Using the Forel-Ule index (FUI) to track the water quality of subsidence water bodies across the life cycle of coal mining in eastern China

Wenqi Chen; Lijuan Chen; Yongping Wei; Linlin Ruan; Yanhua Fu; Wei Li; Tingting He; Wu Xiao

doi:10.1016/j.jenvman.2025.124037

Using the Forel-Ule index (FUI) to track the water quality of subsidence water bodies across the life cycle of coal mining in eastern China

J Environ Manage. 2025 Jan 7:374:124037. doi: 10.1016/j.jenvman.2025.124037. Online ahead of print.

Authors

Wenqi Chen¹, Lijuan Chen², Yongping Wei³, Linlin Ruan⁴, Yanhua Fu⁵, Wei Li⁶, Tingting He⁴, Wu Xiao⁷

Affiliations

¹ School of Public Affairs, Zhejiang University, Hangzhou, 310058, China; School of Environment, University of Queensland, Brisbane, 4072, Australia.
² Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China.
³ School of Environment, University of Queensland, Brisbane, 4072, Australia.
⁴ School of Public Affairs, Zhejiang University, Hangzhou, 310058, China.
⁵ School of Economics and Management, Tianjin Chengjian University, Tianjin, 300384, China.
⁶ School of Environment, University of Queensland, Brisbane, 4072, Australia; School of Geography and Ocean Science, Nanjing University, Nanjing, 210023, China.
⁷ School of Public Affairs, Zhejiang University, Hangzhou, 310058, China. Electronic address: xiaowu@zju.edu.cn.

PMID: 39778350
DOI: 10.1016/j.jenvman.2025.124037

Abstract

The water quality and associated ecological risks in subsidence water bodies formed by underground coal mining are an increasing global concern. However, long-term water quality changes in these subsidence water bodies, especially across different spatial regions, remain poorly understood. This paper, by mapping the Forel-Ule index (FUI) a key indicator of water color, using Landsat datasets to reveal the dynamic evolution of water quality in 402 subsidence water bodies in the Huang-Huai-Hai Plain of eastern China from 1990 to 2020, covering their life cycle from formation to extinction. We identified three types of subsidence water bodies, including growing (14.4%), stable (35.1%), and shrinking (50.5%), almost all of which were found to exhibit eutrophic conditions. The findings revealed a blue-shift trend, indicative of improved water quality, was observed in nearly half (45.3%) of the water bodies. During mining, water quality was generally poor with higher average FUI values, but gradually improved at an average rate of -0.09 yr⁻¹. FUI values experienced a brief period of stability before deteriorating post-mining, with an average rate of 0.05 yr⁻¹. Our study provides valuable insights into the governance of subsidence water bodies in coal mining areas by revealing large-scale, long-term trends in water quality evolution.

Keywords: Coal mining; Forel-Ule index; Huang-Huai-Hai plain; Subsidence water body; Water quality.