EFFECTS OF URBANIZATION AND RIPARIAN VEGETATION DENSITY ON WATER QUALITY OF TWO TROPICAL, MACROTIDAL RIVERS

Tropical estuaries are under increasing pressure worldwide from human impacts, but are poorly studied compared to their temperate counterparts. Macrotidal estuaries are dominated by physical processes, with large amounts of suspended and dissolved material being reworked and transported within the estuary, which has major effects on biogeochemical processes in these systems. Their biogeochemistry, however, has been poorly described, particularly in the tropics. For this study, water samples were collected at eight sites along the estuaries of the Bacanga and Anil rivers, which drain the island of São Luis, in northeast Brazil. The Anil River is a predominantly urban river, with reduced riparian vegetation. The Bacanga River run through a state park with extensive riparian buffers for most of its course. Sampling was undertaken during both the rainy season (which runs from December to July) and the dry season (from August to November). In addition, a 36-hour continuous sampling protocol was undertaken at two sites in the Anil River to evaluate the effects of the macrotidal range (up to 6.2 meters during the study period) on the geochemistry of the river-estuary continuum. This presentation will discuss the major results of the biogeochemical assessment of these macrotidal estuaries.