Jr-> n <'-' FKPOPT KO. IABA-R-2845-F

TITLE

Isotopic study of water

PIKAL RKPOPT FOR THE-'PERIOD

I98I-O4-OI - 1984-05-31

AUTHOR(S)

H. Leskovsek-Sefman

INSTITUTE

Institute "Jozef Stefan" Ljubljana Yugoslavia

INTEPKATIONAL ATOMIC EMFFGY ACEKCY

DATE January 1985 FINAL REPORT ON RESEARCH CONTRACT No. 2845/fcB

ISOTOPIC STUDY OF KARST WATER

J. Pezdic, H. Leskovsek-Sefman, T. Dolenec, J. Urbane

April 1981 to December 1983

Ljubljana, 1984

univerza e. kardelja institut "jo2ef Stefan" Ijubljana, jugoslavija univerza o kardeljj institut"jo2ef Stefan" Ijubljanajugoslavija

FINAL REPORT ON RESEARCH CONTRACT No. 2845/RB

ISOTOPlC STUDY OF KARST WATER I J. Pezdic, H. Leskovsek-Sefman, T. Dolenec, J. Urbane I J.Stefan Institute, University E. Kardelj, Ljubljana, Yugoslavia

I April 1981 to December 1983 1 1 I 1 I 1 i Ljubljana, 1984 I I CONTENTS

INTRODUCTION

GEOLOGICAL AND CLIMATIC CHARACTERISTICS 4 Precipitation 4

PLANINA CAVE 8 Streamlet 1 10 I Streamlet 6 and Tihi rov 16 1 CAVE CARBONATES 21 UUBLJANICA RIVER BASIN 27 I THE WATER CATCHMENT AREA OF Rlf ANA 32 i THE WATER CATCHMENT AREA OF 38 CONCLUSIONS 42 i REFERENCES 46 I I 1 I I I Final Report on Research Contract No. 2845/RB - July, 1984 I ISOTOPIC STUDY OF KARST WATER

I J. Pezdic, H. Leskovsek-Sefman, T. Dolenec, J. Urbane I J. Stefan Institute, University E. Kardelj, Ljubljana, Yugoslavia I Summary

I Mass spectrometric investigations of the isotopic composition of some elements in water and in dissolved carbonates from the Slovenian Karst are presented. Additionally, the isotopic composition of oxygen and I carbon in cave carbonates is given. The results allow the conclusion that the waters in karst aquifers do homogenize to a great extent, but qualitative determination of the I retention time and of the prevailing sources for some springs and water flows is nevertheless possible. I The isotopic composition of O in water and of O and C in dissolved carbonates depends on climatic conditions and on denudation processes. So a fairly good estimation of paleoclimatic conditions from the isotopic I composition of cave carbonates also becomes possible.

I INTRODUCTION Measurement of the isotopic composition of water formed part of an I extended investigation of the water drainage system in the Slovenian Karst. These studies were planned to complement geological and speleological investi- I gations (i.e. regular determination of water flows, temperatures, contents of dissolved substances, as well as water tracing with fluorescent dyes) which are I already being performed in this area, with a knowledge of the mechanism of changes in the isotopic composition of water in the natural environment on some smaller (model) locations. As such a location near Posrojna, was chosen where we studied the vertical percolation of meteoric water through the karstified carbonate ceiling, and the water catchment areas of some small rivers in the Slovenian Karst, such as the river basin of the , and - 2 -

the water catchment areas of the rivers Rizana and Idrijca.

In the karst, where water percolation is relatively rapid, changes in the isotopic composition of water owing to rainfall can be significant. I Because of lithological characteristics, differences in porosity of the minerals which are fissured and cracked in many different ways, owing to specificities in I the karstification process, and last but not least, because of different vegetation, the water retention in several parts of the aquifer varies a great deal, and so I characteristic homogenization of the meteoric waters takes place. All the above mentioned influences vary from place to place and as a rule the isotopic compo- 1 sition of the rainfall varies too, so in spite of the homogenization process, the aquifers contain water of different isotopic composition. This enables the tracing I of the predominant sources for various springs and flows at accessible places. In dissolved carbonates, the isotopic compositions of oxygen and carbon were I measured. The oxygen composition is related to that of water by the equilibrium isotopic ratio of oxygen, which shows a temperature dependence. The second parameter - the isotopic composition of carbon - is important, because this element 13 can be incorporated into the dissolved carbonate from CO9 in air (6 C = 13 1 - 7 %o), from CO9 of organic origin (8 C= - 25 %o), or as dissolved carbon- 13 ate from sea carbonates (6 C = - O to + 3 %o), the latter prevailing in +he 13 I area under investigation. The great differences in the 6 C values enable a I relatively exact determination of various components. I - 3 - I I I I I

I / \ jlum VIi I I I I I «•winrti/n?"1" * /'

I T mtUorolojic «tallan I M = I: 500.000 " o «tmpllni pdnt

I Fig. I: The map of the investigated area I 1 n - 4 -

GEOLOGICAL AND CLIMATIC CHARACTERISTICS

The area where the investigations of karst waters took place lies in the SW of . From the geotectonic point of view, it belongs to the northern part of the Dinaric Alps. The landscape is rather mon tai nous, there are many I karstified mountain chains and high plateaus, with scattered karst poljes and I flysch reefs (Fig. 1). Mountains and high plateaus reach a height of 'about 1300 m above sea level; I Snetnik even 1796 m. The Karst poljes are to be found especially along the Ljubljanica river basin. The flysch reefs have the direction of the Dinaric Alps', I which means NW-SE. Surface flows are to be found only on karst poljes and on flysch, while water flows in the karstified limestone area are underground.

I Slovenia belongs to a transitional climatic region between the continental and the Mediferranion climates. Just in the Ljubljanica river basin is this transition I most evident - because of the so-called "Postojnska vrata". In the cooler half of the year, the Dinaric high plateaus are a barrier high enough to divide Slovenia into its inner (continental) part with severe winters and its SW (littoral) Primorje, where the mild winters show the influence of the .

Preci pi tati on

The isotopic composition of precipitation was followed during the entire period of our investigations. The main sampling place was the meteorological station in Ljubljana, which provides basic data for other hydrogeological investigations in Slovenia. All the hydrometeorological data for longer periods are collected together there. So we were able to obtain the average precipitation, air temperature and average humidity in Ljubljana for the last 20 years. The avera- ge rainfall was 1402 mm, the average temperature 9.8 C and the average humidity 7.7 mb. Data for single months and years throughout the period of our investigations are presented in the following table (Table 1), together with

- 18 - - 5 -

UUBUANA, YUGOSLAVIA Lat. 46°04' Long. 14°31' Alt. 299 msl Maan 1956-80, Prac. 1402 mm. Mun 1956-80, w.P. 10.21 mb, Mein 1956-80, Ttmp.

Yt«r Month Prtcip. S18O SO T Tamp. Mean vJ*. mm Ko Ko T.U. 0C milli barr

1981 May 147 - 8.15 - 64.7 70 14.3 112 Juna 171 - 9.39 - 64.0 83 182 15.0 July 94 - 7.19 - 47.6 64 19.6 16.1 Augutt 129 - 6.30 - 30.0 65 183 16J) Stpttmbff 214 - 7.33 - 46.3 26 16.1 13.7 • Octobiir 140 - 7.66 - 54J) 18 12.1 12.7 Nova mt>«f 30 . -11.69 - 86.7 16 3J) 72 I Daoambar 216 - 7JtO - 49.7 15 0.0 4.3

18 Yur Month Pracip. O O SD T Maan tamp. Mun V.P, 0 I mm Ko Ko T.U. C milli barr 1962 Januar 64JO -8.83 - 63.4 40 - IJ) 4.4 Fabruar 18,6 -14.44 -106.0 — - 0.7 A3 March 84.9 - 9.70 - 70.3 19 4.9 6.9 I April 262 -8.33 - 552 32 8.4 7.0 May 199.1 - 7.62 - 54.6 25 14.9 11.7 Juna 2634 - 6.63 - 47.0 31 19.0 15J3 1 July 43J) - 5.11 - 34.7 61 212 17.9 August 1582 - 721 - 49.1 32 19.9 16J) Scptambar 86J) - 5.47 - 31.0 24 17.9 17.0 October 234.6 -8.43 - 57.1 20 11.1 11.6 Novambar 102.0 -13.22 -101.9 14 • 5.9 8.4 Decembar 146.9 -14.33 -113.2 17 3.7 7.0

