Determining rainwater chemistry to reveal alkaline rain trend in Southwest China: Evidence from a frequent-rainy karst area with extensive agricultural production

Jie Zeng; Fu-Jun Yue; Si-Liang Li; Zhong-Jun Wang; Qixin Wu; Cai-Qing Qin; Ze-Long Yan

doi:10.1016/j.envpol.2020.115166

Determining rainwater chemistry to reveal alkaline rain trend in Southwest China: Evidence from a frequent-rainy karst area with extensive agricultural production

Environ Pollut. 2020 Nov;266(Pt 3):115166. doi: 10.1016/j.envpol.2020.115166. Epub 2020 Jul 9.

Authors

Jie Zeng¹, Fu-Jun Yue², Si-Liang Li³, Zhong-Jun Wang⁴, Qixin Wu⁵, Cai-Qing Qin⁶, Ze-Long Yan⁶

Affiliations

¹ Institute of Earth Sciences, China University of Geosciences (Beijing), Beijing, 100083, China.
² Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin, 300072, China; Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin, 300072, China; Puding Karst Ecosystem Research Station, Institute of Geochemistry, Chinese Academy of Sciences, Anshun, 562100, China. Electronic address: fujun_yue@tju.edu.cn.
³ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin, 300072, China; Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin, 300072, China; Puding Karst Ecosystem Research Station, Institute of Geochemistry, Chinese Academy of Sciences, Anshun, 562100, China.
⁴ Puding Karst Ecosystem Research Station, Institute of Geochemistry, Chinese Academy of Sciences, Anshun, 562100, China.
⁵ Key Laboratory of Karst Environment and Geohazard, Ministry of Land and Resources, Guizhou University, Guiyang, 550025, China.
⁶ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin, 300072, China.

PMID: 32682186
DOI: 10.1016/j.envpol.2020.115166

Abstract

Rainwater chemistry plays an important role in the earth-surficial ecosystem, but studies on rainwater chemical composition of karst agro-ecosystem are rare. To explore the rainwater alkalization and the provenance of components responsible for neutralization, two-years chemical monitoring of rainwater was carried out in a karst agricultural catchment in Southwest China. The main findings suggest that SO₄^2-, NO₃^-, Ca²⁺, and NH₄⁺ are the principal ions. All the ionic contents show distinctly seasonal variation (highest in winter) in response to variations in seasonal precipitation because the rain-scour process can efficiently remove atmospheric materials. Source identification indicates that Cl^- and Na⁺ are mainly derived from marine input whereas SO₄^2- and NO₃^- are controlled by anthropogenic emission, in particular, fixed emission sources. The source of NH₄⁺ is attributed to intense agricultural production, while Ca²⁺ and Mg²⁺ are mainly derived from calcite dissolution. The rainwater alkalization caused by the seasonal acid neutralization (via basic components, Ca²⁺ and NH₄⁺) is beneficial to crop growth but also reflect agricultural overfertilization. Sulfur controlled the total wet acid deposition (68%-94%) and could be a potential agent of weathering.

Keywords: Acid neutralization; Atmospheric acid substances; Ion sources; Karst agricultural production; Rainwater.

MeSH terms

China
Ecosystem*
Environmental Monitoring*
Rain
Seasons