Overvåking av vassdrag i Hedmark i 2013

The report presents the results from an investigation of water quality and assessment of ecological status in selected lakes and water courses in the county of Hedmark in 2013. With respect to eutrophication the ecological status was classified as high in the lakes Skasen and Hukusjøen, good in the lakes Harasjøen and Storsjøen in Odal and poor in the lakes Tørråssjøen and Gjesåssjøen. In the two last mentioned lakes, and especially Tørråssjøen, biomasses of phytoplankton and concentrations of total phosphorus were high. In both of these lakes the phytoplankton was dominated by the nuisance flagellate Gonyostomum semen. The monitoring results show that measures to reduce nutrient inputs are necessary in order to achieve the environmental goal, which means good ecological status. The ecological status concerning acidification was classified as good or high in the investigated lakes. The communities of benthic algae and macro invertebrates in the rivers Tverråa and Juråa indicated good or high ecological status with respect to eutrophication. In the rivers Gjesbekken, Tjura, Kveia, Trondsåa and Mangåa the ecological status concerning eutrophication was classified as moderate. This means that these rivers did not achieve the environmental goal of good ecological status and that nutrient reduction measures seem to be necessary. For the river Tjura there was some uncertainty in the classification because of relative large differences between the results for benthos algae (moderate) and macro invertebrates (high ecological status). In most of the investigated rivers the ecological status with respect to acidification was classified as high. This is based on analyzes of the macro invertebrate and/or the benthic algae communities. The exceptions were the rivers Juråa and Trondsåa. These rivers seemed to have an acidic water quality and here the ecological status was classified as moderate. However, in the river Trondsåa and especially the river Juråa, the acidic conditions were probably mainly caused by naturally high concentrations of humic acids. In river Trondsåa anthropogenic acidification cannot be excluded as a possible additional cause to the acidic conditions. The concentrations of trace elements (arsenic, cadmium, chromium, copper, nickel, lead and zinc) were generally low in the investigated lakes and rivers.