Dlouhodobé trendy acidifikace tatranských jezer
Historical development of emission trends and atmospheric deposition of sulphur (S) and nitrogen (N) strongly influenced chemical composition and quality of waters and biological communities in the glacial lake ecosystems. Concentration of SO42~ similarly increased in all glacial lakes, whereas concentrations of NO3~ increased only in some lakes. Very high concentrations of NO3- were detected in the lakes located in the drainage areas covered by bare rocks (mean 45 (μmol-1), yet significantly lower values were found in the lakes sited in the drainage areas covered by grasslands (mean 27 μmol-1). Close to zero values were detected in the lakes surrounded by forests. This is the effect of different soil substrates and vegetation covers that varied with the type of lake drainage area. Nitrogen consumption, and thus nitrogen saturation depends primary on biological activity. Even though, there are no available long term data sets on detailed chemical composition of waters, based on biological indicators, the most dramatic changes in the chemical composition happed in the period 1973-78. In this period, species diversity of zooplankton very decreased. Also, the species structure of zooplankton communities turned to be more similar to the present communities of medium or highly acidificated lakes. In the number of lakes zooplankton is gone totally. Moreover, similarly to patterns detected in other European and American lakes, the negative relationship between decreasing species diversity of phytoplankton and increasing acidification was described. Water quality and biocoenoses were the most negatively impacted in the second half of 1980's. In the beginning of 1990's, water quality again started to increase as the result of decline of emissions and atmospheric depositions of sulphur and nitrogen, so the concentration of SO42~ and N03~ also decreased. Decline of SO42~ concentrations was higher in the case of glacial lakes of the drainage area dominated by rock substrate in comparison to the lakes of the drainage areas with higher proportion of soil substrate. It is probably due to ongoing resorption process of sulfites caught in the soil substrates during the previous period. Here, the development of new equilibrium lasts longer time. Contrary to sulfites, nitride concentrations declined in all lakes with different types of drainage areas. It is the result the nitrogen saturation in all ecosystem types. Exceeding nitrogen not used in biotic cycles is discharged down stream. Soil and vegetation coverage in the drainage area limits the concentration of nitrides. Decline of nitrides in the lake waters would continue to the point when increase of biotic processes in the ecosystem, lake-drainage area, starts to be limited by nitrogen. Consequently, the nitrogen concentration should jump down. The trend of sulfite decrease will probably slowly continue. In contrast, stagnation of nitride levels respectively their slight increase is expected due to expected economic growth in the central European region.
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