Water quality in the macro-tidal Kampar estuary, Indonesia: Real-time measurement during significant tidal bore passages

The limited environmental study in the tidal bore-affected estuaries raises a big question about the significant influence of tidal bore on increasing the risk of water quality degradation and eutrophication in the estuarine area. This study attempts to determine the influence of the flood-ebb cycle on the water quality and nutrient variability in the Kampar estuary. We employed the water quality index (WQI) and eutrophication index (EI) to examine the water quality and trophic status within the bore-affected Kampar estuary. Statistical-based assessments were also performed. The results show that temperature, salinity, pH, and dissolved oxygen (DO) were more variable as the bore propagated. While considerable N- and P-nutrients and chlorophyll-a concentration characterized the study area with a seesaw mechanism, resulting in poor water quality (WQI <50) and high eutrophication level (EI > 1.5) downstream. However, the eutrophication is also high upstream despite the moderate water quality. The EI variation significantly correlates with the flood-ebb cycles indicated by the variation in tidal bore height ( r = 0.65 and PC1 loading value of about 0.4), and these factors most likely characterize the estuarine zone. The tendency of riverine water acidification (pH ≤ 5) during the ebb tide is of particular concern in the study area, indicating the tremendous anthropogenic contributions to deteriorating the water condition. Regular monitoring and more aggressive action are needed to control water pollution in the Kampar River for sustainable water resources. • Water quality parameters rely on tidal bore transport in the Kampar Estuary. • N- and P-nutrients characterize the upstream-downstream with a seesaw mechanism. • Poor water quality and high eutrophication most likely affect the estuarine zone. • Water acidification (pH ≤ 5) indicates the downgraded condition in the study area.