Influence of an Artificial Channel in a Well-Preserved Sub-Tropical Estuary

Author(s)

Barrera-Alba, J. J. ; Gianesella, S. M. F. ; Saldanha-Correa, F. M. P. ; Moser, G. A. O.

• Document type: Journal article
• Source: Journal of Coastal Research; v. N/A, p. 5-pg., 2007-01-01.

Abstract

The Estuarine-Lagoon System of Canandia-Iguape is located on the southeast coast of Brazil, with an extension of 10000 ha. It is a complex and naturally eutrophicated ecosystem associated to a broad and relatively well-protected mangrove forest. The system is formed by channels and small islands separated from the sea by a 74 km barrier island, with two main connections to the Atlantic Ocean. Suspended matter, dissolved inorganic nutrients, chlorophyll a and phytoplankton density were studied over complete tidal cycles during a period of five years. Surveys were conducted during dry and rainy seasons in order to investigate the influence of Valo Grande, an artificial channel, onto the estuarine dynamics. This channel is the main freshwater input for the northern portion of this ecosystem, having an annual mean runoff of 435 m(3) s(-1). Since 2002 a dramatic increase in dissolved inorganic phosphate concentrations (DIP) has been observed in estuarine waters. The recommended range of total phosphorus concentration in estuaries and coastal ecosystems to prevent algal blooms is 0.01 to 0.1 mg L-1, according to the Brazilian Environmental Legislation. In the present study, DIP concentrations as high as 2.90 and 1.07 mg L-1 were observed during July 2005 and January 2006, respectively. Suspended matter concentrations higher than 1.0 g L-1 and changes in phytoplankton community were also observed. Present study points out the necessity of driving research efforts to identify the potential pollution sources in the drainage basins of the Ribeira de Iguape River and in the estuarine-lagoon system of Canandia-Iguape. The increase in phosphorous concentrations is leading the estuary to anthropogenic eutrophication processes, as revealed by the decrease in oxygen levels and macrophytes proliferation. So, a monitoring program and public management policies are necessary to improve an environmental conservation plan to control the anthropogenic eutrophication over this preserved area. (AU)