| Summary: | Suspended sediment is an important constituent of freshwater ecosystems that supports biogeochemical, geomorphological, and ecological processes. Current knowledge of suspended sediment is largely based on surface water studies; however, improved understanding of surface and in situ groundwater suspended sediment processes will improve pollutant loading estimates and watershed remediation strategies. A study was conducted in a representative mixed-use, agro-forested catchment of the Chesapeake Bay Watershed of the northeast, USA, utilizing an experimental watershed study design, including eight nested sub-catchments. Stream water and shallow groundwater grab samples were collected monthly from January 2020 to December 2020 (<i>n</i> = 192). Water samples were analyzed for suspended sediment using gravimetric (mg/L) and laser particle diffraction (µm) analytical methods. Results showed that shallow groundwater contained significantly higher (<i>p</i> < 0.001) total suspended solid concentrations and smaller particle sizes, relative to stream water. Differences were attributed to variability between sites in terms of soil composition, land use/land cover, and surficial geology, and also the shallow groundwater sampling method used. Results hold important implications for pollutant transport estimates and biogeochemical modeling in agro-forested watersheds. Continued work is needed to improve shallow groundwater suspended sediment characterization (i.e., mass <i>and</i> particle sizes) and the utility of this information for strategies that are designed to meet water quality goals.
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