HR: 1330h
AN: H13A-08    [Abstracts]
TI: A Mass Balance Analysis of Total Mercury Flux Through a Large, Managed Floodplain
AU: * Springborn, M
EM: mspringborn@bren.ucsb.edu
AF: The Donald Bren School of Environmental Science and Management, 2400 Bren Hall University of California, Santa Barbara, Santa Barbara, CA 93106-5131 United States
AU: Singer, M B
EM: bliss@seismo.berkeley.edu
AF: The Institute for Computational Earth System Science, University of California, Santa Barbara, Institute for Computational Earth Systems Science 3060, Santa Barbara, CA 93106-3060 United States
AU: Dunne, T
EM: tdunne@bren.ucsb.edu
AF: The Donald Bren School of Environmental Science and Management, 2400 Bren Hall University of California, Santa Barbara, Santa Barbara, CA 93106-5131 United States
AB: The fate and transport of mercury are of critical concern in lowland floodplains worldwide. Increasing attention has been paid to the uncertainty of mercury sources and sinks in the Sacramento Valley, which is still recovering from decades of gold mining that used mercury for gold separation. Active in floods, Yolo Bypass is the largest flood-control bypass (or conveyance floodway) on the Sacramento River and is a key conduit for flow (up to 15,000 m(³)s(^-1)) and the transport of fine sediment and adsorbed mercury to the San Francisco-Sacramento Bay-Delta. The 24,000 hectare bypass located in the lower Sacramento Valley has been recently implicated as a likely storage site for mercury with a high risk for methylation and transmission into the food chain at the primary wintering stop on the Pacific Flyway. In order to assess contaminant risk in the bypass, quantitative relationships between (1) total mercury concentration and suspended sediment concentration and (2) suspended sediment concentration and flow were developed for each of its major inputs and outputs using event-based sample data from various sources. These relationships were improved by incorporating dynamics of seasonal exhaustion and intraflood exhaustion (hysteresis) of sediment and mercury. From this characterization of how the flow-sediment-mercury transport system functions we were able to characterize the relative contributions of the various inputs. While the main inflow to the bypass is via flood weirs along the Sacramento River, two major creeks and an agricultural runoff canal made significant contributions to flow, sediment and mercury loads. Using the continuous record of flow to estimate sediment transport and sediment transport to estimate mercury flux we computed the net transfer of mercury through the bypass over a five-year period. Based on the volume and source of the expected change in flow and sediment, we were able to evaluate how mercury loading might change in the future due to proposed structural changes to the bypass. The research results have implications for mercury mitigation and floodplain restoration.
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2005 Joint Assembly