A comprehensive assessment of water quality and pollutant dynamics in the east coastal waters of Sidoarjo, two decades after the Lapindo mudflow disaster

The 2006 Lapindo mudflow, diverted into the Porong River, has had severe and lasting impacts on the East Sidoarjo coastal environment. This study provides a comprehensive assessment of water quality and pollutant dynamics two decades after the disaster. Water samples were collected using stratified purposive sampling from three coastal villages (Kedungpandan, Kupang, and Permisan) in April 2025. Physicochemical parameters, nutrients, and heavy metals (Pb, Cd, Cu, Zn) were analyzed using American Public Health Association (APHA, 2017) protocols. Data were evaluated using descriptive statistics, analysis of variance (ANOVA), correlation analysis, and Principal Component Analysis (PCA), a multivariate statistical tool used to identify dominant factors influencing water quality. Results revealed stable temperature (30.5 °C), a clear salinity gradient (17.3-24.7 ppt), and spatial variation in dissolved oxygen (DO, the amount of oxygen available for aquatic organisms) ranging from 6.27 to 7.83 mg/L. Nutrient levels were generally low, with phosphate identified as the limiting factor. Total Organic Matter (TOM, a measure of decomposable organic material in water) ranged widely (35.76-107.44 mg/L), indicating strong terrestrial input. Although most heavy metals were within safe limits, copper (Cu) concentrations (0.96-3.46 mg/L) greatly exceeded regulatory thresholds and were found at elevated levels alongside high TOM, though their correlation was not statistically significant. PCA identified two main pollution sources: organic-nutrient input from the Porong River and geogenic heavy metals from volcanic material. These findings provide the first long-term baseline dataset for this area, supporting the development of adaptive aquaculture practices and evidence-based coastal management strategies.