USE OF FALLOUT RADIONUCLIDES TO ASSESS FIELD-TO-GAGE SEDIMENT DYNAMICS

A series of studies were undertaken in the priority watersheds of the Great Lakes Restoration Initiative to: (1) quantify the storage of phosphorus associated with sediments stored in the fluvial network, including the edge of fields to stream channels, (2) distinguish the proportion of sediments traveling downstream originating from within the channel bed compared to those recently eroded from the landscape, (3) evaluate in-stream fine sediment travel time between edge-of-field monitoring and watershed outlets. To achieve this, short-term fallout radionuclides, ⁷Be and ²¹⁰Pb_xs were used to elucidate the contribution of in-channel transport and biogeochemical processing of sediment and associated phosphorus transport from field to watershed outlets. Seasonal storm data has been collected over the 2018-2019 seasons at edge-of-field sites in two watersheds. Throughout the 2019 growing season, suspended sediments were sampled from three nested in-stream locations. Patterns in fallout radionuclide activity and ⁷Be/²¹⁰Pb ratio will be evaluated for changes with precipitation events and channel position. At one of the sites, Black Creek in the Maumee Basin, ⁷Be activity was measured in contributing waters to Black Creek, including tile drain effluent. Initial results from 4 storm events indicate that ⁷Be is detectable in tile effluent – indicating a very fast delivery of event water and newly eroded sediment to the stream network.