Characterization of groundwater humic substances: influence of sedimentary organic carbon

Characterization of groundwater humic substances:in¯uence of sedimentary organic carbon

R. Artingera,*, G. Buckaua, S. Geyerb, P. Fritzb, M. Wolfc, J.I. Kima

aForschungszentrum Karlsruhe, Institut fuÈr Nukleare Entsorgungstechnik, 76021 Karlsruhe, GermanybUFZ-Umweltforschungszentrum Leipzig-Halle, Sektion Hydrogeologie, 06246 Bad LauchstaÈdt, Germany

cGSF-National Research Center for Environment and Health, Institute of Hydrology, 85764 Neuherberg, Germany

Received 12 June 1998; accepted 4 December 1998

Editorial handling by R. Fuge

Abstract

A total of 35 groundwaters from 4 di�erent aquifer systems in Germany are investigated for their physico-

chemical properties, dissolved organic C (DOC) and humic and fulvic acids. Humic substances are isolated andcharacterized for their elemental composition, UV/Vis and ¯uorescence spectroscopic properties, size distribution bygel permeation chromatography (GPC) and 14C content. For isolation of su�cient quantities of humic substances a

mobile sampling system is developed based on a combination of reverse osmosis (RO) and XAD±8 adsorptionchromatography. One of the aquifer systems (Gorleben) covers a wide range of hydrogeochemical conditions,whereas the other 3 aquifer systems (Munich, Franconian Albvorland and Fuhrberg) have less diverse properties.

One speci®c feature of the Gorleben aquifer system is the presence of a very high DOC, which, in contrast to otheraquifer systems, contains considerable amounts of aquatic humic acid. This is attributed to the release of aquatichumic substances originating from sedimentary organic C (SOC) that is abundant in Gorleben sediments. Theresults show that aquatic humic substances from di�erent aquifer systems have dissimilar properties which di�er

from one another. Systematic di�erences are found among humic substances from di�erent regions of the Gorlebenaquifer system. Such di�erences are considered to be caused by the mixing of humic substances from the SOC.However, exact quanti®cation of such mixing appears di�cult because overlapping e�ects of di�erent geochemical

processes feigning a dissolution of SOC cannot be excluded. # 1999 Elsevier Science Ltd. All rights reserved.

1. Introduction

Humic substances are ubiquitous in groundwatersystems. They do not show a unique chemical struc-ture, but rather represent a group of organic com-

pounds with polyelectrolytic properties and resistanceto degradation under aquatic conditions. Due to theirlarge hydrodynamic size and their metal ion interaction

properties, they appear in natural water as humic col-

loids that are loaded with metal ions (Kim et al.,1996). Humic substances interact with non-polar or-ganic substances as well. For these reasons humic sub-stances play a crucial role for the geochemical

behavior of non-polar organic pollutants, heavy metalions and a multitude of radionuclides, especially multi-valent actinide ions (Manahan, 1989; Kim et al., 1989;

Kumke, 1994).Humic substances are divided into two fractions,

namely, humic acid (HA) and fulvic acid (FA). Both

fractions exhibit hydrophobic properties at low pH,

Applied Geochemistry 15 (2000) 97±116

0883-2927/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.

PII: S0883-2927(99 )00021-9

* Corresponding author.

E-mail address: [email protected] (R. Artinger)

Table

1

Sampledgroundwaters

andtheirbasichydrologicalparameters,

chem

icalcomposition,DOC

concentrationand

3H

content.

nd=notdetermined

(dueto

oxygen

contact

during

groundwatersampling)

Depth

(m)

Sedim

enttype

Tem

p.

(8C)

pH

Eh

(mV)

Conduct.

(mS/cm)

Oxygen

(mg/L)

Na

KMg

Ca

(mmol/L)

HCO

3ÿSO

2ÿ4

Clÿ

3H

TU

aDOC

HA

(mgC/L)

FA

Gorleben

(coarse,

sand,clay)

Recharge

GoHy±181

15±18

Weichsel

9.6

6.4

29

0.13

0.1

0.35

0.04

0.10

0.27

0.30

0.34

0.19

39

0.5

0.009

0.14

GoHy±411

17±20

Weichsel

9.4

7.0

ÿ10.27

0.1

0.47

0.06

0.16

0.82

1.18

0.53

0.35

21

2.2

0.022

0.70

GoHy±421

10±13

Weichsel

9.3

6.0

53

0.35

0.2

0.92

0.08

0.28

0.53

0.15

0.82

1.04

20

1.9

±0.53

GoHy±611

21±24

Weichsel

8.9

8.4

72

0.20

<0.1

0.47

0.02

0.09

0.84

1.05

0.33

0.38

8.0

1.4

0.11

0.46

GoHy±711

6±9

Weichsel

92

6.0

398

0.19

4.5

0.45

0.07

0.28

0.38

0.15

0.53

0.34

29

0.9

(0.001)

0.35

Transition

GoHy±182

70±73

Elster

102

8.0

ÿ48

0.13

<0.1

0.24

0.03

0.05

0.54

1.04

0.04

0.20

<0.3

0.8

0.126

0.13

GoHy±201

30±35

Weichsel

9.6

7.8

121

0.17

<0.1

0.33

0.02

0.09

0.49

0.75

0.24

0.29

<1.1

0.9

0.05

0.40

EnhancedDOC

GoHy±412

65±68

Elster

10.7

7.6

92

0.36

<0.8

2.50

0.09

0.11

0.51

3.46

<0.01

0.51

<0.2

7.6

1.68

2.6

GoHy±492

35±38

Saale

9.6

8.0

128

2.15

<0.1

21.7

0.08

0.07

0.32

11.6

0.73

8.39

<0.2

127

114

8.9

GoHy±572

70±73

Elster

12.2

8.8

17

0.55

<0.1

5.74

0.03

0.04

0.08

4.74

0.01

0.72

0.5

14.4

9.4

3.2

GoHy±573

134±137

PraÈelster

14.2

8.0

ÿ32

1.63

<0.1

18.3

0.09

0.10

0.23

7.97

0.02

10.3

<0.2

97.2

60

17

GoHy±612

121±125

Saale

10.9

8.4

35

2.06

<0.1

19.8

0.08

0.15

0.56

13.2

0.30

6.59

0.5

184

171

9.2

GoHy±851

57±40

Elster

10.8

8.2

ÿ52.37

<0.1

Z.9

0.08

0.04

0.24

9.85

<0.01

12.7

0.4

169

140

6.7

GoHy±2211

83±85

Elster

12.1

8.1

31

4.99

<0.1

47.0

0.14

0.09

0.35

9.51

0.20

37.7

0.3

93.9

70

22

GoHy±2227

128±130

PraÈelster

14.4

7.8

ÿ58

4.30

<0.1

41.8

0.33

0.20

0.53

7.90

0.32

36.7

<0.3

73.4

58

5.9

R. Artinger et al. / Applied Geochemistry 15 (2000) 97±11698

Channel

Brines

GoHy±193

220±223

PraÈelster

12.9

6.8/7.1

b137

110.8

<0.1

2018

6.47

39.6

25.4

3.85

29.9

1974

<0.2

32

±0.50

GoHy±514

235±238

Elster

16.9

6.3/7.0

b162

170.9

<0.1

4870

20.3

82.3

26.5

2.09

52.9

4766

<0.3

1.6

±0.20

GoHy±653

216±219

Elster

18.9

6.5/7.1

b134

154.3

<0.1

4014

18.8

68.2

23.6

2.96

46.0

4079

<0.3

1.3

±0.24

Uplift-M

ixing

GoHy±341

10±13

Weichsel

8.6

7.0

140

4.84

<0.1

43.0

0.03

0.44

1.30

4.25

0.15

42.3

0.4

64.0

41

15

Munich

(lim

egravel)

