Hydrochemistry and Isotope Geochemistry of the Upper Danube River

Home , Breg (river), Brigach, Donaueschingen, Krems (Lower Austria), Regen (river)

Geochimica et Cosmochimica Acta, Vol. 66, No. 21, pp. 3839–3854, 2002 Copyright © 2002 Elsevier Science Ltd Pergamon Printed in the USA. All rights reserved 0016-7037/02 $22.00 ϩ .00 PII S0016-7037(01)00880-8 Hydrochemistry and isotope geochemistry of the upper Danube River

1,† 1 1,2, FRANK PAWELLEK, FRANK FRAUENSTEIN, and JAN´ VEIZER * 1Institut fu¨r Geologie, Mineralogie und Geophysik, Ruhr-Universita¨t, 44801 Bochum, Germany 2Ottawa-Carleton Geoscience Centre, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada

(Received May 31, 2001; accepted in revised form October 13, 2001)

Abstract—The upper Danube River and 19 of its major tributaries were monitored for 1046 km downriver and seasonally for Ca, Mg, Sr, Na, K, HCO ,CO, Cl, PO , SiO ,NO,NO,NH,SO, ␦13C , ␦18O , 3 2 4 2 3 2 4 4 DIC H2O ␦D , ␦34S , ␦18O , and 87Sr/86Sr. Hydrological considerations and ␦18O/␦D data show that the water H2O SO4 SO4 balance in the river, particularly after its conﬂuence with the Inn, is controlled by the southern tributaries draining the Mesozoic carbonate complexes of the Alps. As a result, chemical balance at Bratislava is mostly a conservative product of its tributaries. The concentrations of Ca, Mg, and Sr in the Danube are 6 to 9 times higher than in “pristine” rivers. Although all these cations are derived from dissolution of Mesozoic

carbonates, the ultimate cause is likely the enhanced generation of soil CO2 due to agricultural and forestry practices. Dissolution of Triassic sulfates is an additional factor for Ca enrichment in the headwater section of the river. Dissolved sulfate, with a comparable enrichment factor to that of alkaline earths, appears to be derived mostly from atmospheric deposition, a proposition based on consideration of its sulfur and oxygen isotopic compositions. Na, K, and Cl are enriched by a factor of 2.5 to 4 times, mostly as a result of industrial and municipal pollution sources. In contrast to the above components, which behave mostly conservatively during the downriver ﬂow of the Danube, biogenic elements such as nutrients and Si are inﬂuenced by in-river processes. The photosynthesis/ respiration balance that impacts the carbon cycle and the oxygen balance has been discussed elsewhere

(Pawellek and Veizer, 1994). NO3,NO2, and NH4 are enriched by a factor of 10 to 16 times from point and diffuse sources along the watercourses, generating at times downflow nitrification plumes from NH4 to NO3. PO4 varies seasonally, chiefly as a result of biologic demand during the warm periods. For SiO2, the biological uptake (mostly for secretion of diatom frustules), combined with the deficiency of this compound that results from the predominantly carbonate lithology of the catchment, results in concentrations that are below those of pristine rivers. Overall, the present-day “salted” characteristics of the river are chiefly a consequence of the long habitation history of the upper Danube watershed. Copyright © 2002 Elsevier Science Ltd

1. INTRODUCTION 87Sr/86Sr of the Danube River from its source to km 1046 (southward bend of the river above Budapest) and of its major The Danube River, the second largest river in Europe after tributaries to study the downstream evolution of river hydro- the Volga River, originates, by definition, at the confluence of chemistry. the Brigach and the Breg in the garden of Donaueschingen castle, and after a 2857-km journey, it discharges into the Black 2. SAMPLING STATIONS AND FREQUENCY Sea at Sulina, Romania. In the studied 1046 km of the upper We sampled the Danube in December 1991 at 36 locations Danube (Fig. 1), the river flows through agricultural areas of over 1011 km and in April and September 1992 at 38 locations the northern Alpine foreland and through the urban centers of over 1046 km. In addition, 18 major tributaries (19 in Septem- Linz, Vienna, and Bratislava, with 0.2, 1.5, and 0.5 million ber) were sampled close to their confluence with the Danube inhabitants, respectively. In the investigated section, the river is (Fig. 1). The sampling in each session was carried out within impounded at 28 locations to manage high spring runoff and to 7 days, progressing downriver at a speed comparable to the ensure minimum navigation depth during the summer. In 1993, flow velocity of the Danube. Most samples are from midriver the much debated Gabeìkovo dam (Slovakia) was added to this sections. To assess seasonal changes in the measured parame- total, but the dam was not in operation at the time of sampling. ters, the Danube and two of its tributaries, the Ilz and the Inn, What is the impact of the above combination of geologic, were sampled monthly between September 1992 and Septem- biologic, and anthropogenic factors on the downstream chem- ber 1993 at Passau (station 19 at km 525). For quantification of ical evolution of the river? What role do tributaries play vs. the lateral homogeneity of the Danube water body, two samplings in-river processes for these dynamics? What are the sources for were carried out at Sandbach (km 455) and Stefanposching (km specific cations and anions for dissolved inorganic carbon and 465) in June 1993, at the center and on either side of the river. for riverine sulfate? The daily cyclicity of parameters related to the aquatic carbon In this contribution, we measured the chemical composition cycle was assessed by measurement at hourly resolution on the and the ␦18O , ␦D , ␦34S , ␦18O , ␦13C , and H2O H2O sulfate sulfate DIC Danube downstream of Passau (km 540).

