[Distribution Characteristics and Pollution Risk of Heavy Metals in River Sediment of Suzhou Water Network Area, China].

The average contents of the heavy metals Cd, Cu, Cr, As, Ni, Pb, and Zn in the sediment of sampling points in the Suzhou water network area were 1.4, 127.4, 83.2, 18.2, 51.7, 145.1, and 350.7 mg·kg-1, respectively, which were 13.7, 5.7, 1.1, 1.7, 1.9, 5.5, and 5.6 times the background values, respectively. The proportions of points exceeding the risk screening values of the GB 15618-2018 standard were 100.0%, 97.3%, 38.4%, 83.6%, 97.3%, 90.4%, and 100.0%, respectively. The pollution degree of single heavy metal elements was evaluated using the improved ground accumulation index method. The pollution degree of the seven heavy metal elements in the sediment of the Suzhou water network area was in the order of Cd>Cu>Pb>Zn>As>Cr>Ni. Among them, Cd showed extremely strong pollution, Cu and Pb showed intense to extremely strong pollution, Zn showed strong pollution, As showed moderate to intense pollution, and Cr and Ni showed moderate pollution. Cd, Pb, Cu, and Zn in the sediment samples of the ancient city area, northwest area, southwest area, and east area were the heavy metal elements with high pollution contributions. The potential ecological risk degree of heavy metals was ranked as northwest>southwest>ancient city area>east. Correlation analysis and principal component analysis showed that Cd, Cu, Cr, As, Ni, Pb, and Zn may have come from anthropogenic factors such as tail gas emissions, the use of chemical fertilizers and pesticides, and the pollutant emissions of the electronic manufacturing industry.

[Pollution Distribution and Ecological Risk Assessment of Heavy Metals in River Sediments from the Ancient Town of Suzhou].

The contents of heavy metals (Cd, Cu, Cr, As, Mn, Ni, Pb, and Zn) in sediments from 20 representative sections of the ancient town of Suzhou were analyzed to determine the pollution degree and potential ecological risk, and pollution sources were identified. The results showed that the average concentrations of Cd, Cu, Cr, As, Mn, Ni, Pb, and Zn in river sediments from the ancient town of Suzhou were 1.1, 142.6, 90.2, 17.2, 800.1, 63.3, 199.1, and 384.2 mg·kg-1, respectively, and the proportions of sampling points that exceeded the soil background value of Jiangsu Province were 100%, 100%, 65%, 95%, 70%, 100%, 95%, and 100%, respectively. The geo-accumulation index indicated that the pollution degree of heavy metals followed the order of Pb > Cd > Cu > Zn > Cr > Ni > As > Mn. In general, high Pb pollution, moderate Cd, Cu, Zn, and Cr pollution, slight Ni and As pollution, and no Mn pollution were observed. The potential ecological risk index for heavy metals was determined to follow the order of Cd > Pb > Cu > As > Ni > Zn > Cr > Mn. Generally, Cd, Pb, and Cu presented moderate potential ecological risk, and the others presented low potential ecological risk. The average concentration of heavy metals, geo-accumulation index, and potential ecological risk index of river sediments in the northern and southern of ancient town were all higher than that of Ganjiang River and Huancheng River, indicating that the control of heavy metals should focus on the inner part of the ancient town. According to correlation analysis and principal component analysis, Cd, Cu, Cr, As, Ni, Pb, and Zn might be derived from man-made factors such as fertilizer, road aging, tire wear, exhaust emissions and so on, which Mn was mainly derived from natural factors.

[Distribution Characteristics of Carbon, Nitrogen, and Phosphorus Bearing Pollutants in the Ancient Town Rivers of Suzhou].

Suzhou is a water-deficient city with water quality issues. Despite water conservation measures, emission reductions, source control, and pollution interception, water quality remains poor. To understand the total mass and distribution characteristics of carbon, nitrogen, and phosphorus bearing pollutants and inform decisions regarding river dredging, sediment and water samples were collected from 20 representative sections in the town's rivers during the spring of 2019. The depths of the sediments were measured along with the concentrations of carbon, nitrogen, and phosphorus bearing pollutants in the sediments and water, and the pollution degree was evaluated. Variations in various parameters were predicted for change water, diversion water, rainfall, and dredging. The results show that the sediment depths ranged between 22 and 1025 mm (average=266 mm), and the total mass of sediment was approximately 5.2×105 t in the ancient town rivers of Suzhou. The average proportions and concentrations of TOC, TN, NH4+-N, TP, and AP in the sediments were 3.4%, 2074 mg·kg-1, 140.2 mg·kg-1, 1765 mg·kg-1, and 57.2 mg·kg-1, respectively, indicating a moderate level of pollution. The concentration of TP in the sediments at 90% of the sampling points exceeds the national standard. Huancheng River was found to have the highest concentration of TP, suggesting that dredging shuld be targeted here first. In the water samples, the average concentrations of TOC, BOD5, COD, TN, NH4+-N, Kjeldahl nitrogen, TP, and PO43--P were 7.8, 0.6, 13.1, 2.5, 0.643, 1.3, 0.18, and 0.09 mg·L-1, respectively, indicating a severe level of pollution. Overall, water quality in these rivers falls below Class V surface water, and the concentration of TN seriously exceeds the national standard. Based on the patterns of total carbon mass and nitrogen and phosphorus bearing pollutants, the recommended order of dredging in Suzhou is the Huancheng River, the northern rivers of the ancient town, Ganjiang River, and the southern rivers of the ancient town. Under the rainfall scenario, the initial concentrations of pollutants in runoff were high, which leads to a decline in water quality. The total mass of TN in the water was reduced by 0.2 t under the change water and diversion water scenarios, and was further reduced by 4.58 t and 2.19 t, respectively, after dredging. Phosphorus bearing pollutants in the sediment were mainly imported from other sources, meaning that the total mass of TP in the water may increase following dredging activities.