MS±UP±178

0.5±23

Wu Èrm

/Riû

9.3

7.2

523

0.63

8.1

0.17

0.06

0.89

2.13

5.23

0.25

0.91

37

0.6

±0.12

MS±U1±630

6±18

Wu Èrm

/Riû

9.4

7.3

634

0.63

8.8

0.75

<0.01

0.88

2.29

5.38

0.26

0.75

34

0.9

±0.34

MS±KP±916

2±7

Wu Èrm

/Riû

9.0

7.3

330

0.67

5.6

020

0.06

0.87

2.34

5.75

0.25

1.22

36

0.7

±0.12

FranconianAlbvorland

(sandstone)

Laibstadt

76±144

Keuper

12.9

6.3

594

0.26

6.0

0.08

0.16

0.34

0.86

1.92

0.24

0.07

<0.4

0.5

±0.06

J-S-T

III

110±166

Keuper

18.6

6.8

283

0.57

<0.1

0.21

0.51

0.85

1.99

5.10

0.92

0.04

<0.7

0.1

±0.01

GredingI

80±92

(Lias)-K

euper

18.4

7.3

172

0.75

<0.1

0.45

0.83

0.96

2.26

5.79

0.15

0.03

<0.8

0.4

±0.03

GredingII

83±143

(Lias)-K

euper

19.1

7.4

185

0.42

<0.1

0.19

0.50

0.69

1.51

4.54

0.06

0.03

<0.7

0.3

±0.03

Beilngries

80±88

Keuper

15.6

7.4

41

0.52

<0.1

0.74

0.78

0.69

2.22

5.08

0.57

0.06

<0.5

0.4

±0.04

Fuhrberg

(sand)

FF±OW

1.3

below

forest

9.4

4.3

nd

0.24

nd

0.50

0.08

0.10

025

0.01

0.82

0.69

18

6.1

±1.3

FF±OA

1.8

below®eld

10.0

4.8

nd

0.42

nd

0.55

0.46

0.41

0.93

0.02

0.63

0.67

16

16.8

±4.0

FF±T1-4

4Weichsel

10.0

5.8

nd

0.66

nd

0.86

0.71

0.58

1.81

0.24

1.25

0.98

17

11.9

±3.0

FF±T3-11

11

Weichsel

10.0

5.5

nd

0.53

nd

0.45

0.07

0.73

1.60

0.21

2.34

0.88

18

4.4

±0.67

FF±N5-12

12

Weichsel

10.3

5.0

nd

0.33

nd

0.38

0.42

0.26

0.80

0.10

1.02

1.01

22

6.9

±4.5

FF±N10-4

4Weichsel

10.0

5.3

nd

0.54

nd

0.37

0.45

0.47

1.78

0.26

1.00

0.92

15

11.5

±3.2

FF±N10-6

6Weichsel

10.0

5.9

nd

0.56

nd

0.35

0.45

0.50

1.96

0.45

1.04

1.06

16

7.9

±2.0

FF±N10-12

12

Weichsel

10.0

5.9

nd

0.45

nd

0.68

0.27

0.32

1.48

0.55

1.70

1.49

32

11.3

±1.8

FF±N10-14

14

Weichsel

10.0

6.0

nd

0.51

nd

0.75

0.36

0.34

1.34

0.85

1.64

1.31

36

9.8

±1.8

aTU

3H

unit(1

TU=

0.118Bq/L).

bpH

correctedaccordingto

Runde(1993).

R. Artinger et al. / Applied Geochemistry 15 (2000) 97±116 99

which are used for the isolation of aquatic humic sub-stances by chromatographic separation on the non-

ionic acrylic ester resin XAD±8 (Aiken, 1988;Thurman and Malcolm, 1981). The part of DOC thatis not sorbed on XAD±8 at low pH is classi®ed to be

made up of hydrophilic compounds. HA and FA showdi�erent characteristics with respect to, amongstothers, the elemental composition, functional group

content, hydrodynamic size distribution and spectro-scopic properties (Kim et al., 1990; Stevenson, 1982;Steelink, 1985; MacCarthy and Rice, 1985; Beckett et

al., 1987; Pullin and Cabaniss, 1995; Chin et al.,1994).Important aspects for the role of humic substances

in transporting pollutants along with a water path are

their generation, migration behavior, residence timeand stability against degradation. If the stability ofaquatic humic substances is su�ciently long, their mi-

gration behavior often follows that of an ideal tracerand, thus, 14C measurements can be used for ground-water dating. Recent investigations demonstrated that

radiocarbon dating can contribute to the understand-ing of their migration behavior and residence time ingroundwater systems (Geyer et al., 1993; Geyer, 1993;

Geyh and BruÈ hl, 1991; Wassenaar et al., 1991;Pettersson and Allard, 1991; Purdy et al., 1992).However, in the presence of 14C free organic depositsthis dating method may result in too high groundwater

ages, if it is assumed that all the dissolved humic sub-stances originate from the surface (Artinger et al.,1996). Therefore, knowledge of their origin is necessary

to reconstruct the migration behavior of humic sub-stances in aquifer systems with organic deposits.In this paper aquatic humic substances from 35

di�erent groundwaters samples of 4 di�erent ground-water systems in Germany are quanti®ed and charac-terized. Three of the aquifers investigated haverelatively well known hydrological and geochemical

conditions (Munich, Franconian Albvorland andFuhrberg). The fourth aquifer (Gorleben) investigatedhas organic deposits, a very complex geohydrology

and a wide range of geochemical conditions. The dis-cussion focuses on the applicability of di�erent charac-terization methods for the distinction between HA and

FA in®ltrated via groundwater recharge and thoseoriginating from sedimentary organic C (SOC).

2. Aquifers and investigation

Four di�erent aquifer systems in Germany (Munich,

Franconian Albvorland, Fuhrberg and Gorleben) areused for the investigation. The sampled groundwatersare shown in Table 1 together with their characteristic

parameters. The aquifer systems are described as

follows:

Munich. This aquifer is located in the eastern out-

skirts of the city of Munich in southern Bavaria. It

is an uncon®ned lime-gravel aquifer and consists of

quaternary ¯uviatile alternating sandy, ®ne and

coarse pebbles. The sediment is mainly calcium car-

bonate and dolomite (>98%) and practically free

from organic deposits. The DOC content of the

groundwater varies from 0.3 to 1.5 mg C per liter

(mg C/L) according to season (Zahn, 1988). From

this aquifer 3 samples were taken from the top of

the groundwater level. All 3 groundwater samples

are saturated with O2 and contain 3H in concen-

trations of about 35 tritium units (TU), re¯ecting a

contamination by atmospheric nuclear testing. This

aquifer provides data for humic substances in

young recharge groundwater (<40 a) without inter-

ference by the in situ generation from sedimentary

organic C (SOC).

Franconian Albvorland. This aquifer is located in the

Franconian Albvorland in northern Bavaria. It is a

con®ned sandstone aquifer of the Upper Triassic

Keuper sequence and hydrogeologically well investi-

gated (Rietzler, 1979; Eichinger, 1981). The aquifer

extends over a distance of about 25 km to the SE

and declines moderately with an average water

table gradient of 0.8-. The sediments are free from

SOC. The groundwater is found to be of

Pleistocene origin (>12 000 a) at the end of the

¯owpath (Geyer, 1993; Eichinger, 1981). A mixing

with younger water along the groundwater ¯ow is

not probable since the aquifer is covered by thick

clay layers of the Upper Middle Keuper

(Feuerletten). This is also supported by non-detect-

able 3H concentrations (cf. Table 1). The aquifer is

anaerobic beyond 8 km of groundwater recharge

and SO4 reducing beyond 18 km. The DOC concen-

tration varies between 0.1 and 0.5 mg C/L. This

aquifer allows the characterization of HA and FA

in reducing groundwaters with ages exceeding

12 000 a presumably without interference of in situ

generation from SOC.

