
    Malm-Renöfält, Birgitta
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of hydropower generation and opportunities for environmental flow management in Swedish riverine ecosystems2010In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 55, no 1, p. 49-67Article in journal (Refereed)
    Abstract [en]

    Hydropower is often presented as a clean and renewable energy source that is environmentally preferable to fossil fuels or nuclear power. Hydropower production, however, fundamentally transforms rivers and their ecosystems by fragmenting channels and altering river flows. These changes reduce flow velocity and the number of rapids, and reduce or alter wetland, floodplain and delta ecosystems. Dams disrupt dispersal of riverine organisms and sediment dynamics and may alter riverine biodiversity composition and abundance. Freshwater ecosystems now belong among the world's most threatened ecosystems.

    Water managers are beginning to recognise the need to combine demands for social and economic development with the protection of the resource base on which socioeconomic benefits rely. Environmental flows can help to balance ecosystem and human needs for water, both when constructing new dams and in re-licensing existing dams.

    We briefly review the impacts of hydropower generation on freshwater ecosystems by discussing different types of dams and development, and by providing examples from Sweden of how environmental effects of hydropower production could be mitigated. Special emphasis is given to flow regulation through re-operation of dams.

    Regulated rivers in Sweden were developed with little consideration of ecological effects, with most dams lacking migration pathways or minimum flow releases. There is thus a substantial potential for improvement of ecological conditions, such as naturalisation of flow regimes and reestablishment of connectivity, in regulated river reaches but technical hurdles imply major challenges for rehabilitation and mitigation. Most regulated rivers consist of cascades of consecutive reservoirs and impoundments, further constraining possible actions to improve ecological conditions.

    Most environmental mitigation measures require flow modifications to serve ecosystems, implying reduced power production. An important challenge for river management is to identify situations where measures involving relatively small production losses can have major ecological advantages.

    Climate change during the 21st century is expected to increase runoff in northern and central Sweden and make the annual hydrograph more similar to variation in electricity demand, i.e. a lower spring flood and increased run-off during winter months. This could provide opportunities for operating dams and power stations to the benefit of riverine ecosystems. On the other hand, demands to produce hydropower are likely to increase as fossil fuels are phased out, leading to increased pressures on free-flowing rivers and aquatic ecosystems.

  • 27.
    Malm-Renöfält, Birgitta
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Landscape scale effects of disturbance on riparian vegetation2008In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 53, no 11, p. 2244-2255Article in journal (Refereed)
    Abstract [en]

    1. Differing responses in riparian species richness and composition to disturbance have been reported as a possible explanation for the differences along and between rivers. This paper explores the role of physical disturbance in shaping landscape-scale patterns of species distribution in riparian vegetation along a free-flowing river in northern Sweden.

    2. To test whether sensitivity to disturbance varies across large landscapes, we experimentally disturbed riparian vegetation along an entire, free-flowing river by scouring the soil and the vegetation turf, cutting vegetation, applying waterborne plant litter, and after a period of recovery we measured vegetation responses. The experiment was repeated for two consecutive years.

    3. We found no significant effect of disturbance on species composition, but all three forms of disturbance significantly reduced species richness. There was no downstream variation in community responses to disturbance but morphological groups of species responded differently to different kinds of disturbance. Graminoids were most resistant, suppressed only by litter burial. All forms of disturbance except cutting reduced the density of herbaceous species, and species density of trees + shrubs and dwarf shrubs was negatively affected by both scouring and cutting. We also evaluated the effects of disturbance in relation to varying levels of species richness. In nearly all cases, responses were significantly negatively correlated with control plot species richness, and relative responses indicated that species-rich plots were less resistant to scouring and cutting.

    4. Our results suggest that although all disturbance treatments had an effect on species richness, variation in sensitivity to disturbance is not the most important factor shaping landscape-scale patterns of riparian plant species richness along rivers.