Sums 1418.0 Maani + 10J 10.6 Wt. muni - 8.66 - 62.3 26.1

8 Yfar Month Pracip. o' O SD T Maan tamp. MHn VP. 0 mm Xo Ko T.U. C milli barr 1983 Januir 36.3 - 9.68 - 68.8 27.6 1.3 6.5 Februar 110.6 -14.06 -104.2 16.2 1.1 4J3 March 147 A -11.63 - 87.6 23.6 6.1 6.9 April 48.9 - 6.43 - 42.7 202 12J) 92 May 168.0 -8.45 - 60J 22.9 152 12.0 Juna 94.6 - 7.51 - 49Ji 36.4 18.4 14.3 July 313 - 4.17 - 22J3 61.6 22.6 17J) August 117.4 - 535 - 34.0 32.9 19.7 16Ji Saptambar 91.7 - 7.69 - 62.7 20J) 16.6 13.7 Octobar 127.5 - 9.81 - 70.1 202 10.0 OJB Novambtr 30.7 - 6.19 - 402 11.7 1.7 5.9 Dacamb«r 145.4 -10.00 - 71.7 30.7 0.4 6.1

Sumi 11492 Maans 102 10.1 Wt. maans - 9.06 - 64.3 24.4

TABLE 1: Avaraga monihly precipitation in Ljubljana from 1981 to 1983. - 6 -

1.983

Month Ljubljana Planina Smarata Kozina Crni vrh

January 35.3 78.1 49.8 48.7 89.1

February 110.6 123.5 85.1 124,1 176.0

March 147.8 134.8 112.5 88.0 240.6 I April 48.9 82.6 48.6 66.2 144.6 May 168.0 180.4 88.0 119.5 244.2

I June 94.6 171.4 192.7 71.7 151.8 I July 31.3 23.4 22.7 22.5 44.4 August 117.4 87.7 93.4 43.6 92.6

I September 91.7 . 112.8 92.3 94.4 121.7 I October 127.5 91 .0 110.5 95.6 267.6 November 30.7 46.0 30.0 35.6 105.4

I December 145.4 229.1 134.5 140.4 311.3

1149.2 1360.8 1060.1 850.3 1989.3

TABLE 2: Total precipitation as well as its distribution from some meteorological stations on the Slovenian Karst. For such a small area the differences are considerable. To explain it different littoral, alpine and continental climatic influences are to be taken into account. Similarly the isotopic composition of the precipitation for various district of the investigated area - which we have how been following for some years - is characteristic for each location. Vhod Tlofis Entronet PLANINSKA JAMA Plan 4- opazovani curki observed trickles vrtaca dolinc vodnt rov active «voter channel prclom fault

apnenec limestone

do'.omitizirana i apnena breca dolomite limestone b'tcca I Gcotcski podatki • R. Gospodaric 1978

Rak

Vzdolzm prcrcz Sotocje Longitudinal section Cdgata

Fig. 2: Planina Cave, the location of sampling places - 8 -

the isotopic composition of the rainfall and other standard hydrological parameters.

In order to know the hydrological conditions in the investigated area in some detail, we additionally measured the isotopic composition of rainfall in Planina and in Kozina. These results are graphically presented in the Chapters "Planina Cave" and "The water catchment area of Rizana". There the exact daily rainfall amount is given. The characteristic values of the oxygen isotopic composition for various periods are shown in the diagrams of the variations in the isotopic composition of springs and flows. I For 1983 some additional meteorological data were gathered: rainfall amounts in CVni vrh (near ) and in Smarata (Loiko polje). These data are collected I in Table 2. If we compare monthly and yearly precipitation at various locations, we come to the conclusion that the rainfall regimen varies a lot over this area. I This is extensively presented in the project: "Underground water tracing in Slovenia", 1976. 1

I PLANINA CAVE

I Planina Cave was chosen as a model location to allow investigations of vertical percolation in a Karst environment to be made.

I Planina Cave lies about 10 km NW from in the river basin of the Ljubljanica, where the rivers and join each other to form the river Unec (Fig. 2). The cave is relatively wet and contains various species of cave carbonates. Through different partly charged fissures in the walls and ceiling water percolates or streams into the cave and flows further into the river. Longer periods of heavy rain can result in water flows of about 100 l/mi n in a single fissured zone.

Water accumulates in the karstfied carbonate ceiling above the cave. Its surface consists of several dolines up to 10 m wide (typical erosion features in - 9 -

the Karst). Such a doline is mostly filled up with freshly decomposed matter, "terra rossa", covered with a thin humus stratum. It is very probably the collecting area for a single streamlet in the cave. Minerals in the ceiling are mostly blocks of limestones and dolomites, which are rectonically folded and stratigraphically dislocated. The surface is covered by pine or mixed woods (with abundant brush wood).

I For a detailed investigation of vertical percolation Streamlet 1 was chosen. For comparison, Streamlet 6 was sampled for some time; later the source in Ti hi rov I was added. As is shown in the chapter dealing with precipitation, rainfall was sampled over a somewhat larger area, and its sampling changed according to the I demands of the investigation. I By measuring the isotopic composition of oxygen and hydrogen, as well as the tritium content, in the percolating water and in the rainfall, we intended to characterize the vertical percolation. These data would be a further contribution to already existing investigations (H. Moser et ai. 1976, J. Kogovsek and P. Habic, 1981, I. Gams, 1980). As the investigations proceeded it became apparent that we needed more data for a thorough interpretation, so the isotopic composition of dissolved carbonate was determined, the water flow (discharge) was followed continuously, while water and rain temperatures were measured at each individual sampling.

Sampling took place from June 1981 till May 1984. At the begining samples were taken weekly without any regard to actual water flow. During the year 1983 we sampled in longer intervals (14 days or even one month). Our aim was to minimize the direct influence of the rainfall on the variability of the measured 18 13 parameters (S O, 5 C, S D and T) in Streamlet 1. This seemed to be the way to get a better insight into the water retention in the aquifer around the Stream- let. Sampling of the "water-waves" was exceptional; here samples were taken at 30 - 60 minutes' interval. (ANSI and ISO TEST CHART No 2)

- 10 -

Streamlet 1

Streamlet 1 in a permanent trickle from the ceiling in the Planina cave. It lies about 250 m from the cave entrance and is active even during the longest dry periods. Its discharge varies from 20 ml to 80 l/min, this means in the ratio of 1 .-4000. The height of the cove ot this location is about 20 m. The ceiling is about 100 m thick and it consists predominantly of limestones of a light grey colour, with a cover of "terra rossa" and humus (the thickness of the later being some 10 cm).

The air temperature in cave varied from 4 to 16 C during the investigation period, while the water temperature in the Streamlet varied from 4.8 to 15 C. If we consider that the isotopic composition of oxygen in the rainfall in Planina I changed from -4,23 to - 17.33 %o, we can conclude that water flows, tempera- ture and isotopic composition of the rainfall vary considerably.

I The investigations which we going on during the last three years proved that the water in the aquifer homogenizes to a great extent. During the whole period I the isotopic composition of oxygen was in the range from -8,13 to - 9.60 %o and that of hydrogen from -53 to -67 %o (Diagram 1). The tritium concen- I tration in the years 1981 and 1982 changed from 26 to 61 TU . I In the year 1983, when we were sampling at low discharges, the isotopic compo- sition of oxygen varied between -8.34 and -8.94%o, which means a difference I of only 0.6 %o. The variations of isotopic composition are lower at low discharges, so one can conclude that bigger variations are caused by the direct influence of I rainfall. Partly this fluctuation is due to seasonal changes, but generally water is thoroughly homogenized during a longer period. Evapotranspiration could not be I accurately determined, but we believe that the average retention time for water is six months, while seasonal influences can be proved for about two to three months. The direct influence of meteoric water was determined by investigation of "water waves". By a "water wave" we mean the increased streamlet discharge caused by rain. Such periods have a duration of some hours up to some days.

