Multiple isotopic tracing for sulfate and base cation sources of precipitation in Hangzhou city, Southeast China: Insights for rainwater acidification mechanism

Yao Wu; Wenjing Liu; Yifu Xu; Zhifang Xu; Xiaode Zhou; Lian Zhou

doi:10.1016/j.envpol.2021.117770

Multiple isotopic tracing for sulfate and base cation sources of precipitation in Hangzhou city, Southeast China: Insights for rainwater acidification mechanism

Environ Pollut. 2021 Nov 1:288:117770. doi: 10.1016/j.envpol.2021.117770. Epub 2021 Jul 9.

Authors

Yao Wu¹, Wenjing Liu², Yifu Xu³, Zhifang Xu⁴, Xiaode Zhou³, Lian Zhou⁵

Affiliations

¹ Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, 130102, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
² Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China; CAS Center for Excellence in Life and Paleoenvironment, Beijing, 100044, China; University of Chinese Academy of Sciences, Beijing, 100049, China. Electronic address: liuwenjing@mail.iggcas.ac.cn.
³ Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
⁴ Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China; CAS Center for Excellence in Life and Paleoenvironment, Beijing, 100044, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
⁵ State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, China.

PMID: 34284213
DOI: 10.1016/j.envpol.2021.117770

Abstract

Acid deposition has been regarded as a serious factor in the deteriorative water environment and ecosystems. Despite the powerful acid emission control measures have been implemented by the Chinese government, many areas (especially Southeast China) are still suffering from acid deposition. The chemical and isotopic (δ³⁴S and ⁸⁷Sr/⁸⁶Sr) compositions of rainwater in Hangzhou, a typical megacity in Southeast China with serious acid rain problem, for one year were studied with the aim to better constrain potential sources and explore the causes of rainwater acidification. Most rainwater samples were acidic, with a VWM pH value of 4.65. SO₄^2- was the dominant anion and the main acid ion in rainwater. Sulfur isotope and the quantity equilibrium model revealed that sea salt, crustal, biogenic, and anthropogenic sulfur represented 2.3%, 0.1%, 16.7%, and 80.8% of the SO₄^2- source in rainwater, respectively. The back trajectory and strontium isotopes indicated that the base cations (BCs) in rainwater originated mainly from anthropogenic sources. The relatively low neutralizing capacity caused by limited BCs input and emission control measures undermines some efforts to reduce rainwater acidity. This case study demonstrated that a valuable tool to probe the source of acid rain and unravel the mechanism of rainwater acidification can be provided by multiple lines of evidence, including rainwater chemical compositions, stable sulfur isotopes, and stable strontium isotopes.

Keywords: Acid deposition; Neutralizing capacity; Source identification; Stable isotope.

MeSH terms

Cations
China
Ecosystem*
Environmental Monitoring*
Hydrogen-Ion Concentration
Sulfates

Substances

Cations
Sulfates