Impacts of multiple stressors on phytoplankton community in shallow lakes

Date

2023-3-31

Author

Filiz, Nur

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In this Ph.D.-research, the main aim was to study the relationship between multiple stressors (increase in temperature, eutrophication and changes in hydrology) and phytoplankton community and size structure or chlorophyll-a. This expands our understanding from simple single stressor studies to dynamic, multiple-stressor studies using a range of approaches and scales. Three approaches were used in the present study: a short-term mesocosm experiment with two nutrient and three temperature levels including one month heat wave; a long-term mesocosm experiment with two nutrient and two temperature levels; and time series analysis of chloropyll-a and in-lake nutrient concentrations with long-term water and nutrient budgets of two inter-connected semi-arid Mediterrenean lakes. High nutrient conditions were mostly dominated by cyanobacteria with a tendency of increasing toxic cyanobacteria species which had a negative effect on phytoplankton taxa and genus richness, while low nutrient conditions were richer in genera. The sensitivity of the phytoplankton community structure to high temperatures depends on nutrient availability. The study revealed the increasing vulnerability of freshwater ecosystems phytoplankton community to warming as well as heatwaves with declining nutrient concentrations. It is hard to generalise phytoplankton size responses to multiple stressors; both increasing and decreasing effects of higher temperatures on phytoplankton size structure were observed although the expectations was a reduction with increasing temperatures. These effects of higher temperatures vary with the different nutrient cncentrations. In the following decades, increased evaporation and less precipitation are predicted by climate change scenarios for semi-arid Mediterrenean climates. This poses a serious threat to shallow lakes and could have negative effects on the water quality depending on the water and nutrient balance. Even with modest external loading, the nutrient concentrations in shallow lakes in semi-arid climates can rise under low precipitation; these peaks are associated with increasing internal loading and nutrient accumulation from evaporative water loss. Nutrient control remains the most obvious mitigation strategy for water management and to lower the abundance of cyanobacteria in freshwaters, and this becomes even more crucial in a warmer climate.

Subject Keywords

Phytoplankton, Multiple Stressors, Eutrophication, Climate Change, Cyanobacteria, Water Budget, Nutrient Budget, Chlorophyll-a

URI

https://hdl.handle.net/11511/103054

Collections

Graduate School of Natural and Applied Sciences, Thesis