PHYSICAL AND CHEMICAL CONTROLS ON PARTICULATE MERCURY IN A FORESTED HEADWATER CATCHMENT

Mercury, atmospherically deposited onto terrestrial surfaces, can be mobilized during storm events and transported to streams. High-flow events account for the majority of total mercury export from watersheds in streamwater. It is important to understand particulate as well as dissolved mercury dynamics because different chemical properties, affecting the availability for methylation, and physical properties, affecting transport mechanisms, may result in very different downstream fates. Our study location is Staunton River in Shenandoah National Park, Virginia, where monitoring has revealed that streamwater mercury is dominated by the particulate fraction. This study aims to determine if a relationship exists between total suspended solids (TSS), specifically the organic fraction (particulate organic carbon), and particulate mercury. We aim to establish a predictive relationship between particulate organic carbon and TSS, and ultimately between TSS and particulate mercury. Additionally, we will determine if an in situ turbidity sensor could be used to estimate particulate mercury fluxes, using turbidity as a proxy for TSS, which will allow for a high temporal resolution estimates of particulate mercury concentrations. Starting October, 2009 we have measured particulate mercury and TSS (both the inorganic and organic fractions), over a range of discharge. Concurrently, an in situ multi-parameter water quality sonde has collected turbidity measurements on an hourly basis. This analysis will allow us to determine how discharge and the mineral and organic suspended solids affect particulate mercury dynamics in this watershed.