Spatial variation in dissolved phosphorus and interactions with arsenic in response to changing redox conditions in floodplain aquifers of the Hetao Basin, Inner Mongolia

Yao Li; Chen Yu; Bo Zhao; Dou Chen; Haolin Ye; Christiane Nagel; Wen Shao; Yvonne Oelmann; Harald Neidhardt; Huaming Guo

doi:10.1016/j.watres.2021.117930

Spatial variation in dissolved phosphorus and interactions with arsenic in response to changing redox conditions in floodplain aquifers of the Hetao Basin, Inner Mongolia

Water Res. 2022 Feb 1:209:117930. doi: 10.1016/j.watres.2021.117930. Epub 2021 Dec 8.

Authors

Yao Li¹, Chen Yu², Bo Zhao², Dou Chen², Haolin Ye², Christiane Nagel³, Wen Shao³, Yvonne Oelmann³, Harald Neidhardt⁴, Huaming Guo⁵

Affiliations

¹ State Key Laboratory of Biogeology and Environmental Geology, School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China; Geoecology, Eberhard Karls University Tübingen, Tübingen 72070, Germany.
² State Key Laboratory of Biogeology and Environmental Geology, School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China.
³ Geoecology, Eberhard Karls University Tübingen, Tübingen 72070, Germany.
⁴ Geoecology, Eberhard Karls University Tübingen, Tübingen 72070, Germany. Electronic address: harald.neidhardt@uni-tuebingen.de.
⁵ State Key Laboratory of Biogeology and Environmental Geology, School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China. Electronic address: hmguo@cugb.edu.cn.

PMID: 34894444
DOI: 10.1016/j.watres.2021.117930

Abstract

Increasing numbers of studies have reported groundwater with naturally high phosphorous (P) and arsenic (As) concentrations, which can potentially threaten the environment and human health. However, the cycling of P and its interactions with As in groundwater under changing redox conditions remain largely unknown. In this study, 83 groundwater samples and 14 sediment samples were collected from the Hetao Basin, Inner Mongolia, for systematic hydrogeochemical investigation and complementary geochemical evaluation. The results showed that P cycling in floodplain aquifers was tightly constrained by redox conditions. Under oxic/suboxic conditions, mineralization of organic matter and weathering of P-bearing minerals were the two dominant processes that mobilized considerable amounts of P in groundwater. When redox conditions became reducing, Fe(III)-oxide reduction dominated, resulting in enrichment of both P and As in groundwater. In Fe(III)-reducing conditions, secondary Ca/Fe(II)-minerals might serve as an important sink for P. When redox conditions became SO₄^2--reducing, preferential adsorption and incorporation of P over As on Fe(II)-sulfides might constrain the As immobilization pathway, resulting in immediate retardation of P and hysteretic immobilization of As. This P-immobilization pathway in natural aquifers has not been described before. This study provides novel insights into P cycling and As enrichment in groundwater systems. Understanding the roles of Fe(II)- and S(-II)-minerals in the immobilization of and interaction between P and As in response to SO₄^2- reduction may help to inspire effective in-situ remediation of contaminated groundwater, in which P and As coexist and remain mobile for decades or longer.

Keywords: Arsenic; Changing redox conditions; Competitive immobilization; Mobilization; Phosphorus, Cycling.