Constrains of biological recovery of the Bohemian Forest lakes from acid stress

Jaroslav Vrba1, Jindriska Bojkova1, Michal Sorf1, Jan Fott2, Linda Nedbalova2, Veronika Sacherova2, Jiri Kopacek3, Miroslav Macek3, Tomas Soldan3, Miroslav Papacek4
1 Faculty of Science, University of South Bohemia
2 Faculty of Science, Charles University
3 Biology Centre ASCR
4 Faculty of Education, University of South Bohemia

O 1.8 in Long term trends in the functioning of ecosystems

14.07.2014, 16:15-16:35, H18

We evaluated long-term data from eight glacial lakes in the Bohemian Forest. For many decades, these central European mountains of acid-sensitive crystalline bedrock had been exposed to airborne pollution from both local and remote emission sources. Owing to historical data, we could document consequent changes in plankton and fish, occurring in parallel with changes in water chemistry (observed and reconstructed using MAGIC modelling). Acidification of the lakes peaked in the middle 1980s and since then we have observed distinct chemical recovery of lake water chemistry, accompanied by somewhat lagged biological recovery from acid stress. The changes in lake chemistry and biota enable us to study biological processes and biodiversity across a gradient of limiting conditions such as pH, aluminium, and dissolved organic carbon (DOC) concentrations, nutrient status, and food web structure. For the 1984–2013 period, we can document overall increasing trends in lake water pH followed by more or less pronounced declines in total and toxic ionic aluminium (Al, Ali) forms. The Bohemian Forest lakes differ in the Al concentrations and speciation, with conspicuous seasonal variations in Ali controlled by actual pH, resulting in summer epilimnetic minima and spring peaks. Our data suggest that this environmental framework, together with nutrient status and DOC concentrations, form major constraints of biological recovery and are responsible for its different trajectories in individual lakes. For four sampling campaigns during 1999–2011, we evaluated species richness and diversity of phytoplankton, ciliates, zooplankton (rotifers, crustaceans), and aquatic insects (mayflies, stoneflies, caddisflies, water bugs) in all eight lakes. Gradual increase in phytoplankton biomass (but not species richness) and certain progress in species diversity of other groups are common signs of starting biological recovery, which is usually delayed compare to the onset of chemical recovery by a decade or two. Particularly in the plankton community capable of reacting quickly to the environmental changes, the increase in species richness and diversity indices in the course of time can be altered by year-to-year changes in water chemistry, especially during any regress to lower pH and higher Ali concentrations. We assume that, besides the environmental factors, biotic interactions (such as competition for resources, their availability or quality, predation by invertebrates or re-stocked fish) control the structure and abundance of plankton. Highly unfavourable plankton stoichiometry, namely the high carbon to phosphorus ratio, and limited dispersion due to the lack of potential source localities may represent additional constraints to biological recovery in the region.

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last modified 2014-04-04