Influence of rainy season and land use on drinking water quality in a karst landscape, State of Yucatán, Mexico

To understand the impacts of dry and wet seasons and land use on water quality in a karst system, twenty-one deep municipal wells were sampled synoptically across the State of Yucatán. Surrounding land uses comprised urban, crop, and livestock as defined by the National Institute of Statistics and Geography of Mexico. Measurements included pH, temperature, specific conductance, Ca2+, Mg2+, Na+, K+, Cl−, SO42−, alkalinity, NO3−, and fecal coliforms. Data were reduced using various geochemical, statistical, and spatial analytical methods and compared to a similar study on cenotes (sinkhole). Results show that 1) groundwater is diluted during the rainy season, but not for all parameters; 2) the geochemical structure of the water is obscured during the wet season; 3) the change in values for most parameters differs from that in the cenotes, however for both, fecal coliforms are higher in the wet season; 4) the relationship of land use to water quantity is unclear, however some influence of agriculture and urban were observed, and 5) water quality is at risk in both dry (NO3−) and wet (fecal coliforms) seasons. It is hypothesized that these results may be explained by changes in dominant flow paths between dry (matrix, fracture flow) and wet (conduit flow) seasons. In addition, results suggest that rock-water interactions, hydrology, and land cover maybe more important in understanding the influence on water quality than land use. Clearly, understanding the impact of both land use and season on groundwater quality in any karst environment is challenging. Further work should include using different methods for defining land use need to be explored and a more diverse set of water quality measurements need to be made.