Source and fate of suspended sediment during stormflow

How atmospheric pollutants reach the atmosphere and, once deposited, are assimilated into the biosphere is broadly understood. However, the intermediate steps connecting these processes remain poorly defined. It is known that fine-grained sediment plays an important role in transporting and sequestering atmospherically-deposited contaminants in fluvial systems. In this context, this study seeks to understand the source and fate of fine-grained sediment in a simple fluvial system during storm events. I pay particular attention to fine-grained channel margin (FGCM) deposits, which previous work has shown to be important storage areas for atmospherically deposited contaminants. Using the mass balance of suspended sediment, Beryllium-7 activity, and stable isotopes of water in streamflow, I conclude that FGCM deposits are created by net transfer of sediment from the streambed to the channel margins during medium-sized storms the resulting flows of which are large enough to inundate channel margins, but too small to effectively erode them. The mass of the sediment deposited onto the margins is a function of storm size. It is likely, however, that as storm size continues to increase, FGCM deposits will be mobilized, perhaps reversing the net transfer of sediment from out of the channel and to channel margin, and back into the channel.