Abstract
Abstract A perceptible degradation in water quality complicates safe water supply for drinking and irrigation purposes. Therefore, this study aims at monitoring water quality changes and effective factors in the Dez River Basin, which are required to manage water resources effectively. To this end, the common influence of flow rate changes on water quality was separated by implementing seasonal Mann–Kendall test on residuals resulting from the LOWESS test. The results show that after adjusting the effects of seasonality and streamflow fluctuations, significant positive trends in most water quality parameters are still observed. It emphasizes the role of other factors controlling river water quality in the basin. Comparison of the trends of modified quality parameter time series (residuals) in different subbasins having natural or mad-made conditions, with or without significant groundwater resources, shows almost the same presented trends in water quality. This supports that, overall, minor changes occurred in land use, groundwater table, and environmental and human factors with no important influences on presented trends in water quality. Our analyses show that overall reduction in precipitation as well as positive trends in temperature and evaporation led to intensified streamflow variations, explaining the main changes in the river water quality of the basin.
Highlights
The Dez River, as the second largest river in Iran and one of the major tributaries of the Karun River, is one of the main water resources in the Khuzestan province in order to provide fresh water needed for drinking, domestic uses, and agriculture purposes
It should be noted that changes in groundwater– surface water relationships (as it is reported as a main cause of trends in river water quality of the Karkheh River Basin after removing the effects of seasonality and streamflow fluctuations by Osati et al ( )) may have some impacts on river water quality, especially in AznaAligudarz and Doroud-Borujerd plains, which are located in the upstream part of the Dez Basin
This study identified the effects of climate change, environmental, and anthropogenic factors on water quality of the Dez River Basin using statistical tests, i.e., modified Mann– Kendall test in conjunction with Theil–Sen method and LOWESS
Summary
The Dez River, as the second largest river in Iran and one of the major tributaries of the Karun River, is one of the main water resources in the Khuzestan province in order to provide fresh water needed for drinking, domestic uses, and agriculture purposes. Assessment of long-term trends in water quality parameters can be considered as an appropriate approach to determine any environmental changes over time, help to identify and analyze the most substantial factors affecting the water quality (Ballantine & Davies-Colley ; Goodrow et al ), and clarify some new aspects of hydrological processes. There are various measures to determine the trend in water quality time series that can be named as time series analysis methods (Long et al ) including parametric (Kundzewicz & Robson ; Yenilmez et al ) and non-parametric tests (Bouza-Deano et al ). Based on several studies, in different parts of the world, the non-parametric Mann–Kendall method and Sen’s slope test (Yenilmez et al ; Naddeo et al ; Ballantine & Davies-Colley ; Entry & Gottlieb ; Niazi et al ; Yevenes et al ; Chen et al ), seasonal Kendall (Helsel & Hirsch ; Ballantine & Davies-Colley ; Dabrowski et al ; Entry & Gottlieb ; Hughes & Quinn ; Cloern ), and LOWESS
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
