CH4 Concentrations and Emissions from Three Rivers in the Chaohu Lake Watershed in Southeast China

This study was conducted at three rivers of the Chaohu Lake watershed during the summer season of 2008, aiming to investigate the diurnal variations of dissolved CH4 concentrations and emissions, as well as the dynamics of CH4 accumulation emission rates over consecutive 72 h. The results showed that CH4 concentrations in the Fengle, Hangbu, and Nanfei rivers ranged from 56.33–124.79, 160.82–341.03, and 213.49–716.81 nmol L−1, respectively, over a daily cycle; while the saturation of CH4 ranged from 188.72–418.07, 538.74–1 142.46, and 715.23–2 401.38%, respectively, which indicated that surface waters were in all cases oversaturated with respect to the atmosphere. An obvious diurnal variation pattern of the dissolved CH4 concentrations demonstrated a higher value during daytime but a lower value for night time. Additionally, the highest dissolved CH4 concentrations were detected in the Nanfei River which received substantial urban wastewater discharges. CH4 emissions measured with floating chambers ranged from 5.82–15.46, 5.77–8.41, and 13.51–49.25 mg C m−2 h−1 for the Fengle, Hangbu, and Nanfei rivers, respectively, over a daily cycle. Significantly higher CH4 emissions were also observed from the Nanfei River. The accumulative CH4 emissions for each river increased with time, while a decline trend on the accumulation rates was investigated over the consecutive 72 h.