Distribution Characteristics and Pollution Evaluation of Nitrogen and Organic Matter in Overlying Water and Sediment of Guyun River and Jinshan Lake in Zhenjiang City

Zhenjiang City is located in the intersection of the Yangtze River and the Beijing-Hangzhou Grand Canal, which is the most important water transportation hub in China, with abundant water resources and a dense river network. In recent years, the water quality in this region has declined with the rapid development of the economy and enhanced anthropogenic activity. Therefore, it is crucial to understand the state of water and sediment pollution in rivers and lakes of Zhenjiang City, which can provide important basic data for improving the water environment quality for this region. In total, 21 sampling sites (including 10 sites from Jinshan Lake and 11 sites from the ancient canal) in Zhenjiang City were selected, and overlying water and sediment samples were sampled in winter and summer, respectively. In addition, the physical and chemical parameters of overlying water and sediment samples were determined, respectively, and the organic index as well as organic nitrogen index were analyzed in order to evaluate the degree of sediment contamination in this region. Results showed that ① The TN concentration of overlying water changed from 1.95 mg•L-1 to 15.71 mg•L-1 in the winter and from 0.64 mg•L-1 to 12.09 mg•L-1 in the summer, with mean values of 4.01 mg•L-1 and 4.07 mg•L-1, respectively, which are higher than those of the surface water Ⅴ class standard. In addition, the ranked order of NH4+-N was as follows: winter<summer and river>lake; ② the TN content in the sediment samples ranged from 394.61 mg•kg-1 to 3 288.09 mg•kg-1 and from 869.21 mg•kg-1 to 3 598.04 mg•kg-1, respectively, with the mean values of 1 928.58 mg•kg-1 and 2 068.40 mg•kg-1. The ranked order of TN, NH4+-N, NO3--N, and Org-N was as follows: winter>summer for lake sediment samples. For river sediment samples, the ranked order of TN was winter<summer, whereas those of NH4+-N and NO3--N were winter>summer, indicating more complicated seasonal distribution for river sediment. In addition, the NO3--N content was higher in lake sediment than in river sediment, whereas that of NH4+-N was higher in river sediment than in lake sediment. The C/N ratio results indicated that the organic matter in sediments primarily resulted from endogenous pollution in this region; ③ Results of organic nitrogen index confirmed that 60% sediment samples from the lake in winter and the river in summer belong to the Ⅳ pollution level, indicating that organic nitrogen pollution existed in these samples. The results of organic index confirmed that 70% and 54.55% sediments samples belong to the Ⅱ pollution level, indicating that the sediments were not severely polluted in rivers and lakes of Zhenjiang City. The results demonstrate that sediments in rivers and lakes of Zhenjiang City are mainly polluted by nitrogen. Our findings provide important basic data for nitrogen control schemes in river water and sediment in Zhenjiang City. © 2021, Science Press. All right reserved.