Gary Speiran has conducted studies of the hydrology and chemistry of a variety of hydrologic systems including streams, lakes, shallow and deep groundwater, and wetlands. Recently, he studied the groundwater chemistry of riparian forest buffers. His current studies include the effects of hydrology and water-chemistry on wetland forest ecosystems and carbon budgets in the Great Dismal Swamp and the effects of sea-level rise on groundwater levels and chemistry as they affect ecosystems and archaeological and cultural resources of Jamestown Island, Virginia.