潮汐作用引起的盐度变化对河水中溶解性有机物组成和性质影响

   河流是地球水文循环中不可或缺的一个环节，承担着将物质从陆地输送到海洋的重要使命。河流的近海河段由于受到海洋潮汐作用的影响，盐度、溶解氧等性质以及水体中的物理、化学、生物反应等过程往往会随之发生变化。已有研究表明，河水和海水混合所导致的盐度变化，会降低水体中DOM的稳定性，影响水体中有机物和痕量金属的迁移、转化。本研究通过一系列盐度梯度模拟实验来探究盐度变化对DOM性质、组成成分的影响，同时通过改变重金属类型和粘土种类及组成比例来研究河流中不同重金属和颗粒物与DOM的相互作用，以及盐度变化对这些相互作用的影响。

   研究结果表明，盐 度增加会促进DOM发生絮凝，影响水体中DOM的含量，特别是在低盐度的水体环境中，盐度升高导致DOM大量絮凝，减少水体中DOM含量，而在高盐度水体中DOM含量随盐度变化较小。盐度的改变还会影响DOM的组成成分，比如盐度增加会诱导更多的荧光组分发生絮凝，导致荧光组分的相对浓度减少，非荧光组分的相对浓度增加。由于粘土和重金属与DOM之间存在相互作用，粘土或重金属的存在会进一步增强DOM在 盐度作用下的絮凝。在低盐度水体中，盐度增加，粘土对DOM的吸附作用增强，重金属对DOM絮凝的促进作用减弱，在高盐度水体中，重金属或粘土的存在对DOM浓度和性质随盐度的变化影响不大。粘土和重金属同时存在时，粘土对DOM絮凝的影响起主要作用。盐度诱导的DOM絮凝还会影响水体中的重金属浓度，对于大多数重金属而言，盐度增加会促进DOM与重金属之间的络合，导致水体中重金属离子浓度逐渐减小。

       DOM在物质迁移、转化和有机地球化学循环中发挥重要的作用，本研究揭示了盐度改变时河流DOM组成、性质的变化，以及不同重金属和颗粒物与DOM之间相互作用的变化，这对于进一步理解潮汐作用对河流DOM组成及性质产生的影响，深入认识DOM自身的转化和输送过程、水体中金属的迁移转化过程都具有重要意义。

     Rivers are an integral part of the hydrological cycle on earth, carrying materials from land to sea. Due to the influence of tidal action, the nature of water and some physical and biogeochemical reactions change in the coastal section of the river. Studies have shown that the salinity changes caused by the mixing of fresh water and seawater decreased the stability of DOM and affected the migration and transformation of organic matter and trace metals. In this study, a series of salinity gradient simulation experiments were conducted to explore the influence of salinity changes on DOM composition and properties, and to study the influence of salinity changes on DOM-clay-heavy metal interactions by varying the contents and types of clay and metals.

     The results showed that the increase of salinity promoted the flocculation of DOM and affected the content of DOM in water. In the low salinity environment, the content of DOM decreased due to a large amount of flocculation caused by increased salinity, while the content tended to be stable with the increase of salinity in the high salinity water. The changes of salinity also affected the composition of DOM. For example, the increase of salinity promoted the flocculation of more fluorescent compounds, resulting in a decrease in the relative concentration of fluorescent compounds and an increase in the relative concentration of non-fluorescent compounds. Due to the interactions with DOM, clay and heavy metals enhanced the flocculation of DOM under the action of salinity. In the low salinity environment, the amount of DOM adsorbed by clay increased with the rise of salinity, and the promoting effect of heavy metals was weakened. In the high salinity water, the influence of heavy metals or clay on the concentration and properties of DOM was little variation with the changes of salinity. Clay played a major role in the flocculation of DOM when both clay and heavy metals were present. The rise of salinity also affected the concentration of heavy metals in water. For most heavy metals, the increase of salinity promoted the complexation between DOM and metals, leading to a decrease in the concentration of heavy metal ions in water.

     DOM plays an important role in the transport and transformation of substances and the biogeochemical cycle. This study revealed the effects of salinity changes on the composition and properties of DOM and the interactions between clay, heavy metals and DOM. It is of great significance to further understand the influence of tidal action on the changes of DOM in rivers and the transformation and transport process of DOM and heavy metals in rivers.

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