The role of groundwater in the acidification of the

Z.HRKAL,J.BUCHTELE,E.TlKKANEN,A.KA pA H O

s

The role of groundwater in the acidification of the

hydrosphere - examples from small catchments in the Bohemian Massif

ZBYNEKHRKAL,JOSEFBUCHTELE,EEVATIKKANEN,ASKOKApAHO&JAROMIRSANTRUCEK

Hrkal,Z.,Buchtele,J.,Tikkan en,E., Kapyah o,A.&Santrucek,J.2002:Therol e of groundwa te rin theacidificationofthe hydrosphere -exam ple s from small cat ch ment s inthe Bohem ianMassif.Norges qeoloqiske undersokelse Bulletin 439, 99-105.

Theaim ofthepresentedst udy wasto assesstheim pac tofthe groun dwateronthedegr eeof acidificati on of sur- face watersinsmall catchm ents.Quantit ati vehydr ogeologi cal analysisbased on theresult s ofthe SACRAMENTO hydrologicalmode lwas aime dat the assessmentof the contribu tio nof baseflowrepr esent in g thegroundwaterdis- charg einthe tot alru noff.Co mparison ofsingle pHmeasureme ntsinsurfacewaterwith thecorr espondingact ua l andmodelledwate rdischarg ewas used asthe informatio nin thequantitat ive part of the dat aprocessing.The obtainedresults showed differentprotectivepowers of the aq uifers against acidifica tio n, a consp icuo usdecreasein thesoil buffercapacity of theKrusnehor y Mts.and asig nifi cant influence ofthrou gh fallprecipitati onsonthe groun dwater qualit y.

Zbynek Hrka l,JosefBuchtele,JaromirSantrucek,Cha rles University,Dept.ofHydrog eo logy,CzechRepublic.

Eeva Tikkanen,Asko Kapyah o,UniversityofHelsinki,Fin land.

Introduction

The Czech Republic is oneof several countries where the effe cts ofant hrogenic atmospheric acidificat ion first began torevealthemselvesin the early 1960s.However,the mass extinctionof forest vegetation,firstin the higherparts of the Krusnehory Mts.and laterin theJizerskehory and Krkonose Mts.,demonstrated the true exte nt ofacid ificat ion.This pro- vided conclusiveevidenceof thewidespread nature of the acidification, but some doubts still prevailed about the degree of acidification of grou ndwat ers. Some regional studies(Hrkal 1992,Hrkal&Fottova1999)reportedevidence of progressiveacidification of shallow,near-surfaceaquifers in the crystalline bedrock complexeswhich revealeda con- siderable decrease in alkalinity leadingto thecomplete dis- appearanceof bicarbonates,decreasein pH,andanincrease in AIand Beconcentr ations. Whilst thequalityof surface watersisaffected byat mospheri c deposit ion direct ly and immediately, the impact of rainfall on the chemi cal composi - tion of groundwate rs is delayed.Ow ing to thecontact of ground water wit h the bedrock enviro nment,and also pri- marilywit hsoil strata,theground waterenjoys adegreeof potential buffering against acidification,and consequently may play animportant role in theresult ingchemistryof sur- face waterdischarge. However,theproportion of ground- water in thetotal discharge varies considerablyin the course of the year,and consequently a similar variation can be seen in the degree of its impact on thefinal chemicalcomposi- tion of surfacewaters.

More precise data on therelationship betw eenthe qual-

it y of surface water and groundwater could have been obtained only from the monitoring of small experiment al catchments. However, in small catchme nt s in the Czech Republ ic,as inot hercountr ies,the contribu tion of ground- wate r discharge and qualit y to surface water was mostly neglected.Comparisons were made between the amount and quality of precip itation onthe one hand,and thesame for runoff on theotherhand, wit houtconsidering the vari- ability of the ground wat ercomponent in the surfacewat er.

In recent years, an investig ation has been sponsored by Grant 11310005 of theMinistry of Educati on of the Czech Republic'Mat erialandenergyflowsin theupper parts of the Earth', and this has been carried out within the 5th FrameworkProgrammesponsored by the Europ ean Union. The LOWRGREP proj ect 'Landscape-useoptimisation wit h regard to ground water resourcesprotection in mount ain hardrockareas'was intended to assess the contribution of groundwater impact on the degreeofacid ification of sur- face waters.

