USE OF FALLOUT RADIONUCLIDES TO ASSESS FIELD-TO-GAUGE CONNECTIVITY IN GREAT LAKES RESTORATION INITIATIVE PRIORITY WATERSHEDS

Short-term fallout radionuclides, Beryllium-7 (⁷Be) and excess Lead-210 (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 in priority watersheds of the Great Lakes Restoration Initiative. Multiple collections took place in Plum Creek (Fox River Basin) and Black Creek (Maumee Basin). Seasonal storm data has been collected over the 2018-2019 seasons at edge-of-field sites in both watersheds. Throughout the 2019 growing season, suspended sediments were sampled from three nested in-stream locations in Plum Creek. Initial Plum Creek results show higher ⁷Be/²¹⁰Pb_xs ratio with downstream position, which we interpret as increased ⁷Be and ²¹⁰Pb_xs sorption to sediments within the wider, downstream portion of the channel. Follow up work will be done to assess the influence of sediment specific surface area on these results. At the Black Creek site, ⁷Be activity was measured in contributing waters to Black Creek, surface water runoff and tile drain effluent from two paired, adjacent fields during eleven events. Tile drain waters carried detectable ⁷Be, indicating event-timescale hydrologic transport to and through the tile network. For one tile, the ⁷Be activity was similar in activity to the surface runoff. For the second tile, ⁷Be was much lower while other chemical tracers of groundwater (e.g. nitrate/nitrite) were much higher, indicating a higher water table. In both studies, ⁷Be has been a useful tracer to discern connectivity on an event to seasonal timescale.