丘陵山区水库沉积物-水界面磷源汇转换机制

Mechanisms of phosphorus source-sink transformation across the sediment-water interface of a hilly and mountainous reservoir

以东南丘陵山区典型深水水库对河口水库为研究对象,开展了1a的原位调研,在主要水域内采集原位柱状沉积物样品,分析了沉积物磷的含量、赋存形态、间隙水剖面特征以及沉积物-水界面交换通量的时空变化特征.结果表明:对河口水库表层沉积物总磷(TP)含量变化范围为(470.8~1012.3)mg/kg,平均值达到(688.4±186.48)mg/kg,呈现从上游至下游逐渐增加的趋势,下游坝前区域磷污染最为严重;沉积物中各形态磷含量大小顺序依次为:铝结合态磷(352.61mg/kg)>铁结合态磷(Fe-P)(98.10mg/kg)>闭蓄态磷(88.77mg/kg)>钙结合态磷(72.42mg/kg)>有机磷(33.38mg/kg)>可交换态磷(1.64mg/kg).全库沉积物总体表现为磷的释放源,其中,秋季释放风险最高,冬季大部分区域沉积物从磷释放的源转变为汇;全年平均静态释放通量和扩散通量分别为(0.81±2.34)mg/(m^(2)·d)和(2.15±3.47)mg/(m^(2)·d),2种方法所得全年磷释放量分别为1.92和3.67t,秋季释放量最大.铁结合态磷(Fe-P)的转化可能是控制沉积物-水界面磷源-汇转换的重要原因,由氧分层导致的沉积物厌氧及铁结合态磷(Fe-P)溶解释放将增加下层水体磷浓度,并在水体逆温后增加水柱总体磷浓度.在秋季大量磷释放之后,应更加关注随后的逆温对整个水体磷浓度的影响.

This study focused on Duihekou Reservoir,a typical deep-water reservoir located in the southeastern hilly and mountainous areas of China.A one-year field investigation was conducted to collect columnar sediment column samples from the main water bodies.Detailed analyses were conducted on the phosphorus concentrations,fractions,interstitial water profile characteristics,and spatiotemporal changes of fluxes across the sediment-water interface.The results showed that the average total phosphorus(TP)concentrations in the surficial sediment of the reservoir ranged from 470.8 to 1012.3mg/kg,with an average of 688.4±186.48mg/kg.An increasing trend of TP concentrations was discovered from the upstream to downstream.The most severe phosphorus pollution was discovered around the dam.The phosphorus fractions followed a descending order of Al-P(352.61mg/kg)>Fe-P(98.10mg/kg)>Res-P(88.77mg/kg)>Ca-P(72.42mg/kg)>Org-P(33.38mg/kg)>Ex-P(1.64mg/kg).Overall,the sediment in the entire reservoir acted as a source of phosphorus to the water,with the highest risk of release in autumn and most of the sediment in winter presenting as a sink of phosphorus.The average static release flux and diffusion flux of phosphorus were(0.81±2.34)and(2.15±3.47)mg/(m^(2)·d),respectively.The annual phosphorus release amounts obtained by the two methods were 1.92 and 3.67 tons respectively,with the highest release amount in autumn.The conversion of Fe-P might be an important factor controlling phosphorus release from the sediment.The anaerobic dissolution and release of Fe-P caused by oxygen stratification will increase the phosphorus concentration in the lower layer of the water column,which would subsequently increase the phosphorus concentration in the whole water column after thermal stratification.After a large amount of phosphorus is released in autumn,more attention should be paid to the phosphorus concentration in the water influenced by the subsequent thermal inversion.