Submarine Groundwater Discharge in Coastal Zones along the Yucatan Peninsula, Mexico

Research was conducted to investigate groundwater discharge in coastal environments along the Northeastern Yucatan Peninsula, Mexico using a combination of tracer mass balances and analytic solutions.  Two distinct submarine groundwater sources discharge to the coastal zone along the Yucatan Peninsula, including water from the unconfined surficial aquifer discharging at the beach face and water from a deeper aquifer discharging nearshore through submarine springs (ojos).  The groundwater of nearshore ojos was saline and significantly enriched in Ra relative to the beach-face groundwater and coastal surface water. Ojos discharge dominated Ra contributions to the coastal environment. Discharge from the unconfined coastal aquifer was fresher and low in Ra. We determined the submarine groundwater discharge at the ojos using short-lived radium isotopes (²²³Ra, ²²⁴Ra) and used dissolved silica and salinity to estimate the freshwater discharge at the surf zone.  In addition to freshwater discharge, analytical calculations were used to estimate wave setup and tidally driven seepage in the surf zone.  Preliminary results suggest SGD from ojos is on the order of 15 L min^-1 m^-1. Freshwater discharge at the beach face was estimated at 3.9 and 0.8 L min^-1 m^-1 using salinity and dissolved silica respectively, and wave setup and tidally driven discharge was estimated at 2.4 L min^-1 m^-1.    Although discharge from the ojos is larger in volume than discharge from the beach shoreline, nutrients are significantly higher in beach porewaters and may contribute significant nutrient loads.  Dissolved inorganic nitrogen fluxes from ojos and the beach interface are estimated at 246 μmol min^-1 and 157 μmol min^-1, respectively, and demonstrate the importance of considering the beach zone as a significant nutrient source to coastal waters for future management strategies.