Impactos da piscicultura intensiva sobre a qualidade da água de um reservatório no semiárido

Abstract

Intensive fish farming in reservoirs has been growing worldwide, representing an important source of income for riverine human populations. Nevertheless, fish tanks enrich the water bodies with nutrients, mostly nitrogen and phosphorus, from fish excrement and food not consumed. Such increase in nutrient concentrations leads to eutrophication and decrease in water quality. This study estimates the effects of fish cage tilapiculture on water quality of a multiuse reservoir. The Camalaú reservoir is located in the semi-arid region of Brazil and since 2001 is part of a larger project for implementation of intensive farming of tilapia in net cage tanks. Fish production begun in 2008, declined in 2009 and was resumed in 2010 only to be abandoned in 2011. Bimonthly samplings where performed from March 2008 to June 2011. Water temperature, pH and transparency were measured in the field and in the laboratory the alkalinity, dissolved oxygen, chlorophyll a and inorganic nutrients (ammonium, nitrite, nitrate, total phosphorus and soluble reactive phosphorus) were measured. The trophic state and support capacity were also estimated. Results show that the water was well oxygenated and the temperature, pH and alkalinity varied significantly during the study period. Nitrate and total phosphorus showed higher concentrations during the years of greater fish production. The study reservoir was mesotrophic and eutrophic during the study period. Given the high concentration of phosphorus, the study reservoir do not present conditions that support pisciculture, being necessary mitigating measures to reduce phosphates concentration to the sustainable fish farming.