TRACE METAL STORAGE IN COAL LEGACY SEDIMENTS DEPOSITED ALONG THE NORTH BRANCH SUSQUEHANNA RIVER, PENNSYLVANIA

The North Branch Susquehanna River (NBSR) basin contains many historical and modern anthracite coal mining operations. The alluvial landscapes of this river have been trapping pollutant-laden sediment from floodwaters for over 200 years, with an estimated 1-6 meters of coal-contaminated legacy sediment stored in the floodplain. In this study, we investigated a total of eight representative alluvial landscapes, consisting of four tributary deltas and four river islands. Each study site was cored to at least 1 meter in the field to evaluate soil morphology (n = 12) and soil samples were taken by horizon for laboratory analyses (n = 94). Each collected sample was analyzed for physical (bulk density, particle size distribution, coal percentage) and chemical (total elemental analysis via X-Ray Fluorescence, pH) properties. Coal fragments and metal enrichment increased with depth in all landscapes regardless of modern watershed land use. Enrichment factors (EF) were calculated to assess the degree to which anthropogenic forces have impacted trace metal content in alluvial landscapes. All core samples showed enrichment factors of less than 5.0, indicating minimal to moderate enrichment, with the highest EF values (>2.5) associated with soil horizons at depth. Soil bulk density values were used to scale-up total heavy metal (As, Pb, Cr) storage values to a landscape level. Total soil As pools ranged from 84.0-251 kg/ha, Pb ranged from 289-938 kg/ha, and Cr ranged from 555-1596 kg/ha. Trace metals were positively correlated with coal contamination as opposed to being a function of a particular portion of the fine earth fraction, with higher coal percentages corresponding to increased metal concentrations. This research indicates that alluvial landscapes of the NBSR have provided crucial water quality improvement functions in their ability to sequester eroded coal tailings and associated heavy metals. Evidence of coal on the modern alluvial soil surface suggests that beneficial sediment trapping continues even today and that floodplain landscapes along the NBSR should be maintained in their forested condition to maintain these important ecosystem services into the future.