Doctor of Philosophy (PhD)
Oceanography and Coastal Sciences
Wetland groundwater hydrology was investigated at different spatial scales to assess the usefulness of the information to coastal managers. Specific objectives were to: (1) review studies related to coastal groundwater discharge, evaluating techniques and identifying controls; (2) understand regional trends in groundwater flow along the U.S. East and Gulf coasts; (3) evaluate the applicability of naturally occurring radioisotopes as indicators of groundwater in a shallow deltaic system; and (4) evaluate groundwater-surface water exchange within Barataria Basin, Louisiana. Results of the review confirmed discharge estimates vary over several orders of magnitude, due to differences in precipitation and tidal prisms. In addition, in very few areas such as the Sippewissett Marshes, Massachusetts, groundwater information was extensive enough for management planning. A regional water budget study performed for 29 watersheds along the East and Gulf of Mexico indicate a likely insignificant net annual (30-year average) export of groundwater in the northeast (17 cm). However, a net import was found in the southeast (10 cm), and eastern Gulf coast (14 cm). The mid-Atlantic and western Gulf showed no net groundwater flow. In Barataria Basin estuary, 222Rn increased exponentially from the mouth to 120 km upstream. Significant excess 222Rn activities suggest that an additional source is required to balance the geochemical budget, such as groundwater. Radium-226 activities demonstrated non-conservative mixing, and appear to indicate an additional source at intermediate salinities, likely desorption of 226Ra from suspended and bottom sediments. Further evaluation of groundwater in Barataria was performed using more in depth experiments with radioisotopes. Tracer mass balance estimates of SGD at three sites produced a range in SGD flux of 1.6 to 9.6 cm/d, with the highest groundwater flux at Kenta Canal. A comparison of results from the water budget and mass balance for Barataria Basin confirm that the water budget was the lower estimate of SGD. Coastal managers can utilize SGD information in planning as better estimates and consistent techniques become available. In Barataria Basin, a further study of stratigraphy, groundwater flows, and SGD-derived nutrients is necessary if Louisiana’s coastal planners are to fully understand the hydrology and resulting impacts on its wetlands.
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Inniss, Lorna Veronica, "Scientific and management perspectives in wetland groundwater hydrology" (2002). LSU Doctoral Dissertations. 1759.
Jaye E. Cable