Spatiotemporal heterogeneity characteristics of dissolved oxygen and their influencing factors in typical channel-type reservoir of the Minjiang River Basin

Abstract

[Objective] The hydrodynamics in channel-type reservoirs exhibit dual characteristics of both rivers and lakes, significantly influencing the longitudinal gradient distribution of water environmental factors. The Minjiang River is the largest river in the coastal region of southeastern China, but the spatiotemporal heterogeneity characteristics of dissolved oxygen(DO) and its influencing factors in mainstream reservoirs remain unclear. [Methods] Based on the hourly monitoring data from 2020 to 2024 in the upstream tributaries and reservoir area of the Shuikou Reservoir in the Minjiang River, an integrated analytical method suitable for channel-type reservoirs was developed by combining STL time series decomposition, modified Mann-Kendall trend testing, Pettitt' s test for change-point detection, and Pearson correlation analysis. This method followed a progressive research framework of data processing, feature characterization, trend assessment, and attribution analysis, thereby systematically elucidating the spatiotemporal evolution patterns of DO in the Shuikou Reservoir. [Results] The result showed that the surfacelayer DO in Shuikou Reservoir exhibited significant longitudinal heterogeneity, with DO concentrations gradually decreasing from the riverine zone(6. 5~7. 3 mg/L), through the transition zone(5. 6~6. 8 mg/L), to the lacustrine zone(5. 2~6. 2 mg/L). Consequently, the risk of hypoxia increased correspondingly, specifically manifested as hypoxia probabilities of 0. 7% ~16. 9% in the riverine zone, 16. 1%~38. 3% in the transition zone, and 27. 6% ~ 46. 1% in the lacustrine zone. The dominant driving mechanisms of DO exhibited significant differences among these zones, and the influence degree of each driving factor dynamically changed over time. Furthermore, the same external events demonstrated significant temporal lag effects across different zones, with response delays ranging from 1 to 4 months. [Conclusion] It is evident that the established integrated analytical method can fully extract deep information from high-frequency monitoring data, elucidating the spatiotemporal heterogeneity characteristics of DO and their driving mechanisms. This provides a basis for further implementing systematic improvement measures, such as external source management in the riverine zone, hydrodynamic-pollution regulation in the transition zone, and internal source control and ecological regulation in the lacustrine zone.

Keywords

channel-type reservoir / dissolved oxygen / spatiotemporal differentiation / longitudinal heterogeneity / hypoxia risk / zonal management / Minjiang River Basin / influencing factors