Diffuse sources dominate the sulfate load into Finnish surface waters.

Area of Science:

• Environmental Chemistry
• Ecosystem Science
• Water Quality Management

Background:

• Sulfate (SO₄^2-) is crucial for biogeochemical cycles of carbon, nutrients, and metals.
• The impact of human activities on sulfate loads in aquatic systems remains understudied.
• Naturally sulfate-poor freshwaters are particularly sensitive to sulfate enrichment.

Purpose of the Study:

• To quantify source-specific sulfate fluxes to Finnish surface waters.
• To identify the contribution of different land cover types and point sources to sulfate loading.
• To assess the implications of anthropogenic sulfate on aquatic ecosystems.

Main Methods:

• Calculation of specific sulfate loads based on land cover, atmospheric deposition, and point sources.
• Estimation of source-specific sulfate flux to Finnish surface waters.
• Analysis of the contribution of different sources to the total sulfate flux.

Main Results:

• Agricultural fields on acid sulfate soils are the largest source of sulfate flux (24%), predominantly to the Baltic Sea.
• Forests on mineral soils contribute the second-largest flux (21%).
• Pulp and paper mills are significant point sources (20%), and agricultural fields on non-acid soils contribute 16%.

Conclusions:

• Anthropogenic activities substantially elevate sulfate levels in Finnish waters.
• Increased sulfate can alter nutrient cycling, metal mobility, and greenhouse gas formation in freshwaters.
• Systematic inclusion of sulfate in monitoring and pollution control is recommended.