  • 28.
    McKie, BG
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Malmqvist, B
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Assessing ecosystem functioning in streams affected by forest management: increased leaf decomposition occurs without changes to the composition of benthic assemblages2009In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 54, no 10, p. 2086-2100Article in journal (Refereed)
    Abstract [en]

    1. Landscape management practices that alter energetic linkages between aquatic and terrestrial habitats can affect associated ecosystem processes, and ultimately the provision of ecosystem services of importance to humanity. Such effects cannot always be inferred from current biomonitoring schemes, which are typically based on assessment of community structural parameters rather than functional attributes related to important ecosystem-level processes.

    2. We investigated effects of forest clearcutting, a major landscape-level disturbance known to alter the energetic basis of aquatic food webs, on headwater streams in northern Sweden. The key ecosystem process of leaf decomposition was measured as an index of ecosystem functioning. The biomass of detritivorous shredders was also quantified, along with various community structural parameters associated with the diversity, composition and functional guild organisation of benthic macroinvertebrate assemblages.

    3. No differences in macroinvertebrate abundance, diversity or assemblage composition were detected between forested and clearcut streams, and most functional guilds were similarly unaffected, though species density of scrapers was higher in forested than clearcut channels.

    4. In contrast, mass loss of two leaf species was elevated in all clearcut streams, with evidence for increases in the efficiency per degree-day of both the microbial and detritivore mediated fractions of decomposition.

    5.  Increased rates of leaf mass loss in the clearcut streams were associated with greater phosphate concentrations and shredder biomass, and with an increased relative abundance of broadleaves in standing stocks of benthic litter. Together, these findings indicate a more rapid transfer of energy and nutrients through the detrital pathways of our clearcut streams.

    6. These results demonstrate the utility of litter decomposition assays for monitoring effects of forest management on stream ecosystem functioning, and have implications for nutrient cycles in landscapes extensively influenced by forest management. The markedly different responses of our functional and structural measures to clearcutting highlight the value of incorporating methods for the functional assessment of ecosystems into biomonitoring schemes.

  • 29.
    Nilsson, Christer
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Polvi, Lina E
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lind, Lovisa
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Extreme events in streams and rivers in arctic and subarctic regions in an uncertain future2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 12, p. 2535-2546Article in journal (Refereed)
    Abstract [en]

    We review the predicted changes in extreme events following climate change in flowing waters in arctic and subarctic regions. These regions are characterised by tundra or taiga ecosystems in either erosional or depositional glacial landforms or presently glacierised areas of the Northern Hemisphere. The ecological and geomorphic effects of extreme meteorological and hydrological events, such as episodes of strongly increased precipitation, temperatures and flows, can be exacerbated by altered base conditions. For example, winter temperature variations between frost and thaw will become more frequent at many places because mean temperature during the winter is closer to 0 °C, potentially leading to changes in the production of ice and intensified disturbance of riparian and aquatic habitats during extreme floods. Additionally, thawing of permafrost and glaciers can lead to increased bank erosion because of thaw slump and glacial outburst floods. We discuss the abiotic and biotic effects of these and other extreme events, including heavy precipitation, floods, drought and extreme air or water temperatures, and summarise our findings in a model that aims to stimulate further research in this field.

  • 30.
    Norlin, Linnea
    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.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre (CIRC), Department of Ecology and Environmental Science, Umeå University, Abisko, Sweden.
    Johansson, Martin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Liess, Antonia
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Climate change will alter amphibian-mediated nutrient pathways: evidence from Rana temporaria tadpoles in experimental ponds2016In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 61, no 4, p. 472-485Article in journal (Refereed)
    Abstract [en]

    1. With global warming, mean temperatures and brownification of many waterbodies are predicted to increase. This may have unknown consequences on aquatic consumer life histories and nutrient content, consumer-mediated nutrient recycling, and nutrient transport between water and land.