Fuhrberg. This aquifer is situated about 30 km N of

the city of Hanover in the drinking-water recovery

area of Fuhrberg. The aquifer consists of

Quaternary ®ne and coarse grained, and partly

gravel sands of 20 to 30 m thickness. The free

groundwater surface is in sandy podzols with a low

humus content. The groundwater samples are all

young (<40 a) as seen by the high 3H concen-

trations (>15 TU) and mass balance calculations

(BoÈ ttcher et al., 1985). In¯ux of DOC with ground-

water recharge along the main ¯owpath varies with,

amongst others, local vegetation conditions, includ-


ing variations in agricultural activity. The DOC

concentration varies between 17 mg C/L at ®eld

sampling sites near the surface and 5 mg C/L at a

depth of 11 m near the waterworks well. This aqui-

fer allows the characterization of humic substances

from groundwaters under recharge conditions, i.e.,

young, oxidizing groundwaters with relatively high

DOC concentrations.

Gorleben. This aquifer system is located at

Gorleben in the Northern German Plain (Lower

Saxony). The aquifer extends down to 280 m below

ground surface and is situated in the rock covering

and surrounding a Permian salt dome under

exploration for construction of a nuclear waste

repository. In the upper part of the aquifer system

freshwater is found in ¯uviatile sediments of highpermeability. Below this, clayey sediments of low

water permeability are found. At higher depths in

the vicinity of the salt dome, dissolution of salt

results in groundwater with higher salt concen-

tration. Furthermore, the so-called Gorleben chan-

nel is located on top of the salt dome. During the

Elster glaciation, the cap rock was removed along

this channel, followed by deposition of sand and

marl.

According to the regional groundwater model, the

main recharge area is located S of the salt dome with

the Gorleben channel extending towards the NE. For

the part of the Gorleben aquifer system discussed in

this paper, Pleistocene origin (>12 000 a) is only

expected for nearly salt saturated channel brines in the

direct vicinity of the salt dome as shown by numerical

¯ow modeling and d2H and d18O isotope signatures

(BfS, 1990). Signi®cant 3H concentrations are only

found down to 25 m sampling depth Table 1 (cf. also

Sonntag and Suckow, 1993). One speci®c characteristic

of this aquifer system is the large variety of DOC con-

centrations, from <1 mg C/L up to more than 200 mg

C/L (Buckau, 1991) (cf. also Table 1). The very high

DOC concentrations are generally attributed to in situ

generation from local Miocene brown coal and

Fig. 1. Schematic description of setup for the enrichment and isolation of aquatic humic substances (from Artinger et al., 1996).


Pleistocene peat deposits (BfS, 1990). Due to the largevariation of the DOC concentration and the assumed

large contribution of in situ generation from SOC es-pecially in some deep groundwaters, this aquifer o�ersthe possibility to study aquatic humic substances from

both recharge and SOC as well as mixtures of them.

3. Experimental

3.1. Enrichment and isolation of aquatic humic

substances

For the characterization of HA or FA, an amountof at least 100 mg of the isolated substance is required.

The principle scheme for preparing these HA and FAsamples from groundwater consists of (i) enrichment;(ii) isolation; and (iii) separation of HA and FA. For

enrichment and isolation of aquatic humic substancesa mobile ®eld operation system has been developed.For enrichment the developed system utilizes reverse

osmosis (RO) (Wilhelm Werner Co., Germany).Isolation is done by sorption on XAD±8 (Rohm andHaas Co., USA) at low pH (Thurman, 1985).

The mobile ®eld operation system for enrichmentand isolation of humic substances is described in Fig.1. This setup works automatically and allows the pro-cessing of 5000 L groundwater per day.

Simultaneously with the enrichment of DOC by RO, asmaller side stream of DOC concentrate is processedby acidi®cation and sorption of humic substances on

XAD±8. Thereby, build-up of the salt concentration inthe DOC concentrate is kept within acceptable limitsin order not to inhibit the RO process. Depending on

the chemical composition and DOC concentration ofgroundwater, the enrichment and isolation scheme ismodi®ed. At low salt concentrations and su�cientlyhigh DOC content, enrichment is conducted in the

®eld and the resulting 50 L of DOC concentrate isfurther processed in the laboratory. For high DOCgroundwaters enrichment by RO is not applied and for

channel brines the high salt concentration does notallow the application of RO. In the latter case, up to1000 L of groundwater are directly processed in the

®eld using a XAD±8 column of 8 L volume. Allgroundwaters are pre®ltered at 450 nm pore size toseparate the suspended particles. For waters with a

high Ca content an ion exchanger (Serdolit CSG,Serva Co., Germany) for water softening is addition-ally installed upstream of the RO to avoid calcite pre-cipitation at increasing Ca enrichment in the DOC

concentrate.Separation and processing of isolated humic sub-

stance are accomplished by standard procedures

(Buckau, 1991). After elution from XAD±8 with 0.1 MNaOH, HA ¯occulate is separated from FA by cen-

trifugation after acidi®cation to pH 1 (HCl). IsolatedHA is dispersed in 0.1 M HCl followed by separation

of supernatant via centrifugation. This washing pro-cedure is repeated 3 times. Finally HA is freeze-dried.The FA remainder in the acidic solution after separ-

ation of HA is puri®ed twice by sorption on XAD±8,followed by alkaline elution. Finally, FA is puri®ed bycation exchange over BIO REX 70 or AG MP±50

(BIO RAD Co., Germany) in order to remove theexcess salt prior to freeze drying.

3.2. Contamination due to sampling

Great care is taken with respect to possible contami-nation during sample enrichment, isolation and hand-

ling. This is a critical issue especially in view of thelow humic substance concentrations in many of thesampled groundwaters. For estimating the maximum

contamination, the impact on the 14C concentrationdue to the applied humic and fulvic acid samplingmethods is tested, using (i) a young 3H containing

granitic groundwater with low DOC concentration(<0.1 mg C/L) of high 14C concentration, and (ii) asolution containing humic acid with a very low 14C

concentration (Aldrich Co., Germany, 14C concen-tration approximately 1% modern C (pmc)). For thelarge ®eld sampling with the XAD±8 column, a smallincrease in the 14C concentration is found. Assuming a14C concentration of 137 pmc for the source of con-tamination, a total amount of an additional 0.11 mg Cduring isolation can be calculated. Such a 14C contami-

nation source corresponds to, for example, cellulosethat may originate from soxhlet treatment of XAD±8for its puri®cation. For enrichment and isolation of

aquatic humic substances by the ®eld sampling reverseosmosis system coupled with a small XAD±8 column,a small decrease of the 14C concentration is observed.It corresponds to a total contamination of 0.20 mg 14C

free C in the isolated humic substance. Using the ionexchanger for water softening of 660 L groundwater,the 14C concentration of isolated humic substance is

also reduced, corresponding to an addition of 0.9 mg14C free C. Contamination by 14C free C may originatefrom, for example, tubings, membranes or construction

parts of the apparatus of petrochemical origin. Theresults show that contamination of humic substancesduring enrichment, isolation and handling are of no

great importance for sample amounts of more than 20mg C.