3. ANALYTICAL TECHNIQUES * Author to whom correspondence should be addressed ([email protected]). The treatment of water samples was as follows. Tempera- † Present address: Grosser Ring 109, 46286 Dorsten, Germany. ture, conductivity, and pH were measured in the ﬁeld after 3839 3840 F. Pawellek, F. Frauenstein, and J. Veizer

Fig. 1. (a) The upper Danube catchment with sampled tributaries and sampling locations. Full circles ϭ tributaries; open circles ϭ the Danube River. The sampled locations on the Danube were as follows. 1. Donaueschingen (km 0). 2. Beuron (km 55). 3. Untermarchtal (km 128). 4. Ulm west (km 162). 5. Ulm (km 164). 6. Dillingen (km 217). 7. Donauwoerth (km 240). 8. Donauwoerth East (km 242). 9. Merxheim (km 254). 10. Vohburg (km 304). 11. Kehlheim (km 341). 12. Saal (km 345). 13. Mariaort (km 365). 14. Regensburg West (km 370). 15. Regensburg East (km 374). 16. Straubing (km 421). 17. Deggendorf (km 461). 18. Osterhofen-Tundorf (km 477). 19. Passau (km 525). 20. Pyrawang (km 539). 21. Schloeggen (km 564). 22. Linz (km 615). 23. Asten (km 633). 24. Pyburg (km 641). 25. Ybbs West (km 692). 26. Ybbs East (km 697). 27. Aggbach-Dorf (km 723). 28. Grafenwoerth (km 764). 29. Zwentendorf (km 779). 30. Tuttendorf (km 808). 31. Stapfenreuth bei Hainburg (km 870). 32. Dobrohost (km 909). 33. Sap (km 939). 34. Nova Straz (km 981). 35. Radvan nad Dunajom (km 993). 36. Kravany East (km 1011). 37. Sturovo (km 1035). 38. Kamenice (km 1046). The sampled tributaries were the following: Brigach (km 0). Breg (km 0). Iller (km 163). Wo¨rnitz (km 241). Lech (km 252). Altmu¨hl (km 341). Naab (km 366). Regen (km 372). Isar (km 469). Ilz (km 526). Inn (km 526). Traun (km 626). Enns (km 639). Ybbs (km 694). Kamp (km 767). Krems (km 767). Traisen (km 767). March (km 871). Va´h (km 985). Hron (km 1031). (b) Simpliﬁed geology of the upper Danube catchment. Danube hydrochemistry 3841

Table 1. Areal proportion of lithologies in the watersheds of muntersuchung (DEWAS) (1990). Concentrations and satura- Danube tributaries. tion values of dissolved oxygen were measured with the WTW Igneous/ Clastic Tertiary/ field oxymeter OXI 96 (Hu¨tter, 1988). The alkalinity was Lithology metamorphic Carbonates rocks Quaternarya measured with a Hach digital titrator, titrating with sulfuric acid within8hofsampling, with samples kept at ϳ4°C. Brigach 28 30 42 0 Ca, Mg, and Sr concentrations were measured by inductively Breg 85 15 0 0 Iller 0 0 16 84 coupled plasma–atomic emission spectroscopy (Philips PU Wo¨rnitz 0 7 0 93 7000) and Na and K concentrations by atomic absorption Lech 17 0 26 57 spectrophotometry (Varian AA 300) with reproducibilities bet- Altmu¨hl 0 40 58 4 ter than 3 and 5% of the measured concentrations, respectively. Naab 52 41 4 3 Regen 94 4 0 2 Bicarbonate concentrations were calculated following the ap- Isar 0 17 0 73 proach outlined in DEWAS (1990). Chloride concentrations Ilz 98 0 0 2 were measured by an Orion anion selective electrode with a Inn 42 18 0 40 detection limit of 1 mg/L. All other anions were determined by Traun 0 61 5 29 Enns 19 63 14 4 photometric spectrometry following the procedures specified in Ybbs 0 69 0 31 Hu¨tter (1988), with reproducibilities better than 10% of the Kamp 91 0 0 9 measured concentrations. Krems 96 0 0 4 The sampling strategy and analytical procedures for deter- Traisen 0 66 0 34 ␦13 March 33 17 21 29 mination of the C for the DIC were described elsewhere ␦18 Va´h21112444(Pawellek and Veizer, 1994). The Owater was determined by Hron 74 4 0 22 a modified method of Epstein and Mayeda (1953) and O’Neil

a et al. (1975) on a Finnigan MAT 251 and Delta-S mass spec- Predominantly clastic sediments with subordinate carbonates. ␦ trometers with a reproducibility of 0.14‰. The Dwater was prepared by reduction with zinc at 500°C (Coleman et al., unpressurized filtering through a paper filter (0.45 ␮m) by use 1982) and measured on the Delta-S, with reproducibility of of standard methods (Hu¨tter, 1988) and used (together with 1‰. The specifications for Sr isotope measurements, after alkalinity) for calculations of dissolved inorganic carbon (DIC) preconcentration, were described in Buhl et al. (1991), with Ϯ ϫ Ϫ6 speciation and pCO2 following the procedures given in the NBS 987 values during this project of 0.710238 10 10 . Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlam- The dissolved sulfate in filtered water samples (0.45 ␮m)