    2. Using a large-scale experimental pond facility, we altered temperature (ambient/+ 4 degrees C) and brownification (clear/humic) in a 2 x 2 factorial design (n = 16 pond sections) to test two aspects of climate change on Rana temporaria tadpole life-history traits and on tadpole-mediated nutrient pathways. On day 16 after hatching, we examined tadpole-mediated nutrient recycling by measuring tadpole nutrient excretion and egestion rates and tadpole body nutrient content. We estimated tadpole growth and development rates from hatching to emergence and measured emergent frog body size and body nutrient content.

    3. Brownification increased total pond water nutrient availability and total pond water nitrogen (N) : phosphorous (P) ratios. Warming positively affected tadpole growth and development rates, whereas browning increased tadpole growth rate only under ambient temperatures. Emergent frog body P content decreased with warming, but only in the clear treatments. But despite these variations in body nutrient content, body stoichiometry remained within a relatively narrow stoichiometric range for both emergent frogs (P content: 1.4-1.8%, N content: 11.4-11.8% and carbon [C] content: 46.9-51.3%) and tadpoles (P content: 1.1-1.2%, N content: 10.1-11.7% and C content: 48.0-50.5%). Warming increased tadpole body P content and browning had a positive effect on tadpole body N content and tadpole N excretion rates, probably mediated by the increased pond water total N availability.

    4. We conclude that warming and brownification will interact in changing aquatic consumer growth and body nutrient stoichiometry. In addition, warming has the potential to affect emergent frog body nutrient content and may thus affect nutrient transport from water to land. Last, by increasing pond water N availability, brownification appears to intensify consumer P limitation and thus amplify consumer-meditated N recycling.

  • 31.
    Petrin, Zlatko
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Malmqvist, Björn
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Does freshwater macroinvertebrate diversity along a pH-gradient reflect adaptation to low pH?2007In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 52, no 11, p. 2172-2183Article in journal (Refereed)
    Abstract [en]

    1. The impacts of anthropogenic surface water acidification are much better known than those of natural acidity. Recent studies have indicated biodiversity is not degraded and species composition unaltered in naturally acidic compared to circumneutral watercourses.

    2. Here, we use a geographically extensive dataset comprising sites in more than 200 Swedish streams to test whether the lack of effects on macroinvertebrate species diversity is due to exaptation and adaptation to natural acidity.

    3. To this end, we modelled pH associated with spring flood episodes, which inflict the most challenging hydrochemical conditions to the biota. We compared taxonomic richness and species composition along the modelled pH gradient in northern Sweden, where acidity is largely natural, with southern Sweden, a region influenced by significant anthropogenic acidification.

    4. We found Plecoptera richness did not respond to varying pH either in northern or southern Sweden. Ephemeroptera richness was sensitive to pH in both regions, while that of Trichoptera increased with increasing pH in southern Sweden, but decreased in the north. The taxonomic composition of Plecoptera changed along the pH gradient in both regions, whereas that of Ephemeroptera and Trichoptera changed more strongly with pH in southern Sweden.

    5. Our results support the hypothesis that stream invertebrates are able to tolerate low pH through exaptation or adaptation, but that this capability varies among taxonomic groups.

     

  • 32. Pinay, Gilles
    et al.
    Gumiero, Bruna
    Tabacchi, Eric
    Gimenez, Olivier
    Tabacchi-Planty, Anne Marie
    Hefting, Maria Margaretha
    Burt, Tim P.
    Black, Valerie A.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Black, Virgil
    Bureau, Fabrice
    Vought, Lena
    Petts, Geoffrey E.
    Décamps, Henri
    Patterns of denitrification rates in European alluvial soils under various hydrological regimes2007In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 52, no 2, p. 252-266Article in journal (Refereed)
    Abstract [en]

    1. Denitrification in floodplain soils is one of the main biological processes emitting and reducing nitrous oxide, a greenhouse gas, and the main process responsible for the buffering capacity of riparian zones against diffuse nitrate pollution.

