环境因子对长江口咸淡水混合水体中硅酸盐浓度的影响

The influence of environmental factors on the silicon concentration in the freshwater-seawater mixing plume at the Changjiang Estuary

中文关键词: 硅酸盐（SiO₃-Si）  长江口  咸淡水混合  稀释模式  迁移转化

英文关键词: Silicon (SiO₃-Si)  Changjiang Estuary  Freshwater-seawater mixing plume  Dilution mode  Migration and transformation

中文摘要:

      通过室内培养实验，模拟了不同条件下（水体盐度、温度、pH值、富氧缺氧等）长江径流淡水和东海外海水的混合过程，初步了解了上述主要环境因子对长江口硅酸盐（SiO₃-Si）混合模式的影响。结果表明，在实验条件下:1）长江淡水（包括已滤和未滤）与外海水在混合过程中，SiO₃-Si浓度在大约40 h后可基本达到平衡。2）混合水体中SiO₃-Si浓度与其盐度表现出良好的负相关关系，长江口SiO₃-Si浓度主要受物理混合稀释影响，已滤长江淡水与未滤长江淡水同外海水混合，二者混合水体中SiO₃-Si浓度随盐度的变化无显著差异。实验条件下，水体泥沙等颗粒物的存在对SiO₃-Si在稀释过程中的浓度没有显著影响。3）随着混合水体温度升高，其SiO₃-Si浓度略有升高，表明长江冲淡水对外海海域SiO₃-Si的补充存在季节性差异。4）pH为4-8时，混合水体中SiO₃-Si浓度相差不大，pH=10时，SiO₃-Si浓度发生改变，可能是悬浮颗粒物对SiO₃-Si的解吸增加、pH影响了SiO₃-Si的存在形式。5）在富氧和缺氧状态下长江淡水同外海水混合，混合水体中SiO₃-Si浓度无显著差异。

英文摘要:

      In order to study the migration, transformation, and the dilution mode of nutrients in the freshwater-seawater mixing plume at the Changjiang Estuary, we simulated environmental factors in the laboratory, such as salinity (S), temperature (T), pH, and dissolved oxygen (DO), and explored their influences on the silicon (SiO₃-Si) concentration in the mixing plume of the diluted Changjiang River water and the external seawater. Our results and their implications are: (1) when the external seawater was mixed with either filtered or unfiltered diluted Changjiang River water, the concentration of SiO₃-Si stabilized after 40 h. (2) The SiO₃-Si concentration in the freshwater-seawater mixing plume showed a clear negative correlation with the salinity, indicating that the SiO₃-Si concentration at the Changjiang Estuary was mainly affected by the physical mixing dilution. In the mixture of the external seawater and the diluted Changjiang River water, the concentration of SiO₃-Si showed no significant difference no matter whether the Changjiang River water was filtered, which suggested that the suspending particles in the water had no effect on the SiO₃-Si concentration in the freshwater-seawater mixing plume. (3) The concentration of SiO₃-Si slightly increased as the temperature of mixed water rose. This implied that there may be a seasonal change in the flow of SiO₃-Si from the diluted Changjiang River water to the offshore area of the East China Sea. (4) The SiO₃-Si concentration in the mixed water remained unchanged at pH 4-8, but altered when pH was 10. Simple explanations were that higher pH enhanced the SiO₃-Si desorption by suspending particles, or changes in the pH affected the form of SiO₃-Si. (5) The oxygen levels (anoxia or oxygen-enriched state) did not affect the SiO₃-Si concentration.