岩溶动力学的理论探索与实践

Karst Dynamics Theory in China and its Practice

国土资源部岩溶动力学重点实验室的研究群体自1990年以来连续成功实施了3个国际岩溶对比计划项目，包括IGCP299、IGCP379、IGCP448，在岩溶形成、碳循环、岩溶生态和水资源等领域，为国际岩溶学术界提供了共同解决岩溶地区资源环境问题的机会，将地球系统科学思想引入现代岩溶学，建立岩溶动力学理论，有力地推动了国际岩溶学科的发展。目前正在执行的IGCP513“岩溶含水层与水资源”项目继续引领国际岩溶地质研究方向。相关成果为在中国桂林建立联合国教科文组织“国际岩溶研究中心”（IRCK）奠定了坚实基础。由此回顾了20多年来岩溶动力学理论在中国的发展过程。概述了其主要的科学成果和应用前景。指出了地球系统科学的引入、全球视野的研究和及时将理论用于解决岩溶地区的资源环境问题在现代岩溶学发展中的重要意义。经过20余年的不断探索，形成了岩溶动力学理论的基本思路，并创造性地总结了一套捕捉碳、水、钙循环的行踪的工作方法。通过全球对比，提出“岩溶形态组合”概念，将岩溶形态组合与岩溶形成环境条件建立对应关系，解决异质同相、同质异相这一令岩溶学者迷惘的问题。将岩溶学引入全球变化研究，一方面把岩溶作用与全球碳循环紧密的联系在一起，通过对CO2-H2O-CaCO3系统（岩溶动力系统）的定位观测，发现全球最大的碳库-碳酸盐岩体在全球碳循环中仍甚活跃；另一方面，岩溶动力系统（KDS）对环境变化十分敏感，响应及时，其相关沉积物可记录全球变化。将岩溶地质过程与生态学联系在一起，将现代岩溶学理论的研究推向应用，与生产实践结合。在岩溶动力系统运行机制和运行规律、我国岩溶动力系统的类型划分和分布规律、在表生岩溶系统碳循环与大气CO2源汇关系、利用石笋记录重建古气候、古环境变化过程及中国西南岩溶生态系统研究等方面均获得了突出成果，如首次估算了我国和全球因碳酸盐岩溶蚀回收大气CO2的量，中国为1.774×10^7t／a，而全球为6.08×10^8t／a；证实了西南岩溶区典型表层岩溶泉水化学的季节、日变化与暴雨动态，表层岩溶泉水化学取样的频率需要重新审定，而且水文水化学的连续监测对于岩溶作用强度和岩溶作用碳循环的高精度评价是十分必要的；要了解岩溶系统水化学的变化，仅考虑水-岩相互作用是不够的，我们还必须重视CO2气体对岩溶系统中水化学变化的影响，即岩溶系统水化学动态的变化是CaCO3-H2O-CO2三者相互作用引起的，水-岩-气相互作用的概念必须引入岩溶水化学的研究中；揭示了过去0．16Ma来亚洲季风和低纬度地区降雨变化的特征，说明太阳辐射强度增高，驱动了盛问冰期的出现，重建了荔波地区2．3ka来古气候环境的演变历史，贵州董哥洞石笋提供了低纬度、低海拔地区，可较好定年，更接近水汽来源区的古气候变化的替代指标；石笋记录发现末次冰期以来存在有多次冷事件-Heinrich冷事件H1-H5跃变事件，新仙女木事件在我国南方的洞穴沉积物中具有显著的反映。对西南8省区市岩溶县、石漠化严重县统计和空间分布特征的分析研究表明地质地貌条件对岩溶区资源、环境和社会经济具有制约作用，认为西南岩溶区石漠化综合治理首先要在岩溶地质条件的基础上，结合气候、水文和社会经济状况，才能深入分析岩溶区石漠化的成因、危害和类型。划分出岩溶区石漠化综合治理区域8大区成为“西南岩溶石漠化综合治理规划大纲”编写的重要基础。

