Critérios de priorização espacial baseados em padrões de qualidade da água para orientar a gestão hídrica da Represa Billings

Abstract

The increasing pressure on urban water resources in Brazil, particularly in densely populated regions, has strengthened the need for environmental monitoring capable of capturing the spatial and temporal complexity of reservoirs subjected to intense anthropogenic loads, as in the case of the Billings Reservoir, one of the main water bodies of the São Paulo Metropolitan Region. This study investigates how the integration of monitoring protocols can guide and support water-resource management in the reservoir. The study analyzed data produced by the CETESB monitoring network between 2014 and 2024 and complemented them with in situ measurements obtained using portable technology, specifically the AlgaeTorch fluorometric probe. The methodological approach included temporal trend analyses (Mann–Kendall and Sen’s Slope), spatial assessments (thematic GIS-based maps), and multivariate procedures (Factorial, Hierarchical Cluster and Canonical Discriminant Analyses). Three central patterns were identified: (i) a gradual improvement in water quality after 2017, marked by reductions in total phosphorus, reactive nitrogen, and chlorophyll-a, directly influenced by the hydrological regime and rainfall regularization; (ii) strong spatial heterogeneity, distinguishing compartments with distinct ecological functions: accumulation zones, resilient transition areas, and upstream sectors that are less impacted; and (iii) the persistence of a hypereutrophic state, although followed by a decline in phytoplankton productivity due to the low bioavailability of phosphorus. The multivariate methods enabled the identification of coherent environmental groups and latent ecological processes not captured by the conventional monitoring network, revealing limnological signatures associated with hydraulic operation, diffuse pressures, and water residence time. Measurements obtained using portable fluorometry demonstrated a high potential as a complementary tool to enhance the spatial resolution of the assessment, allowing the detection of algal biomass gradients in areas not covered by CETESB’s monitoring stations. The integration of these approaches constitutes an effective strategy to support water-resource management, as it does not require drastic interventions in the CETESB monitoring practices but rather adjustments in data-analysis methodologies and their complement with low-cost, rapid-response technologies capable of generating reliable information and indicating which areas and types of actions should be prioritized. The study contributions support advances in the governance of metropolitan water supply systems, aligned with the principles of water security, territorial planning, and sustainable cities.