Abstract

Physico-chemical characterization of two mangrove estuaries of Golfito bay, Pacific coast of Costa Rica. The temporal and spatial distributions of salinity, temperature, dissolved oxygen, Secchi disk depth, suspended matter, dissolved inorganic nutrients and chlorophyll a, were determined in two mangrove estuaries at Golfito Bay, Golfo Dulce, Pacific coast of Costa Rica. Sampling was performed monthly at high tides in a total of eleven cruises, from February to December 1998, at 12 sampling stations. Salinity profiles showed these are vertically mixed or well mixed estuaries, with no anoxic conditions, although two stations were found with low dissolved oxygen saturation of 13.6% and 49.5%, respectively. Silicate was the nutrient always present in the estuarine waters in concentrations ranging from 12.7 to 739.5 μmol/L in the dry season, and from 6.82 to 979.9 μmol/L in the rainy season. Nitrite showed values ranging from not detected (nd) to 1.05 μmol/L. Nitrate had values from 0.55 to 17.69 μmol/L in the dry season and from nd to 62.9 μmol/L in the rainy season. Phosphate was between nd to 4.86 μmol/L in the dry season, and from nd to 6.67 μmol/L in the rainy season. River station nutrient concentrations were higher than in stations at the estuary along the mangrove forest. For example, nitrate: during the dry season the highest concentration at the river station from Purruja estuary was 17.7 μmol/L; at the middle estuary 7.06 μmol/L and at the marine station 4.79 μmol/L. During the rainy season the values were 62.90 μmol/L, 7.06 μmol/L and 4.79 μmol/L, respectively. Chlorophyll a exhibited higher concentrations during the dry season in a distribution from nd to 7.19 mg/m3. In general, the main estuaries in this tropical mangrove forest do not suffer from significantly polluted water discharges, except for two sites that received waters from a pigsty, a tannery and sewage. Rev. Biol. Trop. 54 (Suppl. 1): 241-256. Epub 2006 Sept. 30.
Keywords: tropical estuaries, nutrients, dissolved oxygen, chlorophyll a, suspended matter, mangrove, Golfo Dulce, Costa Rica