Fig. 2. Contribution of tributaries to the runoff of the Danube River from its “spring” to the conﬂuence with the March (km 871). 3842 F. Pawellek, F. Frauenstein, and J. Veizer

was precipitated as BaSO4 and, adding SiO2 and V2O5 6. HOMOGENEITY OF THE RIVER (Coleman and Moore, 1978; Yanagisawa and Sakai, 1983), thermally decomposed to SO2 at 1200°C for subsequent mea- Like all rivers, the Danube is prone to inhomogeneities in surement of ␦34S. The measurements were performed on a four dimensions: longitudinal (downstream), transverse (across Finnigan MAT 251 mass spectrometer, with a reproducibility river), vertical, and temporal. for a BaSO4 standard (Caribbean seawater sulfate) of 0.2‰. The first two inhomogeneities are often interrelated, partic- ␦18 For O, we used a modified approach of Sakai and Krouse ularly below the confluence with tributaries, leading to parallel (1971) and Shakur (1982), where BaSO4 was homogenized at “braids” of water bodies (Yang et al., 1996). By using conduc- 1:1 molar ratio with active carbon and thermally decomposed at tivity, a conservative water property, as a measure of the degree 1200°C for 15 min to produce CO2. Because of the formation of homogeneity, it was established (Pawellek, 1995), that once of a high-temperature complex S phase, the technique yielded the volume of the Danube water exceeds that of its tributaries results 3‰ heavier than a set of calibration samples. This by a factor of 10 to 15, a situation attained at ϳkm 350, the offset, however, was systematic, and the reproducibility for the main channel maintains its longitudinal homogeneity. The Caribbean sulfate was 0.44‰. transversal variability in conductivity was 22% (relative to Pawellek (1995) and Frauenstein (2000) describe further minimal value) at km 455 (Sandbach), but only 5% at 10 km details of analytical techniques and sampling procedures and provide lists of data. downriver (Stefanposching). Reliable results for vertical homogeneity could not be ob- tained because of high flow velocities that generated turbulence 4. GEOLOGY OF THE CATCHMENT around the sampling device, but because of this, it seems likely that the water body was vertically well mixed. This may not The Danube, between its source in southwest Germany and have been the case within reservoirs with their potentially Budapest (Hungary), drains the igneous and metamorphic Pre- stratified water bodies, and sampling at such localities was cambrian and Paleozoic block of the Bohemian Massif, Meso- avoided. In terms of daily evolution (temporal homogeneity), zoic carbonate sediments of the Swabian and Franconian Alb, measured at hourly resolution at Passau, the variability in the young orogenic belts of the Alps and Western Carpathians, conductivity, regardless of the season, was only 4%. Seasonal and the Cenozoic sediments of the Alpine molasse (Fig. 1b). variability, where pertinent, will be discussed below. For the most part, it follows the suture between the older In summary, we conclude that surface sampling of the Da- continental crust in the north and the young fold belts in the nube water at localities depicted in Figure 1 provides a reason- south. As a result, drainage basins of most tributaries are dominated by sedimentary, mostly carbonate, lithologies, with able approximation of chemical and isotopic characteristics of only some, relatively small and mostly northern, tributary the water body, particularly below km 350. catchments (Breg, Regen, Ilz, Kamp, Krems, and Hron) having predominantly silicate composition (Table 1). 7. WATER BALANCE OF THE DANUBE: ␦18O AND ␦D CONSTRAINTS 5. HYDROLOGY Both oxygen and hydrogen of precipitation, due to Rayleigh The long-term average water discharge of the Danube distillation processes, are progressively more depleted in light ϳ 3 River below Vienna is 2300 m /s (Regionale Zusammen- isotopes with increase in latitude and altitude (Craig and Gor- arbeit der Donaula¨nder, 1986). The bulk of the water (82 to don, 1965; Yurtsever, 1975; Siegenthaler, 1979), with deple- 92% during the sampling campaigns) is provided by the tions proportional to temperature gradients. Alpine precipita- southern Alpine tributaries, rendering the Danube discharge tion has ␦18O values as low as Ϫ18‰ and ␦D values as low as seasonally variable (Fig. 2). This seasonality becomes most Ϫ130‰ (IAEA WMO, 1998; Pastorelli et al., 2001). In con- pronounced after the confluence with the river Inn at Passau, trast, the “lowland” precipitation in Germany is ϳϪ8to which about doubles the Danube water volume, to ϳ1500 Ϫ10‰ for ␦18O (Rozanski et al., 1993). As a consequence, the m3/s in the spring. Danube discharge below Passau (km 525), controlled mostly by The 28 storage reservoirs—17 of these above Regensburg at the contribution from its southern Alpine tributaries (Fig. 2), km 372—can influence the hydrochemical characteristics of has an oxygen isotope signal depleted by ϳ1to2‰ relative to the water in three ways. First, the prolonged residence time of water in the reservoirs may either promote or retard internal the upstream section of the river (Fig. 3). The somewhat erratic nature of the ␦18O signal in the upper reaches of the Danube riverine processes, such as photosynthesis/respiration or gas H2O Ͻ exchange with the atmosphere (Mu¨ller and Kirchesch, 1986, ( km 350) can be attributed to incomplete mixing of tributary 1990). Second, dam spillovers and discharge via turbines gen- waters, as discussed in the section on homogeneity. The ␦D signal resembles that of the ␦18O , particularly erate turbulent flow that homogenizes the water body. Third, as H2O H2O a consequence of damming, the Danube water level is in many for the tributaries, with data points falling at or near Trimborn’s locations higher than the local groundwater table. As a result, (1993) meteoric waterline for southern Germany (␦D ϭ 7.74 ⅐ the general seepage direction is from the river outward and has ␦18O ϩ 6.50). This coherence suggests that evaporation from to be restrained by deep bulkheads along portions of the river open water bodies (here, the Danube and tributaries), a process course (Heikell, 1993). Groundwater influx therefore plays that would lead to deviation from the local meteoric waterline, only a marginal role in the water balance of the Danube. is negligible for the upper Danube riverine system. Danube hydrochemistry 3843

nents, with alkaline earths, bicarbonate and seasonally SiO2 tentatively assigned to geologic factors (carbonates vs. silicates), alkali metals and chloride to anthropogenic pollution,

