Wood ash and dolomite treatments of catchment areas: Effects on mercury inrun-off water

The planned restoration of the mineral nutrient balance in forest soils by recycling wood ashes has led to environmental concern. The objective of thi s study was to determine whether treatment of forest soil with granulated w ood ash and dolomite led to changes in the export of total mercury (TotHg) and methyl mercury (MeHg) in run-off, and to determine whether any observed changes could be correlated to changes in dissolved organic carbon (DOC) a nd/or H+ concentration. Three catchments in central Sweden were investigate d: one treated with wood ash, one with dolomite and one control. Samples of run-off water from the three catchments were taken weekly or monthly durin g 1 yr with the higher sampling frequency during high water flow periods. T otHg, MeHg, pH and DOC were measured in all samples. MeHg and TotHg as well as H+ and DOC in run-off water were lower in the limed area in comparison to the other two areas. TotHg varied between 1 and 10 ng l(-1) in all three areas. The average concentration in run-off from the limed area was 67% of that from the reference catchment. TotHg in the ashed and reference areas were not significantly different (p > 0.1). TotHg covaried with DOC and wat er supply (both run-off and rainfall) and inversely with pH. TotHg concentr ations in run-off were determined by the leaching of Hg-containing DOG. Dec reased pH probably increased the leakage of Hg-loaded DOC from the soils. M eHg was 0.1-0.3 ng l(-1) in the limed area and 0.2-112 ng l(-1) in the othe r two areas. The average concentration in the limed area was 31% of the ave rage in the reference area. MeHg covaried with DOC and temperature, indicat ing that microbial activity was the most important factor determining MeHg in run-off.