Historiske og fremtidige endringer i løst organisk karbon i Farrisvann

Abstract

I denne rapporten analyserer vi med bruk av sedimenter og modellering historiske og fremtidige trender i organisk karbon Farrisvann. Vi har brukt en historiske sediment-rekonstruksjon fra en representativ referansesjø, lange dataserier for Farrisvann, klimascenarier for den aktuelle regionen i Norge, samt den nyeste vitenskapelige dokumentasjonen på karbondynamikk i nedbørfelter for å modellere fremtidige endringer i konsentrasjoner av organisk karbon frem til 2050. Modellprediksjonene viser at konsentrasjonene av organisk karbon i Farrisvann kan fortsette å øke med den samme takten som overvåkingsdataene har vist fram til i dag. Vi anbefaler de ansvarlige for vannbehandlingsanleggene å forvente videre økning i organisk karbon og vannfarge også i tiden fremover.

The aim of this project was to provide historical and future changes in organic carbon (OC) for Farrisvann using sediment reconstructions and simple modelling tools. Sediment cores were taken from the lake in 2016 and dated using Pb dating, attempts were made to reconstruct historical OC (VNIRSmethod) but sediment geochemistry showed that redox reactions controlled the sediment profile and OC reconstructions could not be trusted.

We used data from another Norwegian lake, long-term monitoring data available for Farrisvann and the most novel scientific knowledge to the model future changes in OC concentrations until 2050. We predicted the future changes in OC using different scenarios based on historical sediment reconstructions, monitoring data, and scientific literature.

We predict that concentrations of OC in Farrisvann could continue to increase at the same rate as the monitoring data has shown due to increases in precipitation predicted by the climate models for Norway. It is unlikely that a combined acidification and climate signal will drive OC concentration in the future as the recovery from acidification has been substantial. As we were not able to reconstruct historical OC for Farrisvann, we cannot estimate how much OC changed during acidification. We recommend the water treatment plants to expect further increases and browner waters in Norway in the future