Impact of cascade hydropower development on spatial-temporal variation of water quality in the middle and downstream of Hanjiang River
The hydropower development has a certain impact on the river.In order to comprehensively assess the cumulative impact of cascade hydropower development on spatial-temporal variations of water quality in the middle-lower Hanjiang River,the monitoring data of permanganate index(CODMN),total nitrogen(TN),total phosphorus(TP)and ammonia nitrogen(NH3-N)of seven sections of the middle-lower Hanjiang River in recent 5 years were collected.The monitoring data of permanganate index,total phosphorus and ammonia nitrogen of 4 sections in recent 10 years were collected.Based on the analysis of temporal-spatial variations in water quality,the Pearson correlation coefficient and Mann-Kendall mutation test and one-dimensional hydrodynamic model were used to comprehensively analyze the impact of cascade construction on the spatial-temporal variation of water quality and hydrodynamic environment changes in the middle-lower Hanjiang River.The results show that:The construction of the dam site may make the downstream permanganate index increase briefly,and the dam site construction has no significant effect on the total phosphorus concentration of the upstream and downstream sections,but the downstream total phosphorus concentration increases with the construction of the dam site.Ammonia and nitrogen mutation occurred in 2012,the mutation of ammonia and nitrogen in the other sections all occurred after 2015.The time of permanganate index and total phosphorus mutation in the four sections occurred between 2010 and 2015.The correlation coefficient of permanganate index,ammonia,nitrogen and total phosphorus in the Danjiangkou dam and Xiangyang sections upstream of Xinglong dam site is significant,with no obvious correlation between Xiantao section and Jijiazui section.After the construction and operation of Yakou dam,the water level will be increased and the velocity will be decreased.After the completion of the middle and downstream of Hanjiang River,the flow velocity in each reach slightly decreased.
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