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Characterizing mercury concentrations and flux dynamics in a coastal plain watershed using multiple models and data
Citation:
GOLDEN, H. E., C. D. KNIGHTES, P. Bradley, G. Davis, T. Feaster, S. Benedict, C. Journey, P. Conrads, AND M. Brigham. Characterizing mercury concentrations and flux dynamics in a coastal plain watershed using multiple models and data. Presented at 10th International Conference on Mercury as a Global Pollutant, Halifax, NS, CANADA, July 24 - 29, 2011.
Impact/Purpose:
The EPA Office of Water has recognized a critical need for states and federal agencies to be able to quantitatively assess the condition of the Nation’s wetland resources. Currently, >85% of states, tribes, and territories are lacking even rudimentary biological assessment methodologies for wetlands. Additional important needs identified include obtaining base line nutrient and physical/chemical conditions to aid in understanding the role of wetland systems (isolated wetlands in particular) in ensuring aquatic life and beneficial uses of lakes, rivers, and streams in the watershed. To address these challenges, the following research on isolated wetlands is proposed: Within a region, 1) Develop a probabilistic sampling design that stratifies isolated wetlands by type and size (also targeting reference conditions); 2) Collect biotic data using macroinvertebrates, macrophytes, and diatoms; 3) Collect abiotic (water and soil chemistry) data to establish base line conditions, quantify wetland contribution to landscape nutrient dynamics, and establish a spectral library for future rapid assessment of nutrient sequestration abilities of isolated wetlands; 4) Assess wetland condition with Level 1 (geographic information systems - GIS) and Level 2 (rapid assessment) characterization methods; 5) Develop metrics and correlate biotic signature to local and landscape assessments; 6) Report on the condition of systems across region and recommend assessment methods to states and tribes; 7) Model isolated wetland contribution to landscape nutrient dynamics based on analyses using visual and near-infrared spectrometer (VNIRS) data. Key outputs for regions and states from the proposed research include: tools for remote GIS-based assessment, tools for rapid on-site assessment, and tools for intensive biological assessment of isolated wetlands; comparison between local and landscape assessment measures; functional assessment of isolated wetland contribution to landscape nutrient dynamics (using VNIRS); baseline water and soil physical/chemical conditions; baseline flora and fauna of isolated wetland systems; and a fuller understanding of watershed condition and regional environmental health.
Description:
Mercury-related fish consumption advisories are widespread in the coastal plain of the southeastern U.S., where atmospherically deposited mercury interacts with an abundance of wetlands and high-dissolved organic carbon (DOC), acidic waters. Recent trends in decision making processes require knowledge of mercury cycling at a variety of spatial scales (e.g., mesoscale watersheds, regions) and within diverse land cover types to better understand and manage the effects of this challenging water quality issue. Watershed models are primary tools for advancing questions related to such ecological exposure research. Spatially explicit process based watershed models can (1) improve spatial and temporal linkages between controls on environmental processes and subsequent water quality when observational studies are limited, and (2) predict future changes in surface waters by using mathematical formulations. However, the science of spatially explicit watershed scale mercury modeling is just beginning to emerge and most approaches have not been applied in mixed land cover, coastal plain watersheds. In response to this gap in current knowledge, we quantify total mercury concentrations (HgT) and fluxes from McTier Creek Watershed, South Carolina, USA, using three novel independently developed watershed mercury models (a grid based watershed mercury model (GBMM), the VELMA-Hg model, and the TOPMODEL-Hg model) and measured in-stream HgT concentrations and fluxes. The study watershed is located in an upper coastal plain landscape, an area with more diverse land cover, a larger drainage area, and a different geophysical setting than many previous sites of mercury research in North America, i.e., small forested headwater boreal or northern forested catchments. Therefore, we aim to improve the characterization of mercury cycling in coastal plain watersheds, identify important watershed processes influencing total mercury loadings to surface waters on daily and seasonal time scales, and advance the developing science of watershed-scale mercury modeling. Based upon our understanding of the diverse mercury dynamics represented within each model, simulated HgT fluxes at the watershed outlet using these models, and observed HgT data, this study moves toward our goals.