Spatio-temporal Variations and Influencing Factors of Dissolved Oxygen in Xinfengjiang Reservoir
As a typical subtropical oligotrophic reservoir,Xinfengjiang Reservoir is an important drinking water source for Guangdong-HongKong-Macao Greater Bay Area.Dissolved oxygen(DO)is usually considered as the only key indicator that determines the water quality type of Xinfengjiang Reservoir.To understand the monthly and seasonal variation characteristics of DO and its influencing factors,five approaches including continuous wavelet transform(CWT),cross wavelet transform(XWT),maximum information coefficient(MIC),correlation coefficient(CC)and multiple linear regression(MLR)were applied based on five consecutive years'data obtained from Apr.2018 to Nov.2022.The results showed that DO monthly concentration were between 6.94 mg/L and 9.48 mg/L and all met class Ⅰ or class Ⅱ set by the"Surface Water Environmental Quality Standard"GB 3838-2002).The DO changed in a cycle of 11～12 months and 35～37 months from 2018 to 2022 a V-shaped change presented on temporal distribution,and the low DO values appeared in September or October.The DO spatial variation was small and all met class Ⅰ set by the"Surface Water Environmental Quality Standard"(GB 3838-2002).The annual average concentration of DO was between 7.95 mg/L and 8.16 mg/L at six stations,the difference of maximum and minimum value was only 0.2 mg/L.DO concentration gradually decreased from upstream to downstream.MIC,XWT,CC and MLR analysis between DO and environmental factors showed that DO were subjected to a comprehensive influence of multiple factors,among them,water temperature was the key factor affecting DO,followed by pH value.The present study has great significance for further understanding the impacts and mechanisms of DO change in oligotrophic reservoir.
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