Hydrogeology: a Phivileged Field for Environmental Stable Isotopes Applications Some Italian Examples
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REND/CONT/ Soclef<l Itallana dl Mlneralog;a e Pdralogla. 38 (3): pp. 1197_1212 Coinunlca:;:lone prer;enta.ta alla. Rlunlone dellll. SlMP In Rende-cetn\ro (Cosen,.a) 11 27_10_1982 HYDROGEOLOGY: A PHIVILEGED FIELD FOR ENVIRONMENTAL STABLE ISOTOPES APPLICATIONS SOME ITALIAN EXAMPLES GIAN MARIA ZUPPI, GIANCARLO BORTOLAMI lstituto di Geolollia dell'Universita, via Accademia delle Scienze 10, 1012J Torino RUSSUNTO. - Vengono presentati alcuni esempi other reasons, delaying publications, We ap di utilizzazione degli !sotopi stabili ('''0, "H, "5) preciate Ihe opportunity of this meeting « to oello studio di tre parameui fondamentali del bi· lando idrologico: prccipitazioni, deflusso superfi· discharge », in part, the debt with the friends dale e drcolazione sotterranea (= infiltrazione). to whom we are obliged, at least, for the Per le precipirazioni sono state definite otigine e assistance in Ihe analytical services. drcolazione delle masse d'aria umida nelle Alpi Occidentali, Prealpi Venete cd Appennino Centrale. Thus, the paper would be a kind of « sum t stato studiato it oomportamento isotopioo dei ma» of many problems tackled and some· principali oorsi d'acqua della Pianura Padana e times solved using Stable Isotopes, dell'Italia Cemrale. These hydrogeological problems concern Gli esempi di utili:aazione delle tccniche isota piche allo studio della ciroolazione sotterranea ri three Italian regions: Piedmont, Venity and guardano i mezzi permeabili per porosita primaria Central Italy. (senore piemontese e veneto della Padania), per fessurazione nei massicei cristallini (Alpi Occiden 2, Precipitation8 tati) e per carsismo (Alpi Marillirne cd Appennino Centrale). Due to its geographical position the Italian peninsula is submitted to meteorological ABSTRACT. - Some examples of environmental events with different origins: cold and ge isotopes application to three paramerers of hydro logical budget (precipitation, runoff and under nerally dry air masses coming from Eastern ground flow) are presented. Europe, and warm and humid air masses Origines and circulations of wet air masses on coming from the west (Atlantic Ocean) and the Western Alps, Venetian Prealps and Central the south (western and central Mediterranean .Apennines are defined, Cyclic flucruation of river waters isotopic com basin). position has been investigated in the Po Valley and The influence of one on the other com in Central Italy. ponents originates a remarkable different Underground circulation in porous media situation with implication to the hydro (Piedmontese and Venetian areas on the Po Valley), in crystalline rocks (western Alps) and in Karst geological problems. (Maritime Alps and Central Apennines) has been studied by means of stable isotopes, 2 I, GRADIENTS In the western Alps, mainly the Mari 1. Introduction time ones, precipitations had normally origi. For mOre than iO years some hydro nated from Atlantic air masses and secondary geologists of the Turin University are in from Mediterranean ones. Therefore, the cross volved in the application of Nuclear Tech of the alpine system originate a significant niques to hydrogeological problems, covering isotOpic fractionation with the altitude several areas in and outside of Italy. either if air masses are coming from the west Some of the data, presented herewith, have or from the south. The gradient with the alti been already published; however a major tude (fig. 1) is 3.1 5f~ and 25 %~ per thousand part of the data can be considered as meters in oxygen-iS and deuterium respecti « drawer data », For yearS, the authors have vely (BORTOLAMI et al., 1978). A similar committed a misdemeanour, for sloth or relationship has been determined from sam- 1198 G.M. ZUPPI, G. BORTOLAMI ._,r---------, .. .......·.".. '.IIOl .......,..., ,. ~. .. .. .. • .. o .. " '" o ' .~ .. .-.....,...,.....,......., .. .. .. -_. --., ." .. ~"'''J>o,., 3 .. ·•.. _1 - - ., Fig. 1. - Oxy~n-l8-altilude gradient in Maritime '- Alps. The determination codiidents (r') for October 1974 and aprH 1976 are 0.98 and 0.99, respectively, ~. • whereas the standard errors are 0.13 (October) and 0.1:5 (April). .. Squares indicate samples for October; circles for ~. April. Onc can note thaI, generally, the mean tem ." peratures for October and April are quite near the ~. annual mean lernperamre. Therefore, the combi -_. bination of these two equations closely describes - the avenge annual isotopic gradient as a function '- of the ahitude: Fig. 2. - Isotopic gradient' with altitude on tbe UO = (J.12 ± 0.10) 10-1 h - (8.03 ± 0.13). Tyrrhenian C.) and Adriatic Cb) basins. Upper curves: summer correlation; lower curves: winter oorre1ation; mean c:urves: average annual cor· pies collected on French side of western Alps relation. To explain the difference in gradiertlS (MaSER. and STICHLER. 