Monitoring of watercourses in connection to the Larvikitt quarries in the Larvik area. Results from the sampling of the macroinvertebrates in 2014

Summary

The macroinvertebrate indices that are normally used to indicate acidification (Raddum 2) and pollution load (nEQRof ASPT) may be unreliable for many of the stations in this study since the macroinvertebrate communities are reduced due to a dominance of fine sediment particles in the bottom substrate. This applies also to the reference stations, which appear to be in the same status as the affected stations. All locations, including the reference locations, are classified as being in a poor or bad ecological status based on the nEQR. Despite the nEQR possibly being unreliable, the overall impression from the stations is a generally poor ecological status. The proportion of filter feeders appears to be reduced in the stations being affected by runoff from the quarries relative to the reference stations. These results are uncertain but indicate a possible negative effect of the quarries.