Spatiotemporal dynamics of water pollution and mass loading capacity in the Bengawan Solo Rivers: Shifting to dynamic management

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The Bengawan Solo River, the longest fluvial system on Java Island, Indonesia, faces severe anthropogenic pressures endangering its role as a critical water resource. This study provides a comprehensive, decadal spatiotemporal assessment of water quality dynamics across two strategic monitoring stations (Jurang Gempal and Jurug) from 2015 to 2025 using the Storage and Retrieval (STORET) index based on nine core physicochemical and microbiological parameters. Concurrently, a high-resolution analysis of daily mass loading and dynamic carrying capacity (CC) was evaluated at these core urban-industrial nodal points from 2021 to 2025. Decadal STORET profiles revealed chronic pollution gradients shifting from slightly polluted in upstream agricultural reaches to severely polluted (Class D) in urban-industrial midstream zones. Mass loading assessments demonstrated that critical parameters, most notably Biochemical Oxygen Demand (BOD), Orthophosphate (PO 4 -P), and Total Coliform, exceeded the assimilative CC by up to 100% during dry seasons at the Jurug monitoring node. The severe degradation is primarily driven by unregulated textile effluents (home based batik industries) and deficient communal sanitation infrastructure. Statistical modeling indicated that seasonal hydrometeorological variations drastically contract the river's self-purification capacity during low-flow periods. This study establishes a replicable framework for shifting from static regulatory compliance to dynamic mass-load management in heavily stressed tropical river basins.