Regional distribution of livestock manure and response characteristics of water environment in Chongqing

Correct calculations of livestock pollutants discharges are required for determination of the impact of livestock on water environment. The existing estimation methods of livestock pollutants discharges are insufficient and confusing in terms of definition of discharge coefficients, and therefore induce mistakes in breeding cycle calculations and livestock elimination rate. Aiming to meet these problems, the paper established calibration methods for calculating production coefficient and discharge coefficient of pollutants, and breeding cycle of livestock, based on livestock breeding data and pollution control methods of Chongqing City of China. And the producing and discharging amounts of livestock in Chongqing City were estimated with the methods. According to ecological function of five functional areas of Chongqing City and discharge characteristics of chemical oxygen demand (COD_Cr), total nitrogen (TN) and total phosphorus (TP), the equiscalar pollution loading ratio and comprehensive pollution index were used to investigate regional distribution of livestock manure and water environment response and to identify the main pollutants and polluted areas in Chongqing. The results provided the needed decision support for industrial development and environmental protection. Results showed that the breeding cycles of pig, dairy cattle, beef cattle, laying hens and broilers were 122, 365, 365, 52 and 365 days, respectively. The corresponding discharge coefficients for COD_Cr were 0.049, 0.626, 0.170, 0.002 and 0.001 kg·head^-1·d^-1, respectively. Also the corresponding discharge coefficients for TN were 0.013, 0.081, 0.048, 0.001 and 0 kg·head^-1·d^-1, respectively. Then the corresponding discharge coefficients for TP were 0.012, 0.024, 0.030, 0.001 and 0.003 kg·head^-1·d^-1, respectively. A total of 411.81×10⁴ equivalent pig heads were raised in 2013 in Chongqing City, and 2.27×10⁶ tons manure, 1.66×10⁶ tons urine and were discharged containing respectively 3.03×10⁴ t, 0.72×10⁴ t and 1.87×10⁴ tons of CODCr, TN and TP. Based on pollution evaluation, the main contaminated areas were urban development area and northeast ecological conservation development area, with TP as the main pollutant. The synthetic index of water potential quality range was 0.22–4.12. The results also showed that the development of livestock breeding was significantly correlated with function regionalization. Water pollution was not the main environmental problem in urban core function area, which was the center of politics, economy and culture defined some sections as “forbidden region for raising livestock”. Urban development area was the main polluted region, where implement industrial planting was promoted in order to solve the contradictions between economic progress and environmental protection. The northeast ecological conservation development area was another main polluted region, where the ecological red lines were needed to build to restrict project implementation and protect the Three Gorges Reservoir.