In August 1981 a smaller water wave was sampled (by colleagues from the Institute for Karst Research, SAZU, in Postojna). - 11 -

HtIHM „„: nccinitmas

I PttlOl-lOO»! «ICVI I CNSCHdCC - WtKBWS I 11 I fC4'l"ll'lil'l'»'»'«'"ll'lil'! l I '»'«'f I' ulliui I

•I" «I»

M» I**

IUtOfI JK HIKNUII MMVfI CMIOuriS

1*3

Diagram 1: The measurements of precipitations, discharge, temperature and isotopic composiHon of water and of dissolved carbonate in Curek 1. - 12 -

This "water wave" followed a dry period of several months and the discharge increased from 30 to 300 ml/minute. The wave appeared 4 hours after a typical summer shower and the water flow reached its maximum one hour later. The data (presented in Table 3) show that the isotopic composition of oxygen in the streamlet water varied only slightly (from -8.74 to -8.99%o). It is quite clear that the rainfall did not percolate directly into the cave.

Date Time Water flow 5 VO SD T ml/mi n %o %o T.U.

21.08.1981 9.55 70 - 8.80 - 60.6 10.10 - 8.79 I 10.20 120 - 8.74 - 60.5 39.0 10.30 - 8.74 1 10.40 270 - 8.99 - 63.9 10.50 - 8.92 i 11.00 300 - 8.94 11.10 - 8.81 - 59.7 39.6 I 11.20 300 - 8.79

I 18 Table 3: Isotopic composition (S O, 6 D and T content) of the water in I Streamlet 1 on 21.08.1981

The second "water wave" which was thoroughly investigated was sampled during the first heavier rain in September 1981. The increased water flow in Streamlet 1 owing to rainfall exhibited a delay of 6 hours, while the maximum flow rate was determined 8 hours after the rain started. The flow rate increased from 0.2 to 60 litres/minute.

The "water wave" was followed for 24 houri. The sampling was performed as described previously. Additionally, the isotopic composition of the rainfall was determined. In 11 hours there was 38 mm of rain, 33 mm of it in the first six hours. We took 4 samples of rain; the average rainfall of the first 4 hours, that def - rain

i

OJ

T (air) = 285 K T (water) =285.3 K

Diagram 2: Oxygen and hydrogen isotope composition in correlation with flow changes in Streamlet 1 on 14.09.1981. Table gives the isotopic composition of oxygen for rain water at the same time. - 14 -

PRETOK DISCHARGE I I I I izotopska sestava ogtjika carbon isotope composition

i karbonaina trdota mgCaCfo/l /^ carbonate hardness •••—•>_• J) 200 \l •,. I- i Ca trdota Ca hardness

ISO Vu--

Diagram 3: lsotopic compciition in comparation with water flow and hardness of Streamlet 1 on 14.09.1981. - 15 -

from the 4 to the 6 hour and (hat from the 6 to the 11 hour, as well

as an average sample during the 11 hours.

The isotopic composition of rainwater became more and more negative as the

downpour proceeded.

Diagram 2 gives the measured isotopic composition of oxygen and hydrogen,

together with flow changes in Streamlet 1 and the isotopic composition of

precipitation. Before the flow rate increase the isotopic composition of

Streamlet 1 was quite similar to the average value (i.e. on 7.09.1981: 18 S °O = -8.98 %o and 6D = -62.6 %o). At the maximum flow rate, these 18 values were: S O= - 8.20 %o and 8D = - 57 %o, which is practically

the same value as that of the rainwater at the same time. After 4 hours the

isotopic composition of the streamlet water was again equal to that before the

rainfall. Then the values grew more and more negative, and after 20 hours 18 they reached the values 5O= -9,42 %o and SD = -66.1 %o.

The isotopic composition indicates that at maximum discharge a direct streaming I of meteoric waters occured and after it the precipitation water poured directly into the cave. This is shown by the similar isoropic composition of the Streamlet

water compared to precipitation in the second part of the water wave.

Beside the isotopic composition of water in the "water wave", the isotopic I composition of the dissolved carbonate was also measured. The results are presented in Diagram 3, where also discharge and water hardness are given. I The high content of organic carbon even before the discharge reached its maximum and small changes in both carbonate and Ca hardness should be I emphasized as characteristic and very interesting. We can conclude that during the dry period in July and August greater amounts of decayed organic matter I were formed on the surface; they contained much carbonate which was rinsed into the cave by this first heavy rain in September. The "water wave" in 13 August 1981 is represented only by an average sample with S C=- 10.8 %o.

Taken with the results described above for water analyses, it clearly indicates

that this time no direct streaming of meteoric waters into the cave occurred. - 16 -

' Because the changes in isotopic composition of carbon during the water wave proved so interesting, we wanted to find out more about organic carbon distri- bution over a longer period. The results are summarised in Diagram 1 . The isotopic composition of carbon in the dissolved carbonate of Streamlet 1 changed from -10.19 to - 16.10 %o. In autumn 1981 and 1982, as in spring 1983, water showed an increased concentration of the light carbon isotope, but in autumn 1983 no increased concentration of organic carbon was detected. These results allow the conclusion that increased concentration of light carbon do not occur regularly and that each influence can be observed for 2 to 3 month. This matches well with the other, already described characteristics of seasonal waters.

Streamlet 6 and Tihi rov

Streamlet 6 arid the source in Tihi rov were additionally sampled only for com- parison. These sampling points are deeper in the cave. The isotopic composition of water samples from Streamlet 6 showed that the 18 variability of S O and 5D in Streamlet 6 differs from that in Streamlet 1 . This is evident from Diagrams 4 and 4a, which show the results for a 6 months period. 18 The differences in the variabilities of 8 O and 8D between the two streamlets are obviously due to different thickness of the ceilings above them. The ceiling above Streamlet 6 is only about 50 m thick.

The characteristics of the source in Tihi rov are quite different. This water springs through the cracked carbonate material in the side wall of the cave and I carries a lot of clayey material. The discharge (about 1 l/min) does not vary markedly with rainfall. Here, the estimated ratio between the lowest and the I highest water flow is 1 : 5, whilst this ratio is about 1 :4000 for the streamlets previously described. The temperature is quite constant as well. According to our I measurements over two years, it varies only between 7.8 and 9.0 C. (Table 4). I In the Streamlets 1 and 6 these variations were between 4.8 and 15 C. - 17 -

287 U

u, 285 I I 283 rr. ui - • Vodo-Walir \ ^\ TEMP I 279 i . i

VII VIII IX X I 100 . I uin-' 80 - I BO - I I «0 - I I J I 20 - I n n 0 JUUUII s f • • i i I VIl VIII IX Xl I 611O eo Hi loi (X) - A I s!