Method of data processing

The select ion of test siteswasthefirst step of the work.For this reason, datafrom the experimental small catchment network GEOMON (Fottova 2000) have been used. The degree of acidification in singlecatchm ent sis controlledby groundwater to a varying extent.The comparison of pH input, represented by atmospheric precipitati on and throughfall, and the output, represent edby pHandalkalin- ity of surface runoff,was usedto assess the degreeof resis-

NGU-BULL 439 ,2002 - PAGE 10 0 Z. HRKAL,J.BUCHTELE,E.TlKKANEN,A.KApAH O

e

trvrty of individual catchment s against acid atmospheric deposition. It was found that the greater the difference between thepH of atmospheric wat er and in run off anda higheralkalinityin surface wat er,the greaterwas the buffer- ing capacityof thehydrogeological environmentand conse- quentlyitsresist ance againstaciddeposition .

However,the basic informationconcerning the qualityof groundwa terswas still missing when assessingthe degree of groundwa te r impact on the final chem ist ry of surface water.Monito ring of the groun dwater quality wit hin the LOWRGREP project comm enced in two small catchments (Jezeri and NaLizu,see Fig.1)as late as in the beginningof the year2001.The first resultsfrom these localitiesrevealed that theground water has a morealkaline reaction that the surface water and, consequent ly,the ground wat ershould restraintheimpact of 'acid flashfloods'on the pH of surface waters.On the other hand, itis obviousthat the chemistryof groundwaterdependsclosely on the type of host rock envi- ronment.lnother words,the pH of groundwaterconfinedto granite will differ from that,for example,in serpentinite.

Therefore,the chemicalcomposition of surface waterdoes notdepend only onthe quantitativeparameter,i.e.the pro- portion of groundwater in thetotal runoff,but alsoon the qualityof thegroundwater.

The workwas carried out in two main stages; first ly,a qualitative assessment,which in turn provided datafor a quantitative analysis. The quantitative hydrogeologica l analysis was aimedat an assessment of the cont ributionof baseflow,representing the ground water discharge in the totaI runoff.

The firstestimateofquantity ofthe baseflowis derived fromCasta ny's meth od(Castany etal.1970). Thiscalculates the long-term,groundwa ter runoff assessment in two steps.

First,the arithmetic average from a 30-day period of mini- mum total runoffin each hyd rolog ical year expresses the low est year's runoff. Then, the long-term ground wate r

• Lys in. and PluhuvBorcatchm ent in theSlavkovskyforest

assessment is based on the median from these arithmetic averages.Cast any et al.(1970) are of the opinion thatreliable results can be obtained from a seriesof measurementsover a minimu m of 10 years,whereas currently the longest period of monitori ng extends onlyover 5 years.Consequently,the presented result s should beviewed withsome caut ion.

Toincorporateamoreprecise baseflow assess ment,the SACRAMENTa soil moist ure accounti ng model has been used (Burnash 1995). This model,in combination with the Anderson snow model(Anderson 1973),enables continuous simulat ionsto be carriedoutover a period of severalyears. For simulations of the annual rainfall-runoff process,the dailytime seriesare usually used.This is a conceptual water balancemod el with lumped inputs,with the possib ilit yfor its implementation inasemidistributedmode.

There are altoget her six runoff componentsgenerated by the model:

DIR- direct runoff,from thosepart s of the basin which become impervious aftersaturation,

IMP - the runofffrom the permanentlyimpervious part of basin,

SUR- surfacerunoff, IN - interflow,

SUP _.supplementary baseflow,i.e.,essentiallythesea- sonal component of baseflows,

PRM- primary baseflow,i.e.,the long term part of base- flow.

Thedailyprecip it ation and temp eraturedatatypicalfor the catc hment areahavebeenused asthe inputdata.The model runoff simulat ionwas then calibrated to the mea- sured surface runoffdata andthe model assessment of the baseflowcompa red withthe minimum runoff data.

