香溪河库湾沉积物-水界面的氮磷赋存特征及磷释放风险

Occurrence Characteristics of Nitrogen and Phosphorus at Sediment-Water Interface in the Xiangxi Bay and Phosphorus Release Risk

为研究三峡库区支流营养盐动态分布特征,于2016年6月—2022年6月调查了香溪河库湾沉积物、间隙水、上覆水中总氮(TN)、总磷(TP)的时空分布规律,并分析了磷的释放风险。结果表明:在完整的淹水-落干周期(2016-06—2017-03),春夏季沉积物中TN、TP含量大于秋冬季,中上游沉积物中TP含量高于下游;沉积物中TN和TP含量随着深度的增加而降低;上覆水与间隙水中TN、TP浓度(指质量浓度)均值差异性显著,TN 2.32 mg/L(上覆水)和11.41 mg/L(间隙水),TP 0.19mg/L(上覆水)和0.45 mg/L(间隙水)。年度变化(2016-06、2019-06和2022-06)结果显示:沉积物中TN和TP含量年度变化不显著;上覆水中TN浓度随时间下降趋势明显;上游采样点S1上覆水与沉积物TP含量的年度变化趋势一致,逐年下降。沉积物TP释放通量变化范围为0.024~0.140 mg·m^(-2)·d^(-1),说明沉积物中的磷可能充当“源”的角色,有向水体释放的风险。

To investigate the dynamic distribution of nutrient salts in the tributaries of the Three Gorges Reservoir Area,a survey was conducted from June 2016 to June 2022 to examine the temporal and spatial distribution of total nitrogen(TN)and total phos⁃phorus(TP)in the sediment,interstitial water and overlying water of the Xiangxi Bay in the Three Gorges Reservoir Area,and the risk of phosphorus release was also analyzed.The results showed that during the complete flooding-drying cycle(June 2016 to March 2017)the total TN and TP contents in spring and summer were higher than those in autumn and winter,and the TP con⁃tents of sediments in the upper and middle reaches were higher than those in the lower reaches;the TN and TP contents decreased with increasing depth.There were significant differences in the TN and TP mean contents between overlying water and interstitial water(TN:2.32 and 11.41 mg/L,TP:0.19 and 0.45 mg/L,respectively).The annual variations(2016-06,2019-06 and 2022-06)indicated that there were no significant annual changes in TN and TP contents in the sediment.The TN contents in over⁃lying water showed an apparent decreasing trend over time.The annual variation trend of TP contents in the overlying water of the upstream sampling site(S1)was consistent with that in the sediment,decreasing year by year.The range of TP release fluxes from sediments was 0.024~0.140 mg·m^(-2)·d^(-1),demonstrating that phosphorus in sediments might act as a“source”and pose a risk of release into water bodies.