Publication

Summary

The report sums up the results of the operational monitoring of the river Glomma at Borregaard industries in Sarpsborg, conducted by NIVA during 2016. Using heterotrophic growth as quality element (measured by the indices HBI and the improved version HBI2) showed that the vannforekomst achieved poor or bad ecological status. The status recorded this year is in line with the surveys reported during the past years. Data on CODMn revealed no differences between the reference station upstream Borregaard and stations further downstream. BOD7 was mapped in August from ten different stations, and we recorded a weak increase from the reference site upstream, but the data could not be specifically related to the known pollutant discharge points along the stretch. 44 juvenile salmons were sampled on station 5 “grusørene”, and densities of salmon is assumed to be in line with previous two years, and the density has clearly increased since the years 2009-2010. Most fish were untagged and hence associated with natural spawning. Oxygen concentration in sediments and gravel around station 5 was generally below the assumed minimum levels needed by salmon eggs, but showed significantly increased levels in a fresh spawning pit, indicating that spawning itself could possibly improve egg survival. – Recommendation for possible follow up monitoring activities are given.