The quantitative part of the data processing was fol- lowe d by analysis of the groundwaterimpact on the final chem ical composition of the surface flow.The follow ing meth odwasusedto express theimpact of groundwate ron thechemistry of the surfacerunoff.The hydrogram of the total runoff hasbeen separated into threepart s.One part includes theperiod when theground water discharge con- sti t utes at least 50% of the tot al runoff and when the groundwater chemi stry hasmost effect on the quality of surface waters.The oppo sitecaseis representedby a period when the contr ib ut ion of groundw at er discharge in total runoffdecreased below 25%.In such a case,the qualit y of at mo spheri cwater plays a decisiverolein the qualit yof the tota l runoff.The period during which the contribution of grou ndwa ter discharg e in total runoff varied between 25 and50%was considered amixed period in which none of the explore d parametersplays a decisive role.Comparison of singlepH measurement sinsurface water with the corre- sponding act ual water discharg e was used as the initia l information in the data processing.Seasonal variations in the pH of atm ospheric wate rsexpressedas monthly aver- ages were treated separately.

18'

Slovakia Poland

• Jezericatchm ent

"* NaLizucatchment

I.'

:~Prague CZECHR£J>UBLIC

,....""~. . . . .",,,;;l 00 km N

=

*

o

~ ^{Sum ava.M Is.}

Fig.1. Location of thetest sites.

Z.HRKAL,J.BUCHTELE,E.TIKKANEN,A.KApAHO&J.SANTRUCEK NGU-BULL43 9,2002 - PAGE 101

Table1.Resistanceof individual catchments within theGEOMONnet- work to acidification expressed asa relationship betweenthepHof rainfalland pH of runoff.

Selection of test sitesfrom GEOMON smallcatch- ment network

The process ofacidifica tionin the Czech Republi chasbeen mo nitored in 44 small catchmentsoftheGEOMON syste m (Fig.1).Each ofthesecatchment s representsadifferent geo- logical,morphological or vegetatio n type. They also differ from eachother in the intensity ofimpactsof at mospheric deposit ion. The method ofdata collection and assessment ofthe hydrochemical budget andelementflow corresponds with international standards,and the result s achieved are thereforecomparable withlocalitiesabroad.

As follows from Table 1, all studied catchments are affected by acidat mosp heric deposition.The averagepHof at mospheric precipit ation was always below 5, independent of the posit ion of the localit y.The long-term arit hmet ic meansof pHin throughfall are alwayslowerthanthosefor precipitation at the same locality.Thedifferencesbet ween the pHofprecipitation and throughfall areat theirhigh est in the vicinityof the sourcesof the pollut ion.

As follows from this five-year mon it orin g and collect ion ofdata,the nat ureof thegeologycausesvariousresistance to acidification.Thediffer encebetween pHofat mospheric precipit ation orthrou ghfall and pH of surface runoff was used as a parameter expressing the deg ree of buffering against acidi fication. Using this parameter, the stud ied catchment s canbedivided into differentgroup s characteris- ticof low,medium orhigh resista nce(Table1).

Tw opairs of experimental sites have been selected on thebasis ofthe above-mentione dresults.The first is repre- sente d by the Jezerf and Na Lizucatchment s,characterised byanidenticalgeological background butdifferent intensi- tiesofimpactof acid deposition.The catchments Lysina and PluhuvBor(Kram & Hruska 1994),an example of extreme differences of lit hological composition (acid granite at Lysinaand ultrabasic serpentinite at Pluhov Bor),represent the second pair of testsit es.

Results from selected catchments

TheJezeri and Na Lizucatchments

Thesetwo localiti es were selected in order to provide evi- dence forthedegree ofresistanceof the geologica lenviron- ment against the prolonged impact of acid atmospheric deposition.It isnoteworthy that bot hcatc hmentsare very similar toeachot herasfar astheir geologyand mor phology areconcerned.Bot hliein mountainareasatalt it udesrang- ing bet ween 475 and 924m (Jezerf) and 828 to 1024(Na Lizu) ma.s.l.,and both areunderlain by Prot erozoic meta- morph ic rocks,paragneisses in particu lar.How ever, they dif- ferconsiderably in theintensit y of anthropogenic impact.

