Title : Urbanization dynamics and water vulnerability: An analysis of non-point source pollution surrounding the Chavantes reservoir, Brazil
Abstract:
The trajectory of human civilizations is inextricably linked to the availability of water resources. However, unplanned urban expansion and increasing population density impose severe anthropogenic pressures on aquatic ecosystems. In Brazil, the unregulated occupation of ecologically fragile zones, such as Permanent Preservation Areas, exacerbates soil degradation, erosion, and subsequent water contamination. While traditional watershed management focuses on point-source control, there is a critical gap in monitoring non-point source (NPS) pollution, a primary byproduct of land-use transformation. NPS pollution is inherently complex to quantify as it results from the wash-off of surface-accumulated pollutants during rainfall events. This study hypothesizes that rapid urbanization along the margins of the Chavantes Reservoir acts as a catalyst for land degradation and NPS loading. This issue is of heightened legal and environmental significance within the Angra Doce Special Area of Tourist Interest (AEIT), where landscape integrity is vital for regional sustainability. To assess the spatial distribution of NPS risk, this research applied the Potential Non-Point Pollution Index (PNPI) within a Geographic Information System framework. The methodology integrates three indicators: the Land Cover Indicator (LCI), which evaluates the contaminant potential of different land-use types; the Run-Off Indicator (ROI), assessing the transport capacity based on pedology, slope, and soil permeability; and the Distance Indicator (DI), weighting the proximity to receiving water bodies. The application of PNPI in the Chavantes Reservoir region reveals that land-use patterns are the primary determinants of water quality degradation. Urbanized areas exhibited a mean LCI of 8.22, significantly higher than rural or native vegetation classes. Soil sealing (impermeabilization) in these areas prevents infiltration, increasing runoff volume and velocity, which carries microplastics, oils, and heavy metals directly into the reservoir. Satellite imagery analysis corroborates these findings, showing peak concentrations of total suspended solids in bays adjacent to urban hotspots. Temporal analysis indicates an 83% increase in urban land cover between 1993 (49 km²) and 2023 (90 km²). This expansion without sustainable drainage infrastructure exponentially increases water vulnerability. We conclude that mitigating land degradation in this strategic basin requires a shift in land-use policies, prioritizing green infrastructure and stricter controls on urban sprawl in high-sensitivity zones to ensure the long-term conservation of the AEIT Angra Doce.
