气候变化对高纬度流域中汞和甲基汞迁移转化的影响——以降水量增加为例

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	气候变化对高纬度流域中汞和甲基汞迁移转化的影响——以降水量增加为例
其他题名	Climate change and mobilisation of mercury and methylmercury in boreal forest soil——Effects of artificially increased precipitation
	商立海
	2006-09-15
学位授予单位	中国科学院地球化学研究所
学位授予地点	地球化学研究所
学位名称	博士
关键词	甲基汞气候变化同位素土壤甲基化流域地表径流
摘要	全球变化的研究发现：19世纪以来全球平均气温大约上升了0.6℃，并预计在21世纪会升高更多。温室效应的直接结果是导致全球地面增温，温度的升高会增加下垫面的蒸发量。根据全球水平衡原理，蒸发量应该与降水量相等，因而降水量也会相应增加。气候变化的情景模式研究表明，世界各地雨量变异大，在高纬度地区，包括北欧地区，降水会增加。流域是水生系统的一个重要的汞和甲基汞的输入源。欧洲淡水系统中，鱼体汞含量过高的湖泊主要局限于北方的高纬度森林地区。在斯堪的纳维亚半岛，就有上万湖泊中的鱼体汞含量超过了健康食用标准0.5 mg/kg。水生系统甲基汞输入源包括：水体或沉积物通过甲基化形成甲基汞，通过大气干、湿沉降输入的甲基汞和陆地生态系统的地表径流输入的甲基汞。本研究的主要目标是搞清楚未来气候变化引起的大气降水量的增加对北方高纬度森林流域土壤中汞的迁移和形态转化有何影响。未来大气降水量的增加可能会增强森林地区流域土壤中汞的迁移，进而对水生系统的汞循环产生影响。一方面，如果地下水水位上涨，当水流过富含有机质结合含汞土壤层时，将会增加土壤中汞和甲基汞的迁移性，由此而导致流域向河流、湖泊等水生系统中汞输出通量的增加。另一方面，氧化还原电位改变、DOC和营养物质的释放会加剧汞在土壤中的释放过程，并且可能会促进汞的形态转化，可能增加毒性较强的甲基汞的产量，最终导致甲基汞从土壤向水生系统的输出通量的增加。本研究选择瑞典西海岸花园湖（Gårdsjön）的G1流域作为研究对象，在流域内进行人工模拟增加降雨试验，模拟未来气候变化降水量增加的情景，观测流域地表径流中汞和甲基汞的变化。并在流域内选择四个点（1×1m²），进行汞同位素加入示踪试验。测定土壤剖面甲基汞和总汞及其同位素组成，来分析汞的迁移和形态转化。主要研究结果如下： 1. 通过对G1流域土壤中甲基汞分布的调查，发现甲基汞含量范围为0.020-3.1ng/g，甲基汞含量与TOC含量具有正相关的关系，表明土壤甲基汞的迁移受TOC迁移的影响。估算G1流域的甲基汞储库通量为123g/km2，G1流域甲基汞储库容为0.65g。 2. 通过甲基汞含量和甲基汞储库在土壤剖面的分布，可以看出表层腐殖质层甲基汞浓度最高，甲基汞最富集，而在较深的土壤层位甲基汞储库容量最大，表明甲基汞具有向下迁移的趋势。 3. 根据总汞同位素组成结果，汞同位素（198Hg(NO3)2）加入土壤中后，202Hg/198Hg比值迅速下降，然后随时间推移而上升，表明加入土壤中的汞与土壤中原始汞形态不同，具有不同的迁移方式，且加入土壤中二价汞的迁移性比土壤中的原始汞更强。计算表明，外界加入的汞，将有50-60%长期滞留在土壤中。 4. 根据甲基汞的同位素组成结果，Wet点的新加入的198Hg甲基汞分数要大于其它三点，表明湿润土壤中汞甲基化速率要快于较干燥的土壤中。另外，Wet点的甲基汞分数比以前无人工模拟增加降雨的同位素示踪结果高很多，表明降水量增加会导致汞的甲基化作用在土壤中的形态转化过程中占主导地位，最终导致甲基汞产率的提高。 5. 人工模拟增加降雨试验进行后，地表径流中总汞的浓度没有发生变化，而甲基汞的浓度增大了很多，从0.03ng/L增大到了1ng/L以上，表明降水的增加可以促进土壤中汞的甲基化作用。 6. 地表径流向流域外总汞和甲基汞的输出量的计算显示，受人工模拟增加降雨的影响，流域地表径流量也会增加，最终年地表径流中总汞和甲基汞的输出通量都变大。
其他摘要	According to the research result of Global Change, a main change is that the increase in global mean air temperature, about 0.6℃ since the end of 19th century, and is predicted to intensify during the 21th century. The increase of the global mean temperature,which resulted from the Green House effect, will lead to the increase of the evaporation on the earth. Since the evaporation should be equal to the precipitation in terms of the global water balance, the precipitation will increase too. Future climate scenarios suggest large variabilities in precipitation levels in different parts of the world. In North Europe, large increase of precipitation is expected. Catchment is an important mercury source, including methylmercury, of the aquatic systems. The elevated concentrations of mercury in European freshwater fish are mainly confined to sites in the boreal forest zone. In Scandiavia, fish in tens of thousands of lakes have mercury levels above the guideline of 0.5 mg/kg (WHO) that makes them unsuitable for human consumption. There are three methylmercury sources of aquatic systems that are from mercury methylation in the water body or sediment, atomerspheric dry and wet deposition, and runoff inputs of the terrestrial systems, respectively. The boreal forest catchments play an important role in the mercury input of aquatic systems. The increasing precipitation, one of the climate changes, is the main concern of this study. What are the effects of the increasing