Distribution, dynamic and influence factors of groundwater arsenic in the Manas River Basin in Xinjiang, P.R.China

Abstract

High arsenic (As) groundwater in Xinjiang is mainly found in deep aquifers in the Manas River Basin (MRB) and the Kuitun River Basin (KRB) in the southern Junggar Basin. Groundwater samples (n = 21; including two phreatic water samples and 19 deep confined groundwater samples), were collected along hydrogeological profiles (north-south and west-east) in a high As groundwater area in the MRB in 2021. Inorganic As species, DOC and DIC were determined. As (V) was the major inorganic As species in 95% of the groundwater samples. High As groundwater was mostly found in reducing/sub-oxidizing and alkaline environments. Along the south-north groundwater flow path, a significant positive correlation was found between groundwater As, phosphate and carbonate, suggesting that competitive desorption may have been an important arsenic mobilizing process. Further, a significant negative correlation between groundwater As and the sulfate/chloride ratio and between DOC and the sulfate/chloride were observed - this suggests that sulfate reduction mediated by microorganisms may also have been an important mobilizing process. The lack of correlation between groundwater As and DOC suggests that the composition of organic matter as well as its concentration may have been an important controlling factor in arsenic mobilization.