Sirvi Autor "Lauridsen, Torben" järgi
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Kirje Bimodality and alternative equilibria do not help explain long-term patterns in shallow lake chlorophyll-a(Springer Nature, 2023) Davidson, Thomas A.; Sayer, Carl D.; Jeppesen, Erik; Søndergaard, Martin; Lauridsen, Torben; Johansson, Liselotte S.; Baker, Ambroise; Graeber, DanielSince its inception, the theory of alternative equilibria in shallow lakes has evolved and been applied to an ever wider range of ecological and socioecological systems. The theory posits the existence of two alternative stable states or equilibria, which in shallow lakes are characterised by either clear water with abundant plants or turbid water where phytoplankton dominate. Here, we used data simulations and real-world data sets from Denmark and north-eastern USA (902 lakes in total) to examine the relationship between shallow lake phytoplankton biomass (chlorophyll-a) and nutrient concentrations across a range of timescales. The data simulations demonstrated that three diagnostic tests could reliably identify the presence or absence of alternative equilibria. The real-world data accorded with data simulations where alternative equilibria were absent. Crucially, it was only as the temporal scale of observation increased (>3 years) that a predictable linear relationship between nutrient concentration and chlorophyll-a was evident. Thus, when a longer term perspective is taken, the notion of alternative equilibria is not required to explain the response of chlorophyll-a to nutrient enrichment which questions the utility of the theory for explaining shallow lake response to, and recovery from, eutrophication.Kirje Effects of warming and nutrients on the microbial food web in shallowlake mesocosms(Elsevier, 2018) Zingel, Priit; Cremona, Fabien; Nõges, Tiina; Cao, Yu; Neif, Érika M.; Coppens, Jan; Işkın, Uğur; Lauridsen, Torben; Davidson, Thomas A.; Søndergaard, Martin; Beklioglu, Meryem; Jeppesen, Erik; Centre for Limnology. Institute of Agricultural and Environmental SciencesWe analysed changes in the abundance, biomass and cell size of the microbial food web community (bacteria, heterotrophicnanoflagellates, ciliates) at contrasting nutrient concentrations and temperatures during a simulated heat wave. We used 24mesocosms mimicking shallow lakes in which two nutrient levels (unenriched and enriched by adding nitrogen and phosphorus)and three different temperature scenarios (ambient, IPCC A2 scenario and A2+%50) are simulated (4 replicates of each).Experiments using the mesocosms have been running un-interrupted since 2003. A 1-month heat wave was imitated by anextra 5◦C increase in the previously heated mesocosms (from 1st July to 1st August 2014). Changes in water temperatureinduced within a few days a strong effect on the microbial food web functioning, demonstrating a quick response of microbialcommunities to the changes in environment, due to their short generation times. Warming and nutrients showed synergisticeffects. Microbial assemblages of heterotrophic nanoflagellates and ciliates responded positively to the heating, the increasebeing largest in the enriched mesocosms. The results indicate that warming and nutrients in combination can set off complexinteractions in the microbial food web functioning.Kirje Global patterns in the metacommunity structuring of lake macrophytes: regional variations and driving factors(Springer, 2018) Alahuhta, Janne; Lindholm, Marja; Bove, Claudia P.; Chappuis, Eglantine; Clayton, John; De Winton, Mary; Feldmann, Tõnu; Ecke, Frauke; Gacia, Esperança; Grillas, Patrick; Hoyer, Mark V.; Johnson, Lucinda B.; Kolada, Agnieszka; Kosten, Sarian; Lauridsen, Torben; Lukács, Balázs A.; Mjelde, Marit; Mormul, Roger P.; Rhazi, Laila; Rhazi, Mouhssine; Sass, Laura; Søndergaard, Martin; Xu, Jun; Heino, Jani; Centre for Limnology. Institute of Agricultural and Environmental Sciences. Estonian University of Life SciencesWe studied community–environment relationships of lake macrophytes at two metacommunity scales using data from 16 regions across the world. More specifically, we examined (a) whether the lake macrophyte communities respond similar to key local environmental factors, major climate variables and lake spatial locations in each of the regions (i.e., within-region approach) and (b) how well can explained variability in the community–environment relationships across multiple lake macrophyte metacommunities be accounted for by elevation range, spatial extent, latitude, longitude, and age of the oldest lake within each metacommunity (i.e., across-region approach). In the within-region approach, we employed partial redundancy analyses together with variation partitioning to investigate the relative importance of local variables, climate variables, and spatial location on lake macrophytes among the study regions. In the across-region approach, we used adjusted R2 values of the variation partitioning to model the community–environment relationships across multiple metacommunities using linear regression and commonality analysis. We found that niche filtering related to local lake-level environmental conditions was the dominant force structuring macrophytes within metacommunities. However, our results also revealed that elevation range associated with climate (increasing temperature amplitude affecting macrophytes) and spatial location (likely due to dispersal limitation) was important for macrophytes based on the findings of the across-metacommunities analysis. These findings suggest that different determinants influence macrophyte metacommunities within different regions, thus showing context dependency. Moreover, our study emphasized that the use of a single metacommunity scale gives incomplete information on the environmental features explaining variation in macrophyte communities.Kirje Lake ecosystem changes after increase in water clarity: effects of zebra mussel invasion in eight lakes in the River Gudenå system, Denmark : [presentation](Aarhus University, 2023) Søndergaard, Martin; Lauridsen, Torben; Johansson, Liselotte S.; Jeppesen, ErikThe presentation took place at the 11th International Shallow Lakes Conference.Kirje Lake Monitoring in Denmark since 1989 : [presenation](Aarhus University, 2023) Johansson, Liselotte Sander; Søndergaard, Martin; Andersen, Peter Mejlhede; Lauridsen, Torben; Jeppesen, ErikThe presentation took place at the 11th International Shallow Lakes Conference.Kirje Pelagic niche shift by fishes following restorations of a eutrophic lake(Springer, 2024) Berthelsen, Andreas S.; Søndergaard, Martin; Kiljunen, Mikko; Eloranta, Antti; Lauridsen, TorbenLake restoration by biomanipulation or phosphorus fixation has been commonly applied methods to improve the ecological status of lakes. However, the effects of lake restoration on foodweb dynamics are still poorly understood, especially when biomanipulation and nutrient fixation are used simultaneously. This study investigated the combined effects of a 70% fish removal (mainly roach (Rutilus rutilus Linnaeus, 1758) and bream (Abramis brama Linnaeus, 1758) and Phoslock® treatment on fish trophic ecology in Lyngsø (area: 9.6 ha, mean depth: 2.6 m), Denmark. The lake restoration resulted in decreased nutrient levels, increased water clarity, and increased coverage of more structurally complex submerged macrophytes. Following lake restoration, significant changes in diets of the dominant fish species were observed. Stomach content analyses of roach and perch (Perca fluviatilis Linnaeus, 1758) revealed significantly reduced detritus utilization and increased foraging on macrophytes and macrophyte living invertebrates. Results from stable isotope mixing models indicated a shift from littoral benthic to more pelagic food resources by the dominant fish species. Our findings provide further evidence that lake restorations can lead to substantial changes in lake food webs and fish communities, thereby potentially facilitating a shift toward an ecological state resembling the pristine reference state, less influenced by anthropogenic factors.Kirje Role of nitrogen in Danish lakes: Evidence from monitoring and long-term experiments : [presentation] (Aarhus University, 2023) Jeppesen, Erik; Søndergaard, Martin; Davidson, Thomas A.; Lauridsen, Torben; Johansson, Liselotte S.; He, HuThe presentation took place at the 11th International Shallow Lakes Conference.