and N and P compounds as well as O2 to complementary anthropogenic and biologic factors. SO4 does not show any clear pattern. If the tributaries were indeed the most important controlling factor of downriver evolution for the Danube, the sum of their inputs would have to approximate the chemical characteristics of the main stem river at our terminal sampling points. Any large deviations from the conservative behavior would argue ␦18 for an important role of internal riverine processes on down- Fig. 3. Downstream evolution of OH2O for the upper Danube River (the band incorporates all seasons) and for its tributaries stream evolution of hydrochemistry. (squares). To test this hypothesis, we calculated the weighted flux for each measured constituent of the dissolved load at Bratislava (station 32, Dobrohost). Accepting conductivity as a measure 8. DISTRIBUTION OF CHEMICAL SPECIES IN RIVER of total dissolved load, a poor match between the calculated and WATER the measured fluxes (Fig. 4) enables us to interpret deviations The previous discussions of hydrology, conductivity, and for individual constituents as being a result of in-river draw- ␦18O /␦D systematics demonstrated that the Danube wa- down or release. These balance calculations show that the H2O H2O ter balance is chiefly controlled by its tributaries; groundwater distributions of NH4 and PO4 are clearly affected by in-river input and evaporation are of limited impact. It is therefore processes; NO3,NO2, SiO2, and perhaps CO2 may be season- likely that tributaries control also the chemical characteristics ally affected; and alkaline earth (Ca, Mg, Sr), Na, and bicar- of the Danube. Taking into account that the tributaries reflect a bonate behave conservatively, as do Cl and K, except for the much broader variety of geologic, biologic, and population April sampling season. Sulfate shows only slight departure patterns than does the main stem river, it is of interest to look from conservative behavior. We conclude that the balance for common features reflected in their hydrochemistry. Factor calculations result in similar groupings to those from the factor analysis of the entire chemical and isotopic data set for the analyses for the tributaries and can therefore model the down- tributaries suggests three dominant factors as controlling pa- river hydrochemical evolution of the Danube in terms of con- rameters (Table 2), tentatively interpreted as geologic, anthro- trols indicated in Table 2. pogenic, and biogenic influences. These same factors were 8.1. Alkaline Earth Elements extracted for each sampling campaign (December, April, Sep- tember) despite some seasonal variations. Such treatment of the The downriver evolution of Ca2ϩ,Mg2ϩ, and Sr2ϩ is de- database enables us to discuss the results as groups of compo- picted in Figures 5 and 6. All these cations show a strong

Table 2. Factor analysis of the measured chemical parameters for the Danube tributaries.a

Geologic Anthropogenic Biogenic

Parameter Dec. Apr. July Dec. Apr. July Dec. Apr. July

Conductivity ϩϩϩ pH ϩϩ ϩϩϩ HCO3 Ca ϩϩϩ Mg ϩϩϩ Sr ϩϩϩ Na ϩϩϩ K ϩϩϩ Cl ϩϩ ϪϪ SiO2 ϩϩϩ O2 ϩϩϩ NO3 ϩϩϩ NO2 ϩϩϩ NH4 ϩϩ PO4 ϩϩ SO4 Percentage of variance 32 33 32 16 17 16 15 17 15 explained

a Separate factor analyses were run for the December 1991, April 1992, and September 1992 campaigns. Factor analyses were performed with the statistics program Statistica, version 5. Single varimax rotation was applied, and three multiple loading factors were extracted, which are interpreted as geologic, biogenic, and anthropogenic factors. Together, they explain between 63 to 67% of the total variance of data. In this summary, only loadings Ͼ 0.55 (ϩ)orϽϪ0.55 (Ϫ) are included. 3844 F. Pawellek, F. Frauenstein, and J. Veizer

cesses is of minor importance. Indeed, particularly after the conﬂuence with the Inn (km 526), the Danube only rarely attained supersaturation with respect to calcite (Fig. 7). Super- saturation was more of a rule in the upper “sulfate” reaches of the river, but this section contributes only subordinate quanti- ties to the overall water discharge at Bratislava.

8.2. Riverine Carbon Cycle

Dissolution of carbonates, the prime source of conductivity in the Danube River water, is closely coupled with the riverine carbon cycle, as discussed by Pawellek and Veizer (1994). In that contribution, it was concluded that carbonate dissolution in

soils, mediated by bacterial- and plant-derived CO2, was the main source of DIC in the Danube River water and that photosynthesis caused the post-Passau downriver trend of declin-

ing pCO2 during the warm season. The latter conclusion was based on the observation that the downriver decline in pCO2 ␦13 was accompanied by rising CDIC and O2 saturation levels. Although we endorse this conclusion, we would like to add some qualiﬁcations. Aquatic photosynthesis, particularly in the