    2. The aim of this study was to measure denitrification rates under a wide range of current climatic conditions and hydrological regimes in Europe (from latitude 64°N to latitude 42°N and from longitude 2°W to longitude 25°E), in order to determine the response patterns of this microbial process under different climatic and hydrological conditions, and to identify denitrification proxies robust enough to be used at the European scale.

    3. Denitrification activity was significant in all the floodplain soils studied whatever the latitude. However, we found an increase in rates of an order of magnitude from high to mid latitudes. Maximum rates (above 30 g N m-2 month-1) were measured in the maritime conditions of the Trent floodplain. These rates are similar to mineralisation rates measured in alluvial soils and of the same order of magnitude as the amount of N stored in herbaceous plants in alluvial soils.

    4. We used Multivariate Adaptative Regression Splines to relate the response variable denitrification with five relevant predictors, namely soil moisture, temperature, silt plus clay, nitrate content and herbaceous plant biomass.

    5. Soil moisture, temperature, and nitrate were the three main control variables of microbial denitrification in alluvial soils in decreasing order of importance.

    6. The model developed for denitrification with interaction effects outperformed a pure additive model. Soil moisture was involved in all interactions, emphasising its importance in predicting denitrification.

    7. These results are discussed in the context of scenarios for future change in European hydrological regimes.

  • 33.
    Stenroth, Karolina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Polvi, Lina E
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fältström, Emma
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Land-use effects on terrestrial consumers through changed size structure of aquatic insects2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 1, p. 136-149Article in journal (Refereed)
    Abstract [en]

    We assessed the influence of agricultural land use on aquatic-terrestrial linkages along streams arising from changes in the emergence of aquatic insects. We expected that terrestrial predators would respond to a change in the abundance and/or the size structure of the emerging aquatic insects by an increase or decrease in population size. We measured the flux of emergent aquatic insects and the abundance of terrestrial invertebrate predators and birds along 10 streams across a forest-to-agriculture land-use gradient. We also performed stable isotope analyses (hydrogen, carbon and nitrogen) of terrestrial invertebrate predators. Small aquatic insects (Nematocera) were most abundant under agricultural land use, whereas larger bodied aquatic insects (Plecoptera and Trichoptera) were more associated with forest land use. Carabid beetles and linyphiid spiders were associated with agricultural streams (where there was a high abundance of small aquatic insects), whereas lycosid spiders and birds were associated with forest streams and a high abundance of large-sized aquatic insects. The contribution of aquatic insects to the diets of riparian Lycosidae, Linyphiidae and Carabidae was estimated to be 44%, 60% and 43%, respectively, indicating the importance of aquatic subsidies to the terrestrial system. Our results show that agricultural land use in an overall forested landscape can have significant effects on the abundance and diet of terrestrial consumers through its impact on the size structure of the assemblage of emerging insects, rather than the overall magnitude (numbers) of the aquatic subsidy. Hence, our results suggest that the composition, not just quantity, of a cross-habitat resource may influence the recipient system.

  • 34.
    Ström, Lotta
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Projected changes in plant species richness and extent of riparian vegetation belts as a result of climate-driven hydrological change along the Vindel River in Sweden2012In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, no 1, p. 49-60Article in journal (Refereed)
    Abstract [en]

    1. Riparian plant communities are primarily structured by the hydrologic regime of the stream. Models of climate change predict increased temperatures and changed patterns of precipitation that will alter the flow of rivers and streams with consequences for riparian communities. In boreal regions of Europe, changes will result in stream flows with earlier spring flood peaks of lower magnitude, lower flows during the summer, and higher flows in autumn and winter. We quantified the effects of predicted hydrologic change on riparian plant species richness, using four different scenarios for the free-flowing Vindel River in northern Sweden.

    2. We calculated the hydrologic niche of vegetation belts by relating the occurrence of species and vegetation belts to data on flood duration for 10 years preceding vegetation survey. We then used the flood duration predicted for 2071–2100 to estimate expected changes in the extent of each vegetation belt. Using species accumulation curves, we then predicted changes in plant species richness as a result of changes in extent.