3.3. Characterization methods

DOC is determined using the TOC analyzer Tocor 2(Maihak Co., Germany). The inorganic C of water

samples is removed by degasi®cation of CO2 with Arafter acidi®cation to pH 2.5±3. The DOC concen-


Table 2

Aquatic humic and fulvic acids isolated from the investigated groundwaters and their 14C concentration, speci®c absorption at 300

(E3) and 400 nm (E4), their ratio E3/E4, ¯uorescence intensity, gel permeation chromatography distribution (in Dalton: distri-

bution maximum, size average Ms and number average Mn), and their size ratio (Ms/Mn). nd=not determined (mainly due to lack

of sample amount); �: values from di�erent groundwater sampling occasions

Sample 14C

(pmc)aE3

(Lgÿ1 cmÿ1)E4

(Lgÿ1 cmÿ1)E3/E4 Fluorescence

intensity

(relative units)

GPC

distr. max.b

(Dalton)

GPC

Ms

(Dalton)

GPC

Mn

(Dalton)

Ms/Mn

Munich Fulvic acids

MS-UP-178 72.821.1 4.9 0.59 8.2 0.49 2900 2350 690 3.4

MS-U1-630 76.021.1 5.4 0.73 7.3 0.61 3100 2880 830 3.5

MS-KP-916 45.223.1 6.5 0.88 7.4 0.74 3750 3690 1080 3.4

Franconian Albvorland

Laibstadt 79.821.0 3.5 0.38 9.1 0.33 2450 1900 560 3.4

J-S-T III 29.321.9 nd nd nd nd 3000 1780 540 3.3

Greding I 15.621.3 nd nd 8.0 nd 3400 3710 860 4.3

Greding II 25.422.0 nd nd 6.7 nd 4850 2510 640 3.9

Beilngries 13.925.6 3.4 0.57 6.0 0.51 2950 3110 760 4.1

Fuhrberg

FF-OW 74.521.1 6.2 1.1 5.8 0.60 3750 3700 1040 3.6

FF-OA 85.021.2 8.6 1.5 5.8 1.34 5450 4670 1530 3.1

FF-T1-4 79.920.6 8.1 1.4 5.9 0.87 5450 4030 1120 3.6

FF-T3-11 117.322.3 6.4 1.0 6.6 nd 4100 3940 1220 3.2

FF-N5-12 85.321.3 8.1 1.4 5.7 0.68 5450 4050 970 4.2

FF-N10-4 80.321.1 9.9 1.8 5.5 0.90 4800 4180 1290 3.2

FF-N10-6 81.521.1 7.1 1.3 5.7 0.17 3400 2910 830 3.5

FF-N10-12 138.423.9 9.9 1.8 5.4 0.75 6950 5730 1290 4.4

FF-N10-14 119.222.1 10.4 1.9 5.3 1.05 5800 5440 1670 3.3

Gorleben

recharge

GoHy-181 75.921.2 6.6 1.2 5.8 0.43 4500 3490 790 4.4

GoHy-411 109.721.4 5.7 0.80 7.2 0.70 4300 3680 940 3.9

GoHy-421 92.521.5 6.4 1.0 6.2 0.56 3300 2750 770 3.6

GoHy-611 38.225.4 11.0 2.4 4.6 1.05 6250 5000 1380 3.6

GoHy-711 100.921.5 4.4 0.57 7.6 0.34 2450 2060 570 3.6

Transition

GoHy-182 46.121.2 7.0 1.4 6.0 1.01 7050 5130 1230 4.2

GoHy-201 58.622.4 7.9 1.6 4.9 0.70 6350 4810 1230 3.9

Enhanced DOC

GoHy-412 8.122.2 10.6 2.0 5.3 1.64 8200 7170 2090 3.4

GoHy-492 4.720.2 10.4 2.1 5.2 1.50 8250 7090 3400 2.1

GoHy-572 13.520.4/23.621.8� 10.4 2.1 4.9 1.34 8100 7740 2430 3.2

GoHy-573 7.023.2/ < 3.6� 14.9 3.6 4.2 1.89 9600 8120 3110 2.6

GoHy-612 26.722.3 12.1 2.2 6.2 1.97 8100 7120 2800 2.5

GoHy-851 11.320.4 12.0 2.7 4.5 1.35 9450 8330 3610 2.3

GoHy-2211 13.420.4 17.5 4.5 3.9 1.84 9350 8340 3310 2.5

GoHy-2227 10.623.3 16.4 3.7 4.4 1.82 9550 8080 3290 2.5

Channel brines

GoHy-193 46.821.1 4.2 0.77 6.6 0.65 7100 8220 2440 3.4

GoHy-514 20.321.3 5.8 0.87 6.7 1.12 6550 7390 1940 3.8

GoHy-653 40.021.3 3.9 0.55 7.2 0.70 6350 7280 2530 2.9

(continued on next page)


tration is measured by IR detection of CO2 from cata-lytical thermal oxidation of organic C.

Elemental composition (C, H, N, O and S) is deter-mined by the ``Analytische Laboratorien Malissa undReuter'' (Gummersbach, Germany) or

``Mikroanalytisches Labor des Anorganisch-che-mischen Instituts der Technischen UniversitaÈ tMuÈ nchen'' (Munich, Germany). Carbon, H and N are

quanti®ed by heat conductivity detection after samplecombustion and gas chromatographic separation ofCO2, H2O and N2. Oxygen is pyrolized with C at11508C in a He atmosphere to CO. After oxidation

with CuO, CO2 is detected by heat conductivity. Sulfuris determined as SO2ÿ

3 by relative conductimetry inH2O2/H2SO4, following sample combustion with O2 at

13008C.UV/Vis spectroscopy is performed with a Cary 5

spectrophotometer (Cary Co., USA). UV/Vis spectra

of humic substances are dependent on pH, ionicstrength, and the extent of complexation with highervalent metal ions (MacCarthy and Rice, 1985; Buckau,

1991). Consequently, a comparison of results requirescontrolled conditions. The following medium is used:0.1 M NaCl, 10ÿ3 M tris(hydroxomethyl)amino-

methane, and 10ÿ3 M EDTA at pH 8.5. EDTA wasadded to avoid a possible in¯uence of higher valent

metal ions by complexation with humic substances.FA and HA concentrations are about 20 mg/L.Gel permeation chromatography (GPC) separates

entities mainly with respect to their hydrodynamic size.Nevertheless, due to charge exclusion or sorption onthe gel matrix, a deviation of the hydrodynamic size

may occur. Although a tailing is observed, especiallyon humic and fulvic acids from the Gorleben rechargegroundwaters, the results are presented as a mean hy-drodynamic size (in Dalton) in this paper. This should

not suggest that the given hydrodynamic sizes alwaysdescribe the real hydrodynamic size correctly, butrather that this is a convenient way to compare results

from GPC under consistent experimental conditions.Fractogel TSK HW±50 (Merck Co., Germany) is

used as gel. Under the given experimental conditions it

is found to allow the fractionation of substances withhydrodynamic sizes up to around 130 000 Dalton. Thehydrodynamic size of humic and fulvic acids varies

with pH, ionic strength and the degree of complexationwith metal ions (Shaw et al., 1994, Buckau, 1991). Toensure reproducible and intercomparable results, an

Table 2 (continued )

Sample 14C

(pmc)aE3

(Lgÿ1 cmÿ1)E4

(Lgÿ1 cmÿ1)E3/E4 Fluorescence

intensity

(relative units)

GPC

distr. max.b

(Dalton)

GPC

Ms

(Dalton)

GPC

Mn

(Dalton)

Ms/Mn

Uplift-Mixing

GoHy-341 56.320.8 10.4 2.3 4.5 nd nd nd nd nd

Gorleben Humic Acids

recharge

GoHy-181 15.421.3 19.9 6.1 3.3 0.22 8750 ±c ±c ±c

GoHy-411 26.321.2 22.1 6.9 3.2 0.30 8800 ±c ±c ±c

GoHy-611 13.820.6 nd nd nd nd nd nd nd nd

Transition

GoHy-182 3.421.4 23.9 7,3 3.3 035 9000 ±c ±c ±c

Enhanced DOC

GoHy-412 3.121.2 nd nd nd 0.26 10100 ±c ±c ±c

GoHy-492 < 1.0 32.1 12.3 2.6 0.21 30700 ±c ±c ±c

GoHy-572 2.121.7 23.4 8.9 2.6 0.15 27900 ±c ±c ±c

GoHy-573 < 1.3 27.3 9.5 2.9 0.28 22800 ±c ±c ±c

GoHy-612 1.721.1 28.0 10.6 2.6 0.20 40300 ±c ±c ±c

GoHy-851 < 1.7 21.1 8.6 2.5 0.15 31000 ±c ±c ±c

GoHy-2211 1.020.9 25.5 9.4 2.7 0.12 26100 ±c ±c ±c

GoHy-2227 1.721.1 28.3 9.8 2.9 0.38 21700 ±c ±c ±c

Uplift-Mixing

GoHy-341 9.520.1 27.3 10.5 2.6 0.20 24550 ±c ±c ±c

a pmc percent modern C (1 pmc=0.226 Bq 14C per g C).b GPC peak at exclusion limit not accounted for (cf. Fig. 6 and Fig. 7).c Not evaluated due to an unknown fraction at the exclusion limit of the gel column (cf. Fig. 6).


