File S2. The method for calculating annual discharge amount of total nitrogen, total phosphorus and chemical oxygen demand by livestock husbandry in the TGRA from 2003 to 2012. Annual amount of major livestock and poultry in the TGRA from 2003 to 2012 (head). Year Swine Cattle Poultry 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 11461435 12055101 12723790 12308071 13108754 11711007 12536977 12499750 12522783 12660272 1120155 1137375 1129662 647972 690405 694419 721078 778419 764701 795314 133167000 142188900 156194500 154338900 135656700 169400500 185134700 204167500 216299400 230882800 Feeding cycle (days) Animal Feeding cycle Swine Cattle Poultry 199 365 55 Data collected from Insights into the production potential and trends of China’s rural biogas. Discharge coefficient of livestock husbandry (g/day per head) Animal TN TP COD Swine Cattle Poultry 19.74 104.10 1.16 4.84 10.17 0.23 403.67 2235.21 20.50 Discharge coefficients collected from Discharge Coefficients of Livestock and Poultry Farming Pollutants in the First National General Survey of Pollution Sources. Calculated formulas: ππ = ∑ πΉπ πΆππ πΉπΆπ ππ = ∑ πΉπ πΆππ πΉπΆπ πΆππ· = ∑ πΉπ πΆπΆππ· πΉπΆπ Fi: feeding capacity of ith animal; CTN: discharge coefficients of TN; CTP: discharge coefficients of TP; CCOD: discharge coefficients of COD; FCi: feeding cycle of ith animal.