Spatial characterization of water quality in a karstic coastal lagoon without anthropogenic disturbance: a multivariate approach

Dzilam Lagoon, located in the central coast of Yucatan, Gulf of Mexico, is a shallow water body with average depth of 0.6m and area of 9.4km2. Numerous groundwater inputs are distributed along the system representing a continuous source of nitrates and silicates. Due to scarce anthropogenic activity, it is well preserved. Such pristine conditions suggest that changes on nutrient dynamics are mostly related to natural behavior. Monthly samples were taken from September 1998 to August 1999. Physicochemical parameters, inorganic nutrients and chlorophyll-a were measured in nine stations. A multivariate analysis showed salinity gradient and nutrient concentration as the most significant variables in describing lagoon hydrologic heterogeneity. On the basis of those critical parameters, classification analysis of Dzilam Lagoon identified three hydrological affinity zones (HAZ); East and West Zone characterized by higher water residence time and lower salinities during the rainy season; Central Zone with lower residence time and lower inorganic nutrients concentration. Dzilam Lagoon was a NO 3 sink and a net source for NO 2 and NHþ4 . Soluble reactive phosphorus was slightly defined and soluble reactive silica was close to conservative condition.