Comparative Analysis of Physico-Chemical and Trophic Water State of Czaniec and Goczalkowice Dam Reservoirs in the Period of 2011-2015

Analysis of changes in physico-chemical quality and trophic status of waters from the intakes of two dam reservoirs in Southern Poland, i.e. Czaniec and Goczalkowice, was performed for the period of 2011-2015. The Index of Trophic State (ITS) was used to assess trophic state of both reservoirs as well as to determine dynamics of its changes for the analyzed period. Since the main function of both reservoirs is drinking water storage for the Silesian agglomeration with about 3.5 min population, special attention was paid to the physico-chemical indices describing the utility function of water and reflecting impact of eutrophication on water quality. Despite similar functions, the two reservoirs differ fundamentally in terms of their morphometric parameters, level of impact of the catchment area and potential vulnerability to degradation. The land utilization structure for both reservoir catchments varies too. Water quality was determined on the basis of temperature, electrical conductivity, BOD5, and the amount of total suspended solids, nitrates and phosphates. For both dam reservoirs, indicators values remained within the levels of very good water quality that corresponded to the A1 category of water utility for a public water supply. Only a few BOD5 measurement results for water from Goczalkowice dam reservoir corresponded to the A2 water category. According to the trophic state assessment, the Goczalkowice dam reservoir was classified as a mesoeutrophic while Czaniec dam reservoir - as a mesotrophic water body. In the examined 5-year period, the dynamics of trophic state changes in both dam reservoirs was comparable, and their ecological status was characterized as stable. This ensures good quality of water near the discussed intakes, despite the relatively high trophic status of the reservoirs.