warm season, causes large drawdown of CO2 and generates O2. Fig. 4. Measured vs. calculated loads of dissolved ion species in the To constrain such in-river photosynthetic rates, we measured Danube River at Dobrohost. the July net respiration and photosynthesis at Passau by use of the closed-bottle method of Mu¨ller (1975). The measured val- covariance (seasonal r2 ϭ 0.81 to 0.97), except for the head- ues for the transparent bottle were Ϫ0.00547 and ϩ0.00572 waters, where only Mg and Sr covary. The overall coherence mmol/L per hour for CO2 and O2, respectively. For the dark among alkaline earth elements can be attributed to their com- bottle, they were ϩ0.00367 and Ϫ0.00463 mmol/L. With these mon origin: dissolution of carbonates in the soils (Stumm and values, we calculated the impact for the Passau-Bratislava Morgan, 1996). The origin of alkaline earth elements from stretch of the river. The results (Pawellek, 1995) suggest that dissolution of Mesozoic carbonates is supported by the 87Sr/ aquatic photosynthesis in the Danube may account for ϳ1‰ 86 ␦13 Sr ratio of the dissolved Sr (Fig. 6), which resembles the downriver increase in the CDIC, or some one-third of the Mesozoic value for seawater at 0.707 to 0.708 (Burke et al., observed signal. This, in conjunction with the observation that ␦13 1982; Veizer et al., 1999). The silicate-dominated subcatch- the downriver CDIC trend agrees well with the one based on ments (Table 1), despite their high 87Sr/86Sr values, have little weighted contributions by the tributaries (Pawellek and Veizer, impact on the Sr (and Ca ϩ Mg) budget of the Danube as a 1994) and that the DIC in the main stem river is largely result of their subordinate water flux and low concentrations of conservative (Fig. 4), suggests that approximately two-thirds of alkaline earth elements. the photosynthetic drawdown of CO2 is accomplished within Accepting the 87Sr/86Sr ratio of silicate sources to be 0.716 the tributary subcatchments and approximately one-third in the and that of carbonate sources to be 0.708 (Fig. 6), ϳ93% of Danube itself. dissolved Sr in the Danube at Bratislava originates from carbonates, with a maximum of 7% derived from weathering of 8.3. Alkali Metals and Chloride silicates. This is comparable to global estimates for world rivers (Wadleigh et al., 1985; Goldstein and Jacobsen, 1987; Palmer The “jumpy” downriver distribution of ClϪ, the conservative and Edmond, 1989). anion, in the Danube illustrates several previously advocated The anomalously high Ca concentrations that persist up to points. First, the tributary and the Danube trends mostly mimic the confluence with the Inn (km 526 in Fig. 5a), as well as each other, confirming that the hydrochemistry of the latter is comparatively low Mg (Fig. 5b) and Sr, can be attributed to essentially a conservative property of the tributary inputs (Fig. dissolution of gypsum in the headwaters of the Danube as a 8). Second, the spiky nature argues for the importance of local result of outcrops of Triassic evaporites (Walter, 1992). This point sources, at least some of them of anthropogenic origin interpretation is consistent with the concurrent trend for sulfate (Table 2), but not all necessarily related to tributary inputs. For concentrations, discussed below. The “evaporite” signal is lost example, the highest peak, at km 633, was present during all mostly within the first 50 km (Figs. 5a, 6), although the tail end sampling campaigns, regardless of the magnitude of ClϪ input persists until about km 300 and beyond (Fig. 5). Subsequently, by the Traun tributary. This points to a source in the immediate the river maintains a stable molar Ca/Mg ratio of ϳ2, which is vicinity of the sampling station rather than within the broader typical of most large rivers (Meybeck, 1996) dominated by tributary catchment. Third, the ClϪ concentrations vary sea- weathering of carbonates. sonally, with September values mostly around 0.1 Ϯ 0.1 Considering that the alkaline earth elements in the Danube mmol/L, as opposed to April and December, with values in the behave conservatively (Fig. 4), it is reasonable to assume that ϳ0.5 Ϯ 0.3 mmol/L range. ϩ ϩ precipitation of CaCO3 by evaporative or photosynthetic pro- The concentrations of Na and K show similar erratic Danube hydrochemistry 3845

Fig. 5. Downriver evolution of Ca2ϩ concentrations and Ca2ϩ/Mg2ϩ ratios in the upper Danube River. downriver trends, with a clear seasonal variability. For Naϩ, The large scatter of Na/Cl values, well beyond 1:1 mol/L the April 1992 values hovered around 0.3 Ϯ 0.1 mmol/L, ratios, argues against NaCl from anthropogenic and natural whereas the December 1991 and September 1992 concentra- sources as the sole contributor of these species. Naϩ and Kϩ tions were mostly in the 0.7 Ϯ 0.1 mmol/L range, the latter with correlate highly (Table 2), but their ratios decline with the local spikes at double these values in the vicinity of Regens- decreasing concentrations from ϳ10:1 to ϳ4:1. This suggests burg, at km 697, and below Bratislava, conﬁrming again that that at low concentrations, a greater proportion of both cations, localized sources are the main contributor (Table 2). For Kϩ, and particularly Kϩ, may originate from dissolution of silicate the April values were at ϳ0.06 Ϯ 0.02 and the December– minerals. Such an assertion is consistent with the observation September values were at ϳ0.08 Ϯ 0.02 mmol/L. that the Danube water samples plot directly on the illite (mus- 3846 F. Pawellek, F. Frauenstein, and J. Veizer

