Flux and form of phosphorus in overlying water at the effluent section of the Three Gorges Reservoir from 1998 to 2019

• DOI: 10.18307/2023.0201
• Publication Date: 2023-03-13T02:20:25Z
• Authors: Lou Baofeng; ; Ouyang Xuejiao; Yang Xia
• Keywords: Three gorges

总磷是长江流域备受关注的污染物。来自长江上游的物质输送对长江中下游、对入海口水域水生态都具有重要影响。研究了1998-2019时期长江上游和中下游之间的衔接断面暨三峡水库出水断面的磷通量及形态变化。整个研究时段分为3个阶段:1998-2002(阶段Ⅰ,三峡水库运行之前),2003-2013(阶段Ⅱ,作为过渡时期)及2014-2019(阶段Ⅲ,三峡水库实现175 m正常蓄水位且金沙江下游段向家坝和溪洛渡水库运行后),以阶段Ⅰ、Ⅲ为重点时段进行对比分析。研究表明,2014-2019年总磷年通量平均为5.67万t/a,比1998-2002年减少了38.0%;溶解态磷年通量为4.02万t/a,增加了60.0%;颗粒态磷年通量为1.67万t/a,减少了74.9%。磷的主导形态由颗粒态变为溶解态,溶解态磷通量占比由27.5%上升为70.9%;相应地,颗粒态磷通量占比由72.5%下降为29.1%。总磷、溶解态磷和颗粒态磷通量均表现为丰水期>平水期>枯水期。近20年来,水沙关系发生了巨大变化,含沙量(SS)与水量(Q)正相关性大幅下降,其拟合方程的斜率由1.44下降为0.10,R²由0.83下降为0.57。溶解态磷月通量在总磷月通量中的占比(λ_DF)随输沙量或泥沙含量(SS)的增加而减小的规律基本未变,2014-2019年λ_DF与SS的经验模型为λ_DF=1.2883-0.3688×lgSS(mg/L)。三大水库的拦沙作用和流域水土保持作用导致的水沙条件变化是磷通量及形态变化的主要原因。三峡水库出水生物可利用磷浓度升高及光能吸收增强对初级生产力的促进作用及藻类密度的影响等生态效应值得关注。;Phosphorus (P) is a pollutant of great concern in the Yangtze River basin, which has an important impact on water ecology basin. The P flux and form at Three Gorges Reservoir (TGR) outlet section during 1998-2019 were studied, whole period was divided into three stages: 1998-2002 (stage Ⅰ, pre-TGR period), 2003-2013 Ⅱ, as interim 2014-2019 Ⅲ, after TGR achieved 175 m normal level completion Xiangjiaba Xiluodu Reservoir), Ⅰ Ⅲ key periods comparison. results show that average annual total phosphorus (TP) stage 5.67×10⁴ t/a, 38.0% less than Ⅰ. Wherein, dissolved (DP) particulate (PP) 4.02×10⁴ t/a 1.67×10⁴ with increase 60.0% decrease 74.9% comparing to respectively. main changed from dissolved. In 1998-2002, DP accounted for 27.5% TP flux, but rose 70.9% 2014-2019. Accordingly, percentage PP decreased 72.5% 29.1%. Seasonality TP, are shown wet season>even season>dry season. past two decades, relationship between runoff (Q) suspended sediment (SS) greatly, positive correlation them significantly, slope equation 1.44 0.10, R² 0.83 0.57. rule monthly decreases increasing SS remains unchanged, empirical model established λ_DF=1.2883-0.3688×lgSS (mg/L) based data changes characteristics mainly attributed trapping reservoirs soil conservation Attention should be paid ecological effects resulted bioavailable concentration enhancement light energy absorption.