Operational monitoring of waters in connection to the larvikite quarries in the Larvik area in 2019.

Summary

Macroinvertebrate samples were collected from brooks affected by the quarries in Tvedalen and Tjølling in 2019. Samples were collected from previously established, and new, stations. The stations are placed such that they will show effects of fine sediments in runoff from the quarries. Reference stations that are little affected or unaffected by runoff from the quarries are also included. The PSI index (Proportion of Sediment-sensitive Invertebrates) is used in Great Britain in rivers affected by particulate material and fine sediment. The index has now been used to monitor runoff from quarries in the Larvik area since 2017. The last years of data indicate that the PSI-index respond satisfactory to particle runoff and provides valuable information about the effect of sedimentation on macroinvertebrates. The results from 2019 shows that several of the quarries (Vevjeåsen, Tvedalen vest, Håkestad, Stålåker and Skallist) do not have a clear negative effect on macroinvertebrates, but some quarries (Tvedalen towards Askedalsbekken and Klåstad towards Klåstadbekken) have a negative effect (more than at the reference stations). The negative effects of fine particulate runoff from these two quarries have diminished after the establishment of sedimentation dams, which has reduced the runoff of particulate matter. The stations by the quarries Aak and Saga Pearl also shows negative effects, but it is unsure whether this is a result of runoff from the quarries or something else. It has been difficult to find unaffected reference stations with a high enough and stable water flow in the area, and many reference stations are also affected by other sources than the quarries (e.g. agriculture). None of the stations, including the reference stations, are classified as good or better ecological status according to the ASPT-index (Average Score Per Taxa). The macroinvertebrate communities show signs of organic pollution and it is apparent that there are other sources than quarries that affect them. Especially the eastern area, Tjølling, is severely affected by farming (and potentially sewage). The extent to which runoff from the quarries affect the macroinvertebrate communities have varied considerably between sites and years, and we recommend that future monitoring is planned based on the results presented in this study.