Water quality characteristics, sources, and assessment of surface water in an industrial mining city, southwest of China

Abstract

This study analyzed the physiochemical factors, spatial-seasonal variations, and correlations of main pollutants, water quality evaluation and possible sources of nitrogen in the surface water of Anning, an industrial mining city, southwest of China. Seventy surface water samples were examined through an analysis of 41 physiochemical indices in the dry and wet seasons in April and July 2019, respectively, while a part of water site samples collected in July 2020 was taken for isotope detections. To identify the water quality, single-factor pollution index (SI), Nemerow pollution index (NPI), and water quality comprehensive pollution index (CPI) were calculated based on 13 pollutants using GB 3838-2002 class III water standard values. Results pointed to typical pollutants of TN, TP, and F with ranges of l.d.-44.8 (2.00 ± 3.69) mg/L, l.d.-250 (2.07 ± 15.35) mg/L, and l.d.-11 (1.48 ± 7.34) mg/L respectively with high spatial variability. The concentrations of heavy metals present in the water samples followed the sequence: Zn > Ni > Cu > As > Pb > Cd > Hg, and most of the samples showed low values relative to the standard permissible limits. In three methods, the water quality evaluation results of SI method were obviously worse than NPI and CPI methods. The NPI and CPI values had ranges of 0.116-887.40 (8.12 ± 74.89) and 0.03-111.54 (1.17 ± 9.40), respectively; consequently, the water quality was considered generally well, with more than 65% of sites classified as "cleanness" or "sub-cleanness." Most of the values of δ¹⁵N and δ¹⁸O had ranges of 6.62-20.05‰ and - 6.53-4.70‰, which suggested the livestock manure resources were the possible sources of nitrogen that entered the surface water causing more pollution in the wet season. Part of sites with serious water pollution had very high concentrations of P, F, or heavy metals and might be closely correlated with the point source pollution of phosphate chemical industry or iron ore mining and smelting. The results of this study can provide the basic data for efficient water management and human health protection for local government.

Keywords: Anning; Nitrogen; Pollution sources; Spatial and seasonal variations; Water quality assessment method.