IGCP-513 “Karst Aquifers and Water Resources”（2005-2009） is a karst-related IGCP project that continues the trend of international karst geology research. Since 1990, three karst-related IGCP Projects （ IGCP 299, IGCP 379 and IGCP 448） have been implemented successively with Prof. Yuan Daoxian from the Institute of Karst Geology, CAGS, as Leader of the International Working Group. All these four projects have provided opportunities for karst research communities worldwide to study together and solve resources and environment problems in the fields of karst formation, carbon cycle, karst ecology and water resources. Earth System Science has been introduced into the study of modern karstology, and Karst Dynamics Theory has been established, thus improving the development of karst science. The achievements of these projects have laid a solid foundation for the establishment of the International Research Centre on Karst （IRCK） under the auspice of UNESCO in Guilin, China. From this point, this paper presents a review of the development of Karst Dynamics Theory in China during the past couple of decades. The major scientific achievements are summarized, and the perspectives of their practical utilization are illustrated. The importance of Earth System Sciences and Global View in the development of modern karstology in China is emphasized. The history of the development of Karst Dynamics Theory in China can be traced back to 20 years ago in the study of karst geochemistry, in which a series of field portable facilities were used to reveal the behaviors of Karst Dynamics System as well as the directions （ dissolution or deposition） and intensity of karst processes, thus providing the methodological background for the development of the Karst Dynamics Theory. The Karst Dynamics Theory is defined as the discipline for studying structures, behaviors, functions and types of the karst dynamics system （KDS） in the world. The KDS is the karst system of material, the energy transfer in the forms of carbon cycling, water cycling, calcium and other element cycling on the interfaces between lithosphere, atmosphere, hydrosphere and biosphere. Conse-quently, the major functions of KDS are：①the forcing of the formation of karst;②the regulation of the greenhouse gas in the atmosphere and environment acidification;③the promotion of the migration or deposition of elements, thus forming mineral deposits and bringing about impacts on human life;④to record the processes of climate and environmental changes. As the KDS is influenced by geological, hydrological, climatic and biological processes, there are different types of KDS in the world. The idea of Karst Feature Complex （KFC） is an important part of the Karst Dynamics Theory. The KFC is defined as a group of karst features which include macroscopic and microscopic forms, surface and subterranean forms, and dissolution forms as well as depositional forms developed under similar environments. The idea of KFC helps karst re- searchers avoid the confusion of isomorphism, thus benefiting the global karst comparison and the smooth running of IGCP299. Through years of monitoring on dozens of typical karst dynamic system sites both in China and abroad, the differ-ences in the behaviors of different types of KDS as well as their relationships with rainfall, especially thunderstorm events, vegetation, and soil condition were revealed. The largest carbon reservoir （ carbonate rock mass） obviously remains active in global carbon cycle, the data from the site automatic records indicate that KDS is highly sensitive to environmental change, and the response time scale may be hours or even minutes. Continuous site observation shows that the seasonal and diurnal hydrochemical variations tend to co-vary with thunderstorm events. Hydrogeochemical sampling strategies for epikarst springs in karst areas with monsoon climate like southwest China should be redesigned, and continuous hydrogeochemical observation is needed for accurate evaluation of karstification intensity and carbon cycle. It is also found that the considera- tion of only water-rock interaction is not sufficient for understanding the hydrochemical variation in karst systems, that the variable effects of CO2 on the system should be evaluated, and that the consideration of water-rock-gas interaction as a whole is thus a must in understanding the regularity of the spatial and temporal variations in KDS. Taking the advantage of the CO2 involvement in karst processes, the Karst Dynamics Theory contributes to the global change study in 2 ways：①Concerning the carbon sink or carbon source of the atmospheric CO2 through the karst process, it is estimated that about 17.74×10^6 t of carbon is removed by dissolution of carbonate recks from the atmosphere in the karst regions of China, whereas the amount from the atmosphere in global karst regions is 6.08×10^8 t, i. e., about 1/3 of the missing carbon sink. On the other hand, a lot of CO2 outgassing points from active tectonism were identified along the Tethys zone from Ti-bet westward to France, which become an important source of atmospheric CO2;②For the purpose of providing high resolution past climate change proxies from karst sediments, especially speleothemes for the test of GCM, some abrupt changes in paleomonsoon on termination I, Ⅱ were revealed. A lot of papers in this aspect have been published in important interna-tional journals such as Science, Holocene and Quaternary International. For example, thorium-230 ages and oxygen isotope ratios of stalagmites from Dongge Cave in China characterize the Asian Monsoon and low-latitude precipitation over the past 160000 years. Numerous abrupt changes in ^18O/^16O values result from changes in tropical and subtropical precipitation driven by insolation and millennial-scale circulation shifts. The Last Interglacial Monsoon lasted 9.7±1. 1 thousand years, beginning with an abrupt （less than 200 years） drop in ^18O/^16O values 129.3±0.9 thousand years ago and ending at an abrupt （less than 300 years） rise in ^18O/^16O values 119.6±0.6 thousand years ago. The start coincides with insolation rise and measurements of full interglacial conditions, indicating that insolation triggered the final rise to full interglacial conditions. The paleoclimate environment evolution since 2300 years ago in Libo, China, was reconstructed by lots of paleoclimatological records of stalagmite. Many cold Heinrich events H1-H5 since the last glacial stage and abrupt events such as Younger Dry events are clearly recorded by stalagmites of south China. The Karst Dynamics Theory has been applied to the sustainable development of karst regions in China, especially to the rehabilitation of the rock desertification areas in southwest China which covers about 100000 km2 with a population of about 30 millions. Because of the leakage of water resources, the shortage of soil, and the alkaline background of carbonate rocks, the karst ecosystems are characterized by petrophile, xerophile, and calciphile on the surface. The lack of sunshine, the rather stable temperature, and slow under-ground metabolism constrain the biodiversity in karst areas. Under the guidance of karst dynamics, plants that enjoy both ecological and economic benefits are selected under the particular KDS geochemical background to be used in the rehabilitation of rock desertification areas, and water resources in thousands of underground streams in southwest China are managed in accordance with the special behaviors of KDS. The development and utilization of Karst Dynamics Theory is designated as a principal target of the newly approved International Research Centre on Karst （IRCK） in Guilin under the auspices of UNESCO. This discipline will be developed continuously under the joint effects of karst scientists both from China and abroad.