Sampling of sulfate soil in Södra Sunderbyn, outside Luleå.
23 January 2026
Acid sulfate soils pose increasing environmental risks in northern Sweden
Acid sulfate soils can alter water and soil chemistry, affect biodiversity, and cause infrastructure problems. A new doctoral thesis from Luleå University of Technology provides detailed insights into how these soils behave when exposed to oxygen, and how metals and acidity are released during weathering. The findings offer important knowledge for environmental management and land-use planning in coastal regions.
When waterlogged, sulfate-bearing sediments are harmless. But once exposed to oxygen, sulfide minerals begin to oxidize. Federico Alvarellos, who recently defended his dissertation in applied geochemistry, investigated two acid soil profiles in Södra Sunderbyn using geochemical analyses, advanced mineralogical methods and incubation experiments.
“Even short exposure to oxygen triggers rapid oxidation of framboidal pyrite, that is iron disulfide. This leads to the formation of sulfuric acid and releases metals such as copper, nickel and zinc into the soil and groundwater,” said Federico Alvarellos.
The oxidized zones showed low pH, formation of secondary iron minerals such as jarosite and iron hydroxide, and high concentrations of mobilized elements including cadmium, copper, manganese, molybdenum and nickel.
Groundwater responds to seasonal changes
Groundwater levels fluctuate throughout the year, altering the redox conditions that control oxidation processes. During low-water periods, metal concentrations increased significantly in the oxidized profile due to sulfide oxidation.
“When the water table drops, oxygen reaches deeper into the soil and oxidation accelerates. During high-water periods, secondary minerals dissolve and more elements are mobilized. This seasonal cycle increases the environmental risk,” said Federico Alvarellos.
Implications for planning and environmental protection
Acid sulfate soils are a global issue. In northern Sweden, glacial isostatic uplift exposes new sulfide-bearing sediments every year, intensifying the challenge.
“To limit acid generation and metal release, sulfide-bearing sediments must remain waterlogged or be handled with great care. Our results show how rapidly chemical conditions can change,” said Federico Alvarellos.
The research provides valuable knowledge for municipalities, planners and environmental agencies working in areas affected by sulfate-rich sediments.
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