Water quality variability and eutrophic trends in karstic tropical coastal lagoons of the Yucatán Peninsula

Coastal lagoon ecosystems are particularly vulnerable to eutrophication due to often restricted water exchange with the adjacent ocean, leading to an accumulation of nutrients from the surrounding watershed. The coastal areas of the northern Yucata´n (SE Mexico) show similar geological characteristics: carbonate soils, and strong groundwater discharges (SGD), which are a source of fresh water and dissolved inorganic nutrients. However, due to differences in land use and human impact, these coastal lagoons have different water quality characteristics. To determine the variables and processes that influence water quality and eutrophic status of these tropical coastal lagoons with different hydrological regimes and human impacts, bimonthly samplings were carried for a year at 11 stations in Celestu´n and Chelem lagoons. The results indicate that Celestu´n is influenced by bioturbation (resuspension and nutrients inputs from waterfowl) and SGD with high concentrations of nitrate and silicate, leading to oligo-mesotrophic conditions. Chelem had high ammonium and phosphate concentrations, reflecting impacts by wastewaters from the surrounding urban area, resulting in meso-eutrophic conditions. Forcing functions such as climatic patterns, water residence time and local aquifer pollution are probably the main variables that explain the observed patterns.