elution medium is chosen consisting of 0.1 M NaCl,0.05 M Na2HPO4, 10

ÿ3 M EDTA at pH 8.5 and 10

volume % of methanol. Samples of 20 to 100 mL areinjected with humic or fulvic acid concentrationsbetween 0.7 and 4.0 g/L. The elution pro®les are deter-

mined by absorption at 254 nm (Hewlett-Packard8452A diode array spectrophotometer).For calibration of the GPC column, the exclusion

volume is determined with Dextrane blue and the totalvolume with sodium azide. In the working range thecolumn is calibrated with globular proteins, namely,

Albumin (67 000 Dalton), Ovalbumin (43 000 Dalton),Ribonuclease (13 700 Dalton) and Cytochrome C(12 400 Dalton). The outcome of the GPC is character-ized by general properties of the elution pro®les, the

hydrodynamic size at maximum absorption, and thesize average (MS) and number average hydrodynamicsize (Mn). The latter two are evaluated in accordance

with Yau et al. (1979). Reproducibility is found to beapproximately 2500 Dalton for sizes around 10 000Dalton and approximately 22000 Dalton in the size

range around 30 000 Dalton (cf. GPC distributionmaximum of around 2500 to 10 000 Dalton for fulvicacids and about 10 000 to 30 000 Dalton for humic

acids (cf. Table 2)).Fluorescence spectroscopy is carried out in addition

to the absorption detection of the GPC elution pro-®les. The excitation wavelength for the ¯uorescence

measurement is 340 nm. The detection of the emitted¯uorescence light is made via optical ®ber using adiode array spectrophotometer IRY 700 GR

(Spectroscopy Instruments Co., USA) at 425 nm. The¯uorescence yield of humic substances is determinedby integration over the ¯uorescence signal of the whole

GPC elution pro®le.14C measurement on a sample amount of 0.5 g C or

more is made by conventional liquid scintillationcounting after combustion to CO2 followed by syn-

thesis of benzene (Eichinger et al., 1980). For the com-bustion method used, the maximum C contaminationis determined to be equivalent to 0.24 mg C with a 14C

concentration of 115 pmc. For smaller sampleamounts, accelerator mass spectrometry is used(Isotrace Laboratory, University of Toronto)

(Beukens, 1992). The 14C concentration is given inpmc (% modern C) referred to 94.9% of the activityconcentration of the NBS oxalic acid standard in 1950.

All given values are corrected with respect to theimpacts of sample handling.

4. Results and discussion

The results have been obtained for individual

groundwaters of di�erent aquifer systems.Groundwaters from the Gorleben aquifer are divided

into di�erent groups/areas based on their hydrologicaland geochemical characteristics, namely, (i) recharge

area with shallow groundwaters having 3H concen-trations of 8 TU or more; (ii) transition area with deepgroundwaters with no signi®cant 3H concentrations

(<1 TU); (iii) high salinity brines from the Gorlebenchannel; (iv) deep groundwaters with enhanced DOCconcentrations (between 7.6 and 169 mg C/L contrast-

ing with <3.2 mg C/L in non-enhanced DOC ground-waters; and (v) one near surface groundwater withenhanced DOC (GoHy±341) where young recharge

water is mixed with up-lifting water from the depth(`uplift-mixing'). Re¯ecting the important hydrologicaland geochemical di�erences, this classi®cation ofGorleben groundwaters is applied throughout this

paper.

4.1. DOC, humic acid, fulvic acid and 14C concentration

The concentration and composition of DOC in thesampled groundwaters is shown in Table 1 and Fig. 2.

Besides the Gorleben aquifer, DOC in most aquifers isfound to be composed of 10 to 40% fulvic acid but,no detectable amount of humic acid, while the rest is

made up of hydrophilic compounds. The relativelyhigh DOC concentrations in the Fuhrberg ground-waters, as compared to the values in other rechargeand transition groundwaters, must be attributed to

di�erences in soil and vegetation conditions, includingagricultural activities, because the 14C concentration ofFuhrberg fulvic acids are comparable to those of

recharge fulvic acids from the Gorleben aquifer (cf.Table 2). This fact infers that the SOC contribution tothe aquatic fulvic acid is not signi®cant.

In Gorleben groundwaters varying concentrations ofhumic acid are found, with its fraction increasing withthe DOC concentration. Very small concentrations ofhumic acid are found in recharge, transition and chan-

nel brine groundwaters, whereas in enhanced DOCand uplift-mixing groundwaters humic acid is a domi-nant part of DOC. The very high humic and fulvic

acid concentrations in some deep Gorleben ground-waters (enhanced DOC and uplift-mixing ground-waters) can be explained by the presence of SOC,

especially lignite deposits. Analysis of drill cores fromthe GoHy±573 and ±2227 wells show lignite fractionsof more than 20% in some layers (Kim et al., 1996).

Very low humic acid concentrations are found in therecharge areas and thus the humic acid in enhancedDOC groundwaters may be considered as resultingsolely from SOC. Also an enhanced concentration of

fulvic acid is found in enhanced DOC groundwaters,although the increase is signi®cantly lower than that ofhumic acid. Therefore, a less pronounced contribution

of fulvic acids from SOC can be concluded (cf. Table1).


In Fig. 3 the 14C concentration of fulvic acids is rep-resented versus the fraction of humic acid of DOCthat is taken as an indicator for the in situ generation

of aquatic humic substances originating from SOC. Inthe deep enhanced DOC groundwaters, 14C concen-trations of fulvic acid are found to be typically below

20 pmc. These groundwaters are of Holocene origin(Artinger et al., 1996) and, therefore, between theirrecharge and present time, a maximum 14C decay ofapproximately 2 hal¯ives is possible. Considering that

recharge fulvic acid has 14C concentrations of around80 pmc (Artinger et al., 1996), a considerable contri-bution of fulvic acid from SOC seems reasonable. The

release of fulvic acid from SOC may be considerablenot only in deep groundwaters but also in young 3Hcontaining recharge groundwaters. This may be the

case in the recharge groundwater GoHy±611 whichshows a fulvic acid 14C concentration of 38 pmc aswell as a signi®cant contribution of humic acid to theDOC (8%).

In Fig. 3, the channel brine fulvic acids showdecreasing 14C concentrations although no humic acids

are found. The concentrations and characteristic prop-erties of the channel brine fulvic acids (cf. below) re-semble those of recharge fulvic acids and the 14C

concentrations re¯ect the expected groundwater age(Artinger et al., 1996). Therefore, an absence of fulvicacid from SOC can be assumed in the channel brines

and a decrease in the 14C concentration may be relatedto radioactive decay. In the uplift-mixing groundwaterGoHy±341, the speci®c hydrogeological and geochem-ical conditions result in a humic acid concentration

similar to the average value found in enhanced DOCgroundwaters, but the 14C concentration is rather simi-lar to the values in recharge and transition ground-

waters.To sum up, DOC, humic acid and fulvic acid con-

centrations as well as their 14C contents provide im-

portant information concerning the origin of aquatichumic and fulvic acids in di�erent groundwaters. Inthe Munich, Fuhrberg and Franconian Albvorlandaquifers, aquatic fulvic acid originates predominantly

from the humus horizon with no detectable amount ofaquatic humic acid. In Gorleben, and especially in

Fig. 2. DOC concentration and composition of investigated groundwaters.


some deep groundwaters, the release of aquatic humicand fulvic acids from SOC takes place in addition toaquatic fulvic acid from the soil horizon. The discus-

sion below is focused on the possibility of identifyingthe origin of aquatic humic and fulvic acids by theircharacteristic properties. Here, it should be borne in

mind that the extended residence time of aquatichumic substances in a given groundwater may changetheir characteristic properties due to the prevailing

physico-chemical conditions of the groundwater irre-spective of their origin.

