Estado trófico em reservatório urbano raso - estudo de caso: açude Santo Anastácio, Fortaleza (CE)

Abstract

Urban reservoirs face a growing deterioration in the quality of their waters due to lack of sanitation, mainly related to the incorrect disposal of domestic wastewater and solid waste. This promotes the contribution of contaminants through point and diffuse sources, causing significant impacts on the reservoir. One impact is eutrophication, which is the excessive algae growth due to high nutrient loads, especially nitrogen and phosphorus. This phenomenon is observed mainly in lentic environments, which contributes to the development of phytoplankton and aquatic weeds at levels above the natural growth. This study evaluated the process of eutrophication in a shallow urban reservoir, the Santo Anastácio Dam, located in the State of Ceará, NortheasternBrazil, which was taken as a case study. To identify the trophic status of the reservoir, the Trophic State Index (TSI) was used. The total phosphorus and chlorophyll-a analysis were used to calculate the average TSI and classify the reservoir as hypereutrophic. It was found that the reservoir is under an advanced process of eutrophication, which is still increasing over time. The results of the monitored parameters compared with Resolution CONAMA 357/05 for freshwater class 2 remained outside the established standards, except for the pH parameter. The total phosphorus exhibited much higher concentrations than the limits established by the environmental legislation, which reflected directly in the trophic level of the reservoir.