自然資源部巖巖溶動力學重點實驗室

I. Carbon Cycle in Epigenic Karst Systems

1999-07-10KDL 3184

Part III Contributions

I. Carbon Cycle in Epigenic Karst Systems

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The role of chemical weathering of carbonate rocks
in the geochemical Cycle of CO2

Kazuhisa YOSHIMURA*?and Youji INOkURA**

*Chemistry Laboratory, College of General Education, Kyushu University,
Ropponmatsu, Chuo-ku, Fukuoka 810, Japan
**Research Division of University Forests, Faculty of Agriculture, Kyushu
University, Hakozaki, Higashi-ku, Fukuoka 812, Japan

(from Chikyukagaku(Geochemistry)27,21-28(1993) )

The geochemical cycle of CO2?in a carbonate rock area was discussed by using for an example obtained for Akiyoshi-dai Plateau (Yamaguchi Prefecture), one of the biggest karst plateaus in Japan. The calcium concentration of the baseflow of the groundwater in the area showed seasonal fluctuations, and followed changes in CO2?concentration in the soil.Soil CO2?measured in the meadows which cover most of the area varied from a minimum of 0.08% at a soil temperature of 3.8oC and a maximum of 1.2% at 20.8oC.The calcium concentration in the groundwater is controlled by water-limestone dissolution equilibrium, under open system conditions depending on the meadow's Soil CO2?concentration. At the runoff peak of groundwater issuing from Akiyoshi-do Cave, which has the biggest drainage basin in Akiyoshi-dai Plateau, 18.5 km2, the calcium concentration increases due to the flushing out of water with a long residence time in the deeper phreatic zone. During 1983 - 1986, a yearly average of 2,100 tons of limestone was dissolved in 2.1?á107m3?of groundwater issuing from Akiyoshi-do Cave, its catchment basin including 16.5km2?of a limestone area: the mean solutional denudation rate is 51 mm/ka.

The amounts of CO2?utilized on chemical weathering in carbonate rock areas in the world, corresponding to the same amounts of chemically weathered carbonate rocks in mol, were estimated by using the limestone denudation rate of 50mm/ka and found to be 8 ?á1011?kg /y.The role of chemical weathering of carbonate rocks cannot be ignored in the geochemical cycle of CO2.

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Solution Ratio of limestone Tablets and CO2?Contents in
Soils of Minamidaito Island

Kazuko URUSHIBARA-YOSHINO (Komazawa University),
Hiroyuki KINA (Minamidaito Meteorological Observatory),
Kazuo ARAGAKI(I (OKinawa Meteorological Observatory),
Masakazu SASAKI (former Minamidaito Meteorological Observatory),
Franz-Dieter MIOTKE(Hannover University)

(From KOMAZAWA GEOGRAPHY,No.23 1997,P47)

Secular change of solution ratio used by limestone tablets was measured in Minamidaito Island in 1993, 1994 and 1995. The tablets were made from the Slovenian, Guilin, Chichibu and Minamidaito limestones. The solution rates were maximum in the air and in the soils in 1993, when the water deficit was the smallest and CO2?contents in soils were high. On the other hand, the solution rates were minimum in the air and in the soils in 1995, when the water deficit was the minimum and CO2?contents in soils were small during dry spell. Generally, the limestone tablets of Guilin show the highest solution ratios. However, the tablet of Minamidaito limestone shows higher solution ratio than the Guilin limestone tablet in B2?horizon in 1995. In these 3 years, the solution ratios of B2?horizon were always higher than A3?horizon, because the CO2?contents of B2?horizon were higher than A3?horizon in almost all seasons during these 3 years. CO2?contents in soils were examined by the Drger method in the depression areas on the limestone wall and sugar cane fields on August 24 and 25, 1994. The values were higher in B horizons than A horizons. In the soils of sugar cane field, the CO2?contents values are small in the plough layers, but the values are high in B horizons deeper than 40cm. It is considered that CO2?gas produced in A horizon and plough layers might be gone out into the air, but the CO2?gas might be kept longer time in B horizons, because of heavy clay and tight soil structure.

