Higher long-term nutrient losses from forestry drainage than previously believed

With the emerging bioeconomy it is important to understand how forestry drainage affects nutrient losses. A new paper has used long-term data to assess export at different spatial scales in Finland. The authors found that long-term impacts of forest drainage are much higher than previously estimated. Hence, drained areas of forests are hotspots for the export of total nitrogen, total phosphorus and total organic carbon (TOC).

The authors formulated statistical equations based on a large, long-term runoff and streamwater quality dataset, which was collected from 28 pristine and 61 managed boreal forest catchments located around Finland. They concluded that forest management contribute to 17% of the total nitrogen export from forests, 35% of the phosphorus export and 12% of the TOC export, respectively. This is more than two times higher than previous estimates of nitrogen and phosphorus exports. The differences may be explained by the long-term impacts of forest drainage.

It was also found that the concentrations increased with temperature, in other words, they increased from north to south. Nitrogen, phosphorus and TOC concentrations increased with the proportion of drained areas in the catchment. Nitrogen and TOC also increased with the proportion of peatlands. Whereas nitrogen and TOC increased over time, P concentrations showed a decreasing trend over the last few decades.

The results indicate that drained peatland forests are hotspots for nutrient and TOC export, especially in the river basins draining to the Gulf of Bothnia.

Finér, L. Lepistö, A. Karlsson, K. Räike, A. Härkönen, L., Huttunen, M. Joensuu, S., Kortelainen, P. Mattsson, T., Piirainen, S., Sallantaus, T., Sarkkola, S. Tattari, S. Ukonmaanaho, L. 2021. Drainage for forestry increases N, P and TOC export to boreal surface waters. Sci. Tot. Environ. Vol 762, 2021, 144098, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2020.144098.

Feature photo by Maria Rajakallio.