• / IZO l ISCT l

VII VIII IX Xl

Diagram 4: The measurements of temperature, electrical conductivity, water flow and isotopic composition of oxygen' of Streamlet 1 in Planina cave - 18 -

214

2 2 213 2 f 212

211 VII VIII IX Xl 1 (OO . ItSn' jf SS 300

VII ViII IX Xl

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S£ 20

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VN VIII IX Xl

8'1O g (•1 SO U) 5 1 -8.5 2 v» • HOP S BTOP I — — --IS t i i i VII VIII IX Xl tlai-Cu I Diagram 4a: The measurements of temperature, electrical conductivity, water flow and isotopic composition of oxygen of Streamlet 6 in Planina cave. OEZ RAIN 100 l/m* 50 Illll, I .1 I ill .1 I. III.. J i InI 1 .111 il JJA SOM DlJFMAMJJ AS ' 0 ' M ' O

611O -7 -11 -8 -U -11 -6 -8 -5.5 -10 I -10.8 I -12.7 -U.5

-o i

CURCKI

^ TIHI ROV

-10 MJJASONDJFMAMJJASOND 1982 1983

1 A Diagram 5: Comparison of 5 O variability in waters of Streamlet 1 and Tihi rov with precipitation amounts and their oxygen isotopic composition. - 20 -

13 Date 618O water W « cc 0C %o %o

14.12.1982 9.0 - 8.28 - 12.94 27.0'l .1983 8.0 - 8.71 - 8.5J 25.02. 7.8 - 8.98 - 11.46 16.04. 8.6 - 9.45 - 12.09 28.05. 8.3 - 9.42 • 12.36 24.07. 9.1 - 9.30 - 11.66 18.08. 9.0 - 9.10 - 11.42 I 20.09. 8.9 - 8.74 - 12.02 17.10. 9.1 - 8.91 - I 17.11. 8.8 - 9.10 10.99

Table 4: Isotopic composition of oxygen in water and of carbon in dissolved 1 carbonate in Tihi rov (Pianino cave) 1 The temperature changes already indicate that Streamlets 1 and 6 take their I origin from meteoric waters percolating through a rather thin ceiling, while the source in Tihi rov comes from a far bigger aquifer which is indifferent to air I and rainfall temperatures. The flow is more laminar compared to Streamlets 1 and 6, and the isotopic composition of oxygen shows greater seasonal changes 18 and a longer retention than the water of either streamlets. Its 8 O exhibits regular cycles during the years of investigation (from -8.28 to - 10.04 %o) I (Diagram 5).

The isotopic composition of carbon in the dissolved carbonate shows a far lower variability, changing in the interval from - 11.42 to - 12.94 %o. The dissolved carbonate from 27.01.1983 is an exeption, being enriched with the heavy carbon 13 isotope (SC = -8.53 %o). We cannot explain this, because it exhibits no other special characteristics. - 21 -

CAVE CARBONATES

Because investigations of karst waters and of their dissolved carbonates gave a thorough insight into the variability of the isotopic compositions of oxygen and of carbon, we further investigated some cave carbonates, typical of the Slovenian Karst. The samples were taken from , cave, I Skocjan cave, Dimnica cave, Divaca cave and Kamnik cave.

The results are shown in Diagram 6 and in Table 5.The diagram shows a rather good positive correlation between the values for the isotopic composition of oxygen and those of carbon. The majority of the samples (Planina cave, Postojna cave, Skocjan cave, Dimnica cave, Predjama cave) is grouped in a regular way. Only the samples from Kamnik cave and those from Divaca cave show significant- I ly different isotopic composition. 13 I The samples from Kamnik cave exhibit a higher C concentration compared to the others. This could be due to scanty vegetation on the surface over the cave I (1400 m above sea level). This hypothesis can only be verified by analysing samples from other similar caves. The isotopic composition of two straw I stalactites from Divaca cave shows a significant influence of heavy precipitation and relatively intense decomposition of the above vegetation. 13 18 I The correlation between S C and 8 O speaks in favour of the theory that 13 the 5 C reflects the regional climatic changes and the intensity of the vege- 18 I tation above the cave. The higher values of S O in the regions where the 13 1 temperatures are low are accompanied by similar 5 C values because of com- paratively scantier vegetation. So the cave carbonates in the upper part of the I diagram on the right side are obviously formed in cooler periods, while those of the left lower part were formed under warmer conditions. These interpretations I should be made very cautiously because these correlations may vary for different conditions of cave carbonate formation. It is very instructive to calculate the temperature at which various cave carbonates crystallized from water. Up to now only recent waters were considered but a method which could make use of water inclusions is being prepared. The above A 611O -7 -5 1POB

-1 -2 -3 -4 -5 -6 -7 -8 *•«! • -9

• Planina Cave • -W • Skocjan Cave + Dimnica Cave mi ^ Postojna Cave A Kamnik Cave tt. OivaCa Cave o Predjama Cave 18 13 Diagram 6: 8 O versus 6 C for cave carbonates - 23 -

I PLANlNSKA JAMA - PLANINA CAVE SKOCJANSKE JAME - ÖKOCJAN CAVE Vzorec 618O Vzorec S13C PDB PDB PDB I Sample Sample PJ-I -6.93 -9.73 SK-1 -6.60 -6.96 PJ-2 -6.22 -6.98 SK-2 -4.98 -0.70 I PJ-3 -7.01 -8.07 SK-3 -6.71 -8.68 PJ-4 -6.15 -7.81 SK-4 -5.88 -4.90 PJ-5 -6.09 -7.56 SK-5 -5.30 -2.10 I PJ-6 -6.4S -8.30 SK-6 -5.43 -4.86 PJ-7 -6.66 -9.18 SK-7 -6.04 -5.20 PJ-8 -6.43 -7.87 SK-8 -6.45 -8.04 I PJ-9 -S.33 -2.81 SK-9 -6.24 -9.01 PJ-IO -6.39 -8.73 PJ-11 -6.36 -8.22 PJ-12 -6.64 -6.44 PJ-13 -6.16 -6.51 DIMNICE PJ-14 -6.15 -8.06 PJ-15 -6.42 -8.18 Dl-1 -4.54 -5.74 PJ-16 DI-2 -6.00 -5.69 -4.85 -6.79 PJ-17 -5.98 -7.13 Dl -3 -6.09 -8.51 PJ-18 -2.17 + 4.01 Dl-4 -654 -929 PJ-19 DI-5 -6.34 -5.19 -3.68 -7.36 PJ-20 -6.21 -7.82 DI-6 -5.66 -4.42 PJ-21 -5.21 -5.30 Dl-7 -6.24 -7.61 PJ-22 -2.91 -0.62 DI-8 -5.45 -6.79 DI-9 -5.16 -3.75 DI-IO -5.09 -4.21

POSTOJNSKA JAMA - POSTOJNA CAVE DIVASKA JAMA - DIVACA CAVE PO-I -6.92 -7.10 PO-2 -7.52 -9.23 DJ-1 -4.91 -8.11 PO-3 -6.93 -9.08 DJ-2 -5.20 -9.24 PO-4 -8.5 -8.56 I PO-5 -6.85 -8.95 PO-6 -7.04 -8.75 I KAMNISKA JAMA - KAMNIK CAVE KJ-I -6.41 -0.97 KJ-2 -6.61 + 1.51 KJ-3 -7.35 -2.00 I PREDJAMA - PREDJAMA CAVE KJ-4 -6.95 + 1.42

PR-I - 6.42 - 7.39 KJ-5 -6.48 + 1.06 I KJ-6 -6.51 -2.62 KJ-7 -7.10 -3.72

Table 5: lsoropic composition of oxygen and carbon in speleothems from

several caves in Slovenia. for Korst Research, SAZU, in Postojna).

- 24 -

mentioned temperature can be calculated from various empirical formulas, each I giving its own results that differ from the others. Analyzing a still growing straw stalactite (here the water temperature as well 1 as 8 O for water and for the growing stalactite were known), it was concluded f that the following equation gives the best results: 1000 . In a = A . 106 . T"2 + B I T = temperature (K) 1 A = a constant; we used A = 2.78 B = a constant; we used B = - 3.4 1 a = the fractionation factor for the calcite-water equilibrium; it can be calculated from the expression

I IWO + 1000 a = — 1 CC I V + 1000

O = 51 8O for the cave carbonate f CC The above cited relationship between temperature, isoropic composition of oxygen I in the cave carbonate and in water is presented in Diagram 7. Here the isotopic composition of 5 young straw stalactites is presented. The samples were taken in I Planina cave, Predjama cave, Kamnik cave and Divaca cave. The diagram enables a comparison of the calculated equilibrium temperatures with the measured I values to be made. The matching is relatively good, though the measurements for the carbonate saturated water are not long term averages as they should be.

