[Pollution Characteristics and Nitrification and Denitrification Potential of Superficial Sediments from Streams in an Urban-Rural Fringe].

From May 2015 to June 2016, seasonal sediment samples were collected from three headwater streams in the urban-rural fringe of Hefei, Chaohu Lake basin, China. The nitrogen pollution characteristics of sediments were preliminarily investigated for the three streams. Three metrics, that is, potential nitrification rate (PNR), areal nitrification rate (ANR) and rate of denitrification were quantitatively determined, and their spatial and temporal variations were discussed subsequently. Moreover, the relationship between PNR, ANR or denitrification rate and a list of environmental factors was discriminated by using partial least-squares regression analysis. Results showed that:① Guanzhenhe Distributary was the most polluted stream with a mean content of 4516.39 mg·kg-1 for TN, which was 2.56 and 1.36 times higher than those of Modian Stream and Taochong Stream, respectively. Similarly, the highest values for NH4+-N and NO3--N emerged in Guanzhenhe Distributary while the lowest existed in Modian Stream. ② There were distinct seasonal variations in PNR and ANR, namely, the maximum values emerged in summer, minimum in winter, and almost equivalent in spring and autumn. And the arrangement in order for PNR and ANR was Taochong Stream > Modian Stream > Guanzhenhe Distributary. ③ The mean rate of denitrification in Guanzhenhe Distributary was 10.59 mg·(kg·h)-1, which was 3.16 and 1.75 times higher than those in Modian Stream and Taochong Stream, respectively. In addition, both denitrification rate and denitrification activity in summer were higher than those in spring for the three streams. ④ According to the variable importance plot (FVIP), ANR, PNR and rate of denitrification were almost all significantly correlated with such physical and chemical factors as pH, OM, NH4+-N, NO3--N, TN and TP in sediments for the three streams.

[Fractions and Release Risk of Phosphorus in Surface Sediments of Three Headwater Streams with Different Styles of Water Supply].

From May to September 2015, seasonal sediment samples were collected from three headwater streams and ditches which were discharged from sewage plant tail water, food processing wastewater and agricultural drainage-groundwater seepage, respectively, in Hefei, Chaohu Lake basin. The stream-bed sediments were analyzed for phosphorus fractions. The risk assessment on phosphorus release from sediments was conducted using the phosphorus sorption index (PSI), degree of phosphorus saturation (DPS) and the phosphorus release risk index (ERI). Moreover, nonparametric tests method was used to explore the difference among the three studied streams and ditches. Study results showed that:1 Guanzhenhe Distributary and Taochong Stream were seriously damaged by phosphorus pollution both in waters and stream-bed sediment, and the phosphorus pollution levels could be arranged in the order of Guanzhenhe Distributary >Taochong Stream >Modian Stream. The mean content of total phosphorus (TP) in sediments in Guanzhenhe Distributary was 1376.95 mg·kg-1, which was 2.94 and 1.91 times as high as those of Modian Stream and Taochong Stream, respectively. 2 Significant differences and different sort orders in contents of phosphorus fractions were found for each of the three streams. 3 Obvious seasonal variations existed in PSI for the three streams, and all the sampling points in the same stream had similar changing law, namely, the maximum content emerged in autumn, followed by winter, and the minimum occurred in spring or summer. 4 The same conclusions were drawn in phosphorus release risk according to the PSI, DPS and ERI, and the risk ranked as follows:Guanzhenhe Distributary >Taochong Stream >Modian Stream. 5 According to the difference analysis, significant differences existed in almost all of the indexes among the three streams.