Synoptisk provtagning i vattendrag med eutrofieringsproblem
En studie för att identifiera områden för prioritering av åtgärder
In Halland, agriculture is the major source of eutrophication of water. In the study, synoptic sampling were performed in the three watercourses Nyrebäcken, Skintan and Vinån all located in the county of Halland. Sampling occurred during the period February to May on three occasions with different flow rates: high, low and base flow. Samples were taken in the mainstream and tributaries with intention to show how big the impact of eutrophication it is in the water and to assess the impact of the tributariesThe results show that all watercourses are affected by eutrophication. Nyrebäcken has the highest concentrations of nitrogen and phosphorus in the mainstream, then Skintan and last Vinån. Vinån is much less affected by phosphorus than the other watercourses, which may depend on the surrounding landscape and that the edges of the watercourse are less steep than at Nyrebäcken and Skintan. The concentration in the tributaries varies widely, from low concentrations to extremely high. In all watercourses there are tributaries that have a big impact on the mainstream, just as there are tributaries that have a small impact. The concentration also varies with the different flows and in generally the highest concentrations of nitrogen and phosphorus are measured during high flow.To estimate the impact of the tributaries the results of total nitrogen and total phosphorus have been classified according to classification system previously used in Sweden. The classification means a rating from 1 to 5 where 1 is the lowest and 5 the highest. The classification has been made for each tributary in the respective watercourses at different flows. The mainstream was classified according to the mean of all sample points in the mainstream at the respective flow.Sampling was only done on three occasions during a short period and to improve the results further sampling have to be done.