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Karst denudation in Irkutsk Region

Elena Trofimova
Institute of Geography, Siberan Branch of Russian Academy of Sciences
Ulanbatorskaya str. 1 ,Irkutsk, 664033 Russia

(Paper presented at 12th?ICS, Switzerland,1997)

Using method of pro. M. Pulina karst denudation is tallied up for 93 river basins of Irkutsk Region. Its schematic map was created. Two big regions with karst denuation from 20 to 50 mm/1000 years and three small regions with values from 20 to 30 mm/1000 years are distinguished. Considerable values of karst denuation are explained in the context of peculiarities of karst processes in the region.

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Figure: Karst denuation in Irkutsk Region?
1,<5mm/1000years;2, 5-10;3,10-15; 4, 15-20;5, 20-30;6, 30-50;7,>50

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The influence of the soil air PCO2?on the chemical
composition of karst spring water
(Swabian Alb, SW Germany)

Torsten Clemens, Claudia Mer, Martin Sauter
University of Tbingen, Applied Geology, Sigwartstr. 10, D-72076 Tingen, Germany

Abstract

The principal source of carbon dioxide, available for the dissolution of carbonate rock is found in the soil zone. However only few studies have been conducted where both, the PCO2?in the soil atmosphere and the chemical composition of spring water have been compared. In this study the PCO2?in the soil was measured at various depth beneath the surface and for different types of vegetation in a well defined holokarst groundwater catchment. Further, the chemical composition of the spring water was determined.

The results show that the spring water is always saturated with respect to calcite and that the water reaches the equilibrium concentration of calcium in the subcutaneous zone under open system conditions with respect to carbon dioxide. The CO2?content of the spring water and of the soil decreases during the winter months. The PCO2?in the soil increases with depth and is dependent on the type of vegetation. The comparison of' different groundwater catchments with 50 % and 20 % of agricultural land showed that the calcium content of the spring water is dependent on the vegetation in the catchment area. Therefore the determination of the denudation rate for the geological past should not be based on todays water composition affected by agricultural activity.

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Contribution of carbonate rock weathering
to the atmospheric CO2?sink

Zaihua Liu1, Daoxian Yuan1, Shiyi He1?, Jinbo Zhao2
1?Institute of Karst Geology, Guilin, 541004, P.R. China
2?Xi'an College of Technology, Xi'an, 710054, P.R. China

(paper to be presented at 28th?IAH congress, Las Vegas, Sept. 1998 )

ABSTRACT

To accurately predict future CO2?levels in atmosphere, which is crucial in predicting global climate change, we must determine the fate of source and sink of the atmospheric CO2. In this paper, case studies are reviewed using published and unpublished data. Firstly the sensitivity of carbonate rock dissolution to the change of soil CO2?and runoff will be discussed, and then the amount of CO2?removed from the atmosphere in the carbonate rock areas of mainland China and the world will be determined by hydrochem-discharge method, carbonate-rock-tablet-method and the DBL-model calculation, to get a estimation on the contribution of carbonate rock weathering to the atmospheric CO2?sink. It will be seen that this contribution (in the range of 0.11~0.41 billion metric tons of carbon/a) can not be neglected and should be taken into consideration in the global carbon cycle model.

INTRODUCTION

It has been known?that the combustion of fossil fuels releases about 5.4 billion tons of carbon a year as CO2?into atmosphere. In addition, deforestation practices contribute about 1.6 billion tons of carbon a year to the source of atmospheric CO2. So, the total input of CO2?from human activities is about 7.0 billion tons of carbon a year. However, only about 3.4 billion tons of carbon a year accumulates in the atmosphere. That means there is an atmospheric CO2?sink of about 3.6 billion tons of carbon a year.

To accurately predict future CO2?levels in atmosphere, which is crucial in predicting climate change, we must determine the fate of the CO2?sink. Although extensive efforts have been made for tracing the missing carbon, the explanation is still unclear.

