Impactos da eutrofização na disponibilidade hídrica de reservatórios no semiárido brasileiro

Abstract

Water is an essential factor for the development and maintenance of life on Earth, therefore the sustainable management of this resource is necessary. The semi-arid region of northeastern Brazil presents water deficit due to high potential evaporation and rainfall irregularities, and to overcome this problem, governments adopted the reservoir network system, storing water and thus increasing the region's water security. However, the adoption of this measure, associated to the concentrated (industries, urban areas) and diffuse (agricultural areas) release of nutrients, accelerated the eutrophication process, which depreciated the water quality and hampered the multiple use. The study sought to quantify the impact of eutrophication on the water availability of reservoirs in the Brazilian semiarid region using two approaches: 1) estimate, based on secondary data from the Water Resources Management Company - COGERH, the percentage of time that 50 reservoirs remain in accordance to Class 4 for fresh water of resolução CONAMA 357/2005; 2) use the proposed model Chapra and Canale (1991) and adapted by Lira et al. (2020) to simulate the dynamics of phosphorus content in the São José I reservoir. The main conclusions of this study were that about half of the time the reservoirs in the State of Ceará present water quality in accordance to Class 4. The estimates by the regression of secondary data were presented as a simple and effective way to estimate the water unavailability time. The phosphorus balance modeling well represented an average reservoir situation but failed to reproduce the amplitude of the observed values of phosphorus concentration in the water.