The Jezeri catchment lies in the Krusne hory Mts and belongstothe so-called 'Black triangle',i.e.,the territory of the easternpartofGermany(formerGDR),the southwestern part ofPoland and the northern partofthe Czech Republic, with the highest airpollut ion inEurope.The Na Lizu catch- mentis situated in the Sumava Mts.This territoryis consid - ered to be one of the c1eanest parts of the Czech Republ ic.

EventhoughthepHvalues of precip it at ion on bothcatch- ment sare verysimilar, thelargediff erence inthroug hfall pH valuesisquit esignificant.

Comparablegeolo gy and morpho logy are responsible forsimilar runoff conditionsinboth catchment s.Themodel determination of baseflow in theNaLizucatchment(5.2lis) correspond s well wit h the baseflo w est imate d using Castany'smethod(4.5lis).However, some discrepancy exists between modelbaseflowestimation (8.0lis)andCastany's met hod assessment (4.5 lis)in the Jezerf catc hment. The specific runoff of groundwater in the Jezerf and Na Lizu catchmentsis 3.1I/s/km2and 5.2IIs/km2,respectiv ely. No differences exist in the groundwater runoff coefficien t (share of groundwater discharge in thetot alrun off) ; inthe Jezerf catchment this is equal to 42%, whereasinthe Na Lizu catchment it amounts to 41%.

There areconsiderabledifferences,however,exists in the chemical compositionof surfacewater(Fig.2).Alt hough the average pH valuesof atmospheric water from the period 1995-2000in both catchmentsare more or less identical(pH 4.5-4.6),the qualityof surfacewateris very differen t.The pH of the surface runoff in theNaLizucatchment,c.7.0,is extra- ordinarilystableduringthe courseof the year.Inthe case of the Jezerfcatchment, the average pH isone unit lower. A close relat ionship between the surface wate rquality and water dischargecan be observed in both of these catch- E::l

:c ..

'"

.;;;c Cl c '" 0 GO . - u ~

'iij

~~

GO u

~

'"

2.35 2.27 2.43 2.67 1.04 1.12 1.22 1.58 1.58 1.84 I .2c

a.~

c ~

~:§.

3: u

~ GO GO ~ ..0 a.

GO J:

u a.

c~:t:

GO 0

:t: c

.- :>

'C ~

-0.52 0.52 0.64 0.78

J : = a.:!c~

GO Cl

GO :>

3:0

~ ~ ..o~GO~

GOJ:

u a.

c ,

~:t:GO 0 :t:_.- c_:>

'C ~

2.37 2.38 2.89 1.45 2.11 1.82 1.68 1.97 2.3

2.84

J:a.

GO

~15GO c

> :>

'"

4.14 -0.12 5.14 0.29 4.8 0.74 5.18 1.38 5.53 5.76 6.03 6.28 6.12 6.66

7.33 7.05 6.72 7.05 4.08 3.65 4.21 4.6 4.15 4.36 4.26 4.85 4.06 3.8

4.49 4.68 4.34 4.16 4.66 4.62 4.16 4.4

4.7 4.45 4.62 4.49 4.64 4.81 4.7 4.54 4.82

4.66 gran ulite parag neiss granulite marble gra nite granite paragneiss gra nite

serpentinite sandstone paragneiss amphibolite paragneiss paragneiss gneiss

'"

Clo '0GO Cl

Lysina Loukov Udvou loucek Uhlirska Lesni potok Jezeri Spalenec Modry potok Cervik Polomka

Salacova Lhota NaLizu Anensky potok Pluhuv

bor

NGU-BULL439, 2002- PAGE 102 Z.HRKAL,J.BUCHTELE, E.TlKKANEN,A.K,ii,PAHO&J.SANTRUCEK

Jczcr i catc h me nt ;'\a Lizu catchmcnt

7.0

2000 r---,---~ 7.5

6.5

pH 5.5

7.5 60

7.0 50

40

6.5 _~

l 30

6.0

20

5.5 10

5.0

2000 1995 1996 1997 1995 1999

7.5

I

\ .'--

' /

1999

.\ I·

i \

I I I

" I' . /". j -v .\ •\ .

'/ ....1 _I

-.- pH prec ip it ation

I

1998

o ^totalrunoff

. baseflow

t,; ...\ !';

r: . I

.

.