    3. The two most species-rich vegetation belts; the riparian forest and the willow shrub belts were predicted to decrease most in elevational extent, up to 39% and 32% respectively. The graminoid belt below the shrub belt will mainly shift upwards in elevation while the amphibious vegetation belt at the bottom of the riparian zone increases in size.

    4. In the Vindel River, the riparian forest and willow shrub zone will lose most species, with reductions of 5–12% and 1–13%, respectively, depending scenario. The predicted loss from the entire riparian zone is lower, or 1–9% reduction, since many species occur in more than one vegetation belt. More extensive species losses are expected in the southern boreal zone, since much larger spring flood reductions are projected for these rivers.

    5. With an expected reduction in area of the most species-rich belts, it becomes increasingly important to manage and protect riparian zones to alleviate other threats, thus minimizing the risk of species losses. Restoring river and stream reaches degraded by other impacts to gain riparian habitat is another option to avoid species losses.

  • 35.
    Ström, Lotta
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Projected changes in plant species richness and extent of riparian vegetation belts as a result of climate-driven hydrological change along the Vindel River in Sweden2012In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, no 1, p. 49-60Article in journal (Refereed)
    Abstract [en]

    1. Riparian plant communities are primarily structured by the hydrological regime of the stream. Models of climate change predict increased temperatures and changed patterns of precipitation that will alter the flow of rivers and streams with consequences for riparian communities. In boreal regions of Europe, stream flows will exhibit earlier spring-flood peaks of lower magnitude, lower summer flows and higher flows in autumn and winter. We quantified the effects of predicted hydrological change on riparian plant species richness, using four different scenarios for the free-flowing Vindel River in northern Sweden.

    2. We calculated the hydrological niche of vegetation belts by relating the occurrence of species and vegetation belts to data on flood duration for 10 years preceding the vegetation survey. We then used the flood duration predicted for 2071–2100 to estimate expected changes in the extent of each vegetation belt. Using species accumulation curves, we then predicted changes in plant species richness as a result of changes in extent.

    3. The two most species-rich vegetation belts, riparian forest and willow shrub, were predicted to decrease most in elevational extent, up to 39 and 32%, respectively. The graminoid belt below the shrub belt will mainly shift upwards in elevation while the amphibious vegetation belt at the bottom of the riparian zone increases in size.

    4. In the Vindel River, the riparian forest and willow shrub zone will lose most species, with reductions of 5–12% and 1–13% per site, respectively, depending on the scenario. The predicted loss from the entire riparian zone is lower, 1–9%, since many species occur in more than one vegetation belt. More extensive species losses are expected in the southern boreal zone for which much larger spring-flood reductions are projected.

    5. With an expected reduction in area of the most species-rich belts, it becomes increasingly important to manage and protect riparian zones to alleviate other threats, thus minimising the risk of species losses. Restoring river and stream reaches degraded by other impacts to gain riparian habitat is another option to avoid species losses.

  • 36. Veen, GF (Ciska)
    et al.
    Sarneel, Judith M
    Department of Aquatic Ecology, Netherlands Institute of Ecology, Wageningen, The Netherlands.
    Ravensbergen, Lone
    Huig, Naomi
    van Paassen, Jose
    Rip, Winnie
    Bakker, Elisabeth S
    Aquatic grazers reduce the establishment and growth of riparian plants along an environmental gradient2013In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 58, no 9, p. 1794-1803Article in journal (Refereed)
    Abstract [en]

    1. The establishment of riparian plants is determined by abiotic conditions and grazing, although it is usually presumed that the former are most important. We tested the impact of aquatic grazers on the survival and growth of establishing riparian plants and whether the impact of grazing interacts with abiotic conditions.

    2. We conducted an experiment across 10 Dutch wetlands, covering a large range of water depth and nutrient availability. We introduced 1-year-old plants of an emergent (common reed, Phragmites australis) and a floating (water soldier, Stratiotes aloides) species in individual enclosures (n=5 per site) that excluded predominantly waterbirds, which were the most abundant grazers, and on adjacent unprotected plots. Survival and growth were measured during one growing season.

