Mercury methylation in high and low-sulphate impacted wetland ponds within the prairie pothole region of North America

Using enriched stable Hg-201 injections into intact sediment cores, we provide the first reported Hg methylation potential rate constants (k(m)) in prairie wetland ponds (0.016-0.17 d(-1)). Our k(m) values were similar to other freshwater wetlands and did not differ in ponds categorized with high compared to low surface water concentrations of sulphate. Sites with high sulphate had higher proportions of methylmercury (MeHg) in sediment (2.9 +/- 1.6% vs. 1.0 +/- 0.3%) and higher surface water MeHg concentrations (1.96 +/- 1.90 ng L-1 vs. 0.56 +/- 0.55 ng L-1). Sediment-porewater partitioning coefficients were small, and likely due to high ionic activity. Our work suggests while k(m) measurements are useful for understanding mercury cycling processes, they are less important than surface water MeHg concentrations for assessing MeHg risks to biota. Significant differences in MeHg concentrations between sites with high and low sulphate concentrations may also inform management decisions concerning wetland remediation and creation. (C) 2015 Elsevier Ltd. All rights reserved.