Submarine Groundwater Discharge (SGD) in Barbados Linking Population and the Environment
Abstract
Population and economic activity, like agriculture and tourism, both demand freshwater and supply nutrients, like nitrate, to the freshwater reserves. Freshwater and its pollutant load are delivered to the coastal zone via SGD with consequent impacts on tourism and fisheries thus linking the land-based and marine economic sectors. The spatial and temporal variations in SGD were investigated at two sites on the west coast of Barbados during both the wet season, with average rainfalls above 140 mm/month, and the dry season with an average rainfall of 40 mm/month. The SGD flow was modulated by the tide. As a result, measurements must be averaged over a tidal cycle. At Alleynes Bay, characterized by exposed seepage springs at low tide, the average SGD flow rate dropped from 49 cm/d in the wet season to 26 cm/d in the dry season; also, the component of freshwater in the SGD also decreased from 33% to 21%, indicating a three-fold increase in the freshwater flow to the lagoon during the wet season. The NOx concentrations of the SGD were more than 25 times higher than ambient. NOx varied inversely with salinity from 2.5 mg/L at 3 psu to less than 0.1 mg/L at 34 psu. At Queens Fort Beach, where springs are absent, there was no increase in SGD between the seasons. The difference from 14 cm/d in wet season to 20 cm/d in the dry season was not significant. Neither was there a difference in salinity, or NOx, between the ambient water and SGD. SGD at Queens Fort Beach appeared to be composed entirely of recirculated sea water driven by oceanographic processes. About 60% of the western shoreline of Barbados was estimated to have freshwater component to SGD providing an important source of NOx to the lagoon. The source of NOx to the groundwater would increase with population; during the dry season the population may increase due to a peak in tourism. At the same time, reduced rainfall would reduce dilution thus increasing the NOx concentrations of the freshwater end member. Simultaneously, however, the SGD outflow decreases. Our SGD measurements suggest that the NOx input to the lagoon is decreased as a result of these competing factors during the dry period and is increased during the wet period.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2007
- Bibcode:
- 2007AGUSMOS33C..06C
- Keywords:
-
- 1803 Anthropogenic effects (4802;
- 4902);
- 1830 Groundwater/surface water interaction;
- 1871 Surface water quality;
- 1880 Water management (6334);
- 3021 Marine hydrogeology