TRACE METAL SEQUESTRATION IN RIPARIAN SOILS AND TRANSPORT OF DISSOLVED AND SUSPENDED SEDIMENT IN THE THAMES RIVER WATERSHED

The Thames River Watershed has a historical legacy of trace metal contamination, including toxic metals As, Pb, and Hg. The transport and sequestration of these trace metals in the watershed remains largely unclear. Further lines of inquiry include: are they in mobile form? Is metal export controlled by dissolved or sediment transport? Do different land uses, ie.) forested, agriculture or developed, affect the retention of trace elements? At ten different locations that span the headwaters to estuary of the Thames River watershed, water was collected from February to December 2019 and sediment traps were deployed. Moreover, thirty-four riparian soils where cored using an auger down to 30cm, at 5cm depth intervals at the same 10 locations. Soil mobility of trace metals was determined using a weak acid (Acetic Acid) extraction and total concentrations in soils was measured using XRF. All stream water samples showed As, Pb, Co, Cr, Hg were < 1 ng L^-1. Sediment collected in-situ showed much higher concentrations of As, Pb, Co, Cr, and Hg than stream water samples. When scaled to monthly fluxes, trace metal transport as dissolved phases were comparable to suspended sediment masses. XRF analysis of riparian soils showed great variation of trace element concentrations throughout the watershed. Headwater riparian areas had the lowest concentrations of metal while riparian soils adjacent to developed lands in the Yantic river show elevated Pb concentrations up to 5462 mg kg^-1. Riparian soil mobility was <1% of total concentrations. These results show riparian soils play an important sink in trace metals and both dissolved and suspended sediment control transport.