ABSTRACT
Elevated concentrations of nutrients and mercury (Hg) make Steamboat Creek (SBC) the most polluted tributary of the Truckee River. Since wetlands are considered cost-effective, reliable, and potential sites for methylmercury (MeHg) production, a small-scale wetland system was constructed and monitored for several years in order to quantify both nutrient removal and transformation of mercury. Results indicated seasonal variations in nutrient removal with 40-75% of total nitrogen and 30-60% of total phosphorus being removed with highest removals during summer and lowest removals during winter. The wetland system behaved as a sink for MeHg during the winter months and as a source for MeHg during summer months.
Subject(s)
Environmental Monitoring/methods , Mercury/isolation & purification , Water Purification/methods , Wetlands , Equipment Design , Methylmercury Compounds/isolation & purification , Nitrogen/isolation & purification , Phosphorus/isolation & purification , Seasons , Water Movements , Water Pollutants, ChemicalABSTRACT
Mercury associated with natural enrichment, historic mining, and ore processing is a contaminant of concern in watersheds of the western USA. In this region, water is a highly managed resource and wetlands, known to be important sites of methyl mercury production, are often an integral component of watersheds. This study applied controlled manipulations of four replicated experimental wetland designs with different water and soil mercury concentrations to determine the potential impacts on methyl mercury export. Wetlands were manipulated by drying and wetting, changing hydraulic retention time, and adding sulfate and nitrate to influent waters. In a summer drying and wetting manipulation, an immediate increase in total methyl mercury release was observed with rewetting, however, concentrations decreased quickly. Drying all wetlands over the winter and rewetting in the spring resulted in high net methyl mercury output relative to that observed before drying. Net methyl mercury output was not influenced by changes in hydraulic retention time from 4 to 8 h or to 30 min, or by increasing the nitrate concentration from 0.1 to 10 mg L(-1). The addition of sulfate to the inlet waters of two mesocosms to increase concentrations from approximately 100 to 250 mg L(-1) did not result in a clear effect on methyl mercury output, most likely due to sulfate concentrations being higher than optimal for methyl mercury production. Despite the lack of response to sulfate amendments, the change in sulfate concentration between the inlet and outlet of the mesocosms and temperature were the parameters best correlated with methyl mercury outputs.
