Sediment Fingerprinting Suggests Differential Suspended Particulate Matter Formation and Transport Processes Across Hydrologic Regimes

Sediment fingerprinting techniques are increasingly used to characterize the sources and transport processes of particulate materials in surface waters. However, consensus on the use of biologically labile compounds such as organic carbon and nitrogen for sediment fingerprinting remains elusive. We used multiple biogeochemical characteristics of suspended particulate material (SPM) to characterize the differences in formation and transport processes of these materials during storm events ranging in size from small seasonal rainfall events to hurricanes and tropical storms in a small mid-Atlantic watershed. During storms, particle surface area, percent organic C, percent organic N, percent Fe, and percent Al of SPM decreased with increasing discharge; these contents were lowest during the extreme events Hurricane Sandy, Hurricane Irene, and Tropical Storm Lee. Conversely, SPM C:N values during these storms were among the highest of all samples, and C:N generally increased with discharge. End-member mixing analysis indicated that organic matter and metal contents of SPM collected during high event flows were well described by materials collected from erosional source areas throughout the watershed, while SPM collected during low event flows fell outside of the end-member mixing space. This suggests that physical transport processes govern SPM export primarily from surface and fluvial areas during high flows, while in-stream biogeochemical processes become increasingly important contributors to SPM at lower flows.