Biogeochemistry of Coal-Fired Power Plant Receiving Waters: Tracing Surficial Metalloid Contamination

This is a capstone study of three metalloids - germanium (Ge), arsenic (As) and selenium (Se) - in natural surficial aquatic systems of the Southeastern U.S. This study is based on 17-years of Ge data from rivers and coal-fired power plant receiving waters. These data demonstrate that anthropogenic Ge-input due to coal combustion is several orders of magnitude above natural background on both local and global scales. Because the systematics of Ge volatilization and release from coal-fired power plants are similar to a suite of toxic metalloids (As, Se, Sb), Ge is a potentially valuable monitor for the release and dispersion of these important trace elements in the environment. In addition, because Geâs biogeochemistry during surficial processes is similar to silicon (natural weathering of silicate rocks and soils; diatom Si-uptake and dissolution), natural background Ge-cycling in these waters can be accurately corrected for with Ge/Si ratios, eliminating the complexities inherent in separating natural from anthropogenic processes. We thus propose to test the proposition that Ge/Si enrichments can be used to quantify As and Se enrichments in natural waters from coal combustion, and to clarify the complexities of speciation changes involved in the redox and biomethylation cycling of these two elements during downstream spiraling.

This will be a two-year masters-level graduate study to measure Ge, As and Se concentrations and speciation in rivers receiving ash pond effluents, especially those where power companies have converted to dry ash disposal in attempts to reduce As and Se release. We will establish the extent to which stack-gas release carries volatile Ge, As and Se into the atmosphere. Groundwater monitoring and suspended sediment determinations along streams above and below power plants will help elucidate solid phase partitioning at elevated Ge/Si ratios encountered in contaminated rivers, and the importance for suspended materials in transporting contaminants downstream. We will also test whether the Ge, As and Se contents of shells collected along the length of the Chattahoochee- Apalachicola River reflect the current downstream Ge/Si gradient, from upstream of (pristine) and below Atlanta (below a cluster of power plants with very high riverine Ge/Si ratios) to the mouth of the Apalachicola River (Apalachicola Bay, FL), where Ge/Si ratios are elevated only 10-fold above natural background. Analyses of oyster, mussel and clam shells from around Apalachicola Bay (Indian mounds) will permit us to compare current contaminant levels with pre-anthropogenic levels, and oyster shells preserved by the Apalachicola National Estuarine Research Reserve (collected by oystermen since 1948) will provide a time history of more recent contamination.

The broader environmental context of this work is its potential to contribute to a better understanding of contributions of power plants to riverine burdens of metalloids and their downstream biological transformations, to provide a time history of enrichments in one important marine fishery downstream of a large coal-fired power grid, and provide basic information for environmental planners and regulators concerning toxic metal transport by rivers and streams and the efficacy of dry ash disposal.

below deck photo