Fig. 6. Downstream evolution of Sr concentrations and 87Sr/86Sr ratios in the upper Danube River in December 1991. Also plotted are the respective data for the sampled tributaries. covite)/kaolinite tangent in the mineral stability phase diagram If, despite the lack of lithological correlation, we assume that (Fig. 9), perhaps shifted to this tangent from the feldspar this was the case, the generated sulfate in soil horizons would ␦34 stability field as a result of the biogenic sequestration of SiO2 have inherited the low S values (Ivanov et al., 1983; Gri- (discussed below). nenko and Krouse, 1992) from the precursors (Fig. 11) and 3⁄4 of its oxygens would have been derived from the local water 8.4. Sulfate (Mayer, 1998), the latter having depleted ␦18O values (Fig. 3). Neither the ␦34S nor the ␦18O (Fig. 11) requirement is met by The sulfate concentrations are high at the source but decline the aquatic sulfate data. Atmospheric deposition is therefore rapidly within the first 50 km (Fig. 10). Subsequently, despite 2Ϫ likely the major source of dissolved sulfate (Fig. 11). Such some variability, the seasonal SO4 concentrations show sim- secondary sulfate, formed from oxidation of SO in emission ϳ ϳ 2 ilar downriver trends, a rise from 0.2 to 0.4 mmol/L in the plumes of temperate regions, has ␦18O of about ϩ7toϩ17‰; first 350 km, followed by sulfate dilution and return to higher the mean values for central Europe are about ϩ10 to ϩ12‰ values in the Vienna–Bratislava section and beyond. (Krouse and Mayer, 2000). The mean values for atmospheric The high concentrations in the headwaters can be attributed to ␦34 ϩ Ssulfate for southern Germany and Austria range from 2.1 the previously discussed dissolution of Triassic sulfates, an inter- to ϩ3.5‰ (Mayer, 1998). The isotopic signature of the riverine ␦34 ␦18 pretation supported also by the S and O signals (Figs. 10b,c, sulfate (Fig. 11) is therefore consistent with the proposition that 11). The rise in sulfate concentrations from a postheadwater min- it is chiefly of atmospheric origin. imum, accompanied by a simultaneous rise in isotopes, is due In summary, we propose that the dissolved sulfate in the Յ principally to inputs from the rivers Wo¨rnitz ( 0.84 mmol/L Danube and tributary waters is predominantly from atmo- Յ Յ Յ SO4), Altmu¨hl ( 0.62), Regen ( 0.48), Inn ( 0.45), Ybbs spheric deposition, although a direct attribution to anthropo- Յ Յ Յ Յ ( 0.48), Kamp ( 0.63), Traisen ( 0.56), March ( 1.14), and genic vs. natural sources would require studies specifictoa Յ Va´h( 0.59). A review of the geology of these tributaries (Table given region. 1), and of their low-sulfate counterparts, documents that there is no relationship between aquatic sulfate content (and isotopes) and the 8.5. Nitrogen Compounds lithological composition of the catchments. Theoretically, the source of sulfate in subsurface waters The three measured inorganic nitrogen species (nitrate, ni- could be the oxidation of sedimentary sulfides (Berner, 1971). trite, ammonium) show mainly unsystematic variations along Danube hydrochemistry 3847

Fig. 7. Calcite saturation index for the upper Danube River. the river course (Fig. 12), suggesting that point sources, pre- 1996). Yet the major algal blooms, which usually occur in sumably of anthropogenic origin (Table 2), play an important April (Bothar and Kiss, 1990), do not seem to deplete the role. Somewhat higher concentrations of nitrogen species were riverine nitrate. This may be the result of concomitant washout observed, particularly below the confluence with Wo¨rnitz and of fertilizers from the fields by spring melt waters, as observed Lech (km 241 to 252). in Hungary (Varga et al., 1990). This effect likely masks the The concentrations of the studied nitrate species in riverine high rate of biologic nitrate consumption. systems are usually controlled by processes in the catchment area (Fleckseder, 1993), in central Europe mostly by anthropo- 8.6. Orthophosphate genic inputs from agricultural activities (fertilizers) and from municipal and industrial discharges. These inputs are modified Concentration of orthophosphate, the limiting factor of au- ϩ by biologic processes in the river itself, with oxidation of NH4 totrophic life (e.g., Brehm and Meijering, 1990), showed erratic Ϫ Ϫ to NO2 and subsequently to NO3 (Brehm and Meijering, downstream, but somewhat clearer seasonal, variations. In the 1990), reflected in sequential downriver plumes in the Danube Danube, the maximum of ϳ500 ␮mol/L was reached at km 128 below the confluence with some tributaries. For example, dur- (Untermarchtal) during the December sampling, but the bulk of ing warmer seasons, the Lech, with an input of ϳ0.25 to 0.3 concentrations was less than 100 (usually Ͻ50) ␮mol/L. Near mol/s NH4-N, triggers a cascade of oxidation steps, the first Passau, the mean concentrations were highest in the winter and Ϫ Ϫ by-product being NO2 , with subsequent production of NO3 lowest in the spring/summer, as demonstrated by the monthly downriver (arrow in Fig. 12). measurements of the Danube, the Inn, and the Ilz (Fig. 13). Although the biologic oxygen demand of the Danube water As for nitrogen compounds, the erratic concentration values is relatively low (Ludwig et al., 1990), pointing to an attenuated suggest the importance of anthropogenic sources. According to biologic impact on the nitrogen cycle, important photosynthetic Fleckseder (1993), the Danube acquires approximately one- 3Ϫ activity is clearly indicated by consideration of the carbon cycle third of its PO4 load from diffuse sources, such as agricultural and by concomitant oxygen supersaturation (Pawellek and fertilizers (the bulk of phosphate from manure is absorbed Veizer, 1994). Such photosynthetic processes should promote already in the soils; Mu¨ller, 1988), and approximately two- bacterial nitrification or physical auto-oxidation (Flintrop et al., thirds from point sources, mostly communal wastewater and 3848 F. Pawellek, F. Frauenstein, and J. Veizer

Fig. 8. Concentrations of ClϪ in the upper Danube River and its tributaries in December. sewage. The latter sources account for the calculated “excess” 8.7. Silicic Acid load of phosphate in the Danube at Bratislava, relative to that expected from tributary inputs (Fig. 4) as well as for the H4SiO4 (here reported as SiO2) in the Danube does not show pronounced local variations of phosphate concentrations. any clear trend downriver, with values, except at the source, Ϯ The seasonal decline in the spring/early summer (Fig. 13) mostly in the 0.1 0.06 mmol/L range. Such low SiO2 may result from two independent processes. First, it can be a concentrations are partly because most of the water in the consequence of enhanced biologic uptake during algal blooms. Danube originates from the southern “carbonate” tributaries, Second, the loss may be due to phosphate adsorption on Fe and such as the Inn (Fig. 13), whereas the contribution by the Al hydroxides in the riverine suspended load (Froelich, 1988), “silicate” ones, such as the Ilz, is of lesser impact. In addition, the latter attaining its maximum also at this time as a result of silica uptake by algal blooms, particularly the diatom Steph- Alpine snowmelt (Rank, 1986). We believe that these two anodiscus hantzschii (Kiss and Csutor-Bereczky, 1988), for processes are complementary rather than exclusive. formation of their frustules (Tessenow, 1966; Brehm and Mei- jering, 1990) further depletes silica concentrations in the river. These blooms usually happen in the spring, but their timing may vary from one year to another (Bothar and Kiss, 1990).