\ I <

./

1997 1996

I -

I

I'

I'v' V 1..1 '.i

',...; It \'

1995 40 60

60f----.,---f f - - - - -- --+- i I--~H '20f - - - -

140r - - - -- - -- - - -- -,r--- ---,

'001 - - - -

20

7.5

4.5

3.5 6.5

pH 5.5

1995 1996 1997 1995 1999 2000 1995 1996 1997 1998 1999 2000

Fig.2. RelationshipbetweenpH runoff and total runoff and baseflow,Jezeriand NaLizu catchment s.

ments.A sharp drop in pH occurs when the proport ion of the baseflowdecreases.ThispH drop is more abrupt at the Jezerf catchment,downto 5.1-5.5, incomparison wit h values of only6.0-6.3at theNa Lizu catchment.

There aretwo possib lesolutions toexplainthese diffe r- ences:

1.Soilsin both catchments arepoor in carbonateminer- als.lfany were originallypresent,theyhave long sincebeen dissolved due to theinfil t rat ion ofacid rain.Aluminosilicates in soilplaythe main role in the bufferingofH+ions.Astheir dissolutionis controlledkinetically,thebest buffe ring prop- erties of soil areattained during dry periods,i.e.,at the time of the highestproport ion of groundwaterin surface runoff.

Aftertorrent ial rains or snow melting the surface wateris more acid, not only for the higher proportionof atmospheric water in surface runoff but also for the shorter time of hydrolysis of soil minerals.

2.Throughfallshave a greater im pact on groundwater acidification than precipit ations.Acid gases (sulphur and nitrogenoxides,and perhaps also hydrogen fluoride)are to a large extent adsorbed on the needles of conifers and tog ether with dry depo sit ion arewashed out by rain and infiltrate into soil. Movement of adsorbed gases and dry deposit ion is strictl ylimited and theyremainin the vicinity of their sources.Concentrations of H+ ions are tentimes higher in throughfallthan in precipitat ionsat Jezeri.lnspite

of the sameacidi ty of precipitationatboth catchments,the fast groundwa ter circulat ion and slow dissolution of soil minerals cannot fully neutralisethe huge amount of acids in thethrough fall.

The Pluhuv Bar a nd Lysina catchments

Both catchmentsare affectedby atmosphericdeposit ionto the samedegree.Onthe other hand,they are marked lydif- ferent as regards geology and hydrogeology.Both catch- mentslie intheSlavkov sky lesupland inwestern Bohemia (Fig.1)and are closeto each ot her.Consequently,the cli- matic and morph ological cond it ions and vegetation are identi cal in bot h catchment s.The area of each catchmentis about 0.2km'and the altitude varies between 800 and 950 m a.s.l.Both catchmentsare largelycovered by spruce forest.

The basic difference lies in the bedrock geology.TheLysina catchment occurs exclusively in granit e of the Kynzvart Massif,and the localsoil has the characterof peat gley.The Pluh uv Bor catchment is underlain by serpentinite that is characterised byclayey weathering and very low permeabil- ity.

The results of the precip it ation/runoff model at the Lysinaand Pluhuv Borlocalit ies are lessaccurate relative to those of the preceding pair of catchments. This fact is demo nstrated bythe lower degrees of correlation between themeasured and the simulate dvalues,whichfor the Jezeri

Z.HRKAL ,J.BUCH TELE,E.T1KKANE N,A.K.4PAHO &J.SA NT RUCEK NGU-BULL43 9, 2002 - PA G E103

PluhuvBur ca tch me n t Lysin a catc h me n t

20, - - - -- - - - -- - - - - - ,

20 , - -- - - - - - - - - - - -- - : - -- - ---,

15

~ 10

7.5

6.5

15

~10

o totalrunoff . ba s e flow

- pHrunoff

5.0

45

:I:

C.

199 5 1996 199 7 199 R 1999 2000 1995 1996 1997 199R 1999 2000

\ .

5.0 t, ,

~ ~ ' \ .

4.5 " j', .''. _ ~/ ;.J

\ '\ . ... , \ . -...., I

J ....,.' "

4.0 'J

2000 1999 1998

piIprecipi tation- pllrunoff

199 7 1996 7.5

7.0

6.5 6.0 :I:c.

