CH4 concentrations were measured using a Varian CP-3800 gas chromatograph equipped with a flame ionization detector (FID) and stainless steel packed columns of Porapak Q fused silica columns (2 m length × 28.58 mm diameter); operating conditions for the GC were; 120 °C of injector temperature, 70 °C of oven temperature and 320 °C of detector temperature using a 1.0-mL gas-tight syringe (Hamilton, USA). N2O concentrations were measured using a Varian CP-3800 gas chromatograph with an electron capture detector and stainless steel packed columns of Porapak N (2 m length × 28.58 mm diameter); operating conditions for the GC were: 120 °C injector temperature, 70 °C oven temperature and 200 °C detector temperature using a 0.5-mL gas-tight syringe . The carrier gas was ultra-high purity N2 and the flow rate was 30 mL min−1.