As the world's biggest carbon reservoir, carbonate rock contains about 6.1x107?billion tons of carbon, which is 1694 times and 1.1x105?times larger than those of oceans and world vegetation respectively. Carbonate rocks occupy an area of about 22 million square kilometers in the world.

The basic reaction for carbonate rock weathering can be expressed by:

CaCO3+CO2+H2O- -Ca2++2HCO3-? (1) for limestone

CaMg(CO3)2?+2CO2+2H2O- -Ca2++Mg2++4HCO3-?(2) for dolomite.

where CO2?may come from the atmosphere directly in bare carbonate rock area, or from soil in overlying and/or buried carbonate rock area.

It can be easily visulized from the above reactions that the carbonate rock weathering contributes to the atmospheric CO2?sink (Note that the consumption of CO2?in soil by the weathering decreases the release of soil CO2?into atmosphere, and thus also contributes to the atmospheric CO2?sink). For limestone weathering, the removal of 1 mol CaCO3?needs 1 mol of CO2?from atmosphere; and for dolomite weathering, the removal of 1 mol CaMg(CO3)2?needs 2 mol of CO2?from atmosphere. It is also clear that only half of the carbon in solution is from atmospheric CO2?(eqns. (1) and (2)). On the other hand, the backward reactions of (1) and (2), e.g., the formation of tufas, are related to the release of CO2?into the atmosphere. It is very difficult to estimate the CO2?flux at individual cases. For example, the corrosion rate of limestone tablets in soil indicates only the net CO2?exhausted in the soil, where the deposition of calcite may occur. In addition, the net amount of CO2?removed from the atmosphere in a given catchment area is equivalent to the total amount of limestone dissolved and transported outside the area via groundwater flow and/or rivers.Therefore, the net amount can be estimated by the limestone corrosion and the discharge of groundwater and/or rivers.

In this paper, case studies are reviewed using published and unpublished data. Firstly the sensitivity of carbonate rock dissolution to the change of soil CO2?and runoff, and then the amount of CO2?removed from the atmosphere in the carbonate rock areas of mainland China and the world will be discussed, to get a estimation on the contribution of carbonate rock weathering to the atmospheric CO2?sink. It will be seen that this contribution can not be neglected and should be taken into consideration in the global carbon cycle model.

Methods

a. CO2?partial pressure (Pco2?) at depth of 50 cm in soil was measured in situ with CO2-GASTEC meter monthly to know the variation in soil CO2?with time .

b. Temperature, pH, [Ca2+] and [HCO3-] of water were measured in situ with portable pH-meter and alkalinity meter monthly. CO2?partial pressure in water was calculated with WATSPEC computer program, by using the field observation data. These data were used to examine the sensitivity of carbonate rock weathering to the change in soil CO2, and to give the estimation on its contribution to the atmospheric CO2?sink with data of discharge?(hydrochem-discharge method, see below).

c. To compare the results by the hydrochem-discharge method, corrosion tests with limestone tablets in atmosphere and soil (carbonate-rock-tablet-test method, see below) were used, and finally the maximum potential contribution of carbonate rock weathering to the atmospheric CO2?sink was given by using the DBL Model.

Sensitivity of carbonate rock weathering to the environmental change

Soil CO2?change
As examples, two cases will be shown in the following.

Fig.1 (a)?shows seasonal change in [Ca2+], [HCO3-] and CO2?partial pressure (Pco2) in water, and soil CO2?partial pressure at the observation site of?Yudong (Fish-cave) Underground Stream, which is located at Zhen’an County of Shanxi Province, in climatically transitional zone between North and South China. The mean annual air temperature here is about 11oC, and 850 mm for mean annual precipitation. The karstified rock is predominately Carboniferous-Permian limestone intercalated. Due to the sinkholes in recharge area, the Yudong Underground Stream is connected to the peak-cluster depressions, where terra rossa and loess formed. The length of the stream is about 30 km, with a catchment area of 85 km2?and flood peak discharge of about 10 m3/s.

