Evaluation of trophic state for inland waters through combining Forel-Ule Index and inherent optical properties

Yongxin Liu; Huan Wu; Shenglei Wang; Xiuwan Chen; John S Kimball; Chenlu Zhang; Han Gao; Peng Guo

doi:10.1016/j.scitotenv.2022.153316

Evaluation of trophic state for inland waters through combining Forel-Ule Index and inherent optical properties

Sci Total Environ. 2022 May 10:820:153316. doi: 10.1016/j.scitotenv.2022.153316. Epub 2022 Jan 21.

Authors

Yongxin Liu¹, Huan Wu², Shenglei Wang³, Xiuwan Chen¹, John S Kimball⁴, Chenlu Zhang¹, Han Gao¹, Peng Guo¹

Affiliations

¹ School of Earth and Space Sciences, Peking University, Beijing 100871, China; Engineering Research Center of Earth Observation and Navigation (CEON), Ministry of Education of the PRC, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China.
² Southern Marine Science and Engineering Laboratory (Zhuhai), School of Atmospheric Sciences, Sun Yat-sen University, Guangdong, China; Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangdong, China; Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA. Electronic address: wuhuan3@mail.sysu.edu.cn.
³ Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China.
⁴ Numerical Terradynamic Simulation Group, University of Montana, Missoula, MT 59801, USA.

PMID: 35066030
DOI: 10.1016/j.scitotenv.2022.153316

Abstract

Eutrophication is a severe environmental pollution problem for inland waters and poses significant threats to the water safety. Monitoring trophic state of inland waters using optical remote sensing generally requires the inversion of water quality parameters, such as chlorophyll-a, secchi depth, etc. However, the accurate inversion of these individual indicators remains challenging, while the associated retrieval errors can propagate and degrade the evaluation of trophic state. Hence, we proposed a novel monitoring method by developing a Trophic State Index (TSI) based on optical remote-sensing parameters, i.e., Forel-Ule index (FUI) and non-water absorption coefficient at 674 nm (referred to as a_t-w(674)) retrieved from Sentinel-3 Ocean and Land Color Instrument (OLCI) imagery. The estimated TSI showed favorable correspondence with observed water quality data, including coefficient of determination (r² = 0.91), root mean squared error (RMSE = 5.54), and mean absolute percentage error (MAPE = 10.69%). Using the Sentinel-3 OLCI data, the proposed method also had very good performance in the field spectrum (MAPE = 5.25 % , RMSE = 3.36). The monthly trophic state evaluation also showed congruence (MAPE = 12.51 % , RMSE = 6.41) with surface water quality monthly report (SWQMR) from the Ministry of Environment and Ecology of the People's Republic of China. The monthly TSI showed favorable agreement for 23 ungauged lakes (RMSE = 7.26, MAPE = 12.78%), indicating potential utility for regional lake water quality monitoring. The proposed method was then applied to 47 other large (>50 km²) water bodies in the Middle-and-Lower watershed of Yangtze River and the Huaihe watershed to evaluate the spatial and temporal variation of trophic state from 2016 to 2020. The TSI results revealed several lakes, such as Lake Honghu and Lake Luoma, with rapidly deteriorating water quality during the study period, while other lakes show relative improvement (e.g., Xiashan Reservoir), indicating unbalanced environmental pressure over the region. Overall, this study showed promising performance and potential for satellite-based monitoring of regional aquatic environments.

Keywords: Absorption coefficient; Forel-Ule index; Inland waters; Sentinel-3 OLCI; Trophic state.

MeSH terms

Environmental Monitoring* / methods
Eutrophication*
Lakes
Rivers
Water Quality