Dynamic and maintenance of water purification ecosystem service in the Guandu River Hydrographic Region, Rio de Janeiro, Brazil

ABSTRACT The present study aimed to develop a methodology for analyzing the dynamics and maintenance of the water purification ecosystem service in the water bodies of the Guandu River Hydrographic Region, responsible for water supplying the Rio de Janeiro Metropolitan Region, characterized by the presence of water transfers and low levels of effluent treatment. The dynamics of this service occurs through an ecosystem flow, influenced by the volume of water that moves from one region to another. The methodology consisted of reviewing studies of ecosystem flows, building a database, classifying impacts on water purification in hydrological planning units from a similarity dendrogram, analyzing indicators related to water demands and availability of these units, and developing an ecosystem flow diagram of water purification. The effects of transfers on the maintenance and flow of water purification were also analyzed from the comparison between the real scenario (which considers the presence of the existing hydraulic infrastructure) and the natural scenario (which disregards it). The results showed that the worst situation of maintenance of water purification is in the western part of the region, and the demands for it requires more than double the volume of withdrawn water to supply the local population and industry.