It can be seen that soil CO2?partial pressure changes remarkably during a year, with the maximum in summer growing season, and minimum in cold winter. Related to this, the [Ca2+], [HCO3-] and Pco2?in water also show remarkable coincident change. That means that carbonate rock weathering is very sensitive to the soil CO2?change (refer to equ.(1)).

The sensitivity of carbonate rock weathering to soil CO2?change was also found at the?Guilin Karst Experimental Site, which is situated in the southeast of Guilin, about 8 km away from Guilin City, and near Yaji village (Fig.1 (b)). The site is at the boundary of peak-cluster depression and peak-forest plain. The catchment area of the site is about 1.1 km2. The strata of the experimental site is mainly pure limestone of Upper Devonian, with thin soil cover in the depressions. The major vegetation is bushes and grasses. The annual mean air temperature and the annual mean precipitation are 19oC and 1900 mm, respectively. Precipitation is the sole recharge to groundwater in the site.

In addition to the seasonal change, Fig.1(b) also shows the increase in soil Pco2?in a multi-year scale. The latter is related to the reforestation at the site since 1993, and/or the increase in the atmospheric CO2?content. The increase in soil Pco2?drives the weathering of carbonate rock, resulting in the increase in [Ca2+], [HCO3-] of karst water (Fig.1 (b)). This is also proved by the fact that the corrosion flux of limestone tablets in the Guilin Exp. Site increased from 1993 to 1995 (Tab.1).

Fig1 (a)&?Fig1.(b)?Seasonal and multi-year change of hydrochemistry and its sensitivity to?the change in soil CO2?partial pressure

Tab.1 Change in corrosion flux of limestone tablet in the Guilin Exp. Site from 1993 to 1995(unit: mg. cm-2?a-1)

Sample location

1993

1994

1995

in the air

3.88

-

4.69

on ground surface

4.29

5.04

5.11

20cm below the surface

3.79

7.69

10.22

50cm below the surface

4.71

9.19

11.45

Precipitation-evapotranspiration or runoff change

Sensitivity of carbonate rock weathering to the precipitation-evapotranspiration (P-E) or runoff change is reflected in the relationship between denudation rate of carbonate rocks and runoff. Karst denudation rate is defined as the annual removal of carbonate rock from a carbonate area and is measured in m3km-2a-1. This unit corresponds to an average lowering of the area by 1mm in thousand years (1mm/ka).

Fig.2 gives some reported denudation rates as a function of (P-E). The data points can be fitted by a linear relation DR=0.0544(P-E)-0.0215 with a correlation coefficient r=0.98. That means the carbonate rock weathering is very sensitive to the runoff, i.e., the larger the runoff, the more intensive the carbonate rock weathering. This may be the main reason for the great difference in karstification between south and north China. It also explains why the contribution of carbonate rock weathering to the atmospheric CO2?is much larger in south China, where there is a strong runoff, than that in north China (see below).

Estimation on contribution of carbonate rock weathering to the atmospheric CO2?sink

1. Hydrochem-discharge method

By using hydrochemical and discharge data, the flux of atmospheric CO2?consumed in carbonate rock weathering can be estimated by:

F=1/2?á [HCO3-]?á Q?áM?CO2/MHCO3?(3)

where [HCO3-] is HCO3-?concentration in water (g/l); 1/2 means that only half of the carbon in solution is from atmospheric CO2?(eqns. (1) and (2)); Q is discharge of water in a studied area(l/s), equal to the product of the area and the runoff module; MCO2?and MHCO3?are molecular weight of CO2?and HCO3-?respectively.

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Fig. 2?Relationship between denudation rate of carbonate rocks and runoff

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Tab.2 gives the area of the bare carbonate rocks, HCO3-?concentration in karst water, runoff module of karst water in China (after 1:4,000,000 karst hydrogeological map of China by Li Guofen, 1992), and then the amount of atmospheric CO2?consumed during carbonate rock weathering in both south and north China could be calculated by the equ.(3) (Tab.2). It is seen that the contribution of carbonate rock weathering to the atmospheric CO2?sink is 1.3971013?g/a in the bare karst areas of south China, and 0.3371013?g/a in the bare karst areas of north China. The total is 1.73410?13?g/a. It would be 6.577?1013?g/a and 4.206?1014g/a if the latter is applied to the whole China karst areas (3.44 million km2?) and the whole world karst areas (22 million km2?) respectively.

