GROUNDWATER USE AND ITS IMPLICATIONS IN COASTAL ECOSYSTEMS REQUIREMENTS: A CASE STUDY IN A COASTAL KARSTIC AQUIFER BY GROUNDWATER MODELING

A coastal karstic aquifer highly exposed to anthropogenic pollution and seawater intrusion is the main water supply source for Merida-Progreso inhabitants in Yucatan State, Mexico. In addition, Merida-Progreso region, and in general all the urban areas in the Yucatan Peninsula do not have a municipal sewage system, so wastewater is deposited through several forms to underground. The shallow depth to the groundwater, the almost total absence of soils and the large area of the unconfined karstic aquifer in the region, make groundwater resources in Yucatan particularly vulnerable to pollution. The constant interaction with the seawater of the coastal zone, causes the serious possibility of damages to the coastal ecosystems as the mangrove zones. In addition, there are agricultural, industrial and livestock (swine production, which is very important in the region) wastewaters discharges. The objective of this research was to analyze and understand the hydrogeological behavior in the coastal karstic aquifer and groundwater, and its implications in the coastal area ecosystems requirements in terms of water quantity and quality. In this investigation, a conceptual model of the hydrodynamic functioning of the aquifer was developed and implemented in a numerical model of flow and N-NO₃ transport for a period of 19 years (1995-2013). Subsequently, future scenarios were developed to predict the state of the study region and the coastal area in 2030: 1) laissez-faire of current conditions (2013), 2) increased groundwater extraction by growing population, and 3) increased groundwater extraction by growing population and precipitation reduction (in a 50% of the current one) due to climate change. According to the results of the scenarios 1 and 2 pumping schemes will not bring changes in the hydraulic behavior of the aquifer; on scenario 3 significant variation occurs in the configuration of the water table; it allows to infer that the behavior of groundwater in the study area is highly influenced by natural recharge. The arrival of N-NO₃ in these ecosystems can be a benefit or a problem; this is, can act as a nutrient and in the worst case, it can cause eutrophication (in this case "cultural eutrophication").