Monitoring of The Rusvik Brook, Recipient for filter back wash water from drinking water membrane filters.

Summary

The study of periphyton and bottom animals showed that both the Rusvik brook and the reference brook were heavily impacted by acidification. This is mostly natural acidification and is not an impact from the water treatment plant. The temperature in the Rusvik brook was a little un-normal, with too low temperature in the summer and too high during winter. This is due to the brook being fed by lake water from 13 m depth. The periphyton indicated only low impact from organic loading. The organic loading could not be evaluated by the use of benthic animals, as the ASPT-index is not calibrated for such small brooks. However, the biodiversity of EPT-species (Ephemeroptera, Plectoptera, Trichoptera) were much lower in the Rusvik brook than in the reference brook and it looks like it is “something” that is stressing the fauna, which we, however, have not been able to detect in the water quality analyses. It is necessary to continue the monitoring one more year, and also include water samples during the period when the filter wash water plume is running through the brook. This is necessary to be able to evaluate the needs for abatement measures.