Long-term changes in nutrient status of river water
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Our paper presents changes in the quality of water in the Bytowa River (in 1975-2003) against the background of changes which occurred in the river basin. The basis for an evaluation of those changes consisted of some physicochemical and bacteriological assays completed as part of a surface water monitoring program run by the Inspectorate for Environmental Protection. Based on the collected information, the evolution of the quality of water in the River Bytowa can be divided into two stages. The first, lasting until the late 1980s, was characterized by steadily increasing river pollution. The second stage was a time of gradual improvement of river water quality, which was a result of several overlapping factors related to the political and economic transformation in Poland. Construction of a municipal wastewater treatment plant as well as much lower quantities of fertilizers applied to decreased areas of farmland meant that loads of contaminants both from urban sources and from agriculture were reduced. The comparison of nutrient concentrations at different control points on the Bytowa suggest that from the mid 1970s to the late 1980s the contribution of municipal loads was increasing, and in the peak period such waste prevailed over non-point pollution along a considerable section of the river. From the late 1980s to 2003 both municipal and non-point pollution loads were decreasing, with the former declining to a much greater extent than the latter. In recent years non-point pollution has been dominant in total pollution load. Bacterial contamination was the only remaining evidence of the unsatisfactory condition of the river.
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