Quantification of N₂O and NO emissions from a small-scale pond-ditch circulation system for rural polluted water...

The pond-ditch circulation system (PDCS) is an efficient and economical solution for the restoration of degraded rural water environments. However, little is known about nitrous oxide (N₂O) and nitric oxide (NO) emissions in the microbial removal process of nitrogen in PDCSs, and their contribution to nitrogen removal. The aim of this study was to quantify N₂O and NO emissions from the PDCS, evaluate their capacities, and elucidate the key environmental factors controlling them. The results showed that N₂O and NO fluxes were in the ranges 1.1-2055.1μgNm^-2h^-1 and 0.1-6.8μgNm^-2h^-1 for the PDCS, respectively. Meanwhile, the N₂O and NO fluxes from the two ponds in the PDCS were significantly higher than those in the static system. Moreover, the amount of N₂O and NO emissions in the PDCS accounted for 0.17-4.32% of the total nitrogen (TN) removal. According to the partial least squares (PLS) approach and Pearson's correlation coefficients, nitrate nitrogen in water (W-NO₃^--N), dissolved oxygen in water (W-DO), dissolved oxygen in sediment (DO), pH in water (W-pH), pH in sediment (pH), total kjeldahl nitrogen (TKN), and soil organic carbon (SOC) significantly affected the N₂O flux (p<0.05), whereas W-NO₃^--N, DO, and nitrite nitrogen in sediment (NO₂^--N) significantly affected the NO emission (p<0.05).