Abstract

The Jansen lagoon is a coastal system formed by damming the Ana Jansen Creek, which is located in the northwest of São Luís Island (northern Brazil) and is under high urban influence. The use of indexes to assess the water quality in aquatic systems is important because they show the degradation degree of an area and give support to measures for the sustainability and protection of aquatic life, consequently. For the seasonal and spatial analysis of environmental and biological variables, six bimonthly surveys between November 2011 and September 2012 were carried out at five sampling sites. In addition, indexes such as the index of minimum parameters for the protection of aquatic communities, Trophic State Index, and Aquatic Life Protection Index were applied to evaluate the water quality. High levels of dissolved oxygen (DO), pH, total phosphorus, and chlorophyll a were observed in the lagoon waters. In general, the water quality indexes showed that the Jansen lagoon has a poor water quality due to elevated DO and pH as well as high concentration of surfactants and phenols. These environmental conditions favored the intense process of eutrophication (hypereutrophy) and environmental degradation of the area, affecting the development of aquatic biota.

Keywords: coastal lagoon, water quality, aquatic life protection, eutrophication, pollutants
