Incubation success of brown trout (Salmo trutta) eggs in boreal humic rivers affected by peatland drainage

Effects of peatland drainage on the incubation success of brown trout (Salm o trutta L.) eggs placed inside gravel-filled boxes were studied in two bor eal humic rivers in northern Finland. The survival was 53-84% at the eyed e gg stage and as low as 0.2-9.1% at the pre-emergence stage, depending on th e site. The lowest survivals were recorded at sites affected by peatland dr ainage. The survival was inversely related to particulate matter and Fe loa ding from drained peatlands. The results indicate that the increase in the Fe content of high molecular weight dissolved organic matter transported to rivers followed by its precipitation and sedimentation on the river bed ma y be a crucial factor in weakening the conditions for salmonid reproduction downstream of peatland drainage areas.