Oligotrophication-driven shifts in benthic primary producer assemblages and their cyanotoxin potential

Sammanfattning

Climate change and arctic greening are driving oligotrophication in arctic/alpine lakes by reducing nitrogen (N) and phosphorus (P) inputs. Benthic biofilms are underinvestigated in Swedish lake monitoring, despite their ecological importance. As oligotrophication intensifies, benthic assemblages are expected to shift towards N2-fixing cyanobacteria, affecting food-web trophic transfers and local cyanotoxin exposure. This study compared water chemistry, biofilm primary producer assemblages, toxin gene abundances, cyanotoxin concentrations, and macroinvertebrate bioaccumulation across 13 Swedish lakes in three regions (Uppland, Jämtland, and Norrbotten) using water chemistry analysis, microscopy, quantitative polymerase chain reaction (qPCR), and liquid chromatography tandem mass spectrometry (LC-MS) to investigate latitudinal and water chemistry gradients. The Arctic/alpine lakes (Norrbotten and Jämtland) were found to have lower dissolved organic carbon (DOC) and total phosphorus (TP) compared to the boreal lakes (Uppland). Furthermore, the Arctic/alpine lakes were observed to have twenty times larger average littoral biofilm biovolume, higher relative abundance of N2-fixing cyanobacteria, and a higher bioaccumulation of anatoxin-a in macroinvertebrates than boreal lakes. On the other hand, boreal lakes were observed to have a higher bioaccumulation of microcystins than Arctic/alpine lakes. These findings highlight that littoral benthic habitats are a hotspot for cyanotoxin exposure in oligotrophic Arctic/alpine lakes, emphasising the need to implement more thorough benthic sampling into national monitoring programs. The implementation of more precise national lake monitoring protocols will allow for better early warning signals for potential cyanotoxin exposure in Swedish lakes as climate warming progresses.