Coastal Water Quality Assessment in Pekalongan, Indonesia, during the East Monsoon Using CoWQI and PCA

The dynamics of coastal waters are crucial to marine ecosystems. Rivers in Pekalongan City support household, agricultural, and fisheries activities. Human activities on land significantly influence pollutant inputs to coastal waters. Pekalongan has two major river estuaries with distinct source characteristics: the Loji and Sengkarang Rivers. This study assessed coastal water quality across three east-monsoon sampling campaigns over a 3-year period to identify potential pollution sources and investigate mitigation strategies. This study used Total Suspended Solids (TSS), nitrate, phosphate, dissolved oxygen (DO), chemical oxygen demand (COD), chlorophyll-a, and total coliform as water-quality criteria for the Coastal Water Quality Index (CoWQI). Principal Component Analysis (PCA) was used to identify patterns in complex water-quality datasets and clarify the impact of pollutants. The results showed that water-quality conditions in the Loji and Sengkarang estuaries fell within the poor to very poor criteria. Based on the PCA resultss, three principal components accounting for 80.869% and 78.32% of the total variation were retained for the Loji and Sengkarang estuaries, respectively. The dominance of pollutant components in the Loji estuary, as indicated by COD and total coliform levels, suggests that domestic waste and residential activities are the primary sources of organic and microbiological pollution in the estuary. Meanwhile, the Sengkarang estuary showed a complex pattern of pollutant dominance, with organic loads accumulating alongside physicochemical changes and eutrophication processes, as evidenced by high COD, temperature, and chlorophyll-a and low DO. A sustainable mitigation strategy for the Loji estuary, such as controlling domestic waste and improving sanitation systems, is needed. Meanwhile, management of the Sengkarang Estuary should focus on controlling nutrient and sediment runoff from aquaculture areas and anthropogenic activities through sustainable aquaculture practices. Effective pollution-control enforcement is crucial for restoring the health of Pekalongan's coastal ecosystems.