5.5 5.0 4.5

4.0 3.5 1995

.'.

2000 1999

/\. .

,

/.

. .\

~_'J

..

' < >.

r.

1996 1997 199R 7.5

3.5 1995 6.5

5.5 70 8.0

:a

Fig.3. Relation shipbetweenpHrunoff and tot al runo ff andbasefl ow,PluhuvBor andLysinacatchments.

and Na Lizucat chments were0.89 and 0.86,respectively, whereas at theLysinalocalit yitwas only 0.57 andat Pluhuv Boreven less (0.5).Themodel result s suffe r from thepoor quality of the abundant data on precipitati on.Thesedata come from thearea of MarianskeLazne,and are not suffi- ciently representativeto characterise the act ual precipita- tion in the model region.How ever, anot her analysisand interpretation of the results showed that the accuracy of simulat ionis sufficientin thiscasetomeettheproject objec- tives.

The low perm eabilit y of serpenti nite is reflected in the runoffcondit ionsof thePluhuv Bor cat chme nt. The mod- elled groundwa ter discharge constit utes only 19% of the total runoff.The specificdischarge of the ground water is also low,amo unting to 1.8 lis/km' during the monitored period.

Themodelled, specificgroundwa ter runoff in the Lysina catchment(3.3I/s/km')inclu di ng its runoff coefficient (22%) is,duetothecompletelydifferent geology,greaterthanthat in the Pluhuv Bor catchment.Themodeldetermination of baseflowin theLysinacatchm ent (004lis) corresponds fairly wellwit h the baseflow est imated using Castany'smethod (0.7 l/s).

Hydrogeological conditions considerably affect the quality of waterdrainedfrom both catc hments.Although thecontr ibut io nofgroundwa te r runoff issmallwit hrespect

tothe tota l runoff,the geochemicalcharacte roflocal rocks at PluhuvBorisrespon sibl efor ahighresistivit y againstacid deposition.Even thoughthepHofat mosphericwateris only 4.7,thesurfacewate r maint ainsa neut ralor slig ht lyalkaline react ion through the wholeyear. The valueof pHofsurface wate rvariesbetween 6.3and7.95.Themainreasonfor this is ahydrolysisof basic silicates,e.g.serpenti ne.Their dissolu- tionis oftencongr uent,much faster than the weatheringof acidicrocks, and is able tobuffer free H+ions.Fig.3 demon - strates a fair relationship betw een the proportion of groun dwaterdischarge andthe totalrunoff, includi ng pH,in surfacewater.

The inf luenceof groundwat er on the chemistryof dis- chargedsurfacewateris obviousin theLysina catchm ent. A similar trend exists here too, i.e., the close relationship bet ween the pH of surface water and the proportion of groundwater runoffinthe totalrunoff.Although theloading of acid at mospheric deposition in the Lysina catchment is similar tothatof thePluhuv Bor catchm ent,the quality of surfacewate r in the catc hmentsiscomp letelydiff erent. The Lysinarunoffisthemost acidicamo ngall the investigated catchm ent s (Table1),which is obviously duetothe lit hology of thesoil profile.Thegroundwateritselfin theLysina catc h- ment isveryacid because of humicacidsreleasedfromthe gleyhorizon rich in peat, and con sequentl y it isnot ableto neutralise acid rainfall. Thisfact is parti cularly evident in

NGU-BULL 43 9 ,2002 - PAGE 104 Z. HRKAL,J.BUCHTELE,E.TIKKANEN,A.KApAHO&J.SANTRUCEK

Fig.4.Trends in annualcoalproduc tionin thenort hernCzechRepub lic (Mostbasin).The smallinset boxshow sthe nationw ideindu st rialem is- sions ofSO,(from Novaket al.2000).

consequently in a reduction of emi ssions.The prolonged impact of acid atmospheric deposition result ed in a decreasein the buffer capacity of soil of the Krusne hory crystalline complex.Consequently,the drained waterssuf- fered from adecreasein the concentration ofHCO;ions and a very slowdecreasein theconte nts of SO."ions(Fig. 5).

