Sub-Watershed-Scale Elemental Constituent Regimes in Surface Waters of an Appalachian Mixed-Land-Use Watershed

Abstract:

Geochemical impacts of land-use practices remain an area of greatly needed investigation. A nested-scale experimental watershed study was conducted in an urbanizing, mixed-land-use, Appalachian watershed to advance understanding. Twenty-two study sites, characterized by contrasting land use/land cover and drainage area, were instrumented to continuously monitor stream stage. Weekly grab samples were collected from each site during the 2018 annual year, and analyzed for trace element composition (Al, Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn, and As) via spectrometric methods. Additional physico-chemical parameters, including pH, were measured at the time of sampling. Data were analyzed using a suite of statistical methods, including correlation analysis and Principle Component Analysis (PCA). Results showed a trend of increasing trace element concentrations associated with legacy industrial land use practices (i.e. mining) in the mid watershed, and subsequently decreasing concentrations in the downstream direction. PCA results highlight spatial differences between elemental composition and physico-chemical characteristics of streamwater samples. Results from correlation analyses indicated varying significant (p< 0.05) relationships between chemical parameters and hydroclimate metrics, suggesting the influence of contrasting flow paths and constituent sources. Given the geological, topographical, and climatological similarities between the sites, and their proximity to each other, it is concluded that land use characteristics and associated hydrologic regime contrasts were the primary factors contributing to the observed results. The applied methodology can be used to advance understanding of trace element regimes in mixed-use watersheds, and to more effectively target sub-watershed-scale remediation/restoration efforts, thereby improving the ultimate efficacy of management practices.