The greatest difference is observed for the samples DJ-I and DJ-2 from Divaca cave. The reason for such a discrepancy is not clear. Perhaps the isotopic compo- sition of the water varies considerably and we sampled water of an extreme compo- sition; perhaps the crystallization of this cave carbonate was abnormal. From this carbonate saturated water cave carbonates as well as helectites are formed. These 18 13 two samples from the Divaäa cäve lie far from the 6 O/6 C correlation line, which is characteristic for all the other samples analyzed. 1 VODA -WATER / / / / / -I ////

-5

-6

-7

-8

/ -9

-10 • raEunana temperatura-alculated temperature o merjena temperat ura -measured temperature

-11 /

-12 > • • • • 1 K -10 -9 -B -7 -6 -5 -3 -2 -1

Diagram 7: The relationship between measured and calculated cave temperatures for recently formed carbonates, according to O'Neil, 1968, Ohmoto-Rye, 1970). - 26 -

Temperature ( O Sample Sampling place calculated measured

PJ-I Planina cave 8.5 9.5 PR-I Predjama cave 9.5 10.0 KJ-8 Kamnik cave . 4.3 5.3 DJ-I Divaca cave 4.3 8.7 DJ-2 Divaca cave 5.4 8.7

I In caves with considerable air currents (draughts) and in those with dry air, the evaporation effect can lead to false paleotemperatures. At such places I stalactites are often curved in the draught direction, and the cave carbonates are characteristically rough. Two such samples from Planina cave showed ex- IP 13 I tremely high values for 8 O and « C.

I Sample 818O (PDB) 613C (PDB) I PJ-18 - 2.17 + 4.01 PJ-22 - 2.91 - 0.62 I This can be explained by the strong draught at the entrance to the cave. I This means intense water evaporation occurs during stalactite formation. Because of evaporation, more heavy isotope remains in the carbonate saturated water, I which influences the isotope composition of the cave carbonate.

Beside these few results which allow some suppositions and hypotheses to be I drawn many unsolved problems remain in this topic. These can be solved only by detailed investigation of isotopic equilibria for various conditions of cave carbonate formation. In this way the methods described here will become of use for further research on karst phenomena, as well as on climate and other con- I ditions in the past. I - 27 -

LJUBLJANICA RIVER BASIN

Beside the Karst of Trieste, the Ljubljanica karst river basin is also classified among the classical karst regions, not only of Yugoslavia, but even of Europe. (Fig. 1). The most characteristic features of this area are the sinking rivers Pivka, Unec and Ljubljanica, karst poljes and numerous karst cavities. The river Ljubljanica collects water from the extreme NW part of the Dinaric karst and belongs, as a right hand tributary, to the Danubian part of the Black Sea water basin. In the central part of the Ljubljanica water basin, on the NE side of the high karst plateaus there is a wide belt of lower karst surfaces, mostly between 450 to 600 m above the sea level. The karst poljes are the deepest I depressions there and the only flat areas in the whole Ljubljanica karst water basin, and therefore they are the most densely inhabited.

I Our investigations were aimed at determining the origin of the water catchment in Maine. It has already been proved for this water catchment (by tracing with I dyes) that is gets some of its water from the river Rak. Some water was supposed to come from the underground Javornik flow. Some scientists were of the opinion I that this water catchment can even be influenced by water from the Pivka valley.

Because of the preliminary isotopic investigations of the rivers Rak, Pivka and I Unec which we performed in 1982, as well as because of the results published by Moser et ai. in 1976 (part of the project: Underground water tracing in I Slovenija), we made a thorough isotopic investigation of the large area of I Planinsko polje and Cerknisko polje. For mass spectrometric analyses we took samples from the Lake of Cerknica, I River Rak (upstream of the large natural bridge), River Pivka (before it enters Postojna cave), River Unec (where it leaves Planina cave) and from the Maine spring (at the water catchment). To make insight into the Ljubljanica river basin as complete as possible, two further sources of the Ljubljanica river on the edge of the Ljubljansko barje (marsh) were sampled. We sampled its source Mocilnik permanently while sampling of the source in Bistra took place only occasionally. The samples were taken monthly when the waters were relatively - 28 -

low. The isotopic composition of rainfall was determined (as already mentioned) I for Planina as well as for Ljubljana. Additionally, the amount of rainfall was also determined in the district of Smarata and in that of Cxni vrh, so we could I get an overall insight into precipitation over the ma for part of the Ljubljanica river basin. Precipitation varies considerably from one sampling place to the I other (Table 2), so we can anticipate differences in isotopic composition as well. So far we have followed only changes along the Ljublfanica flow and for I the moment we have neglected the basic-rainfall source of various water catchment areas of individual Ljubljanica river tributaries. The results of the 1 analysis of the isotopic composition of oxygen and of hydrogen in water, of carbon in dissolved carbonates, of the temperature measurements and of tritium i concentration measurements for all the samples under investigation are summarized in Table 6. 1 To make the interpretation of the variations in the isotopic composition easier and more reliable, as well as to give a better understanding, we also followed I the water level at various sampling places. In 1983 the main characteristics were as follows: 1 - the Lake of Cerknica sank at the end of May, and only water at Strzen remained I - the Rak had no surface flow from the middle of July till September; even later water reached the threshold at the large natural bridge only occasionally I - the water levels in Pivko, Unec and Ljubljanico from July onwards were rather low I - in July the water level in Maine spring was considerably below the usual value. The results of isotopic composition of oxygen in water are given in Diagram 8. 18 The Lake of Cerknica had an average oxygen isotopic composition S O about -9.50 %o, and as the lake sank this value reached -6.79 %o. The enrichment with the heavy oxygen isotope is due to evaporation and "heavy" summer preci- pitations. This enrichment was noticed in the Rak and in Maine (20.5.83), which supports the idea that Maine gets its water partly from the Rak (at high water - 29 -

THE CATCHMENT AREA OF THE RIVER LJUBUANICA

9 CERKNICA LAKE RAK Strien Skccjan.

Date 18 13 ! *water W Wer « °w « cc 24.11.82 6.2 - 8.71 - 9.03 14.12. 5.0 - 8.91 -10.80 27.01.83 1 -9.02 2.7 - 9.24 - 9.69 J 25.02. 3 -9.80 4.3 - 9.53 16.04. 12.1 -9.78 9.1 - 9.83 -12.43 20.05. 27 - 6.78 18.3 - 8.69 -11.39 I 5.07. 24 19.5 - 8.42 24.07. 23 18.08. 24 -8.56 12.7 - 9.25 - 9.75 I 20.09. 13.5 -9.47 12.5 - 8.90 -11.44 17.10. 10.0 -9.35 10.4 -9.08 -11.40 I 17.11. 2.0 -9.31 2.5 -9.21 PIVKA MALNE Postojna Source

1 24.11.82 8.5 -8.29 14.12. 5.8 -8.36 27.01.83 1.5 -8.27 3.5 -9.07 - 9.91 I 25.02. 3.5 -8.78 6.0 -9.10 - 9.66 16.04. 8.2 -8.93 9.2 -9.78 -11.71 20.05. 18.0 -8.31 11.9 -8.97 -10.76 1 5.07. 19.5. -8.10 10.0 -9.30 -11.21 24.07. 21.5 -7.99 8.0 -9.22 -12.06 18.08. 24.0 -7.27 8.0 -9.29 -11.80 20.09. 13.0 -6.77 8.1 -9.28 -12.10 I 17.10. 10.2 -7.62 8.0 -9.26 17.11. 2.5 -8.11 7.8 -9.02 1 UNEC LJUBLJANICA Planina cave Moäilnik I Date 818 *water W C Vater O

I 24.11.82 7.6 -8.57 -11.83 14.12. 6.2 -8.56 -11.74 27.01.83 4.5 -8.90 - 10.58 6.5 -9.06 25.02. 5.5 -8.93 - 10.13 7.0 -9.11 IW 16.04. 9.0 -9.49 - 12.93 8.8 -9.85

m 20.05. 10.0 -9.00 -12.12 9.2 -9.45 5.07. 10.4. -9.06 - 13.06 9.5 -9.40 I 24.07. 10.8 -8.49 - 14.12 10.0 -8.92 18.08. 10.5 -8.68 - 12.56 9.7 -9.15 20.09. 10.0 -8.33 - 11.74 9.4 -9.08 I 17.10. 10.3 -8.45 -11.44 9.1 -9.01 17.11. 8.2 -8.22 8.0 -8.48

