Agricultural headwater ditches are important pathways of reactive nitrogen loss from adjacent croplands, and also act as hotspots for reactive nitrogen transformation. In this study, NO emissions from a typical agricultural ditch in the hilly area of central Sichuan Basin were measured by the closed static chamber-chemiluminescence method, from December 2014 to November 2015. The results showed that the cumulative NO emissions from the sediment-water interface without vegetation (NV) and the ditch ecosystem with natural vegetation (Ⅴ) were -0.4 g·(hm2·a)-1 and 14.17 g·(hm2·a)-1, respectively. The combined annual NO emission flux for the agricultural headwater ditch ecosystem was 11.27 g·(hm2·a)-1, with a mean NO emission rate of 0.13 μg·(m2·h)-1. A net source of NO from the ditch ecosystem only occurred in summer, which had a significantly higher cumulative NO emission than those in the other seasons. The seasonal variation in NO emissions was mainly regulated by the seasonal changes in NO3--N concentrations and temperature in the overlying water. Meanwhile, the presence of vegetation in the ditch ecosystem significantly increased NO emission rates, whereas it did not markedly influence the annual NO emission.
Keywords: ditch ecosystem; indirect emission; nitrate; nitric oxide; nitrogen cycling in catchment; temperature.