English|Chinese

International Research Center on Karst(IRCK)/NICK

Home >NEWS > content

Achievements of IGCP661basic study (1): the structure and function of karst critical zone

Date:2018-11-15 Author:IRCK/NICK

Achievements of IGCP661basic study (1): the structure and function of karst critical zone

 

Over the past 30 years, Karst Dynamic System (KDS), Epikarst Zoneand karst ecosystems have been the core of research on karst at home andabroad. It mainly focuses on multiple- interface, multiple-layer and multipleearth’s spheres and the biogeochemical cycles of substance and energy, whichshare some similarity to karst critical zone.

 

The core of KDS is the cycle of carbon, calcium and water in fourspheres, which is almost the same as the range of the earth’s key belts. Research into KDS concentrates on the surface karst belt. Research onkarst ecosystems and key belts aims to maintain the stability of human-relatedsystems and sustainable development. However, the former pays more attention tothe geological-ecological mutual feedback and adaptation mechanisms, and lessto biogeochemical cycle dynamics.

说明: C:\Users\Administrator\Desktop\newsletter\演示文稿1.jpg

Fig. 1 The Structure of karst critical zone

(Yunnan-Guizhou plateau as an example)

Research on karst critical zone takes atmosphere-vegetation- soil-carbonate(cave)-water (soil water, cave drip, spring, underground river, etc.) as acomplete system. It comprehensively monitorsthe hydrological process, biogeochemical process and ecological process as wellas their coupling relations. In view of the development of carbonate rocks, thekey karst belt structure is generally characterized by the surface and underground double-layer structure, regional variation ofthickness, and extreme sensitivity to environmental changes and humanactivities.

 

In terms of the characteristics of groundwater runoff, the karstcritical zone can be divided into up to six belts vertically, namely surfacerunoff belt, vertical seepage belt, seasonal fluctuation belt,submerged-contained water runoff belt, layeredbearing runoff belt, and pressure-bearing runoff strip belt (Fig. 1). The firstfour belong to the shallow circulating runoff zone within one hydrologicalyear’s circulation cycle, where the distance of flow is limited by the surfacewatershed because groundwater is affected by the seasonal variation ofprecipitation. The latter two belong to the deep circulating runoff zone withinyears or even decades of circulation cycle, where the groundwater is notrestricted by the surface watershed because the seasonal changes inprecipitation exert little impact.

 

The base detection of Guohua Guangxi, Puding Guizhou andYangzhuang Shandong shows that the karstsurface zone is generally 5-20m deep, and the shallow circulation zone 50-200m.An exception is the peak-cluster depression area strongly uplifted in Yunguiplateau, where the key zone is 500m deep.

 

The main functions of the karstcritical zone are: driving karstification and various forms produced by it to form the surface and underground double-layer structure;driving carbon cycle for karst carbon sink; driving element migration to formthe calcium-rich and alkaline geochemical background; recording theenvironmental change process.

 

Carbonate dissolution makes apotential contribution to atmospheric CO2 deposition (returns) byconsuming atmospheric or soil CO2. Under the support of the China GeologicalSurvey, through the international cooperation of the International KarstResearch Center and the IGCP661 project, 39 karst carbon cycle monitoringstations have been established in different types of karst areas in China andother nations such as Thailand, Myanmar, Indonesia and Slovenia. The study ofcarbon cycle monitoring in typical karst critical zone shows thatkarstification is closely related to surface ecological processes. A new way ofcarbon sequestration and sinking in karst critical zone has been discovered,such as rocky desertification control and aquatic bio-carbon fixation. Thepositive succession of vegetation has a significant effect on the karst carbonsink. The carbon sink of karstification under the original forest land is threetimes that of the secondary forest and nine times that of the shrub. It has been confirmed that aquaticphotosynthetic organisms significantly immobilize carbon (DIC) from carbonaterock. The carbon sink effect of high carbon sequestration of aquatic plants canbe compared with carbon sinks in terrestrial ecosystems, which may be importantcomponents for global missing sinks. It has been found that the carbon sinkstrength in the tropical karst area is 1.5-2.5 times that of the subtropicalzone under similar geological lithology conditions.

 

Through the analysis of 13C and 14C of waterand aquatic organisms, it is revealed that DOC has exogenous characteristics,and the cycle time of RDOC in karst lakes and river water is 300-1000 years. Itis considered that the carbon sink formed by karst is stable on thehundred-year scale. Therefore, it provides a scientific basis for correctingthe carbon sequestration of geological processes (including karstification) inthe global carbon cycle as a long-term scale of thousands of years.

 

The earth’s key belts emphasize the coupling study of processes indifferent time scales, which opens up a new way for ecological restoration ofrocky desertification and soil erosion. The monitoring study of the typicalpeak-cluster area in southwestern China shows that the soil loss due to thesinkhole accounts for 75%of the total soil loss, but when the vegetation coverage reaches 70%, the soilerosion drops to 10 t/km2.a.

 

Years of atmospheric precipitation-surface ecology-cave drip- systematicmonitoring of modern sediments proves that δ18O in the southwesterncave can reflect climate information such as paleo-precipitation and summermonsoon intensity, and δ13C can be used to indicate the ecological environmentabove the cave. It lays the foundation for restoring the characteristics andpattern of past precipitation changes in the East Asian monsoon region. The δ18Orecord of stalagmite with a resolution of 1-5 a in the Hunan-Yunnan region inthe past 500 years is compared with the climate distribution types in recentdecades, providing a similar climate spatial scenario for future prediction.Together with 210Pb dating and comparison of various age fittingmodes, an accurate stalagmite sedimentary age model based on AMS 14Cdating technology has been established, which is verified by the moderninstrumentation records and other geological records.

 

Edited by Dr. Zhang Cheng


Copyright©2010 International Research Center on Karst
Address:No.50, Qixing Road, Guilin, Guangxi, P.R China Guilin-ICP prepared No. 05009877-2