CURRENT OBSERVATIONS WITHIN THE YUCATAN KARST AQUIFER AND A BOX MODEL OF MANGROVE INTERACTIONS

The Yucatan Peninsula is comprised of Miocene to Late Pleistocence biogenic karst limestone with both a surface portion and a submerged shelf. The karst subsurface is extremely porous, and as a result the peninsula has no naturally flowing rivers and limited surface water bodies. Freshwater, in the form of rainfall instead percolates directly into the ground or through surficial sinkholes, where it creates a fresh water lens that lies atop intruding seawater from the Gulf of Mexico. Many of the surface features near the coast are linked by massive submerged cave networks. The conservation and study of groundwater in the Yucatan Peninsula is of the utmost importance from an ecological and economic standpoint, for both modern and ancient societies such as the Maya.

We have completed multiple studies in the aquifer by placing sensors (conductivity, temperature and pressure) within the large cave networks of coastal Quintana Roo. The sensors have been collected bi-annually for 5 years and have captured the response of groundwater to multiple climate events. The results suggest that mixing in the stratified water column is profoundly impacted by large rainfall events such as hurricanes. Changes in salinity have been detected at depths as shallow as 1m.

Observations have also indicated that the water column responds differently depending on the size of the rainfall event. The current hypothesis is that this difference is due to extremely large rainfall events saturating the surface mangrove-peat layer and then overflowing into the sinkholes. To test the feasibility of this hypothesis a simple box model of the system was created with a switch to represent this overland flow. Preliminary results indicate that this model successfully replicates the observed measurements

These results have a profound impact on the interpretation of paleo-climate records and their association to archaeology, in contrast to surface freshwater lakes which will decrease in salinity with increases in precipitation, the groundwater will become more saline during times of heavy rainfall. Furthermore, since mangroves can act as a heavy metal sink, in the wake of the heavy rainfall events we would expect to find increases in trace element heavy metals allowing for their detection in groundwater sediment cores.