HR: 16:30h
AN: H24A-03    [Abstracts]
TI: An Evaluation of Groundwater Contributions along the Continental Shelf of Louisiana, USA
AU: * McCoy, C A
EM: cam0928@mail.ecu.edu
AF: East Carolina University, 1000 E. 5th St., Greenville, NC 27858 United States
AU: Corbett, D R
EM: corbettd@mail.ecu.edu
AF: East Carolina University, 1000 E. 5th St., Greenville, NC 27858 United States
AB: Recent studies have suggested that groundwater may play an important role in transporting water and bioactive elements to coastal waters along continental shelves, including river-dominated ocean margins. Relationships between groundwater, the substrate through which it flows, and the receiving surface waters are of significant environmental concern since the magnitude of groundwater discharge is not yet assessed along most of the world's coastlines. The goal of this study is to assess the groundwater contribution to the coastal waters of Louisiana, a river-dominated continental shelf environment. We have employed multiple geochemical tracers (222Rn/226Ra, 4He/3He/3H, and short-lived radium isotopes) and will evaluate the groundwater discharge using a mass balance approach. Fieldwork was conducted over the last eighteen months and was designed to assess groundwater contributions under high flow (spring) and low flow (fall) Mississippi River conditions. Land-based groundwater samples were collected from monitoring wells sampled on a quarterly basis and continental shelf samples were collected during six 4-day cruises (fall 2003 and spring 2004). Groundwater samples were analyzed by liquid scintillation techniques with total 222Rn values ranging from 270 to 3077 dpm l-1. Water column samples were collected throughout the study area during each cruise and variability of unsupported 222Rn was evident between the fall and spring with higher bottom water samples found in the spring. Water column inventories during the initial cruise ranged between 0 and 29381 dpm m-2. The majority of the stations sampled on the shelf had significantly higher 222Rn inventories than that supplied simply by diffusion alone. Interestingly, stations beyond the 30m coutour tended to have the greatest unsupported water column inventories. This indicates an additional source of 222Rn to these waters, including horizontal transport or an advective flux. Excess 222Rn values indicate variability between high and low river flow conditions as well as variability within each flow condition.
DE: 4808 Chemical tracers
DE: 4219 Continental shelf processes
DE: 1829 Groundwater hydrology
DE: 1050 Marine geochemistry (4835, 4850)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting