巢湖十五里河河床地貌单元沉积物硝化速率及污染特征

Nitrification Rates and Pollution Characteristics of Sediments with Different Geomorphic Features in the Shiwuli Stream,Chaohu Lake Basin

2017年7月~2018年3月,在巢湖流域十五里河城市段河床地貌特征丰富的两处河段,就深潭、浅滩、砾石滩、点砂坝和常规流水区等5种地貌单元类型,按季节采集表层沉积物样和水样,解析不同地貌单元沉积物硝化速率及其变化性,并开展不同地貌单元硝化速率的差异性和影响因素分析.结果表明:(1)十五里河中上游河段氮磷污染严重,且水体氧化还原电位(ORP)值基本都低于零,表明河水处于显著的还原状态.(2)5种地貌单元沉积物的PNR变化范围为0.002~0.079μmol·(g·h)-1,均值为0.023μmol·(g·h)-1,高低排序依次为:深潭>点砂坝>浅滩>砾石滩>流水区,相应的季节变化规律基本表现为:夏季>春季>秋季>冬季.(3)5种地貌单元表层沉积物ANR变幅为0.140~13.543μmol·(m2·h)-1,均值为3.658μmol·(m2·h)-1,总体表现为浅滩最高,常规流水区次之,砾石滩和点砂坝大体相当,深潭最小,且季节变化规律与PNR相似.(4)差异性分析表明,深潭、浅滩与其他4种地貌PNR均存在显著差异性,超过半数的地貌单元ANR呈极显著差异性.(5)回归分析表明,5种地貌单元的PNR、ANR与上覆水水质指标的相关性相对较强,而与沉积物理化指标的相关性略弱.

Sediment and overlying water samples were collected seasonally from five different geomorphic structures (i.e., pools, riffles, gravel bars, point bars, and runs) from two urban reaches of the Shiwulihe River in the Chaohu Lake Basin dominated by high ammonia concentration between July 2017 and March 2018. Both the sediment potential and areal nitrification rates were measured and their seasonal and geomorphological variability were evaluated. The specific differences between every two geomorphic structures were determined using the Mann-Whitney U test and the relationship between the overlying water environment or benthic sediments and sediment nitrification was explored based on regression analysis. The results show that:① The studied reaches are seriously polluted by nitrogen and phosphorus and most of the oxidation-reduction potential (ORP) values in the overlying water were are below 0 mV, suggesting strong reducing conditions of the water column. ② The potential nitrification rates (PNRs) across the five geomorphic structures range from 0.002 to 0.079 μmol·(g·h)-1, with a mean value of 0.023 μmol·(g·h)^-1. The ranking order of PNRs is pools > point bars > riffles > gravel bars > runs, with a seasonal change pattern of summer > spring > autumn > winter. ③ The areal nitrification rates (ANRs) across the five geomorphic structures range between 0.140 and 13.543 μmol·(m^2·h)^-1, with an average of 3.658 μmol·(m^2·h)^-1. In general, the highest mean value was observed in riffles, followed by runs, and gravel bars and point bars;the smallest value was observed in pools. In addition, ANRs appear to have seasonal change patterns similar to that of the PNRs. ④ According to the difference analysis, there are significant differences between pools or riffles and other features of the PNRs. Extremely significant ANR differences were observed between more than half of the geomorphic structures. ⑤ Regression analysis shows a stronger correlation between sediment nitrification and the overlying water environment, compared with the surface sediment properties.