Climatic and dam-induced impacts on river water temperature: Assessment and management implications.

In a changing climate with a warming trend in air temperature, river water temperature increases as a result of heat exchange with the atmosphere. Moreover, of the different types of anthropogenic activity impacting rivers, the construction of dams appears to have multi-dimensional effects on the river environment, and it especially affects the thermal condition of rivers. The aim of the study is to identify and assess the impact of these two distinct sources of water temperature distortion in relation to the natural thermal conditions of rivers. In the study, linear trend analysis and a complex wavelet transform are used. The analysis focuses on daily river water temperature data for time periods before and after the construction of selected reservoirs in the Polish Carpathians, and on daily air temperature data for neighboring meteorological stations. Three rivers were selected for analysis: (1) Dunajec River, 22km downstream of the Czorsztyn-Sromowce Wyżne reservoir complex, (2) Ropa River, 16km downstream of the Klimkówka Reservoir, and (3) Wisłok River, 33km downstream of the Besko Reservoir. Research has shown that the significant increasing trends identified for water temperature are weaker than analogous trends in air temperature. The Czorsztyn-Sromowce Wyżne and Klimkówka reservoirs appear to exert considerable influence on natural air-water temperature synchronization, because the phase difference increases 5-fold in comparison with conditions prior to the construction of the reservoirs. The weakening of the natural air-water temperature synchrony implies diminished impact of air temperature on stream water temperature. However, this creates an opportunity for preparing appropriate management practices mitigating an increasing temperature trend in order to shape more favorable (natural) thermal conditions for native aquatic biota in impounded rivers.