Table 6: lsotopic composition of oxygen in water and of carbon in dissolved

carbonate from Cerknica and Planina polje in the period from

November 1982 to November 1983. DEZ RÄIN 100- l/m2 50- 0 - •I Il Il hl. 1 i 111 I MJJA S O NDUFM A MJJ A S " O ' N ' D ' 0- 18 6 O -7 -6 -8 -5.5 -8 -1- -10- I LL -10,8 -12,7 -20- -U,5

18 -7 H 6 O

-8- PIVKA PIVKA UNEC

-9 oMALNI RAK . CERKNISKO J. -10 MJJASOHDJFMAMJJASOND

Diagram 8: Comparison of 6 O variability in waters the catchment area of Ljubljanica with precipitation amounts and their oxygen isotopic composition in Planina. - 31 -

18 levels). In the summertime Maine showed 6O = - 9.25 %o +0.05 %o, which indicates a stable source (Javornik flow), and neither the influence of the Rak nor that of meteoric water is shown. Additionally, the temperature in Maine, which was raised to 11.9 C in May, later sank to a stable value of 8°C. The Pivka river has its own isotopic characteristics, the isotopic composition of I oxygen varying from -8.93%o to -6.77 %o.jPartly this is due to evaporation at 18 low water flows, and partly the S O enriched precipitations in the Postojna I valley have to be taken into account. The isotopic composition of oxygen in the Unec changes relatively slowly (from I -9.78%o to -8.22%o).JAs its main tributaries (Rak, Pivka and Javornik flow) have different isotopic compositions, the isotopic composition of the Unec can 1 indicate the prevailing tributary at a given moment. In summer 1983 the Javornik flow predominated. At this time the temperature of the Unec was only I 10.8°C, while the highest temperature in July 1982 was about 15°C. This indi- cates that the prevailing contribution came from the warm surface flows of the I Pivka and Rak. The Ljubljanica source Mocilnik behaved in a similar way to the Unec. The 18 1 fact that the enrichment with O was poorer by about 0.5 %o in the Ljubljanica than in the Unec shows that the Ljubljanica gets its water from various sources. 18 I The Bistra spring on 20.09. showed a S O = - 9.32 %o. This sample is even 18 poorer in 6 O (for 0.3%a) and has an isotopic composition similar to the Strzen 1 of the Cerknica Lake at the same time. The isotopic composition of carbon in dissolved carbonates from the rivers Rak, I Unec and in Maine was also measured. The values for the River Rak change from 613C = - 9.03 %o to - 12.43 %o, those in Maine from 613C = - 9.66 %o to 13 I - 12.06 %o, while samples from the River Unec gave values between 5 C = -10.13 %o and -14.12 %o. The Unec showes an increased concentration of organic carbon which is very probably contributed from the Pivka. - 32 -

THE WATER CATCHMENT AREA OF RIZANA

Investigation of the changes in isotopic composition of light elements in Slovenian Karst water were partly performed on the water catchment area of the Rizana I river. The Rizana is a strong karst flow, which springs from the narrow limestone window in the flysch reef of Hrastovlje. The water flows towards Koper (i.e. towards the Adriatic sea) as a surface stream in this flysch area (Fig. 3).

When we started the investigation in 1981 we supposed that the Rizana takes 2 its source from a large area of some 10 km . In this district there are very few 1 surface waters, because of its extreme karstification, Immediately above the aquifer that saturates the Rizana source, there is a brock (Hrastovski potok) that 1 flows on the surface (on a flysch reef). This brook has a high water level only in rainy periods. On the N part of the supposed water catchment area several I other brooks flow over another flysch reef (the flysch reef of Brkini). They all sink as they come to the karstified limestones. i In view of these hydrogeological conditions we wanted to determine any connection I between the waters of Brkini and those from the Rizana source. The Rizana spring, precipitation in Kozina, as well as the Brsnica brook in 1 Odolina (being one of the mentioned brooks which flow on the flysch reef of Brkini and sinks on its S part into the limestones of Slavnik) were regularly 2 investigated. Odolina has a small water catJiment area, only about 4.5km . Occasionally the brook flowing on the bottom of the Dimnica cave (the cave I developed some kilometres from the Odolina valley on the flysch - limestones border), the well R-I (which is filled from a deep artesian aquifer) and the 1 mentioned brook near the spring of Rizana were analyzed. The isotopic composition of oxygen in precipitation changed during the period 18 I of our investigations (more than three years) from 6 O = - 16 %o in winter to -4.1 %o in summer. In the period from April to November 1982 the average I S O was -5.8 %o, from November 1982 to April 1983 -11.1 %o, and from April to November J983 - 7.1 %o. The average tritium concentration in the I precipitation over this period was 25 T.U. + 10 T.U.; in the years 1980 and I 1981 it was about 80 T.U., and in the years before 1980 even more than 100 T.U. NE Slavnik

KOZINA Brkini

r.Rcko

M= 1:17(1000 CO U

APKEKEC FLlS J_L LIMESTORE FLYSCH

Fig. 3: Geological section of Rizarta water catchment area - 34 - I IQ The isotopic composition of oxygen in Rizana varied from S O = - 9.1 to I - 6.5 %o in the period from 1980 - 1983. (Diagram 9). This means that the 1 fi waters in the aquifer homogenize to a great extent. The results for 5 O show I that the mean values for individual years are rather different, but the oscillations 18 are smaller over shorter periods. In September and October 1982 S O was I - 7.0 %o + 0.5 %o, from April to August we found the values 618O = - 8.5 %o + 0.3 %o, and in the year 1982 the average was 8 O = -8.11 %o + 0.25 %o. I Similar oscillations were observed in Odolina but the cycles during the year were different. The tritium concentration in the springs was from 40 to 80 T.U., and 13 I the 6 C values varied from -8.2 to - 15.2 %o. 1 In the year 1982 the brook at the bottom of Dimnica cave was sampled from May to November. The results for the isotopic composition of oxygen are given in I Table 7 together with those for Odolina and Rizana during the same period. To compare the characteristics of oxygen isotopic composition in various aquifers, I we give here the average values and the oscillation intervals.

DIMNICA ODOLINA RIZANA I 18 Date 8 O 518O I %o %o °/cO 24.05. - 8.16 - 8.54 - 7.80 I 3.06. - 8.25 - 8.52 r 7.86 17.06. - 8.13 - 8.26 - 8.08 6.07. - 8.08 - 8.18 - 7.87 1.09. - 7.77 - 8.01 - 7.87 20.09. - 8.27 - 7.94 - 7.81 18.10. - 7.87 - 8.48 - 8.02 12.11. - 7.83 - 8.20 - 7.85

Table 7: Variations of isotopic composition of water in the cave of Dimnica, the karst valleys of Odolina and in the river Rizana from May to November 1982. DEZ RAIN 150- l/m* 100- 50- • l Il ll.lll.n, l,|,.l)l.lljl ill 111.. I I, . ... 1.1 ll I AHJ J ASO ND1J FMAMJ J ASO ND1J FMAMJ JASOND 1981 1S82 1983 Oj 618O -6 -B -6 -iol r-10 -16 -7 1 618O

RIZANA- ODOLINA*'

-9-J MVJ i A S O-N1O1J1F1M AMJ J ASO NDM FMAMJ JASONO

18 Diagram 9; Comparison of 8 O variability in waters of the water catchment area of Rizana with precipitation amount? and their oxygen isotopic composition in Kozina. - 36 -

Though the changes between various aquifers are only slight, we can draw the conclusion that in this period waters from Odolina and Dimnica show a significant influence of winter waters. This is more expressed in Odolina than in Dimnica. Both brooks have a lowr concentration of heavy isotopes than the Rizana, which is rlso considerably lower than the precipitation in this period.

