Sulfur cycling in a dutch moorland pool under elevated atmospheric S-deposition

Abstract

Atmospheric S deposition, sulfate reduction and the accumulation of reduced S components were investigated in sediments of a Dutch moorland pool. Laboratory ³⁵SO42− tracer experiments indicated that the variation in reduction rate with depth in the sediment could be described by an exponential fit, suggesting first order kinetics. Sulfate reduction rates calculated from a kinetic transport model were highest in June and July (>0.6 mmol m⁻² day⁻¹), and decreased towards the end of the summer (<0.2 mmol m⁻² day⁻¹). Winter reduction rates were low, but increased towards the beginning of the spring. Concentrations of total, organic and inorganic S decreased with depth, consistent with an increasing depositional flux of S over the last century. Increased atmospheric sulfate deposition rates and consumption in the upper sedimentary layers caused a continuous increase in subsurface S concentrations. Present day S-immobilization rates were estimated between 25 to 30 mmol S in⁻² yr⁻¹, in the order of the annual input of S from wet atmospheric deposition. Sulfate metabolism in anaerobic moorland pool sediments may be the most important mechanism of long-term S-accumulation.