| Evaluation of regional aquaculture capacity, based on environmental capacity, is necessary to achieve optimal densities for primary breeding species, reduce pollution from aquaculture and support sustainable develop in aquaculture. The Nanxun district of Huzhou city in Zhejiang Province was selected as the research area, where there is an aquacultural area of 5946.71 hm2 with an annual yield of 90,000 t. In May, August and November 2015, ten monitoring sites were established to investigate the condition of aquaculture and the water environment at Nanxun District and determine the pollution discharge per unit production of six primary aquaculture modes. Based on the results, an aquaculture capacity model was constructed, taking phosphorus loads and Grade II water quality standards as the restricting condition. The model was then used to calculate the optimal ecological capacity of the six aquaculture modes. Results show (1) phosphorus limits water quality in Nanxun district; (2) the phosphorus discharge per unit production for the six primary aquaculture modes (the four major Chinese carps; Micropterus salmoides; Ophiocephalus argus Cantor; Culter alburnus Basilewsky; Trionyx Sinensi and Mylopharyngodon piceus ) were 0.26 g?kg-1, 0.70 g?kg-1, 0.73 g?kg-1, 0.17 g?kg-1, 0.33 g?kg-1 and 0.22 g?kg-1, respectively; (3) The corresponding maximum acceptable P-loading (Pmac) for the six primary aquaculture modes were 7.38 t, 5.79 t, 2.36 t, 1.82 t, 1.51 t and 2.52 t and the corresponding aquaculture capacities were 28370 t, 8271 t, 3236 t, 10698 t, 11648 t and 9685 t. Parameter sensitivity analysis of the aquaculture capacity model was carried out using Markov Chain Monte Carlo (MCMC) methods and the sensitivity coefficients for the phosphorus retention rate, water exchange coefficient and phosphorus concentration in the river were, respectively, 0.365, 0.364 and -0.271. These values indicate that the regional aquaculture capacity estimates, based on TP meeting Grade II water quality standards, are reasonable and provide a scientific reference for decision making in relevant administrative departments. |
