Effects of artificial heating on periphyton and submerged macrophytes in temperate lakes

Experiments investigating the impacts of climate warming on aquatic primary producers and their interactions have often been conducted in laboratories or mesocosms, with contradictory results.  Meanwhile, evidence at the ecosystem level remains scarce. We investigated the impact of artificial heating in a unique system of lakes in Konin, Poland, which is warmed by ~2°C by a power plant, using nearby non-heated lakes as a reference. Periphyton substrates and pre-grown macrophytes (Myriophyllum spicatum, Chara rudis) were deployed at five depths for four weeks. To quantify environmental effects, we used generalised additive models including both fixed predictors and random effects. Periphyton biomass increased significantly with warming and light availability, while grazer abundance had no effect. Macrophyte survival was strongly determined by light, with both species showing reduced survival under shaded conditions. Importantly, temperature had no direct effect on macrophyte survival, whereas periphyton biomass showed a negative effect, indicating that warming influenced macrophytes indirectly through increased periphyton shading. Overall, our results show that warming enhances periphyton biomass and strengthens shading pressure on submerged vegetation. Thus, the primary mechanism by which climate warming threatens macrophytes in temperate lacustrine ecosystems is indirect through periphyton-driven light limitation rather than direct thermal stress.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Michal Brzozowski, Poznan University of Life Sciences (michal.brzozowski@up.poznan.pl)

Authors:

Michal Brzozowski, Poznan University of Life Sciences  (michal.brzozowski@up.poznan.pl)

Sabine Hilt, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (sabine.hilt@igb-berlin.de)