Fractal Measurement of Multi-time Scale Correlations Between Dissolved Oxygen and Permanganate Index in Lake Water
An in-depth understanding of the evolution of correlations between water quality indicators will help clarify the occurrence and evolution mechanisms of algae blooms.In order to explore the multi-time scale nonlinear correlation charac-teristics between dissolved oxygen(DO)and permanganate index(CODMn)water quality indicators in lake water bodies,the ensemble empirical mode decomposition(EEMD)and multifractal detrended cross-correlation analysis method(MFDC-CA)were used to study the long-term persistence and multifractal characteristics of the correlation between DO and CODMn in Lugu Lake and Qionghai Lake from February 1,2022 to August 31,2023.The results show that:1)The DO evolutions of Lugu Lake and Qionghai Lake are mainly affected by meteorological conditions on different time scales.The first eight modes are superimposed to form the high-frequency component mode of DO,which can better reflect the impact of algae growth on DO and reduce the impact of seasonal changes in climate on DO.2)Within the research time scale,the intensity of the correlation between the DO high-frequency component and the CODMn index slowly decays with time in the form of a power function,and its correlation changes in a U-shape at a certain time.Changes in meteorological conditions are the main reason for the mutual correlation between Δh value and algae density.Studying the multi-fractal change pattern of the correlation between DO and CODMn in lake water can provide new dynamic parameters for improving the evolution dynamics of algae and algae bloom prediction and early warning models in lake water.