Chemical-biological analysis to determine the trophic status of Tres Palos Lagoon, Guerrero, Mexico

Abstract

An evaluation of the main physicochemical and biological parameters was carried out in Tres Palos coastal lagoon in 2003; the aim of the study was to evaluate the environmental quality and the trophic status of the lagoon, and to compare these results with the data obtained in 1971. The salinity, temperature and dissolved oxygen remained similar: oligohaline (2-4 ups), warm (28-31°C), with dissolved oxygen oversaturation at the surface and hypoxia or anoxia at the bottom. However, other characteristics changed considerably. In 1971 the coastal lagoon was eutrophic with high densities of phytoplankton (8 x 103 cel mL-1), and blooms of cyanophytes (i.e., Mycrocystis, Anabaena, Spirulina). Thirty-two years later, the trophic status of Tres Palos coastal lagoon evolved to hypereutrophy. Phytoplankton biomass (?100 mg chlorophyll a m-3) and density (i.e., >10 x 104 cel mL-1) increased in response to the large concentration of available phosphorus (3.6 to 80.6 µM); the cyanophyta continued as the dominant group but with different representative species (i.e., Aphanocapsa delicatissima, Merismopedia punctata, Chroococcus dispersus var. minor, Raphidiopsis curvata and Pseudoanabaena limnetica). The ß-mesosaprobic organisms dominated and revealed the large amount of organic matter coming from allochthonous (urban and industrial wastewater) and autochthonous (phytoplankton) sources.