Environmental forcing in a tropical estuarine ecosystem: the Palizada River in the southern Gulf of Mexico

Environmental characteristics of the fluvial deltaic lagoon estuarine syste m of the Palizada River were determined by the assessment of physical, envi ronmental and hydrological variability. Environmental information comprised daily time series of precipitation (1971-85), Usumacinta River discharge ( 1948-94), sea level (1956-91) and wind patterns (1984-87). Hydrology was st udied by weekly measurement of salinity, transparency, temperature, dissolv ed oxygen and pH at 18 stations during 19 months (September 1985 to March 1 987). Water temperature reflected the climatic seasons: dry, rainy and wint er frontal storms (Nortes). During the rainy season fresh water dominated t he whole area, but during the dry season a salt wedge entered as far as Del Este Lagoon. Northern winds allowed saline water to reach intermediate reg ions and occasionally the upstream freshwater head of the estuary. There ar e annual, 6-month and 3.2-month oscillations in the environmental records: the annual signal is modulated by precipitation, fluvial discharge and sea level; the 6-month signal has an implicit periodicity driven by the changes in the wind direction that affect all other parameters; and the 3.2-month period seems to be modulated by the rainy, dry and Nortes seasons. Cluster analysis identified eight ecological regions based on the hydrological vari ables.