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Long‐Term Trends in the Nutrient Input and In‐Lake Concentrations of a Drinking Water Reservoir in a Dense Populated Catchment Area (Erzgebirge, Germany)
Author(s) -
Horn W.,
Horn H.,
Paul L.
Publication year - 1994
Publication title -
internationale revue der gesamten hydrobiologie und hydrographie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.524
H-Index - 52
eISSN - 1522-2632
pISSN - 0020-9309
DOI - 10.1002/iroh.19940790206
Subject(s) - eutrophication , tributary , environmental science , hypolimnion , hydrology (agriculture) , nitrate , nutrient , spring (device) , drainage basin , phosphorus , annual cycle , environmental chemistry , seasonality , chemistry , ecology , geology , biology , mechanical engineering , cartography , geotechnical engineering , organic chemistry , engineering , geography
The concentrations of soluble reactive and total phosphate, silicate, and nitrate in the tributaries and in the watercolumn of the meso/eutrophic reservoir Saidenbach were investigated at weekly or fortnightly intervals. The results are presented as annual averages over 16 years (from 1975 till 1990) and show a gradual increase of the N‐ and P‐concentration in the inlets caused by an intensification of the agriculture in the drainage basin and high domestic sewage releases from the settlements having no waste water treatment. The silicate concentration of the inlets remained constant. Consequently, also a rise of the in‐lake concentrations of the two P‐fractions was observed. The nitrate concentration of the reservoir Saidenbach increased till 1978, but showed no significant trend over the whole investigation period. The drop of the in‐lake silicate concentration during the eighties has to be explained by diminished discharges and, most of all, a higher biological activity as a consequence of the increased P‐loading. Intra‐annual concentrations calculated as winter, spring, summer (epi‐ and hypolimnion) and autumn means show the distinct seasonal periodicity of the phosphorus and silicon cycles. Therefore, annual average in‐lake concentrations of these nutrients are not quite good measures reflecting changes of the trophic conditions, but rather the winter and early spring values are. No correlations were detected between the annual mean concentrations and the loads. On the other hand, no remarkable seasonal cycling of the nitrate concentrations could be observed and, in this case, a clear dependence exists between annual mean concentrations and loads. The results found for the tributaries of the meso/eutrophic reservoir Saidenbach were compared with those observed in the inlets of the neighbouring oligotrophic reservoir Neunzehnhain. Here the phosphorus concentrations remained almost constant during the time of investigation, but the nitrate concentrations increased too. This must be attributed to agriculture, air pollution and forest management.