ASSESSING SUBMARINE GROUNDWATER DISCHARGE (SGD) IN HIGHLY HETEROGENEOUS COASTAL KARST AQUIFERS: CHALLENGES AND SOLUTIONS
We examined the SGD budget of a 16-km shoreline in the Maro-Cerro Gordo Protected Coastal Area (Southern Spain) for almost two years and found that even within this small area, there are at least four different mechanism of discharge to the ocean: diffusive flow through coastal sediments, deep submarine springs, emerged coastal springs, and groundwater-fed creeks.We adopted four different approaches (i.e. salinity mixing models, seepage meters, 222Rn and 224Ra mass balances) to adequately assess each mode of SGD. Additionally, we estimated SGD-derived nitrate fluxes (SGD-N) to coastal waters comparing an intensely populated area with the protected zone.
We found that the total fresh SGD in the study area ranges between 3.6 and 2.4·106 m3 year-1 during wet and dry periods, which can be taken into account for future water resources management. SGD-N is significantly higher (2.7 – 1.9·105 mol year-1) in the unprotected highly developed area; while in the protection zone, with nearly inexistent anthropogenic impact, SGD-N only represents 9.3 – 5.6·104 mol year-1. Extensive nitrate delivery in the unprotected zone occurs in the presence of endemic and endangered species that are rapidly disappearing, therefore, we propose to extend the protection zone as a measure to preserve their remaining population.