4.2. Elemental composition of humic and fulvic acids

The elemental composition (C, H, O, N and S) of

the humic and fulvic acids investigated are shown inTable 3. The individual values are normalized to thesum of the elements analyzed and referred to dried

substances. The results re¯ect the generally founddi�erences between humic and fulvic acids, namely, thehigher C and lower O content of humic acids as com-

pared to fulvic acids (Steelink, 1985; Pettersson et al.,1994). The element ratios of H/C and O/C are lower in

Fig. 3. 14C concentration of Gorleben fulvic acids plotted versus the fraction of DOC consisting of humic acid.

Table 3

Elemental composition as well as H/C and O/C ratios of isolated aquatic humic and fulvic acids from di�erent aquifers. Samples

from the Gorleben aquifer are additionally arranged according to hydrogeological/geochemical aspects. The numbers of samples

studied are given in brackets

Aquifer C (%) H (%) O (%) N (%) S (%) H/C O/C

Munich FA (3) 52.220.6 4.420.2 37.721.2 1.220.1 4.520.8 1.0120.06 0.5420.03

Franconian Alb. FA (4) 56.322.1 6.120.5 35.323.2 0.720.2 2.021.0 1.3120.09 0.4720.06

Fuhrberg FA (9) 52.424.0 4.520.5 38.724.0 1.020.5 3.521.6 1.0220.09 0.5620.11

Gorleben FA

Recharge area (5) 54.622.8 5.020.6 38.321.6 0.520.1 ± 1.1020.09 0.5320.04

Transition area (2) 53.020.1 4.620.8 38.124.1 1.020.3 ± 1.0420.17 0.5920.06

Enhanced DOC (8) 53.022.2 4.320.5 39.922.4 1.620.5 2.322.0 0.9820.12 0.5720.05

Channel brines (3) 51.321.9 5.320.2 42.721.7 0.520.2 ± 1.2320.01 0.6320.05

Gorleben HA

Recharge area (1) 55.0 4.4 36.1 1.7 2.9 0.96 0.49

Transition area (2) 56.821.0 4.420.3 34.421.1 2.520.8 1.921.0 0.9420.09 0.4520.01

Enhanced DOC (8) 58.621.6 4.820.4 33.120.8 2.320.9 1.220.7 0.9820.09 0.4220.02

Uplift-Mixing (1) 57.4 5.1 34.8 1.12 1.6 1.07 0.45

± : large scatter in data including results below detection limit.


aquatic humic acids than in aquatic fulvic acids. Thisis due to the enhanced aromatic entities of humic acid

(Steelink, 1985; Pettersson et al., 1994). On the otherhand, humic acid from humus is reported to have ahigher O/C ratio than humic acid from peat/lignite

(Steelink, 1985).Fulvic acids from young recharge groundwaters with

or without a minor in¯uence of SOC (Munich,

Fuhrberg and the Gorleben recharge area) and fromthe Gorleben transition area show very similar H/Cand O/C ratios. Fulvic acids from the Franconian

Albvorland aquifer with progressively reducing con-ditions along with the main ¯owpath (groundwaterages exceeding 12 000 a), show a lower O/C ratio anda higher H/C ratio. This may be the result of advanced

chemical or microbiological degradation, leading to areduced O content (De Haan, 1983). Fulvic acids fromthe channel brines exhibit relatively high H/C and O/C

ratios. Whether or not this result re¯ects a selectiveionic strength driven precipitation of fulvic acids withless O-containing hydrophilic functional groups and a

higher content of aromatic groups cannot be ascer-tained. For the Gorleben enhanced DOC groundwatersthe H/C and O/C ratios do not deviate signi®cantly

from the values of recharge and transition waters.Regarding humic acids the data are available only forthe enhanced DOC groundwaters and thus no con-clusion can be drawn from the elemental composition.

To sum up, the elemental composition does not pro-vide information on the presence of humic and fulvicacids which might originate from SOC. The di�erences

observed may rather re¯ect the geochemical conditions,such as the ionic strength driven selective precipitationor impact of redox variations over extended periods of

time.

4.3. UV/Vis spectroscopy

UV/Vis spectroscopy is commonly used for thecharacterization of humic substances (Schnitzer, 1978;Stevenson, 1982; MacCarthy and Rice, 1985). The

spectra of humic substances show an increasingabsorption with decreasing wavelength without charac-teristic features. The characterization is made by either

the speci®c absorption at one wavelength (Petterson etal., 1994; Kukkonen, 1992; Pennanen, 1972) or theabsorption ratio at two wavelengths for a qualitative

description of the curvature of the absorption conti-nuum (Chin et al., 1994; Kukkonen, 1992; De Haan,1983; Stevenson, 1982). In this work, absorptions at300 and 400 nm (E3 and E4, respectively) are used as

well as their ratio (E3/E4). These wavelengths areselected for their low impact of background compen-sation and, consequently, good reproducibility. Due to

the high molecular weight and colloidal form of thedissolved humic substances, the absorption spectrum

includes the e�ect of light scattering (Power and

Langford, 1988; Wylie and Lai, 1986; Pennanen,1972).The results of UV/Vis spectroscopy are shown in

Table 2. In Fig. 4 the speci®c absorption (in L/gÿ1

cmÿ1) of humic and fulvic acids at 300 nm and 400 nmis plotted versus the absorption ratio E3/E4. These two

properties vary over a wide range and show the follow-ing tendency: the higher the speci®c absorption, thelower is the E3/E4 absorption ratio for humic and ful-vic acids. Following the published results (Chin et al.,

1994; Kukkonen, 1992; Traina et al., 1990; Gauthier etal., 1987), an increase in the speci®c absorption and adecrease in the absorption ratio are indicative of an

increasing humi®cation, aromaticity and molecularweight of humic substances. A fundamental di�erenceis not observed between the absorption ratio of 465 to

665 nm, often cited in the literature, and the E3/E4ratio used. In Fig. 5 the average speci®c absorption at300 nm (E3) is plotted versus the average absorption

ratio of 300 and 400 nm (E3/E4) for humic and fulvicacids separated into di�erent groups of groundwaters.A signi®cant di�erence is observed to exist betweenhumic and fulvic acids as well as among the humic or

fulvic acids.As a general trend for both humic and fulvic acids,

the speci®c absorption is increasing and the E3/E4

ratio is decreasing in the order of recharge, transition,enhanced DOC. Fulvic acids from Gorleben channelbrines as well as from Munich and the Franconian

Albvorland aquifers resemble the Gorleben rechargefulvic acids. In contrast to this, Fuhrberg fulvic acids

Fig. 4. Speci®c absorption at 300 nm (E3) and 400 nm (E4)

plotted versus their ratio (E3/E4) for investigated humic and

fulvic acids.


resemble Gorleben transition fulvic acids. Fulvic acids

from the recharge groundwater GoHy±611 and theuplift-mixing groundwater GoHy±341 resemble theenhanced DOC fulvic acids. In the Franconian

Albvorland the E3/E4 ratio shows a decrease withincreasing distance from recharge along the main ¯owdirection to the most distant downstream well of

Beilngries. According to the 14C dating of dissolvedinorganic C in the Franconian Abvorland aquifer, thegroundwater in the Beilngries well is of Pleistocenceorigin (Geyer et al., 1993). Furthermore, the redox po-

tential changes from 594 mV to ÿ41 mV from therecharge to Beilngries. This could be an indication foran impact of the residence time on the spectroscopic

properties or changes with the geochemical environ-ment. The range of E3/E4 ratios, as observed for theFranconian Albvorland water, is comparable with the

recharge waters of Gorleben and Munich.Furthermore, fulvic acids from the young near-surfaceFuhrberg groundwaters with no reducing conditionsare found to have lower E3/E4 ratios than those from

other recharge groundwaters and from the reducingFranconian Albvorland aquifer.In the Gorleben young (<40 a) recharge ground-

water GoHy±611 containing 3H, the 14C concentrationof fulvic acid and E3/E4 ratio are signi®cantly lowerthan in other young recharge groundwaters. The 14C

concentration is about half to one third of the concen-

tration found in fulvic acids from other recharge

waters, while the UV/Vis absorption properties re-semble fulvic acids from enhanced DOC groundwaters.In this case, it may be assumed that the origin, i.e.,

release of fulvic acid from SOC, is the governing factorfor the spectroscopic properties rather than local geo-chemical conditions.