Tab.2 The relevant parameters to calculate CO2?sink during carbonate rock weatheringin south and north China

distribution of

carbonate rocks

bare area

(?á1104?km2?)

HCO3-?content

in karst water

(g/l)

runoff module

of karst water

(l/s.km2?)

atmospheric

CO2?sink

( g / a)

South China

44.6

0.236

11.67

1.397?á 1013

North China

46.1

0.245

2.62

3.366?á 1012

2. Carbonate-rock-tablet-test method

Seven monitoring stations which represent the typical karst areas in China were built (Fig.3), where the corrosion tests of the standard limestone tablet (with a surface area of 28.91cm2?and insoluble matter content of 0.97% ) was carried out in the implementation of IGCP 299 "Geology, Climate, Hydrology and Karst Formation" and 379 "Karst Processes and the Carbon Cycle".

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Fig.3 Distribution of bare karst areas and monitoring stations of karst system?
in China??????? 1 bare carbonate rocks;2 reef ;3 monitoring station

Tab.3 gives the corrosion test results from six of these seven monitoring stations (one failed due to the loss of the samples), then the amount (A) of atmospheric CO2?consumed in carbonate rock weathering can be estimated with the following formula:

A= F?áS?áC?áMco2/MCaCO3?(4)

where F is corrosion flux of limestone tablet (g/cm2.a ) , S- the area of studied carbonate rock (cm2), C-the CaCO3?content of the limestone tablet, Mco2?and MCaCO3?- the molar weight of CO2?and CaCO3?respectively.

Tab.3 Corrosion of the standard limestone tablets

in some monitoring stations in 1994(unit: g/a)

sample location Guilin Maolan Huanglong Zhen’an Beijing Taizihe
in the air 0.1356* 0.0290 0.0151 0.0068 - 0.0136
ground surface 0.1456 0.0380 0.0170 0.0013 0.0336 0.0048
average flux

(10-4g/cm2.?a)

48.634 11.588 5.569 1.557 11.622 3.182
20 cm below

soil surface

0.2222 0.1670 0.1690 - 0.0021 0.0014
50 cm below

soil surface

0.2657 0.0520 0.1920 - 0.0018 0.0014
average flux

(10-4g/cm2.?a)

84.399 37.876 62.435 - 0.675 0.484

*-the value in 1995.

The calculation results of the amount of atmospheric CO2?consumed in carbonate rock weathering in various karst types in China are shown in Tab.4. The total amount of atmospheric CO2?consumed in carbonate rock weathering is about 1.696 ?á1013?g/a in China bare karst areas. It would be 6.432?á1013?g/a and 4.114?á1014?g/a if this value is applied to the whole China karst areas and the whole world karst areas respectively.

3. DBL-model calculation

According to Liu et al, the dissolution rate of calcite in CO2-H2O solutions with turbulent motion can be approximated by a linear rate law?R=a (Ceq-C), where ceq?is the equilibrium concentration with respect to calcite and a a rate constant, dependent on temperature T, CO2?partial pressure Pco2, DBL (diffusion boundary layer) thickness e and the thickness of the water sheet flowing on the mineral d . If we take T=10oC, Pco2=5?á10-3atm, d =1cm and e =5?á 10-3cm, which are the reasonable values in the nature26, then a =2.03?á 10-5cm/s and?Ceq=1.62?á10-3mmol/cm3. Taking the average value 2?á 10-4mmol/cm3?of [Ca2+] in rainfall, we obtainR=2.88?á10-8?mmol?. cm-2s-1. This corresponds to 288 mm/ka if water runs down continuously. Assuming rainfall to occur only during 20% of the time26, an annual retreat of bedrock of about 57.6mm/ka will result. That means potential atmospheric CO2?sink by this carbonate rock weathering is estimated to be 2.354?á1014?g/a (or 0.0642 billion metric tons of carbon/a) and 1.505?á 1015?g/a (or 0.41 billion metric tons of carbon/a) in whole China carbonate rock area and the whole world carbonate rock area respectively. These values are about 3.66 times those obtained by hydrochem-dicharge method or by carbonate-rock-tablet-test method (average 0.11 billion metric tons of carbon/a). The latter may represent the net effect of carbonate rock dissolution and deposition. If these values were accurate enough, the effect of carbonate deposition would be 0.3 (0.41-0.11) billion metric tons of carbon/a (returning to the atmosphere).

