Imbalance of Carbon–Nitrogen–Phosphorus Ratios in Coastal Waters as a Constraint for Aquaculture Development in Karawang, Indonesia

Coastal waters are the main water source for traditional aquaculture in many regions of Indonesia, including Karawang, but their suitability is increasingly affected by nutrient enrichment and biogeochemical imbalance. This study evaluated carbon–nitrogen–phosphorus (C–N–P) ratios in Karawang coastal waters and their implications for traditional aquaculture. Water quality parameters measured included chemical oxygen demand (COD), total nitrogen (TN), ammonia (TAN), nitrite, nitrate, and phosphate. A Traffic Light Approach (TLA) was applied using criteria based on national water quality standards and relevant literature. Organic carbon was estimated from COD to determine the C/N ratio, while the N/P ratio was calculated from TN and phosphate concentrations. Results showed that ammonia (0.21–1.36 mg/L), nitrite (0.01–0.42 mg/L), and phosphate (0.018–0.898 mg/L) frequently exceeded recommended limits. Total nitrogen concentrations (4.85–9.32 mg/L) indicated eutrophic conditions. The consistently low C/N ratio (0.10–2.30) suggested carbon limitation relative to nitrogen, whereas the N/P ratio (16–953) reflected substantial nutrient imbalance. These findings indicate that Karawang coastal waters are under ecological pressure and may be less suitable as direct water sources for traditional ponds. Evaluating nutrient ratios provides a more comprehensive assessment of ecosystem condition and may support more sustainable aquaculture management.