Surveillance monitoring of large Norwegian lakes 2017. Testing of methodology for monitoring and classification of ecological status according to the Water Framework Directive

Summary

This report presents the monitoring results for eight large Norwegian lakes in 2017, which is the 3rd year of the Norwegian surveillance monitoring programme for large lakes as required by the Water Framework Directive (WFD). The primary objective of this monitoring programme is to assess their ecological status and provide information for assessment of long-term changes of natural conditions and widespread anthropogenic activity. An additional objective is to test and adapt existing monitoring and classification methods for use in large, deep lakes. Large Norwegian lakes have been monitored also before the WFD, but for most of the lakes, this monitoring has been limited in time and content. Earlier data are not sufficient for a complete classification of ecological status according WFD requirements, but can still be used to consider changes of certain biological and physico-chemical quality elements. Large lakes are often exposed to multiple pressures, e.g. eutrophication, water level regulation, acidification, introduced/invading species and climate change. At the same time, they also have high public interest due to their importance for provision of an array of ecosystem services for the population in their catchments, including water supply for drinking water and irrigation, recreation, fishing, energy (hydropower), flood protection and nutrient retention. The results of the surveillance monitoring are therefore also needed to generate new limnological and ecological knowledge about the impact of multiple pressures on the ecological status of large lakes, as well as on their biodiversity, productivity, trophic interactions and self-purification capacity. This knowledge can be used to improve existing assessment systems, as well as to guide river basin management plans and help optimizing the programme of measures to restore or prevent deterioration of their ecological status and ecosystem services. The monitoring in 2017 included the following lakes: Mjøsa, Øyeren and Gjende in Eastern Norway; Lundevatnet and Byglandsfjorden in Southernmost Norway; Eikesdalsvatnet, Hornindalsvatnet and Vangsvatnet in Western Norway and Selbusjøen in Mid-Norway. Gjende was also monitored in 2015 and 2016, while Selbusjøen was monitored also in 2016. Mjøsa has been monitored annually for its pelagic quality elements since the 1970s, but the monitoring has now been supplemented with more biological quality elements (macrophytes and microcrustaceans).(...)