Tab.4 Distribution of the main karst types and the atmospheric CO2?sink

during carbonate rock weathering in China

Karst type

Distribution

Bare area

(?á 104km2)

Mean annual

rainfall (mm)

Representative

station

CO2?sink

(g/a)

tropical and subtropical karst Guangdong, Guangxi, Taiwan, Zhejiang, Yunnan, Guizhou, Hunan, Jiangxi, west Hubei etc.

44.6

1000-

1850

Guilin

1.305?á1013

high mountain and plateau karst West Sichuan, Tibet, Guilun Mountains

22.1

300-800

Huanglong

3.306?á1012

semiarid karst Shanxi, Hebei,

Henan,

north Shangxi, Shandong etc.

21.4

400-600

Beijing

5.789?á 1011

humid temperate karst Taizihe River basin, Huai River basin

2.6

800-1000

Taizihe

2.097?á1010

Conclusion

It is concluded that the contribution of carbonate rock weathering to the atmospheric CO2?sink is in the range of 0.11 to 0.41 billion metric tons of carbon/a. These values correspond to about 5.5% to 20.5% of the "missing CO2?sink"10.

Moreover, according to the data from Guilin monitoring station in 1993-1995 (Fig.1), the consumption of atmospheric CO2?during carbonate rock weathering increased from 6.129?á109?g c/a in 1993 to 11.582?á 109?g c/a in 1995 due to the increase of soil CO2, which was related to reforestation and/or global increase in atmospheric CO223. This means that the contribution of carbonate rock weathering to the atmospheric CO2?sink increases with the lifting of the atmospheric CO2?content. So, the carbonate rock functions as an adjustor to the atmospheric CO2?.

Therefore, as an important and potential sink for the atmospheric CO2, the carbonate rock weathering should be considered in the global carbon cycle model.

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Characteristics of hydrochemical responses to environmental
change in a carbonate rock Aquifer

Yuan Daoxian

The Institute of Karst Geology
Guilin,Guangxi,China 541004

(Paper presented at the 12th?ICS,Switzerland,1997)

Carbonate rock, the biggest carbon reservoir on the Earth, is the result of the processes in geological history that reduced the C02?content in the atmosphere. By this way, it has played an important role to make the Earth's environment favourable for the development of life and human beings. However, it is considered that this big carbon reservoir is no longer active in the modern carbon cycle since the time scale of mankind.

Recent works show that carbonate rock is still sensitive to global carbon cycle, and has impact on Man's environment both macroscopically and microscopically. These ideas could be explained with a minor example. In Fangtang village, Liujiang county, Guangxi,China, people suffered from the acidic water of a spring which is their major source of water supply, and recharged by a siliceous rock aquifer of Upper Permian. However, in a farmer's private well sunk in the same aquifer just 50m away from the spring, the water is neutralized quickly and improved remarkably because the well is lined by limestone blocks (Fig.1).

The increase in atmospheric C02?following the increasing use of fossil fuel will result in the intensification of carbonate rock dissolution and high content of Ca2+, Mg2+, and HCO3-?in water. However, the process is highly influenced by climatic factor. Long term hydrochemical monitoring in Guilin(1981-1994),Guangxi, China shows not only a general increasing trend of Ca2+, Mg2+, and HCO3-?in limestone or dolomite aquifer,but also their higher content in the dry period(1984-1989), and lower at the wet period (Fig.2, Liu Jingrong,1996).

