辽河口不同类型湿地汞甲基化及汞生物传递机制研究

wetland is not only the source of carbon globally but also the source of mercury. It is a hot study to research the mechanism of the methylation of mercury and the magnification of the food chain in wetland. Liaohe estuarine wetland as a special ecological system, due to the shortage of fresh water, led to water-salt imbalance. Changes in wetland environments, this will certainly affect the wetlands of mercury methylation and bio-magnification of mercury.this study choose Reed wetland in the Liaohe, suaeda wetlands, shrimp and crab as a study area, comparing changes in mercury in different types of wetlands in natural conditions and shortage of fresh water, sea water intrusion through a combination of field research on in situ and laboratory simulation,this study simulate the conditions of redox and the methylation of mercury under different salinity and temperature change and discuss on the effects of water-salt imbalance on wetland soil mercury methylation. This study explore the contribution of different microbial conditions to methylation of mercury. Identifying different types of wetland food web structure by use of 15N isotopes and studying mercury bio-magnification and exploring the biological transmission mechanism of tribute. The results of this project will deepen understanding of the conversion of tribute in the estuarine wetland and ecological risk, and deepen the cognition on ecological risks caused by environment change in estuarine wetland.

湿地不仅是全球重要的碳汇和汞汇，也是重要的甲基汞源。汞甲基化的机理及汞食物链放大是目前湿地汞研究的热点问题。辽河口湿地作为特殊的生态系统，近年来由于淡水缺乏，导致湿地水盐失衡。湿地环境发生变化，这势必影响湿地汞的甲基化以及汞的生物放大。本项目选择辽河口芦苇湿地、碱蓬湿地、虾蟹田作为研究区，拟通过野外原位研究和室内模拟分析相结合，对比不同类型湿地在自然生长状态下和淡水缺乏、海水倒灌后湿地汞的变化；模拟氧化-还原条件、不同盐度、温度变化下汞的甲基化，探讨水盐失衡对湿地土壤汞甲基化的影响；研究不同微生物条件对汞甲基化的贡献；利用15N同位素确定河口湿地食物网结构，研究湿地汞的生物放大，探讨汞的生物传递机制。本项目的成果将深化有关汞在河口湿地转化及其生态风险的理解，加深河口湿地环境改变造成的生态风险的认识。

本项目以辽河口裸滩地、翅碱蓬湿地、芦苇湿地为研究对象，通过野外调研和室内模拟实验，研究了环境温度及淹水盐度改变对土壤中汞和甲基汞的作用机理。研究表明：裸滩土壤随淹水盐度升高，表层和亚表层土壤中Hg均表现降低的趋势；随着温度的升高，土壤汞含量增加。厌氧-好氧实验中，上覆水中THg含量随淹水盐度升高也表现出升高的趋势。干湿交替条件下，淹水时，翅碱蓬土壤在低盐度(<1.00%)条件下MeHg含量较高，自然风干后，土壤在盐度较高(1.0-1.8%)时MeHg含量较高。厌氧-好氧条件下，土壤中MeHg含量随淹水盐度升高总体上也表现出先升高后降低的变化趋势，且在淹水盐度为0.5%-1.0%时较高。土壤淹水状态更利于土壤中MeHg的形成。淹水盐度和环境温度的改变，更容易引起表层土壤中THg的释放和MeHg的产生。各盐度条件下碱蓬土壤、芦苇土壤中均有SRB存在，30℃条件下碱蓬土壤中SRB菌数高于20℃条件下SRB菌数；温度条件相同时，厌氧条件下土壤中SRB菌数高于好氧环境。当培养温度为30℃时，在培养前期(15天)，厌氧环境和好氧环境中土壤MeHg含量与SRB菌数均表现出显著正相关关系，而在培养后期，则没有相关性。芦苇土壤厌氧条件下、土壤甲基汞含量随着培养时间的增加表现先增加后降低的趋势，而好氧条件下，则表现为先降低后增加，芦苇土壤中SRB菌数在培养15-20天时达到最大值。因此，淹水盐度升高会促进湿地土壤中THg的释放，适当盐度有利于土壤中MeHg的产生；适当升高温度和淹水等厌氧条件更有利于土壤中THg的释放、提高SRB的活性和MeHg的产生，SRB对Hg的甲基化作用在30℃时更明显。 .利用15N同位素构建河口湿地食物链，从食物链的营养级关系可以看出，汞在食物链中有一定的累积，对人类健康存在潜在的威胁。因此，辽河口区域的环境问题应引起重视。