Investigating water quality of tropical, macrotidal rivers
Besides providing water for human use and habitat for economically important species, rivers also regulate floods, erosion, sediment supply, and water quality, providing water, energy and nutrients to wetlands, riparian communities, floodplains, and estuaries. Rivers also provides riverside communities countless opportunities for recreation, tourism, and income generation. Since rivers are “hotspots” for human activity, they are among the most sensitive ecosystems to anthropogenic stressors. The most common pollutants are the release of untreated domestic sewage and industrial effluents, including oil and its derivatives, heavy metals, organic chemicals, and waste.
For this study, water samples were collected on 8 sites along the estuaries of the Bacanga and Anil rivers (see figure above), which drain the island of Sao Luis, in northeast Brazil. The Anil River is a predominantly urban river, with reduced riparian vegetation. The Bacanga River runs through a state park with extensive riparian buffers for most of its course.
The harbor is macrotidal, with a maximum tidal range of 6.2 m during the period of study (see figure below), and strong tidal currents that transport material to and from the estuary. Macrotidal zones are dominated by physical processes with large amounts of suspended material being reworked and transported within the estuary. This has major effects on biogeochemical processes.
Samples were collected during both the rainy season (which runs from December to July, with highest precipitation in April) and the dry season (which runs from August to November). A suite of geochemical analysis have been performed on the samples and the results are compiled into a manuscript currently in preparation.
