Reservoir Surface Sediments Show Spatial Heterogeneity between Aquatic Contaminants, Heavy Metals, and Cyanotoxins

Reservoirs are often conceptualized as having three hydrologic zones, i.e., riverine, lacustrine, and transitional. In reality, many are more hydrologically complex, representing a heterogeneous gradient of riverine to lacustrine, depending on inflows. This presents challenges for basin managers in addressing the deposition of contaminants. In this study, we investigated two types of contaminants: heavy metals (As, Cd, Cr, and Pb) and the cyanotoxin, cylindrospermopsin, in a dynamic subtropical reservoir, Lake Seminole, GA, USA. The reservoir receives inputs from three rivers (7th order, seventh order, and fifth order) having different land use types (agricultural and urban) with noteworthy populations of the ecosystem dominating invasive species. Based on hydrological inputs and land use, the reservoir was divided into three hydrologic segments corresponding to each river input plus a segment near the dam, where the rivers converge. Whereas reservoir sediment deposition generally followed particle sorting parameters, our results showed that contaminant distributions were heterogeneous, with heavy metals associated with organic matter and cylindrospermopsin concentrations more associated with the presence of sands. These data demonstrate the complexity of contaminant distribution in reservoir systems while highlighting opportunities for improved precision in reservoir management decisions.