Increased carbon and nitrogen concentrations in boreal forested catchments

Brownification of waters is a threat to aquatic ecosystems over large areas in Europe. A new paper links increasing concentrations of dissolved organic carbon to climate, deposition, and land-use, and the complex interactions between them.

The authors studied 12 small forested headwater catchments in Finland, with monitoring records from 1990 to 2019. The catchments had a large gradient of climate and deposition. In almost all of them, total organic carbon concentrations increased in the 30-year period. The mean air temperature and change in sulphate concentrations had a strong, significant correlation to the change in total organic carbon (TOC).

The authors point out that although sulphate is still detected in the streams, it is becoming less important for TOC leaching, whereas the impact of climate warming as a driver of TOC leaching will be even more pronounced in the future.

Less attention has been given to changes in total organic nitrogen concentrations, even though carbon and nitrogen losses are highly related to each other. The authors found a positive correlation between percentage of area with drainage and increases in total organic nitrogen, which suggests that also land management is important for the losses of organic material. Total organic nitrogen trends were connected to changes in TOC, but not directly linked to decreasing sulphate deposition.

Lepistö, A., A. Räike, T. Sallantaus, L. Finér, 2021. Increases in organic carbon and nitrogen concentrations in boreal forested catchments — Changes driven by climate and deposition. Science of The Total Environment, Vol 780, 146627, https://doi.org/10.1016/j.scitotenv.2021.146627.