"导度—光合"模型广泛应用于植被蒸腾估算,其中气孔导度斜率是模型的核心参数,通常用一个特定于生物群系的固定值进行参数化.然而,有研究指出气孔导度斜率存在季节性变化,故常数化气孔导度斜率的方案将导致植被蒸腾估算产生较大的不确定性.因此,如何优化气孔导度斜率的参数方案是提升植被蒸腾估算精度的关键.已有研究表明,使用叶面积指数对气孔导度斜率进行动态参数化可以有效改进对落叶林植被蒸腾的估算,但目前尚不清楚该方法是否同样适用于林冠季节变化不明显的常绿林.此外,最优性原理进一步解释气孔导度斜率为温度的函数.因此,利用温度模拟气孔导度斜率的效果是否优于叶面积指数也有待研究.针对以上问题,选取6个FLUXNET常绿林站点研究气孔导度斜率与叶面积指数和气温的关系,并对比2种参数化方案的模拟结果.结果显示,气孔导度斜率在各站点都随叶面积指数和温度的变化而变化,二者均呈现显著的负相关关系,动态参数化方案结果均优于常量气孔导度斜率静态参数化方案.这表明在常绿林中利用叶面积指数对气孔导度斜率模拟仍然有效,但温度对气孔导度斜率的解释能力(R2=0.45± 0.12)比叶面积指数的(R2=0.28±0.23)更强.进一步对比基于叶面积指数和温度参数方案所得的气孔导度和植被蒸腾,发现在日尺度上基于温度的方案比基于叶面积指数的结果改进更明显,显著降低了植被蒸腾估算的均方根误差(26.0％±24.4％).以上结果说明基于温度的气孔导度斜率参数化方案具有可行性,并有助于从机理层面改进常绿林生态系统的气孔导度和植被蒸腾动态的模拟.
Coral reef ecosystems are characterized by high primary production and biodiversity,providing rich biological resources and valuable ecosystem goods and services for humans.Reef-building corals survive in coastal areas near several nuclear power plants in China.Additionally,coral islands can potentially support future applications of floating nuclear power plants in remote marine environments for energy supply.Although artificial radionuclides derived from nuclear power plants are released into coral reef ecosystems,there is limited information on the biogeochemical behavior of artificial radionuclides and their radiological impacts on coral reef ecosystems.In this study,key artificial radionuclides,including 14 C, 239+240 Pu 90 Sr, 236 U, 129 I,and 137 Cs,were carefully selected and comprehensively investigated from the perspectives of activity concentration,coral skeletonseawater distribution coefficient （K d value indicating the ability of enrichment）,and radiation dose rates derived from the ERICA model.Based on our previous studies on 14 C, 90 Sr,and 137 Cs in coral reef ecosystems,we reviewed and analyzed the research progress on key artificial radionuclides,which were classified into low-level（K d ≤1 L/kg）,medium-level （1 L/kg＜K d ＜1 000 L/kg）,and high-level （K d ≥1 000 L/kg） enrichment groups according to the Kd value.The Kd values were ranked in descending order as 14 C＞ 239+240 Pu＞ 90 Sr and 236 U＞ 129 I＞ 137 Cs.The radiation dose rates of the above-mentioned artificial radionuclides and naturally occurring radionuclides of 210 Po in coral polyps were simultaneously calculated using the ERICA tool and ranked in the order 14 C＞ 90 Sr＞ 137 Cs＞ 239+240 Pu＞ 236 U＞ 129 I.The total radiation dose rate of artificial radionuclides was estimated to be 4.73×10 -4 μGy/h,which was much lower than the radiation dose rate of 210 Po （6.60μGy/h） and the screening benchmark level of no effect （10μGy/h）.Therefore,artificial radionuclides in the surface seawater of the South China Sea should not pose significant radiological risks to coral polyp populations.Overall,our results provide technical support for the assessment of nuclear safety in coral reef ecosystems in the context of the potential application of floating nuclear power plants in coral islands in the South China Sea.
地下水年龄是重要的水文地质学参数,可以指示地下水的循环时间和更新能力.常用环境同位素测定地下水年龄,但不同的环境同位素由于半衰期不同导致定年范围有限,50～1 000 a成为地下水定年的"短板".然而,50～1 000 a是近代人类活动频繁的时期,地下水资源、水环境和水气候记录档案等研究都需要年龄标尺.32Si可以用来确定50～1 000 a地下水的年龄,但是由于其复杂且费时费力的前处理和测试限制了 32Si定年的应用.32Si衰变生成子同位素32p,32Si和32P在3个月内会达到放射性平衡,放射性活度达到一致.天然状态下50～1 000 a地下水中的32Si与32P一直处于放射性平衡状态,所以直接富集地下水中的32P可以用于50～1 000 a地下水的年龄测定.地下水中32P的富集采用氢氧化镁共沉淀法,方便快捷.因此,放射性成因32P有望解决50～1 000 a地下水的定年"短板".在江汉平原地下水实例研究中发现,放射性成因32P定年结果与32Si定年结果基本一致.因此,放射性成因32P是解决50～1 000a地下水定年"短板"的有效工具,且便捷准确.
Mercury has received widespread attention as a toxic heavy metal contaminant. Organic mercury, especially methyl mercury（MeHg）, is more toxic than inorganic mercury and can easily accumulate in the food chain; therefore, the problem of inorganic to organic mercury conversion has attracted much attention in recent years. Most previous research has focused on mercury methylation in marine environments, and research on freshwater environments, especially wetlands, is lacking. The uniqueness and complexity of the wetland environment make it a prominent MeHg production unit, and the bioaccumulation effect is evident. In the present study, the pathways, mechanisms, influencing factors, and related biological effects of organic mercury conversion to inorganic mercury in wetlands are systematically summarized. Sediments, particulate organic carbon, and periphyton organisms are important microenvironments for MeHg generation, and frequent interactions between organisms guarantee the high methylation potential of wetlands. Therefore, strengthening the research on Hg methylation in various wetlands is of great significance for protecting the ecology of wetlands and the health of residents.
海底碳封存是减少全球温室气体排放的重要途径之一.为确保高效安全地封存CO2,需要在封存前、封存期间和封存后对CO2的潜在运移空间进行勘探、评估和监测.当前可用于海底碳封存监测的方式主要有聚焦海底井筒的内置传感监测、聚焦储层和盖层的地球物理监测以及聚焦海床和海水层的海底环境监测.这3种方式在海底碳封存监测中分别可获得注入、监测井筒附近的温度、压力和声学等数据,深部储层和盖层地震、电磁、重力等数据,以及浅部沉积层和海水层声学、化学和海洋学等数据,对这些数据进行分析有助于识别注入地层CO2的运移特征.但欲获取海底碳封存监测的相关数据,必须首先实现针对相关监测技术和研究方法的集成应用和优质方案的设计,这也成为当前学术界和工程界亟待解决的难题.本着尽可能降本增效的原则,为实现科学有序地进行海底碳封存监测,整理了不同监测方式和相关支撑技术的工作原理、应用现状以及面临的挑战,并展望了海底碳封存监测技术的未来发展.研究结果将为我国海底碳封存作业的实施和发展提供基础指引.