1970). where a betwenl one side and the Olher one of Apennines deuterium gradient equal to 40 per thousand system one can indeed -aount for the «mounlain meters was found; JAMlER. and OLIVE shadow effect •. (1977) calculated a gmdient in oxygen-18 of 3.5 %~ per thousand meters on northern side preclpltations eilher from the ocean to the of Mont Blanc. interior of continents (horizontal gradient) In Central Italy, a cross section of the or on mountain side (vertical gradient). Apennines between Anzio and Ascoli P. (6g. However in our cases. one deals with the 2) indicated that gradients on the Adriatic .. mountain shadow effect)t (YURTSEVER and side are smoother than those in Tyrrhenian GAT, 1981). This is the appearance of pre regions (ZUPPI et al., 1974). Similarly the cipitations on Ihe side of mountains closer gradients in the Venetian Alps (fig. 3, tab. 1) to the vapour source more enriched in heavy give values smoother with respect to those isotopes, al lower altitudes and more de found in Central Europe and more sub pleted at higher altitudes than rain in the jected to oceanic influence (DINGER et al., regions lee side. According to this point of 1970). The case of 1972 is very signi6cant: view, the gradient in a.ltitude is considered practically, during the period April-November to be a consequence of the moisture loss no differences appear in the heavy isotopes from an air mass by cooling, regulated at coOlent of precipitations. the same time by the distance from the Generally the removal of precipitation ocean and by Ihe geographical patterns of from the vapour reservoirs was modelled as the mountains. a simple Rayleigh process (DANSGAARD, 1964), whereby the condensed phase is for. 2.2. DEUTERIUM EXCESS med in equilibrium with the vapour and The .. d )t quantity referred to .. deuterium then removed from the atmosphere as soon excess ~ is usualli dose to + 1000,kfl at oceanic as it is formed. This mood can explain stations (CUIG, 1961). However if a. signi. the diHerences in isotopic composition of ficant part of the vapour mass has originated HYDROGEOLOGY: A PRIVILEGED FIELD FOR ENVIRONMENTAL ETC. 1199 in a closed basin, the «d» parameter characterizes the maximum oceanic compo changes. In the eastern Mediterranean basin, nent in the rainfall (summer and fall), the isotopic composition of the predpitations whereas the increasing chloride paralleled by obeys the relationship: increases in deuterium excess affirme that lB air masses from western Mediterranean 2H=8 O+22 arrive during winter and spring (fig. 4). (NIR, 1967; GAT and CARMI, 1970). A seasonal variation in deuterium excess In this context, because .of the peculiarity has been found in the Latium Apennines of Italy's position the «d. parameter, as with a range of «d. values between +11.1%0 well the chemical load of predpitations, in winler and + 16 %fI in summer and changes with the season as a result of dif- in the Eastern Alps where the range is ferent wind patterns. .... + 10.2 ~o and + 14.0 ~'" respectively in - .... • • - .... .", 0" ." • on '.>. • - ..• • _..... ,J. o ~• - ... m .••••l. • - - - - Fig. J. - Os:y~tg.ahiI\Jde tp'adicnls in Ill('; Venice Region for lhe 1970-1974 period. E\"en in !his casc the c mounlain sNdow effect. is present with prccipitadons on the mountain's sides closer to lhe vapour source ID()r'e enridled in heavy isotopes al lower altitudes and more depleled at higher ahiwdcs Ihan rain in lhe regions I" side. The equalions describing the gradienlS are reponed in table 1. In the Western Alps the deuterium exces~ winter and in summer (ZUPPI, unpublished is varying between + llA %0 and + 1.5.9 5'11 data). The seasonal differences between the (BoRTOLAMI et aI., 1978). This intermediate Western Alps and Eastern Alps and Apen position is due to the meteoric contributions nines are explained by the atmospheric circu which can be defined as «mixed ». Plotting lation: the presence, in the winter, of a the deuterium excess versus chloride activity high pressure regime over the north Tyr (fig. 4) the points representing the fall season rhenian Sea. are closely grouped at the lower end of the Therefore, the major contribution of line, whereas the points of spring show a Atlantic humid air masses occurs during sum larger spread at the upper part of the line. mer in the Western Alps and during winter It is known that the chloride contents in the Eastern Alps and in Central Italy. at a certain distance from the coast become rather low and constant (JUNGE, 1963); the 2.3. SULPHUR-34 constant deuterium excess value (+ 11.2 %0) The sulphur isotopic composition of dis- 1200 G.M. ZUPPI, G. BQRTOLAMt TABLE 1 Annual and seasonal averages for oxygen-18 in Venice region weighted by tbe amount 0/ precipitQtion 1 \I 7 0 1 t 7 1 1 \I 7 2 I 1 \I 7 ) 1 , 7 ~ :m~~ :f~m :ml:~ .~ :mg~ ~.~ mm I ..~ year ""' -8.45 -8.39 _9.05 _8.96 _9.10 _'.03 _9.16 _9.10 _9.et _'.82 1'.0.550 ROLl..! I ' ~ ~, .~ ,.. ~. ,,, ,,, ~. ,,, =. - ='" ." ". '" '''''" '" '" _9.15 _9.02._8.03'" _8.80 _8.75 _9 ,:Ni , _8.28 _8.18 -9.18 _8.53- IlON1'E CRAPH 1857 ,,, 2498 1019 1.655 1382 • ,,, ", ,,, 00.'" "'" - '""" '" ..