Mapping and web-based GIS prediction of pig waste discharge in the Taal Lake

Abstract

Freshwater ecosystems around the world are under growing pressure from agricultural activities, particularly intensive livestock farming that releases untreated waste into rivers and lakes. In the Philippines, Taal Lake, an ecologically and economically important freshwater resource, has shown signs of declining water quality due to the increasing number of pig farms located along its tributaries. This study developed a web-based Geographic Information System (GIS) to better understand, map, and predict how pig waste is transported from farm locations through the watershed and into Taal Lake. Modelling techniques, including Digital Elevation Model processing, flow direction and accumulation analysis, watershed delineation, and source to stream routing, were used to simulate waste movement along natural drainage pathways. Estimated waste volumes were calculated using pig population data and established waste generation rates, allowing potential pollutant loads to be assessed. The results identified Agoncillo, Tanauan, and Talisay as the most critical areas, with Agoncillo alone accounting for approximately 38.1% of the recorded pig farms. Routing analysis showed that waste from these areas tends to converge along specific tributaries, increasing downstream pollution risks, especially during rainfall events. An interactive web-based map was created using GeoJSON and the Leaflet API to visualize pig farm locations, predicted discharge volumes, flow paths, watershed boundaries, and downstream impact zones. Overall, the study shows that combining GIS analysis with an interactive web platform can support clearer understanding of pollution pathways and provide a practical decision support tool for environmental monitoring and sustainable watershed management around Taal Lake.