NITROGEN AND PHOSPHORUS BUDGET IN ENGINEERED RECIRCULATING AQUACULTURE POND

The intensive aquaculture-induced environmental pollution has impeded the sustainable and healthful progression of the aquaculture industry. In order to explore a more sustainable and efficient aquaculture model, we enhanced the circulating aquaculture system in freshwater ponds in this study. The physicochemical indexes and nitrogen and phosphorus budget of ponds were analyzed during the 5-month experiment period. The results showed fluctuating changes in the physicochemical indexes of pond water, with total nitrogen and total phosphorus concentrations measuring 4.85 and 1.04 mg/L, respectively, at the end of the experiment. Notably, the total nitrogen concentrations met the secondary standards for freshwater aquaculture tailwater discharge. Feed and sediment emerged as principal contributors to nitrogen and phosphorus input, accounting for 50.6% and 43.7% of nitrogen input and 49.4% and 46.9% of phosphorus input, respectively. Sediment accumulation emerged as the primary mechanism for nitrogen and phosphorus output in ponds, accounting for 53.3% and 78.7% of nitrogen and phosphorus output, respectively. The nitrogen and phosphorus utilization rates in experimental ponds were determined to be 65.2% and 16.6%, respectively. The utilization rate of nitrogen and phosphorus of carp (Cyprinus carpio) were significantly higher than those of other fish (P<0.05). However, there was no significant difference in the phosphorus utilization rate between silver carp (Hypophythalmichthys molitrix) and bighead carp (Aristichthys nobilis) (P>0.05). The research shows that the enhanced pond circulation aquaculture system can effectively mitigate nutrient load, enhance the nitrogen and phosphorus utilization rate of aquaculture organisms, diminish the impact of aquaculture tailwater on the surrounding environment, and concurrently consider ecological and economic benefits. It represents a low cost, environmentally friendly, and healthful pond aquaculture model.