Long-term monitoring and proposed diffuse pollution control of a tropical reservoir

This paper presents the results of 30 years of water quality monitoring in a tropical water supply reservoir (Vargem das Flores, Brazil). This water body is subjected to eutrophication problems caused by point sources (discharge of untreated sewage) and diffuse pollution (agricultural use in the drainage basin). Emphasis is given here on the estimation of nutrient loads and on the study of the N/P ratio in the water body. In spite of the prevalence of high N/P values, there is a clear trend in the dominance of cyanobacteria in the phytoplankton, which contradicts results from research in temperate aquatic environments. Some restoration measures for Vargem das Flores Reservoir are currently being implemented: construction of wastewater treatment plants, control of recreational activities, erosion control by hydroseeding and use of natural wetlands. Finally some management strategies in order to prevent algae input in the water abstraction system are discussed. Examples of these techniques are the installation of plastic barriers and the construction of an air curtain device.