Scholarly record

REMOTE SENSING DYNAMIC MONITORING OF EUTROPHICATION AND EVALUATION OF WATER QUALITY IMPROVEMENT EFFECTS IN YUQIAO RESERVOIR (2016-2023)

Ya Xie, Jingyi Li

Abstract

Taking Yuqiao Reservoir, a key drinking water source for Tianjin, as the research object, this study utilized Sentinel-2 MSI satellite data and synchronous in-situ measurements to investigate its eutrophication spatiotemporal changes from 2016 to 2023. Semi-empirical models based on the NDCI index were constructed for chlorophyll-a concentration inversion, while the QAA_RGB quasi-analytical algorithm was adopted for water transparency retrieval. The Comprehensive Trophic Level Index (TLI) was further calculated to evaluate eutrophication levels. Results showed severe cyanobacterial blooms occurred in 2016-2017, mainly concentrated in late summer and early autumn, with the 2016 bloom covering 89% of the reservoir area. After 2018, no blooms were detected. TLI exhibited a fluctuating trend: rising from 2016 to 2019 (peaking at 53.1), declining sharply until 2021, slightly increasing in 2022, and improving again in 2023. Spatially, the reservoir shifted from a mix of mesotrophic and lightly eutrophic waters to predominantly mesotrophic conditions, with better water quality in deeper western areas. Correlation analysis indicated meteorological factors had limited impact, while anthropogenic activities such as non-point source pollution and the 2018 sediment dredging project were key influencing factors. The study verified the reliability of the inversion models through comparison with environmental monitoring data (RMSE=4.5, MRE=7.4%), providing scientific support for the protection and management of Yuqiao Reservoir's water environment.

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