When checked during the 1982 the isotopic composition of the aquifer of the R-I 18 well proved to be constant: 8 O being - 7.35 %o + 0.08 %o, the tritium concen- ~ 13 tration 0 T.U. and the isotopic composition of the dissolved carbonate s C = - 13.33 %o+ 0.30 %o.

The isotopic composition of oxygen in the water from Hrastovski potok practical- I ly followed that of the rainfall. In Table 8 the average values and the oscillation intervals of the oxygen isotopic I composition are given for all sampling locations in the water catchment area of Rizana from April to September 1982. In this period we were particularly interested in the differences of oxygen isotopic composition in waters from various sources of this area.

I8 18 Location • 8 o SD AS O AsD %o %o %o %o

Precip. (4 .-9.82) - 5.82 - 36.6 6.40 40.0 I Hrastovski spring - 6.86 - 52.5 R-I - 7.35 - 53.7 0.17 0.9 Rizana - 7.94 - 54.0 0.75 6.7 Odolina - 8.30 - 56.1 0.73 5.2

Table 8: Mean isotopic composition in various sampling places I These investigations, together with other hydrogeological data led to some interesting conclusions about the sources of the Rizana river. 1 All waters are of mixed origin concerning rainfall. In Rizana and in Odolina a part of the precipitation discharges practically directly. The Rizana contains I Table 5: Isotopic composition of oxygen and carbon in speleothems from several caves in Slovenia.

- 37 -

meteoric waters which penetrate directly into the source through dry and fissured I flysch strata or through the karst channels. In Odolina we have to deal with waters which flow on the surface, sometimes over strata of decaying matter.

1 After heavy rain in Rizana such an unretained flow can be observed for some weeks, but in the Odolina only for some days. I Other waters represent well homogenized meteoric waters, on the average up to 3 years old, which was determined from the average isotopic composition of I oxygen and from the tritium concentration. These homogenized waters can be classified according to their different retention times. A minority has the characteristics of the average seasonal precipitation, but the majority shows annual cycles which have a delay of some years. At extremely low water levels we could sample waters which were retained in the fine porous fissures of the aquifer for even longer periods. This part of the aquifer is emptied only at very low hydraulic pressures. The main drainage ways, on the other hand, which allow a greater transmission and a faster water flow, also discharge at higher hydraulic pressures.

Measuring the isotopic composition of carbon we follow the portion of the organic carbon in dissolved carbonates. This increases in the periods of intense minera- lization of organic substances and is rinsed into the aquifer in heavier rain. In Odolina such influences were observed from July to October 1982 and in January 1983, while in the Rizana they could be traced only from May to June 1982 (at high water level).

I The well R-I is bored into a deep artesian well, which is hydraulically separated from the aquifer out of which the Rizana takes it source. The water is older I than 50 years (shown by the tritium concentration measurements). The isotopic composition of cxygen and deuterium is constant, and the changes in the I isotopic composition of carbon are minimal. 1 I WJIlIfJlCJ TJUlIl UlB l/l»Ul.U Mil» I" which is characteristic for all the other samples analyzed.

- 38 -

THE WATER CATCHMENT AREA OF THE IDRIJCA .

The water catchment area of the ldrigca (Fig.4) is one more example of a karst aquifer. The river Idrijca has several small springs in the area of Trnovski gozd and a strong one in the lake of Divje jezero. The discharge from this lake is very changeable. In periods of heavy rain large amounts of water are literal- Iy being thrown out (some m /min) into the river Idrijca, while in extremely dry periods the water from the upper part of the Idrijca even flows into the lake. Investigations in the area of Divje jezero were starred in January 1983. They included mass spectrometric analyses of the isotopic composition of oxygen in the lake water and in water sampled from the upper part of the Idrijca (before the I lake water enters it), as well as the isotopic composition of carbon in dissolved carbonates in the lake water samples. As a rule samples were taken monthly.

I In January 1983 (when the investigations started) water streamed intensively over the dam into the river and the flow increased until April. In periods of I heavy rain it sometimes showed a several fold increase. From May the water levels were low. From June until the end of August the lake did not pour over the dam, but its level was never below that of the river Idrijca. In September it began to rise again, and water reached the dam and flowed over it, though the flow rate was minimal. From November it increased considerably and high water levels persisted to the end of May (abundant winter and spring precipi- I tation) . The temperature of the lake water (Diagram 10) was rather constant until May I 1983 (it changed only between 6.3 and 8.6 C). In summer, when there wo< practically no flow, the water in the lake warmed considerably and in July I reached the temperature of 19 C. When discharge started again the temperature sank to 8.5 C, in November even to 6.2°C (low air temperatures with minimal I water flow at the same time). In the winter spring period of 1984 (considerable flow rates) it changed between 6.8 and 7.9 C. The isotopic composition of oxygen in the analysed samples (Diagram 10) show that in January 1983 predominantly summer-autumn waters (enriched with heavy oxygen) were filling the lake. In February an increase of the light oxygen - 39 - I I I I I KARST SOURCE "DIVJE JEZERO1 I I

OAM T—'—rvOivjijiziro JEZ

10m O 10Om

Fig. 4: Schematic geological section of karst source Divje jezero: a - lake water flows into the river at high water level b - influence of Idrijca river at extremely low lake level - 40 - I OEZ RAIN I 100- l/rn* 50 I III I ,111 I Ii ^J FMAMJ J ASOK D I 6"0 -U -6 -5.5 -10- & H I -U.5

I DIVJE JEZERO I IORIJCA I -9

-10 -^

T'C

10 DIVJE JEZERO IDRIJCA O -I

JFHAHJJASOND 1983

18 Diagram 10: Comparison of 6 O variabilit/ in waters in the water catchment area of Idrijca with precipitation amounts and their oxygen isotopic composition in Planina. - 41 -

isotope concentration is observed (increased influence of the winter water). In 18 spring the melting of snow (average 6 O = - 12.5 %o) took place and at the 18 end of March it rained heavily (average 8 O = - 10.1 %o). The aquifer which I contained the winter-spring water continued to empty until the begining of July, when the lake ceased to flow over the dam. I In the summer period the isotopic composition of oxygen in the lake water was 18 18 I rather constant. Its 6 O varied in the narrow interval between 6 O= -8.42%o and -8.92 %o. These variations are very probably due to evaporation, as well as I to direct influence of precipitation on the stagnant lake. In November the summer waters (enriched with the heavy oxygen isotope) began to flow into the lake I from the aquifer, which has already been partly filled with water. The oxygen in this summer water contained more of the heavy isotope (a difference of 1 %o) I compared to the Idrijca, or to the source water which filled the lake through the underground channel in October. I The influence of the summer and autumn waters can be followed until January 1984, when the winter water begins to prevail. Because the snow in the area I under investigation was very abundant that year, (in some places it did not melt until the end of April), the influence of the winter water is longer compared to I 1983. The isotopic composition of oxygen in the river Idrijca shows the following: though the seasonal temperature changes are considerable (from 2.8 to 17.0 C. 18 I 6 O changes in a narrow interval: between -8.18 %o and -9.20 %o (the average value being -8.7%o). The oscillations from the mean values are very I probably due to the direct influence of the winter and summer precipitation. I The isotopic composition of carbon' in dissolved carbonate is rather constant and varies only from - 11.02%o to - 12.50 %o. For the aquifer which supplies the source in Divje jezero we can conclude - even after only one year of sampling - that its characteristics are very different from those found in Planinska jama or in the water catchment area of Rizana. Though we are also dealing here with mixed water (like in the other two cases), we can observe seasonary filling and emptying of the aquifer with isotopically characteristic precipitation. This was concluded following the explicit isotopic changes of the source water. - 42 -

