Salinity distribution analysis for the region of freshwater influence (RoFI) at the Musi-Banyuasin Estuary, Indonesia

RoFI is a transition zone where fresh water and sea water mix, characterized by water column stratification, with salinity as the key parameter. This study is the first to identify RoFI based on salinity gradients in the Musi–Banyuasin Estuary, aiming to reveal the distribution patterns of salinity and oceanographic parameters that influence RoFI extent. Observations were conducted at 9 stations using CTD, with horizontal and vertical profiles visualized in ODV, and tides and currents analyzed as the primary controllers of RoFI dynamics. The results show that RoFI can be clearly identified through salinity distribution, where the Musi Estuary is characterized by low surface salinity (5 PSU) and water column salinity of 25–30 PSU at high tide, with residual freshwater influence at low tide, while the Banyuasin Estuary is dominated by high salinity (24–28 PSU) throughout the water column, reflecting the dominance of seawater. PCA analysis (80.41%) confirmed that the RoFI area is closely related to tides, currents, and river discharge. However, the limited observation period indicates the need for further season-based studies to understand RoFI dynamics better.