Seasonal and spatial variation of the trophic state index of the Orós reservoir, Ceará, Brazil = Sazonalidade e variação espacial do índice de estado trófico do açude Orós, Ceará, Brasil

Abstract

The aim of this work was to evaluate the water quality of the Orós reservoir. It was studied the physico-chemical and biological relation to identify their contribution to the process of eutrophication as well as the trophic level of water using the Trophic State Index Medium (TSI-M). Water samples were collected at seven sample station every two months from Jun/2008 to Apr/2010. We took six water samples during the rainfall season and five in dry season, totalizing 11 water samples. We analyzed the transparency of the water, concentrations of total phosphorus and chlorophyll “a”. Results showed that the presence of sediments carried by runoff reduced the water transparency and the reservoir was classified as hypereutrophic for both seasons. In relation to the phosphorus concentration, the P1 and P6 are the most critical points in the reservoir during the dry season and its waters classified super-eutrophic. The greater transparency increased the concentration of chlorophyll “a” in the rainfall season. In the dry season the lowest values of chlorophyll “a” and water transparency occurred at the same time. The Average Trophic State Index classified the waters as a trophic level of intermediate (mesotrophic) for rainfall season, while in the dry season the level trophic was classified as eutrophic. =

Keywords

• Water quality
• Eutrophication
• Nutrient