[Nitrification and Denitrification Potential of Benthic Sediments in a Suburban Stream under Intense Human Disturbance Scenarios].

Water and benthic sediment samples were collected monthly from six sites over a 2-km reach in a first-order stream located in the northeastern rural-urban fringe of Hefei City, from May 2016 to January 2017. These sites were scattered in three stream reach types as natural pattern sections (Scenario 1), point source pollution sections (Scenario 2), and severe soil erosion sections (Scenario 3). The potential rates of nitrification and denitrification in the sediments were measured and variable characteristics were evaluated quarterly. Moreover, a difference analysis of each of the three scenarios and an influencing factor analysis for nitrification and denitrification potentials were subsequently conducted. Our results show that:① the mean value of the nitration ratios for total sediment samples is 0.381%, of which the maximum nitration ratio emerged in Scenario 2. As for Scenario 1, the nitration ratio in summer is the larger than in winter. The nitration ratios for Scenarios 2 and 3 rank from largest to smallest as spring > summer > autumn > winter. ② The mean value of the nitrification rate of the total sediment samples is 0.364 mg·(kg·d), of which the maximum nitrification rate is associated with in Scenario 2. The nitrification rate is highest in winter, while similar for all other seasons in Scenarios 2 and 3. There is not much difference all year round for Scenario 1. ③ Average values for the denitrification ratio and denitrification rate for all sediment samples are 37.25% and 57.68 mg·(kg·d), respectively. Both of these are higher for Scenario 2 than the other two scenarios for the same season. The ranking for denitrification for Scenarios 1 and 2 is summer > spring > autumn > winter, and spring > summer > autumn > winter in Scenario 3. ④ According to the difference analysis, significant differences not only exist between the nitrification rates between Scenarios 1 and 2 but also for the denitrification ratios and denitrification rates between Scenarios 1 and 3. In addition, there is an obvious difference in the nitration ratio between Scenarios 2 and 3. ⑤ Partial least-squares regressive analysis indicates that there is significant difference between the important influencing factors related to the nitration ratio and nitrification rate for each of the three scenarios.