Source water quality from 2014 to 2019 in Qingpu District, Shanghai

Background At present, only Qingpu District in the city of Shanghai draws water from water systems around Dianshan Lake and Qingcaosha Reservoir at the same time. However, there is no report comparing the source water quality between them.

Objective This study evaluates the quality of source water of three centralized water supply plants in Qingpu District.

Methods The monitoring data on 93 samples of source water were collected from three centralized water supply plants from January 2014 to December 2019 in Qingpu District, and the unqualified items were compared.

Results Except for ammonia nitrogen and chemical oxygen demand (COD_Mn), other pollutant items did not exceed the national standard limits from 2014 to 2019 in Qingpu District. The ammonia nitrogen concentrationsM (P₂₅-P₇₅) in the source water of the three water plants A, B, and C were 0.16 (0.10-0.24), 0.32 (0.19-0.67), and 0.31 (0.20-0.50) mg·L^-1, respectively, and the corresponding unqualified rates were 2.6%, 32.1%, and 22.2%, respectively. The COD_Mn concentrationsM (P₂₅-P₇₅) were 1.83 (1.66-2.04), 3.58 (2.97-4.24), and 3.76 (2.97-4.15) mg·L^-1, respectively, and the unqualified rates were 5.3%, 71.4%, and 74.1%, respectively. The unqualified rates of ammonia nitrogen and COD_Mn in the source water of water plant A were lower than those of plants B and C (P < 0.016 7). The concentrations of ammonia nitrogen and COD_Mn in source water of water plant A were lower than those of plants B and C (P < 0.016 7). Regarding hydroperiod, in low flow period the level of ammonia nitrogen in the source water of water plant A was lower than those of plants B and C (P=0.004, P=0.013). In low, level, and high flow periods, the levels of COD_Mn in the source water of water plant A were all lower than those of plants B and C (P < 0.05).

Conclusion The monitoring data of 2014 to 2019 reveal that the outstanding source water pollutants in the region are ammonia nitrogen and COD_Mn, and the source water quality of Qingcaosha Reservoir is better than that of the water system around Dianshan Lake.