Abstract
The Lixiahe abdominal area is a representative plain river network in the lower reaches of the Huai River, being an upstream section of south-to-north water diversion from the Yangtze River in Jiangsu Province, China. The assessment of long-term water quality variation and the identification of probable causes can provide references for sustainable water resources management. Based on the monthly water quality data of 15 monitoring stations in the Lixiahe abdominal area, the periodic characteristics and tendency of water quality variation were studied by combining wavelet analysis, the Mann–Kendall trend test, and Sen’s slope estimator, and the correlation between water quality variation, water level, and water diversion was discussed with cross wavelet transform and wavelet coherence. The results show that the comprehensive water quality index (CWQI) included periodic fluctuations on multiple scales from 0.25 to 5 years. The CWQI of 7 out of 15 monitoring stations has a significant decreasing trend, indicating regional water quality improvement. The trend slope ranges from −0.071/yr to 0.007/yr, where −0.071/yr indicates the water quality improvement by one grade in 15 years. The spatial variation of water quality in the Lixiahe abdominal area was significant. The water quality of the main water diversion channels and its nearby rivers was significantly improved, while the improvement of other areas was not significant or even became worse due to the increasing discharge of pollutants. The CWQI of the main water diversion channels and its nearby rivers was inversely correlated with the amount of water diversion. The greater the amount of water diversion, the better the water quality. The water diversion from the Yangtze River has played an important role in improving the regional water environment.
Highlights
Water environment deterioration is a prominent issue in river basin management throughout the world, which has become a serious threat to water security [1]
In previous studies on temporal variation of water quality, multivariate statistical techniques and continuous wavelet transform are used to present a significant and validated picture of the seasonal periodic behavior of water quality, but they do not directly explore long-term periods, variation tendency, and the coherence of the periodic behavior of water quality variables with influencing factors. This present study aims to remedy this shortcoming by investigating long-term periods, variation tendency, and the coherence of water quality with water level and water diversion from outside the basin with combined methods of continuous wavelet transform, cross wavelet transform, wavelet coherence, Mann–Kendall trend test, and Sen’s slope estimator
From 2003 to 2017, the water quality variation in the Lixiahe abdominal area contains multi-scale periodic fluctuations of 3–59 months, and the seasonal variation of 12 months is significant at most stations
Summary
Water environment deterioration is a prominent issue in river basin management throughout the world, which has become a serious threat to water security [1]. Council of Ministers of the Environment Water Quality Index (CCME CWQI) [10,11], multivariate statistical techniques [12,13], such as cluster analysis [14], discriminant analysis [12], factor analysis [13], principal component analysis [15], and artificial neural network [16,17] are widely used in river water. DRASTIC is a widely used indexing method to assess groundwater vulnerability to a wide range of potential contaminants [18,19]. All these methods are used to comprehensively assess the water quality as well as identify spatial and temporal variations in water quality and main sources of contamination
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