三峡库区成库前后干流万州段水体总磷特征

Characteristics of Total Phosphorus in Changjiang Mainstream at Wanzhou Section Before and After Three Gorges Reservoir Impoundment

本研究分析了长江水利委员会水文局长江上游水文水资源勘测局自2002-2017年按照水利部水环境监测规范,在三峡库区的长江干流万州站所测得的干流澄清性水体总磷数据.结果显示:①与蓄水前一年,即2002年6-12月水位平均值相比,2003年6-12月,万州段水位升高了14.66~37.11 m,流速减缓了0.27~1.29 m/s,而水体澄清性总磷增长1.3~6.5倍,由蓄水前的平均每月0.03 mg/L骤升至0.12 mg/L;②2003年蓄水后至今,长江干流万州区澄清性总磷年均变化和丰水期(5-11月)澄清性总磷年均变化正相关性极有统计学意义(p<0.01);③2012年以后,总磷呈现逐年减少的趋势,由0.18 mg/L减至2017年的0.08 mg/L,年均下降超过20%.综上,降雨量的起伏是导致2006年及之后库区长江干流磷浓度变化的主要原因;三峡水库蓄水后,水位上升、流速减缓强化了降雨量对整个三峡库区长江干流磷浓度变化的影响;三峡水坝工程开工伊始,国家在库区实施了退耕还林和库周绿化工程等一系列措施,治理成效在2012年之后逐渐显现,水体澄清性总磷显著降低.

In a study reported in this paper,the total phosphorus(TP)concentration of settled water samples(settling for 30 min after being taken)was analyzed,which werecollected from 2002 to 2017 at the Wanzhou Monitoring Stationby Changjiang Upstream Hydrology and Water Resources Survey Bureau of the Hydrology Department of Changjiang Water Resources Commission,based on"Regulation for Water Environmental Monitoring"made by the Ministry of Water Resources,P.R.China.The results showedthat compared with 2002,the year before the Three Gorges Reservoir(TGR)impoundment,the average water level of June to Decemberin Wanzhou section increased by 14.66-37.11 m in 2003,the water flow velocity decreased by 0.27-1.29 m/s,and TP in settled water samples increased 1.3-6.5 times,rising from 0.03 mg/L to 0.12 mg/L by monthly average;that after 2003,the year of impoundment,there was a highlysignificant positive correlation between the annual change of settled TP and the annual change of settled TP in theflood season(May-November)(p<0.01);and that after 2012,the settled TP decreased on ayearly basis from 0.18 mg/L to 0.08 mg/L in 2017,with an average annual decrease of more than 20%.In conclusion,the fluctuation of rainfall was the main reason for the change of TP in the main stream of the Yangtze River in the reservoir area in 2006 and after.After impoundment of the Three Gorges Reservoir,the rise of water level and the slowdown of flow velocity intensified the influence of rainfall on the phosphorus concentration change in the main stream of the Yangtze River.Since the beginning of the TGR project,the government has implemented a series of measures in the reservoir area,including conversion cropland to grassland and forest and greening project around the reservoir.Their effect began to be appearing after 2012,resulting inthe reduction of settled TP in the mainstream.