Distribution and Transport of Mercury into Jordan Lake, North Carolina

ABSTRACT

Jordan Lake, located in central North Carolina, is currently under consideration as a source of drinking water for communities in the surrounding area. A number of streams that discharge into the lake receive considerable industrial and municipal wastewater effluent, of which the toxic metal mercury is of particular concern. Stream samples, coinciding with low and high flow events, were collected and analyzed for dissolved and particulate total mercury. Mercury loading was estimated from flow-weighted mean concentrations and mean stream flow data. Results indicated that total dissolved mercury concentrations decreased with increasing flow, dilution effects, and that total particulate mercury concentrations decreased sharply with increasing suspended loads. This decrease was attributed to changes in particle size distribution. In addition, variability in particulate mercury concentration decreased dramatically with increased flow. Total mercury concentrations ranged from 54 ng/L to 195 ng/L (mean = 127 ng/L, n = 168). Approximately one-half of the 136 kg/yr of mercury transported to the lake was associated with the suspended fraction, 52 to 65 percent during high flow and 43 to 57 percent during low flow conditions. Greater than 90 percent of the mercury loading into Jordan Lake occurs during high flow events because of heavy suspended solids loading.