SPATIAL DISTRIBUTION AND SEASONAL DYNAMICS OF HYDROLOGICAL, MICROBIOLOGICAL AND CHLOROPHYLLA-A DATA ALONG THE AÇU RIVER, MAMANGUAPE ESTUARY, STATE OF PARAÍBA, BRASIL

Resumo

Some physical, chemical and microbiological parameters, together with chlorophyll-a data, were measured monthly, from April, 1989 to June, 1990, at six stations located along the Açu River, a tributary of the Mamanguape River estuary. The intent was to determine their spatial and seasonal patterns and to characterize the water quality of this ecosystem. A clear influence of th erainfall was detected with regard to salinity, nitrate, nitrite, phosphate, water transparency, chlorophyll-a, and total and fecal coliforms.  Tidal action also has shown an expressive effect on the spatial distribution of the majority of the studied parameters. Evidences of contamination from the extensive sugar-cane plantations near the river head were observed, as demonstrated by the high concentrations of total and fermentative yeasts and of some nutrients salts (particularly nitrate), which may originate from the chemical fertilizers used in those plantations. The high levels of heterotrophic bacteria and filamentous fungi frequently found in the region studied reflect high contents of organic matter and suggest that the Açu River has a high heterotrophic activity. As the spatial and seasonal patterns of such microbiological parameters were dissimilar from those observed for chlorophyll-a and for nutrient salts two different interpretations regarding the trophic state of the Açu River are possible: (1) the system is moderately eutrophic (from the microbiological point of view), and (2) the system shows oligo/mesotrophic phases alternating with eutrophic phases (if only chlorophyll-a and nutrient data are considered).