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Monitoring of Lake Vestvannet and Lake Borredalsdammen in Østfold County, SE Norway, 2019.

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Involved from NIVA
Andreas Ballot
Andreas Ballot, Eivind Ekholt Andersen


NIVA and FREVAR conducted a monitoring survey of the water quality in Lake Vestvannet and Lake Borredalsdammen in Fredrikstad in 2019, focusing on planktonic algae and cyanobacteria. The findings are compared to data from previous years. The Norwegian Food Safety Authorities’ guidelines for drinking water and NIVA’s proposed environmental objectives and class limits for physico-chemical parameters in lakes and rivers (Solheim et al. 2008) are taken into account in the evaluation of the results. In addition, the Norwegian guidance for ecological classification of waters (Veileder 02:2018, Direktoratsgruppa, Vanndirektivet 2018) is used to classify the ecological status of Vestvannet and Borredalsdammen. The concentrations of the nutrients nitrogen and phosphorus have been relatively stable over the the last years. The algal biomass and chlorophyll A concentrations have increased in Vestvannet in 2019 compared to 2018. The same parameters have decreased in Borredalsdammen, compared to 2018. No substantial changes were observed in any of the parameters measured, including algal composition, on either the short or long term. Most of the algal community consists of species that are common in lakes in Østfold county, and these are not toxin producers. Microcystin were detected in low concentrations in Borredalsdammen and Vestvannet in August 2019, and the biomass of cyanobacteria was generally low in both lakes. Lake Vestvannet and Borredalsdammen are classified to good ecological status by the Water Framework Directive guidelines, and both lakes are considered suitable for drinking water with regards to microcystin. In a total assessment of the lakes’ suitability as drinking water, both are considered poor, due to high concentrations of phosphorus in Vestvannet and phosphorus and chlorophyll in Borredalsvannet. However, as FREVAR performs extensive treatment of the water, there is still potential for delivering good quality drinking water.