Assessing hypoxia risk and ecological stability in reservoir-based aquaculture in the Wonorejo reservoir, Indonesia

Abstract

Sustainable aquaculture in inland reservoirs depends on seasonal hydrology, which influences nutrient dynamics and O₂ availability. This study aimed to quantify O₂ and nutrient-based ecological carrying capacity and seasonal hypoxia risk to support sustainable aquaculture planning. This study evaluated the feasibility and ecological capacity of aquaculture in the Wonorejo Reservoir, Indonesia, using a four-pillar framework: feasibility mapping, ecological assessment, carrying capacity estimation, and risk-based ecological management. Monthly water quality data from 2022–2024, supported by in situ validation in March 2025, were analysed using the Vollenweider phosphorus model, O₂ balance calculations, total oxygen demand (TOD), and the ecological balance index (EBI). Spatial analysis identified areas suitable for aquaculture in about 36.2% of the area. Phosphorus loading remained within oligotrophic conditions (0.12–0.28 mg P∙m⁻²∙y⁻¹), indicating that nutrient enrichment is not the dominant limiting factor. Oxygen availability emerged as the dominant ecological constraint under the applied O₂ balance framework. Dry season elevated TOD relative to estimated natural re-aeration capacity. This resulted in chronic O₂ deficits (EBI = 0.50–0.60) and reduced the system’s resilience. Under these O₂-limited conditions, theoretical N-based aquaculture potential (1,250–1,600 mg∙y⁻¹) declined to a sustainable range of 500–900 mg∙y⁻¹. A hypoxia-focused hazard–exposure–vulnerability (HEV) assessment showed high HEV during dry seasons, moderate risk during transitional periods, and low risk during rainy conditions. The findings emphasise that O₂ dynamics, rather than nutrient levels, govern sustainable aquaculture capacity. Oxygen-based stocking regulation, organic load management, aeration, and spatial zoning are recommended to improve ecological stability.