SUBMARINE GROUNDWATER DISCHARGE AND ASSOCIATED NUTRIENT FLUXES TO THE NORTH COAST OF JAMAICA (Invited Presentation)

Submarine groundwater discharge (SGD) and associated dissolved inorganic nitrogen (DIN) and phosphorus (SRP) were evaluated at two locations along the north coast of Jamaica. This region is characterised by karst geology with a coastline of natural beaches, fringing reef systems and reef flats that enclose shallow protected lagoons. There are very few rivers discharging along the coast but chemical species, such as nutrients, are transported to the coastal environment via submerged springs and diffuse seepage through bottom sediments (SGD). SGD has been shown to provide essential nutrients to support healthy coastal habitats, including coral reefs, mangroves and seagrass beds, however, SGD may have deleterious effects on these biologically diverse and economically important tropical marine ecosystems if the groundwater is heavily impacted by anthropogenic inputs. The two areas investigated here, the Discovery Bay Fishery Reserve and the East Portland Special Fishery Conservation Area, are characterised by extensive coral reef systems and important fisheries. SGD was assessed using the naturally-occurring radioactive isotope tracers, ²²²Rn, ²²³Ra, ²²⁴Ra and ²²⁶Ra. Low-speed coastal surveys and time series measurements were carried out following periods of low and high precipitation. Radioisotope and nutrient levels in the groundwater flowing from coastal springs and inland freshwater sites were also measured. SGD rates of up to 62 m³ day^-1 per metre of shoreline were recorded and groundwater DIN concentrations were up to 50 times higher than those found in the coastal waters. Our results indicate that SGD is an important source of land-based nutrients to this region. Although the impact of SGD on these vulnerable nearshore ecosystems is still largely unknown, our multiple isotope surveys and initial estimates of the groundwater fluxes provide a rare study of SGD on the islands of the Caribbean.