Diffuse sources dominate the sulfate load into Finnish surface waters

Petri Ekholm; Jouni Lehtoranta; Maija Taka; Tapani Sallantaus; Juha Riihimäki

doi:10.1016/j.scitotenv.2020.141297

Diffuse sources dominate the sulfate load into Finnish surface waters

Sci Total Environ. 2020 Dec 15:748:141297. doi: 10.1016/j.scitotenv.2020.141297. Epub 2020 Jul 28.

Authors

Petri Ekholm¹, Jouni Lehtoranta², Maija Taka³, Tapani Sallantaus², Juha Riihimäki²

Affiliations

¹ Finnish Environment Institute, Finland. Electronic address: petri.ekholm@environment.fi.
² Finnish Environment Institute, Finland.
³ Water and Environmental Engineering, Aalto University, P.O. Box 15200, FI-00076 Aalto, Finland; Department of Geosciences and Geography, University of Helsinki, P.O. Box 64, FI-00014 University of Helsinki, Finland.

PMID: 33113678
DOI: 10.1016/j.scitotenv.2020.141297

Abstract

Sulfate (SO₄^2-) affects the cycling of ecologically important substances, such as carbon, nutrients and metals, but the contribution of anthropogenic activities in sulfate load entering aquatic systems is poorly known. We calculate specific sulfate loads for land cover types, atmospheric deposition and point sources, and then estimate the source-specific flux of sulfate to Finnish surface waters. The largest sulfate flux, entering mostly the Baltic Sea, originates from agricultural fields on acid sulfate soil (24% of total flux). Forests on mineral soil, which cover 67% of the country's surface area, form the second largest source (21%). Additionally, agricultural fields on non-acid soil cause noticeable sulfate flux (16%). Pulp and paper mills were the key point sources (20%) for sulfate. We find that anthropogenic activities contribute to elevated sulfate levels in waters potentially affecting the cycling of nutrients, metals and formation of greenhouse gases in naturally sulfate-poor freshwaters. Based on these findings, sulfate should be systematically included in monitoring and pollution control measures.

Keywords: Baltic Sea; Biogeochemistry; Eutrophication; Lakes; Monitoring; Water quality.