Abstract
The aim of this paper was to verify hydrological and hydrochemical changes in the Iquiparí Lagoon water column, during three months, as related to an artificial sand bar opening. A drastic reduction in water volume occurred 28 hours after the sand bar opening, exposing the bottom sediment. This was densely colonized by submerged aquatic plants, which were dominant in the ecosystem metabolism, specially near the sand bar. An increase in salinity values, and dissolved and total nutrient concentrations, was observed during the sand bar opening period. In contrast, chlorophyll a concentration decreased. These changes were associated with: 1) mix of remained brackish and marine waters; 2) nutrient release from sediments by physical processes; and 3) submerged plant death. After the sand bar closure, lagoon metabolism was completely regulated by a dense phytoplankton community. We observed that the sand bar opening resulted in an extensile replacement of the lagoon's water and a change in the community mainly responsible for the ecosystem metabolism.
Highlights
Coastal lagoons have peculiar functional and structural characteristics due to their localization between land and sea
Study area Iquiparí Lagoon is a small, isolated, coastal lagoon situated in the northern region of Rio de Janeiro State, in the city of São João da Barra, between 21o44’20” and 21o48’12”S and 41o01’34” and 41o02’04”W (Fig. 1)
Its water surface has been estimated at 1.4 km2 with an extension of 10 km, based on satellite images obtained from the National Institute of Space Research (INPE), in August 1992
Summary
Coastal lagoons have peculiar functional and structural characteristics due to their localization between land and sea They generally show large temporal and spatial variations in hydrochemical characteristics and considerable biological diversity (Yãnez-Arancibia, 1987; Castel et al, 1996). The environmental impact entailed by this management has received little attention (Saad, 1996; Suzuki et al, 1998; Kozlowsky-Suzuki, 1998). These sand bar openings can cause radical alterations in physicochemical, chemical, and physical conditions, including drastic reduction of the water volume and profound alterations in the biotic communities due to brackish water overflow and salt water influx
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