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

The pond-ditch circulation system(PDCS) is an efficient and economical solution for the restoration of degraded ruralwater 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 1.1-2055.1 mu g Nm(-2) h(-1) and 0.1-6.8 mu g Nm(-2) h(-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). (c) 2017 Elsevier B.V. All rights reserved.