Ecological classification based on heterotrophic growth and periphyton in Haldenvassdraget 2009-2017

Summary

Ecological state of 41 locations in Haldenvassdraget, in county Østfold and Akershus, Norway, has been classified in accordance to the Water Framework Directive. The results are based on samples collected in 2009, 2010, 2012, 2014 and 2017. The biological quality elements investigated were heterotrophic growth and periphyton. The selected quality elements are sensitive to the following pressures: Organic material, eutrophication and acidification. The classification is in accordance with the ‘one out – all out’ principle, which means that the biological quality element with the poorest state determines the total classification of a location. The report provides a description of the methodology and an overview of the results for each quality element. According to the periphyton index of trophic status, PIT, only two sites were classified to good ecological status based on results from several years, while four sites were classified to good ecological status based on the 2017-results. Regarding acidification most sites were classified to good or high ecological status. Only two sites were classified to moderate ecological state based on results from all years investigated. According to heterotrophic growth, one site was in poor ecological state, in both 2012 and 2017, while the ecological state increased on two other sites, from moderate in 2012 to good or high in 2017. The remaining sites were classified to good or high ecological state. Periphyton (PIT) was largely decisive in an overall assessment of ecological status because this quality element was the most sensitive one.