9. STATE OF THE RIVER

In terms of its major ion chemistry, the Danube is a typical Ca-bicarbonate river in the sense of Gibbs (1970). The char- acteristic ranges for components studied in this project are summarized in Figure 14, together with the upper ranges of typical values for major rivers, and for major pristine rivers (most common natural concentrations, or MCNC), such as the Amazon and Mackenzie (Meybeck and Helmer, 1989; Mey- beck, 1996). On the basis of this comparison, the Danube falls close to the upper limit of concentrations in major rivers, classed as “salted” by Meybeck (1996). A clear exception is

SiO2, with concentrations below typical natural values. Com- ϩ ϩ Fig. 9. The aK /aH phase diagram for the upper Danube water. pared with pristine rivers, the Danube is characterized by the Danube hydrochemistry 3849

␦34 ␦18 Fig. 10. Sulfate concentrations and downriver trends for SSO4 and OSO4 in the upper Danube. following enrichment factors: alkali metals and ClϪ ϳ2.5 to 4 times. Note also that these characteristics are typical for the ϳ 2Ϫ ϳ times, alkaline earth and bicarbonate 6 to 9 times, SO4 8 entire length of the upper Danube once it attains its critical times, and nitrogen and phosphorus compounds ϳ10 to 16 water discharge at about km 350. Variations in chemistry with 3850 F. Pawellek, F. Frauenstein, and J. Veizer

Fig. 11. Scatter diagram of ␦34S vs. ␦18O for dissolved sulfate in the upper Danube water. The fields for evaporites from Claypool et al. (1980) and the other commonly observed ranges from Krouse and Mayer (2000). Seasons are not differentiated. water discharge do exist, but they are mostly related to seasonal rock weathering (Roy et al., 1999). For the Danube, the appor- hydrology and not to increasing discharge downriver. The only tionment is nevertheless supported by the 13C depletion of its exceptions to this pattern are the components of the carbon DIC (Pawellek and Veizer, 1994). cycle discussed in Pawellek and Veizer (1994). In contrast to the alkaline earth, with enrichment attributed The comparatively high concentrations of alkaline earth (Fig. only indirectly to anthropogenic causes, the enrichments in 14) are partially a product of weathering of carbonate rock alkali metals and chloride appear to load directly on the “an- (Table 2). The MCNC pristine estimates are derived from a thropogenic” factor (Table 2), but attribution to specific compilation of rivers draining the carbonate as well as silicate sources, such as road salting, fertilizers, and industrial and terrains (Meybeck and Helmer, 1985), potentially resulting in a municipal wastes, would require localized studies. For the somewhat attentuated baseline values for the alkaline earth. upper Danube catchment, it is not likely that cyclic salts play an Nonetheless, this is unlikely to account for the observed order important role in the hydrochemistry of the river. Accepting ϳ4 of magnitude difference between the Danube and the MCNC mmol/L as the average ClϪ content for rain in western and concentrations (Fig. 14). The high concentrations in the Da- central Europe (Berner and Berner, 1987), and accepting a Ϫ nube are therefore likely a response to the high HCO3 resulting runoff ratio of 0.42, the recycling marine salts may account at from enhanced bacterial decomposition of soil organic matter. best for the MCNC values in pristine rivers, the latter ϳ2.5 to Some of this enhancement is likely due to agricultural and 4 times more dilute than the Danube. forestry practices and human activity may therefore be an The isotope data for sulfate led to the conclusion that its important factor for alkaline earth enrichment in the Danube source is mainly atmospheric deposition. As for ClϪ, recycled water. The downriver evolution of the carbon cycle, due to marine sulfate can explain only the MCNC concentrations, but photosynthesis/respiration and exchange with the atmosphere, not the ϳ8 times enrichment in the Danube water. Except for which is superimposed on the above imprint, has previously the “sulfate-buffered” headwater stretch of the river, diverse been discussed (Pawellek and Veizer, 1994). Our attribution of anthropogenic inputs are again the likely culprits. The large Ϫ HCO3 to potential sources differs somewhat from that of the enrichments (10 to 16 times) of the Danube water in nitrogen Seine, a river with comparable Ca and bicarbonate contents, and phosphorus compounds, although biologically mediated, Ϫ where the HCO3 was assumed to have originated solely from are ultimately a reflection of anthropogenic impact, the result of Danube hydrochemistry 3851

Ͻ Fig. 12. Concentrations of NO3-N and NH4-N in the upper Danube. Concentrations of NO2-N were usually 0.05 (mostly 0.02 Ϯ 0.01) mmol/L, except for a spike at Lech at 0.12 mmol/L. agricultural and forestry practices (fertilizers in particular), and resulting in concentrations of major ions that are 2.5 to 16 times the industrial and municipal waste discharges (Meybeck, 1982; above those in unaffected watercourses. SiO2 is the only mea- Berner and Berner, 1987). sured component that is present at concentrations less than the In summary, the present-day hydrochemistry of the Danube average for pristine rivers (Fig. 14), reﬂecting the predomi- (and its tributaries) is visibly impacted by human activity, nantly carbonate lithology of the Danube catchment basin and the role of silica as a biogenic element used for precipitation of siliceous tests, principally by diatoms.

