Investigation of factors affecting gaseous mercury concentrations in soils

The purpose of this study was to determine the effects of soil temperature, soil moisture, redox potential (Eh) and soil organic matter (SOM) on the total gaseous mercury (TGM) concentrations in background soils. Our measurements were made in a grass field and deciduous forest at the Piney Reservoir Ambient Air Monitoring Station (PRAAMS) in Garrett County, Maryland. Three plots in each area were sampled every third week from July 2009 to June 2010 at the Oe-A soil horizon interface, the A-E soil horizon interface, and 5 and 10 cm into the E soil horizon. The mean soil TGM concentration for all depths in the forest (2.3 ± 2.2 ng m(-3)) was significantly higher than the mean soil TGM concentration in the grass field (1.5 ± 1.9 ng m(-3)). Soil TGM at all depths was most strongly and consistently correlated to soil temperature. The soil TGM concentrations were highest and most variable at the forest Oe-A soil horizon interface (4.1 ± 2.0 ng m(-3)), ranging from 1.5 to 8.4 ng m(-3). This soil horizon interface had 11 to 26% more SOM and the soil Eh was 100 to 400 mV lower than the other soil depths. Our results suggest that soil temperature, soil Eh and SOM are significant factors affecting TGM concentrations in forest soils. Future studies of TGM dynamics in background soils may benefit from closely monitoring the organic soil horizon.