Therefore, it may be concluded that the UV/Visabsorption properties of aquatic humic and fulvicacids depend on both the origin, including di�erencesin recharge conditions, and to a lesser extent on the

prevailing geochemical conditions in the groundwater.Consequently, the UV/Vis spectroscopic properties ofaquatic humic substances may be useful to identify

their origin.

4.4. Gel-permeation chromatography (GPC)

Some representative GPC chromatograms ofGorleben groundwaters are shown in Fig. 6. In allcases, some degree of tailing is observed, which is

more pronounced for humic and fulvic acids fromrecharge and transition groundwaters and, thus, cau-tion is necessary when interpreting the hydrodynamic

size. With respect to humic acids from di�erent groupsof Gorleben groundwaters, di�erences occur in (i) theoverall elution peak area; (ii) the position of the

elution pro®le in the working range of GPC; and (iii)

Fig. 5. Speci®c absorption at 300 nm (E3) plotted versus the absorption ratio E3/E4 of isolated humic and fulvic acids arranged

according to the di�erent groups of investigated groundwaters. The fulvic acid of the recharge groundwater GoHy-611 is shown

separately.


the presence of the second peak at the exclusion limit

of the column. IR studies on di�erent GPC fractionsof humic acid have shown that the material elutedwith the peak at the exclusion limit is distinctively

di�erent from the rest. In this fraction the typical IRbands for proton exchanging carboxyl groups areabsent (Kim et al., 1990). The elution peak of this

kind is found for humic acids from enhanced DOCgroundwaters, whereas humic acids from recharge andtransition water show very weak indications only in

this range.GPC elution pro®les for Gorleben fulvic acids reveal

that (i) the overall elution peak area re¯ects di�erencesfor fulvic acids from di�erent regions, (ii) the elution

pro®les are shifted towards smaller hydrodynamic sizefor fulvic acids from enhanced DOC, via transition torecharge, and (iii) no peak occurs at the exclusion limit

of the GPC column.In Table 2 the GPC results are given by the hydro-

dynamic size at the elution pro®le maximum (peak at

exclusion limit is not considered), the size average andthe number average of the hydrodynamic size. Asexpected from the relatively symmetric GPC elution

pro®les, the size average and the distribution maximumshow comparable results, the number averages, how-ever, are smaller. The ratio of size average and numberaverage (Ms/Mn) re¯ects the symmetry of the GPC

elution pro®les (Yau et al., 1979). In general, some-what lower values are found for fulvic acids fromGorleben enhanced DOC groundwaters than from

others. The fulvic acid from GoHy±611 resemblesthose from transition groundwaters, but not fromrecharge groundwaters. The humic acid from GoHy±

412 resembles recharge and transition humic acids.This can be understood from Fig. 2, where it is shownthat the humic acid fraction of DOC in this ground-

water is low compared to that from other enhancedDOC groundwaters. This may suggest that the ground-water GoHy±412 is only moderately in¯uenced by pro-cesses leading to release of DOC from SOC.

In Fig. 7 the GPC results are summarized by plot-ting the speci®c absorption at 300 nm versus the hy-drodynamic size of the elution pro®le maximum. The

humic acids from recharge and transition belong toone group, the uplift-mixing GoHy±341 and enhancedDOC groundwaters to another group. The GPC

elution maxima of fulvic acids from Gorleben increasefrom recharge via transition to enhanced DOC. Fulvicacids from the channel brines and GoHy±611 arefound to be in the range of transition groundwaters.

Fulvic acids from the Franconian Albvorland andMunich resemble those of the Gorleben recharge area,whereas Fuhrberg samples fall in the range between

recharge and transition fulvic acids.To sum up, GPC with UV/Vis detection of humic

and fulvic acids reveals some important di�erences

between di�erent aquifer systems as well as within theGorleben aquifer. The presence of a peak at the GPCexclusion limit represents a distinctive di�erence

between the humic acids from enhanced DOC anduplift-mixing groundwaters and between the humicacids from recharge and transition groundwaters. Thehumic acid from GoHy±412 with a moderately

enhanced DOC concentration is found to resemblehumic acids from recharge and transition, rather thanhumic acids from other enhanced DOC groundwaters,

with respect to the absence of a peak at the exclusionlimit and the position of the distribution maximum.

Fig. 6. GPC elution pro®les of selected humic and fulvic acids

from Gorleben groundwater.


4.5. Fluorescence spectroscopy

The results obtained from the characterization by¯uorescence spectroscopy are given in Table 2. Someexamples of ¯uorescence spectra are shown in Fig. 8.The spectra possess the general characteristics of

aquatic humic substances (Hayase and Tsubota, 1985;Miano et al., 1988; Visser, 1983). For ¯uorescencespectra of humic acids from recharge via transition to

enhanced DOC groundwaters, a decrease of theshoulder at the higher wavelength of the spectra canbe observed. The fulvic acids show similar spectra for

the Franconian Albvorland, Munich and Gorlebenchannel brine and recharge groundwaters, whereas thespectra for FA from transition and enhanced DOC

groundwaters with a higher hydrodynamic size areslightly shifted towards a longer wavelength. Theseresults are in accordance with the bathochromic shiftobserved for HA and FA fractions of di�erent hydro-

dynamic size, as obvious for GoHy±411 in Fig. 9. Thesame behavior has been found by Jones and Indig(1996) for di�erent fractions of Aldrich humic acid

(Aldrich Co.). The correlation between the ¯uorescencespectra and the hydrodynamic size of fulvic acids indi-cates that the ¯uorescence spectra may also provide

some information about the origin of humic sub-stances.Somewhat more distinct di�erences can be seen in

the ¯uorescence intensity (see Fig. 10). In general, the¯uorescence intensity of humic acid is lower than of

fulvic acid. While humic acids from di�erent types ofGorleben groundwaters cannot be distinguished fromone another, fulvic acids from enhanced DOC ground-waters have a considerably higher ¯uorescence inten-

sity than other fulvic acids. The ¯uorescence intensitiesof fulvic acids from Fuhrberg, Munich and Gorlebentransition and channel brine groundwaters are compar-

able with the values for Gorleben recharge andFranconian Albvorland fulvic acids. As expected fromthe above discussions concerning the fulvic acid

GoHy±611, the ¯uorescence behavior indicates anadmixture of fulvic acids originating from SOC, as thisis done by the DOC composition, 14C concentration,

UV/Vis absorption and the hydrodynamic size.Therefore, ¯uorescence spectroscopy could be an ad-ditional tool for determining the origin of fulvic acids.

