The hydrology of the Sian Kaan biosphere reserve, Quintana Roo, Mexico

The Sian Ka’an Biosphere Reserve (SBKR) is located on the Caribbean Coast of the Yucatan Peninsula, in the Mexican state of Quintana Roo. This coastal wetland, about 5280 km2 in size, is primarily fed by subsurface flow through the fissured limestone of the Yucatan plain. The reserve is home to a wide variety of wildlife including puma and jaguar and it hosts dozens of colonial waterbird species. SBKR encompasses different types of ecosystems, including freshwater and saltwater marshes, tropical rainforests, coastal dunes mangroves and coral reefs. Pressure on the reserve has been increasing over the years due to accelerated tourism development in the region, increased domestic water demand, contamination with agricultural fertilizers and pesticides as well as infrastructure projects, illegal hunting activities and extensive fishing. This situation calls for an integrated approach towards the management of SBKR. One of the prerequisites of integrated management is good quantitative understanding of the system’s water balance, preferably based on a numerical flow model of the region. The model should take into account the overland flow in the wetland as well as subsurface flow in the Karst aquifer. The most critical issue in this context is the identification of the recharge area where the groundwater flows into the reserve originate. Protection of this area from agricultural pollutants must be prioritized. To identify the main subsurface flow pathways and Karst conduits, and to delineate the recharge area, a high-resolution airborne geophysical survey will be employed. Target variables include the electric conductivity of the subsurface (airborne EM), its magnetic susceptibility (airborne magnetics), gamma emission intensity, brightness temperature (infrared sensing) and dielectric permittivity (microwave).