Biologisk recipientkontroll vid Södra Cell Värö: årsrapport för 2021

Södra Cell Värö is a pulp mill with production since 1971. The composition of substances in the process water has changed over the years, and in this report, the environmental impact of the mill’s continuous operations have been investigated. The foremost focus of the report has been the surrounding marine ecosystem of the recipient area of Värö and of the reference area, Ustö. The monitoring of the mill’s environmental impact began in 1983, and has since then been conducted on an annual basis. The monitoring surveys includes analysis of the potential impacts of the mill’s damming of River Viskan on the upstream migration of juvenile eel, the status of the fish and invertebrate community in the recipient over time, and the potential impacts of the emission from the mill´s outlet pipe on the surrounding seafloor. The migration of juvenile eel has been monitored by collecting juvenile eel from an eel conductor during April to September, while the fish and invertebrate community has been monitored using bottom trawling during September, both in the recipient area, Värö, and in the reference area Ustö. The number of fish caught during trawling, species abundance, species diversity, and mean trophic level, were analyzed and compared between Värö and the reference area Ustö over time. The effects of the emissions from the outlet tube of Södra Cell Värö on the surrounding seafloor has been monitored by underwater filming followed by visual analyses. During the filming in 2021, only a few sessile species were observed growing on the tube, and white spots on the seafloor indicating anoxic conditions were observed in the area closest to the tube. The abundance of migrating juvenile eel has decreased over time since the monitoring started, but slightly increased levels can be seen during the past eight years. However, changes in abundance of juvenile eel over time is most likely linked to large-scale trends in the European eel recruitment, rather than by operations at Södra Cell. The fish and invertebrate community around Värö is monitored through yearly trawl fishing, both in the waters outside Värö, and in a reference area, Ustö. The total catch of fish has decreased over time in the reference area Ustö, but not in the recipient area Värö. The number of fish species caught has increased in both of the monitored areas. Both the total catch of invertebrates and the number of invertebrate species has increased over time in Värö and in Ustö. No significant difference in catch over time was observed when comparing the two areas. In 2021, the diversity of species was slightly higher in Värö than in the reference area Ustö. No significant trends regarding changes in the trophic level were observed in or between the areas, and the trophic level was strongly influenced by the high abundance of the dominant species, dab. The individuals of plaice in the catch 2021 were small. Cod abundance has decreased in both areas, and the individuals caught were small and potentially juvenile. All caught fish were inspected for external symptoms of disease and deformity but none were found.