Oxygen–Nutrient Constraints on Aquaculture Carrying Capacity in Lahor Reservoir, Indonesia

Reservoir-based aquaculture is essential for inland fish production but is increasingly constrained by nutrient enrichment, O₂ depletion, and ecological instability. This study evaluated the ecological and carrying capacity of the Lahor Reservoir for sustainable aquaculture using an integrated framework combining water-quality assessment, nutrient-based capacity, O₂-balance modeling, hypoxia-risk evaluation, and Ecological Balance Index (EBI). Water quality was monitored at three stations from 2022–2024, covering temperature, pH, DO, nitrogen species, phosphate, BOD, and COD. Water Quality Index (WQI) scores classified the reservoir as Suitable to Highly Suitable. However, Total Oxygen Demand (TOD) consistently exceeded in situ DO, resulting in chronic O₂ deficits (–2.50 to –6.75 mg L^-1), especially during the dry season, when TOD peaked at 11.55 mg L^-1. Hypoxia Risk Index (HRI) values indicated moderate to high risk, and nutrient-based trophic conditions fluctuated from oligotrophic to hypereutrophic. EBI results showed At-Risk or Exceeded conditions from March to June, with improvement during the rainy season. Carrying-capacity analysis demonstrated that both O₂ and nitrogen dynamics jointly constrain the feasibility of aquaculture. During the dry season, negative ΔN and strong O₂–TOD imbalances eliminated stocking potential entirely, while the rainy season provided limited windows of feasibility, supporting modest densities of 3–22 fish m^-2.