VOLUME 19 (Supplement)

Ecological status of streams in Zambales riverscape inferred from benthic macroinvertebrates as biological indicators

Lotic ecosystems, such as rivers and streams, play vital roles in sustaining biodiversity, regulating nutrient cycles, and providing key ecosystem services. However, these systems are increasingly threatened by anthropogenic pressures, particularly in tropical regions like the Philippines. This study assessed the ecological integrity of lotic ecosystems in Zambales, Philippines, by integrating benthic macroinvertebrate community structure with physicochemical parameters across six stream sites. Sampling was conducted during the transitional season of October 2023. Physicochemical parameters, including dissolved oxygen (DO), conductivity, total dissolved solids, salinity, pH, and nutrient concentrations (ammonia, nitrite, nitrate, phosphate), were measured and analyzed using principal component analysis to determine environmental gradients and site clustering. Benthic macroinvertebrates were collected and identified to family and genus levels. Diversity metrics (Shannon Index, evenness), EPTC indices (Ephemeroptera, Plecoptera, Trichoptera, Coleoptera), and taxon richness and density were computed to evaluate biological responses. Canonical correspondence analysis revealed strong correlations between environmental stressors and macroinvertebrate assemblage structure. Results indicated that streams traversing forested and less disturbed areas supported higher diversity and more pollution-sensitive taxa, particularly EPTC, whereas streams in residential and industrial zones exhibited reduced diversity and dominance of tolerant taxa such as Diptera. Notably, sites 1 (agricultural land) and 6 (residential area) lacked detectable EPTC taxa and displayed signs of poor ecological health, evidenced by high conductivity, nutrient enrichment, and low DO concentrations. These findings underscore the impact of land use on stream conditions and highlight the value of integrating biological and physicochemical assessments for effective monitoring and conservation of freshwater ecosystems.