Key ecological, functional and biodiversity responses to combined temperature, hydrology/water level and salinity and nutrient effects along a European climate gradient
Abstract: Recent research related to biodiversity is very much driven by the realisation that biodiversity is declining at an alarming rate worldwide across all ecosystems through anthropogenic impacts such as land use, eutrophication, and global warming. We provide a number of case studies documenting the role of environmental forces such as water temperature, changes in the thermal regime of lakes, changes in water level, nutrients or salinity on aquatic species composition (plankton, macroinvertebrates, fish), biomass development (plankton, periphyton) and biodiversity (plankton, fish). The case studies cover a north/south European gradient.
We found climate induced changes in the thermal regime (extension of thermally stratified events during summer) of a polymictic lake to positively affect algal mass development in favour of cyanobacteria dominance, accompanied by a switch to nitrogen fixing cyanobacteria species. This led to a higher proportion of nitrogen fixation- and as such to a change in the ecosystem functionality. Changes in water level turned out to be the major driving forces for determining a shift in phytoplankton species composition in a shallow non stratified lake. High water levels accompanied by high water color and a deterioration of light conditions were estimated as the main driving force underlying the shift towards a highly shade tolerant phytoplankton community dominated by Limnothrix redekei and L. planktonica.
The diversity of fish communities were studied in 1632 lakes across 11 European countries. The study revealed that local fish species richness and diversity were related mainly to morphometric and (bio) geographical/climatic variables. Larger and deeper lakes in warm areas tended to be the most species rich and diverse. Fish density was related mainly to anthropogenically driven productivity but also was sensitive to geographical/climatic factors. Thus, warmer and shallower lower-altitude European lakes, which are usually more eutrophic, had higher fish densities than cold and deeper higher-altitude lakes. Fish size increased with altitude and declined with increasing seasonality and temperature. The potential effects of temperature, salinity and fish on the plant-associated macroinvertebrate community structure and biodiversity were studied in cold-temperate and Mediterranean shallow brackish lakes. Plant-associated macroinvertebrates and free-swimming macroinvertebrate predators were more abundant and the communities richer in species in the cold compared to the warm climate, most probably as a result of differences in fish predation pressure.
Water temperature turned out to be the most important driver to positively affect periphyton growth in lakes exhibiting high and low nutrient concentrations across a north/south European. The slope of the regression between water temperature and periphyton biomass suggested that, for every degree increase in water temperature, summer periphyton biomass was stimulated by 42%.
Overall, in most case studies a modulation of direct temperature, salinity, and water level effects by food web interactions was seen. Thus, care should be taken when predicting the combined effect of changes in multiple factors from their individual effects.
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