The protection of lakes in the face of climate change challenges regarding the preservation of the "good water status" : Explained on the examples of Lake Constance and Lake Neusiedl

Abstract

The focus of this master thesis is put on the effects of climate change on standing water bodies in Austria, based on literature research as well as a comparative study. Explained on the examples of Lake Constance and Lake Neusiedl it intends to show that lakes react differently to the challenges posed by global warming: For the whole of Austria, the temperature increase is expected be faster than on the global average. So far, the mean temperatures in the federal republic have risen for +1,8°C since the 1880s and this trend is very likely to continue in the future. As a result, there will be an increase in evaporation. Precipitation patterns are characterized by regional differences with large insecurities about the future trend. Overall, rainfall levels have slightly increased since the 1970s, with the only exception being Austria's south-east. These changes have an impact on the hydrology of standing water bodies: There is a close connection between the average air and water temperate. The comparison showed that the Neusiedlersee's water balance is mostly dependent on the annual difference between evaporation and precipitation. Because there is little water input from inflows, a complete dry-out scenario is possible and might threaten its survival, which is also endangered by the extension of the reed belt. Lake Constance is strongly influenced by the temperature regime. It is vertically divided into layers with exchange only possibly during spring and autumn/ winter, when the whole water body assumes the same temperature allowing wind to mix it through. Mild winters with warmer-than-average temperatures result in longer periods of thermal stability. This has an impact on the oxygen content in the lake's Hypolimnion, potentially resulting in anoxia. Furthermore, it may cause the mobilisation of nutrients stored in the lake's bed. Taking account of the characteristics of standing water bodies is essential for the achievement and preservation of the "good ecological and chemical water status" as set forth by the Water Framework Directive: By comparing Lake Constance and the Neusiedlersee it becomes apparent that their potential degradation needs to be addressed by management plans which consider the long-term effects of measures.