precipitation in the boreal forest areas on the mercury mobilization and methylation? Our hypothesis is that the increase of precipitation will lead to the increase of mercury mobilization and methylation, furthermore, it will influence the mercury cycle in the aquatic systems. In particular, if ground water levels increase, more water will flow through organic-rich layers where a large fraction of the soil-bound mercury is present. Changing redox conditions and release of DOC and nutrients may enhance this process and cause an increase in methylmercury loading on aquatic systems. The anaerobic conditions in the much wetter catchment will also favor mercury methylation, that may result in the increase of methylmercury input to the aquatic systems. The Lake Gårdsjön is located in the west coast of Sweden, G1 catchment, a catchment in Gårdsjön, was selected as the research area. An irrigation experiment was carried out to simulate the future increase of precipitation. Mercury isotope addition experiment was also carried out simultaneously in four plots of G1 catchment. Runoff water and soil core samples were collected to analyse the total mercury (THg), methylmercury (MeHg ), and the isotope composition of the THg and MeHg. The main results from the study are as follows: 1) MeHg contents in the soil of the G1 catchment are 0.020-3.0 ng/g. A positive relationship between MeHg and TOC was found, which suggested the methylmercury mobilization will be influenced by TOC. The MeHg store was calculated as 123 g/km2, and the MeHg store in G1 was 0.65g. 2) According to the MeHg distribution in soil profiles and MeHg store in the soil profile, MeHg enriched in the mor layer has the highest MeHg concentration. The Bhs layer is the biggest MeHg store, which suggested MeHg mobilized to the lower horizons. 3) The ratio of 202Hg/198Hg in THg decreased sharply after the addition of 198Hg, then the ratio increased with time. An implication is that the different occurrence of mercury between the added mercury and the mercury in soil causes different mercury loss rate from the soil. The added divalent mercury is more easily to lose from soil than the mercury in soil. According to the calculation, 50% to 60% of added mercury was retained in the soil. 4) According to the produced and accumulated methylmercury from the added mercury isotope, more mercury was methylated in wet site than the other three sites, which suggested a higher capability for methylation in wet environment. Compared with the result before, much more MeHg fraction than the reslut without irrigation experiment was found, which can be explained by the influence of the irrigation experiment. 5) THg concentrations in the runoff did not change after the irrigation experiment, while great increases were found in MeHg concentrations, from 0.03 ng/L to 1 ng/L. 6) From the THg and MeHg output calculation from the runoff in the catchment, great increases were found in both outputs, which resulted from the increase of runoff due to the irrigation experiment.
页数	100
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3136
专题	研究生_研究生_学位论文环境地球化学国家重点实验室
推荐引用方式 GB/T 7714	商立海. 气候变化对高纬度流域中汞和甲基汞迁移转化的影响——以降水量增加为例[D]. 地球化学研究所. 中国科学院地球化学研究所,2006.

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