The hydrochemical responses of carbonate rock aquifers to acidic water from mining areas, such as pyritecontained coal mines mainly appeared as the increase in Sulfaes hardness. The over-exploitation of water resources from an evaporite-mixed carbonate rock aquifer has the similar result, but their contributions can be distinguished by an isotopic-hydrological model based on Sulphur isotopic data.

The behaviour of heavy metal pollutants, such as Cd2+?, Cu2+, Pb2+?, Zn2+?etc. in a carbonate rock aquifer are mainly reflected as to their absorption by the wall rocks. The phenomena are observed both in laboratory experiments or field practices. However,where do they stay, how and when will they be mobilized again, remain a concern.

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Fig.1 Hydrochemical contrast between waters from the same siliceous rock aquifer, but different in limestone lining, Fangtang village, Liujiang country, Guangxi, China.

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Fig.2 General trend of HCO3-,Ca2+?rising in a Devonian limestone aquifer of Guilin, China during the past decade, and its impact from change in precipitation (after Liu Jingrong, 1996)

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Special speleothems in cement-grouting tunnels and
their implications of the atmospheric CO2?sink

Zaihua Liu . Dianbin He (the Inst. of Karst Geology, Guilin, China )

Abstract

Based on the analyses and comparisons of water chemistry, stable carbon isotopes and deposition rates of speleothems, the authors found that there are two kinds of speleothems in the?tunnels at Wujiangdu Dam-site, Guizhou, China, i.e., the CO2-outgassing type and the CO2-absorbing type. The former is natural, as observed in general karst caves, and the product of karst processes under natural conditions. The latter, however, is special, resulting from the carbonation of a cement-grouting curtain and concrete. Due to the quick absorption of CO2?from the surrounding atmosphere, which is evidenced by the low CO2?content in the air and the high deposition rate of speleothems (as high as 10 cm/a) in the tunnels, the contribution of the carbonation process to the sink of CO2?in the atmosphere is important (in the order of magnitude of 108?tons c/a) and should be taken into consideration in the study of the global carbon cycle because of the use of cement on a worldwide scale.

?????????????????????????????????????????????????????????????????????? ???

CO2-absorbing type of soda straw in cement-grouting tunnels at Wujiangdu Hydropower Station of Guizhou, China.

These soda straws were formed in 12 years, and the maximum length is 126cm. Due to the quick absorption of CO2?from the surrounding atmosphere, the CO2?content as low as 150 ppmv was measured in some places, such as in the small holes for water-leading and decompression in the figure. This low CO2?content, compared to the local atmospheric CO2?concentration (350 ppmv), indicates that there is an important CO2?sink during the formation of the special speleothems.

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KARST SPRINGS IN THE REGION OF HORNSUND
FJORD (SW SPITSBERGEN)

Wieslawa Ewa Krawczyk
(Geography Department, Selesia University, Poland)

(Paper presented at 23rd?Polar Symposium, Sosnowwiec, 1996)

Two types of karst springs in the region of Hornsund Fjord in the SW part of Spitsbergen are described. On the basis of chemical analyses of spring waters, an attempt is made to describe genesis of thermal springs at Gnalberget and thermomineral springs at Himarfjellet. It was found that glacial waters are part of spring discharge in all cases.

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Figure 1.Location of karst springs in the region of Hornsund Fjord (SW Spitsbergen):
1 - Gnalberget ( Orvin ), 2 - Rasstupet, 3 - Raudfjellet, 4 - Hilmarfjellet.

Figure 2. Differentiation of the Orvin Spring chemical composition in the seasons of polar year: 1, 2, 3 - spring, 6, 8, 10, 12 - summer, 14 - autumn
(1, 2, 3 - numbering of water samples according to Table 1 )

Figure 3. Differentiation of the Hilmarfjellet spring composition:[1], [2] - thermal springs in the region of pools ( C on Figure 5 ), [11] - Trollosen spring ( b )

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