A conspicuousdecreaseinthe buffe rcapacit y of the soil layer of theKrusne hory Mts.hasrecently beensupportedby a study of the Jezerfcatchment(Novaketal.2000).Isotope analysesof sulphurin water entering andleaving the catch- ment show that the sulphurin the runoff comes from the soil horizon.Consequently,it representsasecondary source that wasaccumulated over long decades and from which the sulphur is gradually leached andwashedout. The study by Novak demonstratesthat approxim ately30%of thetotal content of sulphur in drained wat er comesfrom organic matterconfined to the upper humic soil horizon.

The negative roleof theSO/, storage in the weathered substrata has also been demonstratedin theGermanexper-

IndustrialSO.ernessons

-

..

"""

hJiJ'

~ '~

2000 1975 1925 1950 Year 1900 1875 80

0>- ₇₀ enc

52 60

c

~ ⁵⁰

I

c

.Q13 30

:0

"0

e

C;; 10

0

0 0

1850

periods when the proportion of baseflow and the total runoff exceeds 50%.During this period when the surface waterqualityis considerablyinfluencedbythechemist ryof groundwater,the average pH in the Lysina catchment is equal to 4.3.

Discus sio n

The obtained results have shown that the degree of protec- tive power of the aquiferagainst acidificationdepends ona number of factors. An important factor is the composit ion of soilwhich isa product of naturalweatheringofthe bedro ck and the rate of buffering reactions.Neutral or weakly alka- line surfacewater at Pluhuv Bor shows that basic rocks can produce soilwit h a greater protective power against acidifi- cation,in spite of a low proportion of groundwaterin the surface water.

The second important factor is the distance betw eenthe monitored catchmentandthe sourceofthepollution.Some acidic gases(SO"NO,)are accumulated onconiferoustrees by adso rpt ion and then oxid ised to strong acids.These adsorbed gases,aswell as dry deposition,result in the heav- iest acidloading at any locality.

The third factoris the duration of exposure of the soil to acid rain. The soil composition,including the soil buffer capacity,may change durin g the course of time.The first step is a decalcification followed by ahyd rolysis of alumi- nosilicates.The mechanism of the hydrolytic reaction may change dependingon the acidityof the infiltrating water.

The Krusne hory Mts. have been exposed to unfavourable conditions already since the 19th century.

Mining for lignite and its combustion in power plants locat ed in the Krusne hory piedmo nt basins began already in 1860 and culminated in 1988 (Fig.4). Only in the last decadehas therebeen a decline in mining for lignite and

80 18

----~

70

60

~"§, 50

::J

e

:; 40 :t::"'

oe

.s

20

---~ --~­

; \

I :

---_:i-':~:~::-... : 'n-I\----\ . .

~ ^{: I}

- + - - runoff . throughfall - - precipitation

runoff

• ••• through fall precipitation

(c oncentra tions)

(linear trend) 16

14

12 c .2 10 !§

'0.

'u

'"

8

E:

<::

Cl

6 E

4

2

o

1996 1997 1998 1999 2000 2001

Fig.5.Trend sinSO.concent rat ionsin theKrusnehory Mts.,1996-2001.

Z. HRK AL ,J.BUCH T ELE, E.TIK KA N EN,A.^KApAHO&J.SANTR UC EK NG U - B U LL 439, 2002 - PAGE 105

imental catchment Lehstenbach in nort hern Bavaria (Lischeid et al. 2000,Manderscheid etal. 2000).

Rock massifs suchasthe Krusnehory gneisses,whichare more resistant against acidification,can forlonger periods of time protect groundwatersagainstthe impactof acidrains.

On theother hand, after areduction in the impactof acid deposition,it may take along timetoreverttothe orig inal conditions and the rockmassifmay,in cont rast,maintainor support the acidification.Groundwater acidificatio nin such aquiferswill not be easily reversed by a decreasein 50/

deposition because ofthe releaseof previouslystored50/-. Thisappears to be the majorreasonfortherecorded differ- ences in groundwater qualit y between the Jezeri and Na Lizu catchm ent s.

