Spatial and temporal variability in nitrous oxide and methane emissions in urban riparian zones of the Pearl River Delta

Spatial and temporal variability in nitrous oxide and methane emissions were quantified in three seasons using closed chambers in three riparian zone locations of three branches of the Pearl River, Guangzhou, China. The sampling sites were selected in a rapidly developing urban area of Guangzhou and represented a pollution gradient. The results show that urban riparian landscapes can be large source areas for CH4 and N2O, with fluxes of −0.035 ∼ 32.30 mg m−2 h−1 and −5.49 ∼ 37.31 μg m−2 h−1, respectively. River water quality, sediment texture, and NH4-N and NO3-N concentrations correlated with N2O and CH4 emission rates. The riparian zones of the more seriously polluted tributaries showed higher greenhouse gas fluxes than that of the less polluted main stem of the Pearl River. Rain events increased emissions of CH4 by 6.5 ∼ 21.3 times and N2O by 2.2 ∼ 5.7 times. The lower concentrations of heavy metals increased the activity of denitrifying enzymes while inhibited the methane producing pathways. This work demonstrates that rapidly developing urban areas are an important source of greenhouse gas emissions, which is conditioned by various environmental factors.