4.6. In¯uence of physico-chemical/geochemicalconditions

The above discussion has shown that a characteriz-ation may be useful to distinguish humic and fulvicacids from di�erent aquifers, but also from di�erent

sources within an aquifer system, such as Gorleben.The characteristic properties of aquatic humic sub-stances may re¯ect the source, the generation mechan-

Fig. 7. Speci®c absorption at 300 nm (E3) plotted versus the GPC elusion pro®le maximum of isolated humic and fulvic acids

arranged according to the di�erent groups of investigated groundwaters. The humic acid peak at the exclusion limit of the GPC

column is not accounted for. The fulvic acid of the recharge groundwater GoHy-611 is shown separately.


ism and the geochemical conditions (involving also mi-

crobial mediated reactions) at the place of their origin.For example, humic substances originating from thesoil zone will generally re¯ect the oxidizing conditions,

whereas humic substances originating from SOC willre¯ect the reducing conditions. Furthermore, aquaticfulvic acids from the recharge zone may also showvariations, thus re¯ecting di�erent soil/vegetation con-

ditions.The physico-chemical conditions of Fuhrberg

groundwaters can be described as oxidizing with pH

values around 4 to 6. Groundwaters from the otherinvestigated sites have pH values above 6 and redoxconditions which vary from oxidizing to reducing Eh

values. The characteristic properties of fulvic acidsfrom Fuhrberg, however, do not correspond to thoseof the Gorleben recharge groundwaters, but to thetransition groundwaters with reducing conditions and

pH values around 8. Therefore, the characteristic prop-

erties of fulvic acids to a large extent seem to dependon their origin and not on the prevailing local ground-

water conditions.Despite these results, the in¯uence of changing geo-

chemical conditions on the characteristics of aquatic

humic substances during the transport along thegroundwater ¯owpath cannot be excluded (cf. Fig. 11and Fig. 12). As obvious from Fig. 11, the absorption

ratio E3/E4 of fulvic acids appears to decrease withdecreasing redox potential along the ¯owpath in thesandstone aquifer of the Franconian Albvorland. This

is not to imply, however, that the redox potentialdetermines the UV/Vis absorption behavior of fulvicacids, but rather that the redox potential may be an in-dicator of processes in¯uencing the absorption beha-

vior. In Fig. 12 di�erences in the GPC distributionmaximum of fulvic acids from Gorleben, Munich andthe Franconian Albvorland are plotted versus the pH

of groundwater. Although the values scatter consider-ably, a correlation of the hydrodynamic size with thepH of the groundwater can be recognized. As regards

the molecular size of fulvic acids in the FranconianAlbvorland aquifer the change is not ascribed to adi�erent source (sediments presumably free from

SOC). Therefore, the characteristic properties of fulvicacids in the Franconian Albvorland may indeed bein¯uenced by the geochemical condition of the ground-water. However, due to the large contribution of fulvic

acids originating from SOC, this conclusion is notdirectly applicable to the Gorleben aquifer. In thiscase, the pH of the groundwater re¯ects the physico-

chemical condition associated with the release processof humic substances from SOC.In the special case of the saline Gorleben ground-

waters, a signi®cant in¯uence of the ionic strength onthe characteristic properties of the humic substances isexpected. It is conspicuous that in none of the high-saline groundwater signi®cant fractions of humic acids

are found (this work and Buckau, 1991), althoughoverlaying groundwaters contain humic acids. On theother hand, the fulvic acids show a signi®cantly higher14C concentration than those in¯uenced by the SOC.This strongly suggests that the groundwater enteringthe saline Gorleben channel has not been in contact

with organic deposits or that the fulvic acids foundre¯ect a selective ionic strength driven precipitation ofhumic acids and part of the fulvic acids. From the lat-

ter process, it might be expected that the especiallyhumic substances originating from DOC with highmolecular sizes are precipitated preferentially. Theresults of this study suggest the prevalence of the latter

process.To sum up, the origin (including source, geochemical

conditions and processes of generation) appears to

dominate the characteristic properties of aquatic humicsubstances. This results in di�erent properties of

Fig. 8. Fluorescence spectra of humic and fulvic acids (exci-

tation at 340 nm). The spectra are recorded at the hydrodyn-

amic size fraction with the highest ¯uorescence intensity. For

reasons of comparability, the spectra are depicted with the

same height.


aquatic fulvic acids from di�erent aquifer systems as

well as di�erent sources (soil zone versus peat/browncoal deposits) within the Gorleben aquifer. However,

under special geochemical conditions like the saline

Gorleben groundwaters or changes in geochemical con-ditions over extended time periods, as in the

Fig. 9. Fluorescence spectra of di�erent hydrodynamic size fractions of fulvic and humic acid from GoHy-411 (excitation at 340

nm). For reasons of comparability, the spectra are depicted with the same height.

Fig. 10. Speci®c absorption at 300 nm (E3) plotted versus the ¯uorescence intensity of isolated humic and fulvic acids arranged

according to the di�erent groups of investigated groundwaters. The fulvic acid of the recharge groundwater GoHy-611 is shown

separately.


Franconian Albvorland, the prevailing geochemicalconditions also need to be taken into account.

5. Summary and conclusions

Aquatic humic and fulvic acids from di�erent aqui-fers and di�erent locations within an aquifer showdi�erent characteristic properties. These di�erences

appear to depend on the source of the aquatic humicand fulvic acids as well as on the physico-chemical/geochemical conditions of the groundwater. In the

Gorleben aquifer system high DOC concentrations insome deep groundwaters can be attributed to theadmixture of SOC. The same is true for a groundwaterat low depth (10±13 m) that, in view of its mineral

composition and in agreement with the regionalgroundwater model, originates from deep layers.Within this aquifer system the following characteristic

properties of aquatic fulvic and humic acids may be at-tributable to a predominant contribution of SOC: (i) ahigher fraction of humic acid in DOC, (ii) a higher

speci®c absorption and ¯uorescence intensity of fulvicacids, (iii) a lower E3/E4 absorption ratio of fulvicacids, (iv) a higher hydrodynamic size of fulvic and

humic acids. An example of those indicators is theappearance of a large peak at the exclusion limit of theapplied GPC system for humic acids from enhancedDOC groundwaters in contrast to those from recharge

and transition groundwaters. Another example may bethe fulvic acid in the young recharge groundwaterGoHy±611, where the characteristic properties listed

above resemble Gorleben transition or enhanced DOC

groundwaters, which contain humic substances orig-inating from SOC. The characteristic properties ofaquatic humic and fulvic acids from di�erent ground-waters within an aquifer system may also be ascribed

to geochemical properties. The applied characterizationmethods of aquatic humic and fulvic acids may besummarized as a useful tool in identifying the origin of

aquatic humic and fulvic acids. In special cases, a poss-ible in¯uence of changing geochemical conditions andprocesses needs to be taken into consideration.

In conclusion, the characterization of aquatic humicsubstances in the presence of organic deposits is anessential tool for investigations of the role of humics intransporting pollutants. The characterization methods

described above not only provide information aboutthe origin, but also about the mobility and the long-term stability of humic substances. Furthermore, these

investigations are very helpful for the determination ofgroundwater residence times using radiocarbon datingon humic substances. In addition, a better understand-

ing of the fate of aquatic humic substances allows con-clusions to be drawn with regard to the geochemicalevolution of groundwater systems.

Acknowledgements

The authors would like to acknowledge the ®nancialsupport of the Bundesministerium fuÈ r Bildung,Wissenschaft, Forschung und Technologie. The

authors also thank H. Siela� and D. Wesselow of theDBE at the Gorleben site for their assistance in

Fig. 11. Absorption ratio E3/E4 of fulvic acids from the

Franconian Albvorland aquifer plotted versus the redoxpoten-

tial of the groundwaters.

Fig. 12. Hydrodynamic size at the GPC elution pro®le maxi-

mum of the Gorleben, Munich and Franconian Albvorland

fulvic acids plotted versus the pH values of the groundwaters.


groundwater sampling, C. Kardinal and H. Halder forassistance in the DOC sample preparation and charac-

terization, and F. Scherbaum for assistance in the ¯u-orescence measurement. The isotope measurementswere carried out under the supervision of W. Rauert

and P. Trimborn.

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