Regardlessof the reasonableharmony between corre- latedrunoff parameters and chemical compositionof water, an unexpecteddiscrepancyhasbeenrecord ed in some peri- ods. The period between February and June 1997 in the Jezeri cat chmentmay serve as atypicalexample ofsuchdis- cord. A flood wave associated wit h snow melt ing and increasedrainfall duringMarch led to a decreaseinthe share of groundwaterin the totalrunoff.This condit ion, however,is surprising lynot reflect ed in a loweringof pHin the surface water that remainedmore or less stab leat about 5.4. This fact can be explained bythe chemicalcomposi tio nofthe rainfall because the pH of atmosphericwate r inthe same period graduallyincreasedby two orders of magnitud eup to 6.0.Thismeansthat therewas aperiod when the infilt ra- tion ofrainfall had an unexpect ed alkalinereact ion.

Thisexample clearlydemo nstr ates the complexityof the whole probl em, which cannotbe simply reduc edtotherela- tion ship between therock massifandwater.Chemical analy- sisofa watersample from a st reamalways represents amix- ture of surfaceandgroundwa t eror evenat mosphericwater, and theirmutual proport ions may vary con siderably.On the ot her hand,it is obvio us thatthe volumeof ground water in runoffremains oneof themost impo rt ant factors inf luenc- ingthefinit e quality of thedrained water from the catch- ment.Therefore,the degree of grou ndwater acidification should not beneglected.

Ackno wledgements

Iwould liketo than k Drs.David Banksand John Mat her fo r the ir helpful andconst ruct ive reviews,wh ichsig ni ficant ly improve d anearlierver- sio nofth is pap er; and alsoMrs.D.Fottovafo rthevaluab ledatafro m the GEOMONnetw o rk.

References

Ande rson,E.A.1973:NWSRFS Snowaccum ulat ionandablat io n model; NOAA Technical Memo ra nd um NWS HYDRO-17,

us.

Burnash,J.C.R.1995: The NWS River Forecast System - Catchme nt Modeling.ln.:ComputerMod el s ofWate rshed Hydrolog y (ed.by v.P Sing h), WaterResourcesPubli cat ions Colo.,p.311-366,ISBN No.0- 918334-9 1-8

Castany, G., Marg at,J, Alb inet, M. & Dellaroziere-Bouillin,O. 1970:

Evaluati on rapide de ressou rces en eaux d'une reg ion. In:Atti Conveg no Inte rna z.sulleacq uesout terra nee 1970,Palermo.

Fottova,D.2000: Assessmentofthe mass fluxin the sma llcatchment networkGEOM ON in Czech rep ub lic.-MS Annual Report,Czech Geolog icalSurvey.Prague

Hrkal,Z.1992:Acid ificatio nofgrou ndwate r intheBoh emian Massif.- NorgesgeologiskeundersekelseBulletin.422.97-102.

Hrkal,Z.&Fot tova,D.1999:Imp act of atmosp heric dep o sition on the gro undwate r qual ity of the Czech Republi c (in French).

rtydroqeoloqie.2.Orleans,France,39-45 .

Kram,P.&Hruska,J.1994 :Influen ce of bed ro ck geolo gy onelemen ta l fl-uxesin tw ofor ested catch me ntsaffec te d byhigh acidic dep osi- tion.Applied Hydrog eol ogy,Vol.2,No.2/94,50-58.

Lischeid,G.,Mor itz , K.,Bittersohl ,J.,Alewe ll,Ch.& Matzne r, E.2000: Sin ks ofant hro poge nic nitro gen and sulphat einthe Lehste n bachcatc h- ment(Fichtelgebirge)Lessons learntconce rning reversibilit y.-Silva GabretaVol.4p.4I-S0.Vimperk.

Mand erscheid ,8.,Schweisser,T.,Lisch eid,G.,Alewell,C.& Matz ne r,E. 2000: Sulfate poolsin the weat he redsubstr ataofaforested catc h- ment.-Soil ScientificSociety Ame rican Jou rna l64:1078-1082.

Novak,M.,Kirshner,J,W.,Gro scheo va,H.,Havel,M.,Cern y,J.,Krejci,R.,&

Buzek,F.2000:Sulp hurisoto pe dynam icsintwo Central Europ ean wat ersheds affec te d by high at mos phe ric dep osition of Sox.

Geochim icaetCosmochim icaActa.Vol.64.No.3.pp.367-383.2000. ElsevierScie nce.USA.