Limnological characterization of interdune ponds of Curupu Island, Raposa – MA, Brazil

This study was conducted on four freshwater interdune ponds (Jacare; Grande; Duna; Banho) located on Curupu Island within the municipality of Raposa (Maranhao State, Brazil). It focused on a diagnosis of the physical and chemical characteristics of the water and sediment in these water bodies, while at the same time obtaining basic data and information that could support the adoption of conservation strategies for the rational use of these ecosystems. Seasonal sampling of water from these ponds was conducted during the months of August, September and November 2008 and 2009 (dry period) and February, May, July 2009 and 2010 (rainy period), for the purpose of obtaining data on temperature, pH, electrical conductivity and dissolved oxygen, ammonium (NH4), nitrite (NO2), nitrate (NO3) and phosphate ion (PO4) concentrations in the pond water. Sediment sampling also was carried out to determine particle size, carbon, organic matter and phosphorus content. A large variation in most variables, especially the ammonia (NH4), nitrate (NO3) and phosphate (PO4) concentrations, was observed during the study period. The pH values indicated the water in the ponds was mostly alkaline. Based on the average nitrate concentrations (137 μg L−1 during the dry period; 123 μg L−1 during the rainy period), the ponds exhibited primarily eutrophic conditions. The sediment samples exhibited a predominance of fine sand with low carbon and organic matter content, able to be classified by their mineral nature. Due to the fragile nature of the studied ecosystems, disciplinary control of grazing activities and tourism in the area is highly recommended, along with adoption of a basic sanitation infrastructure in the community for the purpose of rational and sustainable use of this ecosystem.