The impacts of dam construction on elemental deposition in a reservoir receiving mountaintop coal mining materials

Abstract Waters MN, Bernhardt ES, Gerson JR. 2023. The impacts of dam construction on elemental deposition in a reservoir receiving mountaintop coal mining materials. Lake Reserv Manage. 39:246–258. Dam construction and associated reservoirs can become depositional basins capable of concentrating material inputs from human-altered landscapes. Landscape disturbances such as agriculture and urban expansion have been shown to impact erosional processes into reservoirs, whereas less is known of material originating from intense mining operations. Mountaintop mining (MTM), a prevalent form of surface coal mining in the Central Appalachian ecoregion of the United States, can impact stream ecosystems by altering flows, conductivity, and associated elements. We applied paleolimnological techniques to determine depositional impacts in the Mud River Reservoir downstream of the Hobet Mine, West Virginia, the largest surface mine complex in the United States. Paleolimnological measurements included carbon (C), selenium (Se), sulfur (S), magnesium (Mg), phosphorus (P), nitrogen (N), calcium (Ca), and photosynthetic pigments. Our study focused on 3 primary objectives: (1) determine the materials associated with MTM that are stored in the sediment, (2) calculate the storage rate of Se, a known contaminant from this area, following dam construction (1995 CE), and (3) identify physical, environmental, and biological mechanisms associated with dam construction and how they influence elemental deposition in reservoirs. Results from sediment cores show increases in the storage of inorganic carbon (IC), Se, and Ca for both core sites throughout the period of reservoir existence, with Se deposition related to physical and environmental conditions that are associated with reservoir genesis. These data show that dam construction altered environmental processes on MTM elements, which could have lasting impacts on reservoir biota and downstream environments long after reclamation efforts are applied.