Sammendrag
This report presents results from the environmental status survey of the Hotran watercourse in 2017. The survey was done on assignment for The County Governor of Nord Trøndelag, with the objective to assess ecological status in respect to eutrophication and organic pollution. Altogether 9 stations in the watercourse were examined, where only station 3 Sundebekken was classified with high ecological status. Station 1 Høyslobekken, 17 Hovselva lower part, 18 Hovselva higher part, and 26 Leirelva lower part was classified with moderate ecological status, while station 20 Myrelva, 21 Ståbekken, 24 Dalingbekken and 27 Lellobekken was classified with low ecological status. The assessment of the ecological status is based on sample collection and analyses of four biological quality elements, periphyton, macroinvertebrates, fish and freshwater pearl mussels. No freshwater pearl mussels were found in the watercourse, and the degree of reliability to the ecological classification of fish was considered to be low/bad. The overall ecological status was therefor based on the classification of periphyton and macroinvertebrates in accordance with “the worst rules” principle. The PIT (periphyton index of trophic status), which responds to nutrient loads and eutrophication, controlled the overall status at all stations, while the ASPT (average score per index) for macroinvertebrates showed better ecological status. With such a difference in response by these indexes, nutrient runoff from cultivated lands seems to be more important for the ecological status than effluent of organic substances from point sources (sewage, manure storage, etc.). Overall ecological status for the Hotran watercourse is considered to be low/bad.
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