CONCLUSIONS

In an investigation lasting three years, the isotopic characteristics of vertically I perco'cting water,collection areas,dominating sources of springs and surface water flows were examined. For .that the isotopic compositions of oxygen, carbon I and hydrogen as well as tritium concentrations was measured. Additionally the isotopic composition of the cave carbonates was analyzed. I In the karst area the retention time is usually short; very short if precipitations find their way through larger channels, a little longer if they percolate through I systems of fissures and cracks, or up to some years in solid aquifers. I a - Determi ni ng the vertical percolation characteristics By following the changes in the isotopic composition of various water samples 1 (rainfcH, streamlets) in Planina cave, the extent of homogenization of the rainfall water because of its retention was determined. The characteristics of the Stream- I let 1 aquifer have now been followed for 30 months. It was found that the water percolates directly during heavy rains (the isotopic composition of the streamlet I becomes similar to that of the rainfall). In the last year (1983) special attention was given to the slow percolation of retained waters. Though we could observe I various rainy periods with quite different isotopic composition of oxygen, the samples taken from Streamlet 1 showed only slight changes (over an interval of I 6 8O = 0.6 %o, the average value being 6 O = -8.67 %o). The rainfall 18 of the same period had an average oxygen isotopic composition 6 O = -9.12%o, 18 I with a very large interval from S O = - 14.5 to - 4.23 %o. If one considers that this year the overall amount of the rainfall was rather low (from November 82 till November 83: 1150 mm) compared with the previous year, one could anticipate that the waters of the Streamlet contain a great deal of the previous year's m«s*«oric waters. carbonate from Cerknica and Planina polje in the period from November 1982 to November 1983.

- 43 - I b - Following the water flows i Water flows, both surface and the underground ones, on Cerknisko polje, on Planinsko polje, in the water catchment area of the Rizana and in that of the I Idrijca were followed. These measurements are intended to contribute to the determination of the prevailing I water sources of the underground flows which can be sampled only from their springs or in accesible caves. Our previous investigations have already given some promising results. We found the following: - At high water levels the water that leaves the Lake of Cerknica through the Rak river appears partly in the spring of Maine. In the summer months, when the surface flows were minimal, the Maine aquifer was filled nearly exclusively by the underground Javornik flow. The direct influence of rainfall was 18 negligible, S O in Maine remaining almost constant for more than 5 months (618O = -9.25 + 0.05 %o). - Water from the Lake of Cerknica appears directly (underground flow) in the Eastern source of the Ljubljanica - at Bistra. That has also been proved by tracing with dyes. - In the river Unec we could follow the various mixing of three water flows: river Rak, river Pivka and Javornik (underground flow). In the summer 1983 the Javornik flow predominated. In some rainy periods the influence of water from the river Pivka became more important. This was easily determined because of its unique regimen of changes in oxygen isotopic composition in this period. -In the water catchment area of Rizana we can observe two different aquifer 2 I systems. Odolina has a small collecting area (4.5 km ) on flysch, while that of Rizana is about ten times this size; its largest part lying on the karstified district of Slavnik. The mean isotopic composition and its changes are similar in both cases, only the influence of rainfall is far longer in the case of Rizana. The isotopic composition at the mean water discharge indicates that we are dealing with highly homogenized rainfall at least 6 months old (this is verified by variations of fi'^O data), but very probably a part of the waters are retained for three years. This was indicated by the tritium concentration measurements. - 44 - i - The characteristic karst source in Divje jezero near Idrija has a quite different catchment area (investigations have been performed for one year only). Here 18 the winter-spring water (S O= -10%o) left the aquifer until summer, i.e. I until it was nearly empty. The summer rainfall was not exhausted before November. Further investigations are necessary in order to find if we have I been observing a regular situation, or whether it was an exeptional case in this extremely dry year.

c -Analyzing dissolved and cave carbonates

During this period several samples of dissolved carbonates from various sampling locations, as well as characteristic cave carbonates of different origin (location, time of formation) were analyzed.

From the isotopic composition of carbon in the dissolved carbonates, the influence of organic carbon (or rather, the influence of organic acids from the humus stratum) on the dissolution of the carbonate strata, as well as on the denudation process and on carbonate transport from the karstified area was measured. The majority of the organic carbon from decomposition of organic matter is concentrating in the form of carbonic acid and other organic acids in the humus stratum above the karstified strata. By heavier rains this carbon is rinsed into the aquifer. De- pending on the saturation step of the aquifer, and further, on the retention time, these acids dissolve carbonate minerals to a different extent. Under some litho- logical conditions carbonic acid reacts with the clayey material in decaying matter. Sometimes during heavier rains the acids can even be detected in the springs.

The investigation of cave carbonates revealed that they have different isotopic compositions of oxygen and carbon because of different locations and also because of their different ages. The water oxygen and the carbon in the dis- solved carbonates are in isotopic equilibrium with oxygen and carbon of the i cave carbonates. The results show that the isotopic composition of the cave carbonates reveals the climatic conditions during crystallization. The isotopic composition of carbon depends on the abundance of the vegetation above the i - 45 - I cave. The equilibrium crystallization temperatures för calcite which were I calculated for some recent cave carbonates (not older than 20 years) and those of the coexisting water agree relatively well with the measured temperature I of the waters in 'the caves. The cave carbonates from caves with an intense I circulation of the air are an exception to the rule.

I

1 precipitation over this period was /3 T.U. + IU l.u.j in me years ITOU ana 1981 it was about 80 T.U., and in the years before 1980 even more than 100 T.U.

- 46 - I I REFERENCES: 1. T. Dolenec, J. KuSej and J. Pezdic: The isotopic composition of oxygen I and carbon in lead-zinc deposits of the Northeren Karavanke, IV ISMIDA Berthesgaden (1981). i 2. I. Gams: Retension water in Karst: Its role in influencing total water hardness and denudation rate. Proc. Symposium on karst Denudation, Aix I en Provence-Marseille-Ni mes (1980). 3. I. Gams: Main factors of karst denudation in the world, Geografski vestnik, I Ul, Ljubljana (1980). 4. H. Gerstenberger, M. Herrmann: Report on the lntercomparison for the Isotope Standards Limestone KH-2 and Polyethylene Foil PEF-I, Leipzig (1982). 5. R. Gospodaric: Sinter generations in classical Karst of Slovenia, Acta Carsologica 9/3 (198°)/ Ljubljana. 6. R. Gospodaric, J. Kogovsek, M. Luzar: Hydrogeology and karst springs in Rakov Skocjan near Postojna, Acta Carsologica 11/2 (1982), Ljubljana. J 7. J.Kogovsek, P. Habi:: The study of vertical water percolation in the case of Planina and Postojna Cave, Acta Carsologica IX/5, Ljubljana (1981). I 8. I. Kubat, E. Ramovic, J. Pezdic, T. Dolenec: Results of investigations of sulfur, oxygen, carbon and lead isotope in some ore deposits in Bosna I and Hercegovina, Herald Geological, Sarajevo, 1980. 9. H. Moser, V. Rajner, D. Rank, W. Stichler: Results of measurements of I the content of deuterium, oxygen-18 and tritium in water samples from test area taken during 1972-1975; Underground water 'racing (Investigations I in Slovenia), 3. SUWT, Ljubljana 1976. 10. H. Moser et ai: Messung von Deuterium, Sauerstoff-18 und Kohlenstoff-13- I Gehalten, Jahresbericht 1977 und 1978, GSF-Bericht R 169 und 207 Institut fUr Radiohydrometrie, Gesellschaft fUr Strahlen und Umweltforschung mbH, MUnchen. - 47 - i 11. B. Qgorelec, M. MUic, J. Faganelli, A. Seroelj, F. Cimerman, P. i Stegnar, J. Pezdic, T. Dolenec: Quaternary sediments of the Secovlje salt marsh-S loveni jo, IAS, 4 European meeting, Split 1983. i 12. J. Pezdic, H. Leskovsek, I. Kobal, T. Dolenec, S. Weiss: An lsotopic Study of Karst Water, IAEA Report No. 2845/RB, Ljubljana 1982 and i 1983. 13. U. Schotterer et al: Isotope Study in the Alpine Karst Region of Rawill, Switzerland, Isotope Hydrology 1978, vol. I., Proceedings of a Symp. Neuherberg, 19-23 June 1978, IAEA-SM-228/20.