    3. Grazing reduced growth (as biomass) of Phragmites and Stratiotes by a mean of 25 and 60%, respectively. Grazing decreased survival of Stratiotes, but not of Phragmites. Shallow water, water-level fluctuations, eutrophic conditions and enough light favoured both growth and survival of Phragmites. Growth of Stratiotes was unaffected by these factors, but they reduced its survival. For both species, grazing effects on biomass were consistent across environmental conditions, but for Phragmites, grazing effects on survival were influenced by abiotic conditions.

    4. We conclude that aquatic grazers significantly reduce the establishment and growth of macrophytes in the riparian zone over a wide range of environmental conditions.

  • 37.
    Wenzel, Anja
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vrede, Tobias
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Survival, growth and reproduction of Daphnia galeata feeding on single and mixed Pseudomonas and Rhodomonas diets2012In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, no 4, p. 835-846Article in journal (Refereed)
    Abstract [en]

    1. Bacteria can be an important resource for zooplankton production in aquatic food webs, although the degree to which bacteria sustain zooplankton growth and reproduction is not clear. We performed a growth experiment with Daphnia galeata feeding on different ratios of P-replete Pseudomonas and Rhodomonas, ranging from a 100% bacterial to a 100% algal diet. 2. A pure bacterial diet did not support survival, growth or reproduction of D. galeata. While a 20% share of Rhodomonas in the food allowed survival of daphniids, the occurrence of offspring on a 50% algal diet indicated that the threshold for successful reproduction was between those two proportions of algal food. Increasing the proportion of the alga further increased growth and reproductive output, indicating that Rhodomonas was a higher-quality food than Pseudomonas. 3. A subsequent labelling experiment demonstrated that D. galeata incorporated phosphorus from Pseudomonas and Rhodomonas with similar efficiency, whereas carbon was incorporated more efficiently from Pseudomonas than from Rhodomonas. 4. Hence, we hypothesise that inadequate levels of essential biochemicals in pure bacterial diets led to decreased Daphnia performance. Concentrations of fatty acids in general, and especially of polyunsaturated fatty acids, were much lower in Pseudomonas than in Rhodomonas. This difference could explain the different growth and reproduction responses, although limitation by other essential biochemicals (e.g. sterols) cannot be ruled out. 5. Hence, where they dominate, bacteria may provide a significant part of the elemental flux to species feeding higher in the food web on the short term. However, the performance of consumers may be constrained by essential biochemicals.

  • 38.
    Ågren, Anneli
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Laudon, Hjalmar
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Terrestrial export of highly bioavailable carbon from small boreal catchments in spring floods2008In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 53, no 5, p. 964-972Article in journal (Refereed)
    Abstract [en]

    1. We assessed the terrestrial export of organic carbon, which effectively supported aquatic bacterial production (BP), from small boreal catchments during spring flood. We analysed stream runoff from nine small catchments with different proportions of peat mires and coniferous forests by monitoring the dissolved organic carbon (DOC) flux in combination with conducting bacterial bioassays.

    2. Multiple linear regression analysis showed that BP during 7-day-dark bioassays (BP7; μg C L-1day-1) was explained by both the quantity and quality (low-molecular weight fractions) of the DOC. BP7 can be used as a measure of export of terrestrial organic carbon that is highly bioavailable.

    3. Total export of DOC during spring flood from the different catchments ranged from 20 to 27 kg ha-1 and was negatively correlated to forest cover (%). However, the export of BP7 carbon was positively correlated to forest cover and varied from about 0.1 kg ha-1 in mire-dominated streams to about 0.2 kg ha-1 in forest-dominated streams.

    4. The high bioavailability of forest carbon suggests that forests are the main contributors of BP-supporting carbon in boreal streams although mires have higher area-specific export of DOC.

1 - 38 of 38
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