Relationship between chlorophyll-a, rainfall, and climate phenomena in tropical archipelagic estuarine waters

Similar to many estuaries worldwide with sources receiving nitrogen and phosphorus, i.e., nutrients, from point and diffuse sources, the waters in Jakarta Bay, Musi Estuary, and Rokan Estuary in Indonesia are facing negative impacts on water quality and ecosystems, i.e., eutrophication, because of rapid urbanization and human activities. The transport of nutrients through rivers and tributaries depends on rainfall and climate phenomena, ultimately dictating chlorophyll-a (Chl-a) concentrations and trophic levels in estuaries. The relationship between trophic level, Chl-a concentration, rainfall, and climate phenomena was explored in this study by examining monthly Chl-a concentrations from 2003 to 2021 in the three estuaries. Remote sensing Chl-a concentrations data from the NASA Aqua MODIS mission was subjected to Geographic Information System (GIS) and statistical analyses. The dynamic fluctuations of Chl-a concentrations in all estuaries showed eutrophic zones appearing at specific times, influenced by local rainfalls and their patterns. The first principal components of the Empirical Orthogonal Function (EOF) analysis of Chl-a concentration anomalies showed significant correlations with rainfall anomalies and the Indian Ocean Dipole (IOD) index. These relationships exhibited distinct patterns influenced by unique climate factors in each estuary. The study highlights the crucial role of wide-area continuous monitoring and early warning systems, facilitated by satellite remote sensing, in preserving the health of coastal ecosystems. The findings also offer valuable insights for designing future monitoring programs and targeted conservation efforts.