HR: 0830h
AN: H41F-1049    [PDF]
TI: Submarine Groundwater Discharge and Associated Nitrogen Flux in Coral Reef Lagoons of Mauritius
AU: * Eagle, M
EM: akeagle@stanfordalumni.org
AF: Stanford University, Department of Geological and Environmental Sciences Braun Hall, BLDG 320, Stanford, CA 94305-2115 United States
AU: Paytan, A
EM: apaytan@pangea.stanford.edu
AF: Stanford University, Department of Geological and Environmental Sciences Braun Hall, BLDG 320, Stanford, CA 94305-2115 United States
AU: Ramessur, R T
EM: ramessur@uom.ac.mu
AF: University of Mauritius, Department of Chemistry, Reduit, 00000 Mauritius
AB: Recent eutrophication in several coral reef lagoons along the Indian Ocean island nation of Mauritius (20$\deg$S, 57$\deg$E) has highlighted the need for a greater understanding of nutrient sources to these lagoon waters. Submarine groundwater discharge (SGD) into the coastal environment is one possible transport mechanism for excess terrestrial nutrients to coral reef lagoons, since groundwater nitrate levels are an order of magnitude greater than coastal nitrate levels (330 and 30 $\mu$M respectively). However, the direct discharge of groundwater into the sea has been difficult to measure, because fluxes may be episodic and patchy in distribution. Here we utilize radium isotopes (224Ra and 223Ra), which desorbs from aquifer sediments when fresh water and salt water interact within the coastal aquifer, as naturally occurring SGD tracers. Given the positive correlations between radium activities, salinity and nitrate concentrations found in the lagoon waters of Mauritius, it is apparent that SGD is a source of nitrate to the coastal lagoons. Based on mass balance of 223Ra activities, submarine groundwater flux per meter of coastline is 116 m3/m along the west coast and more than twice as great on the east coast (323 m3/m). The nitrogen loading associated with SGD in the east coast lagoon (0.28 g N/m3) is likewise twice that in the west coast (0.14 g N/m3). Regions of the east coast lagoon have recently experienced eutrophication, while the west coast has not experienced significant algal blooms, suggesting that the nitrogen loading along the east coast may be negatively impacting the health of the coral reef lagoon. Given the sensitivity of the marine environment to excess nutrients and the potential groundwater transport of such nutrients far from their source, there is a clear need for greater understanding of groundwater nutrient transport to the lagoons of Mauritius.
DE: 1615 Biogeochemical processes (4805)
DE: 1832 Groundwater transport
DE: 4808 Chemical tracers
DE: 4845 Nutrients and nutrient cycling
DE: 4857 Pollution
SC: Hydrology [H]
MN: 2003 Fall Meeting