10. CONCLUSIONS

The upper Danube, because of its considerable lateral homogeneity and essential absence of direct local groundwater influx, represents an example of a river that is suitable for the study of origin and processing of dissolved constituents in river water. The investigated chemical and isotopic parameters in the major tributaries of the Danube reflect a threefold influence of geologic, biologic, and human factors in their catchment and the Danube itself is mostly a conservative mirror of the tributary inputs. The clear exceptions from this pattern are only the component of carbon, nitrogen, phosphorus, and silica cycles that reflect also the influence of in-river biologic activities. Compared with pristine rivers, the Danube is enriched by a factor of 2.5 to 4 times in Na, K, and Cl, 6 to 8 times in Ca, Mg,

Sr, HCO3, and SO4, and 10 to 16 times in N and P compounds, with all these enrichments resulting mostly from anthropogenic

impact on the river and its subbasins. SiO2 is the only species depleted in comparison to pristine rivers, an outcome of bio- Fig. 13. Orthophosphate and silicic acid concentrations in the Da- logic use by diatoms for secretion of their frustules as well as nube, the Ilz, and the Inn from monthly measurements at Passau (km of the predominantly carbonate lithology of the upper Danube 525), between September 1992 and August 1993. catchment. 3852 F. Pawellek, F. Frauenstein, and J. Veizer

The age curves of sulfur and oxygen isotopes in marine sulfate and their mutual interpretation. Chem. Geol. 28, 199–260. Coleman M. L. and Moore M. P. (1978) Direct reduction of sulfates to sulfur dioxide for isotopic analysis. Chem Geol. 50, 1594–1595. Coleman M. L., Shepherd T. J., Durham J. J., Rouse J. E., and Moore G. R. (1982) Reduction of water with zinc for hydrogen isotope analysis. Chem. Geol. 54, 993–995. Craig H. and Gordon L. I. (1965) Deuterium and oxygen-18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperatures (ed. E. Tougiorgio), pp. 1–22. Consiglio Nazionale delle Ricerche, Laboratorio di Geo- logia Nucleare. Deutsche Einheitsverfahren zur Wasser-, Abwasser und Schlam- muntersuchung [DEWAS] (1990) Physikalische, chemische, biolo- gische und bakteriologische Verfahren, Abschnitt D8(ed. Fach- gruppe Wasserchemie in der Gesellschaft deutscher Chemiker in Gemeinschaft mit dem Normenausschuss Wasserwesen im Deut- schen Institut fu¨r Normung e.V.), pp. 1–11. Verlag VCH. Epstein S. and Mayeda T. K. (1953) Variations of the O18/O16 ratio in natural waters. Geochim. Cosmochim. Acta 4, 213–224. Fleckseder H. (1993) Estimates for the Sources of N and P and the Discharge to Sea for the Rivers Rhine, Elbe and Danube. European Water Pollution Control Association Symp. Flintrop C., Hohlmann B., Jasper T., Korte C., Podlaha O., Scheele S., and Veizer J. (1996) Anatomy of pollution: Rivers of North Rhine– Westphalia, Germany. Am. J. Sci. 296, 59–98. Frauenstein F. (2000) Schwefel- und Sauerstoffisotopenverha¨ltnisse in gelo¨stem Sulfat: Methodenentwicklung und Bearbeitung fluviatiler Sulfatproben am Beispiel der Donau. Diplomarbeit. Ruhr Universi- ta¨t, Bochum. Froelich P. N. (1988) Kinetic control of dissolved phosphate in natural rivers and estuaries: A primer on the phosphate buffer mechanism. Limnol. Oceanogr. 33, 649–668. Gibbs R. J. (1970) Mechanisms controlling world water chemistry. Science 170, 1088–1090. Goldstein S. J. and Jacobsen S. B. (1987) The Nd and Sr isotopic systematics of river-water dissolved material: Implications for the sources of Nd and Sr and seawater. Chem. Geol. 66, 245–272. Fig. 14. Typical ranges for specific components in the Danube River Grinenko Y. A. and Krouse H. R. (1992) Isotope data on the nature of water. Also marked are the upper limits for these components in major riverine sulfates. Mitt. Geol. Palaönt. Inst. Hamburg 72, 9–18. world rivers, and median concentrations in pristine rivers (most com- Heikell R. (1993) Die Donau. Edition Maritim. mon natural concentrations, or MCNC) (Meybeck and Helmer, 1989; Hu¨tter L. A. (1988) Wasser und Wasseruntersuchung. Diesterweg. Meybeck, 1996). Internantional Atomic Energy Agency, World Meteorological Organi- zation. (1998) Global network for isotopes in precipitation. The GNIP database. Updated May 2, 1998. Available at: http://www. iaea.org.programs/ri/gnip/gnipmain.htm. Acknowledgments—This study was funded by the German Research Ivanov M. V., Grinenko Y. A., and Rabinovich A. P. (1983) Sulphur Council (DFG), grant Ve 112/5-1/2. We thank Harald Strauss, Bern- flux from continents to oceans. In The Global Biogeochemical Sul- hard Mayer, and Dieter Buhl for help with preparations and isotope phur Cycle (eds. M. V. Ivanov and J. R. Freney), pp. 331–356. ratio measurements and Andreas Diener for assistance in the field. The Wiley. reviews and comments of S. Sheppard and three anonymous reviewers Kiss K. and Csutor-Bereczky M. (1988) Untersuchungen des Phyto- substantially improved the manuscript. planktons und der Ciliatenfauna der Donau von Vilkovo bis Wien im Ma¨rz 1988. In Ergebnisse der Donauexpedition 1988: Internationale Associate editor: S. M. F. Sheppard Arbeitsgemeinschaft Donauforschung (ed. E. Weber), pp. 163–171. Eingen-Verlag IAD. REFERENCES Krouse H. R. and Mayer B. (2000) Sulphur and oxygen isotopes in sulphate. In Environmental Tracers in Subsurface Hydrology (eds. Berner R. A. (1971) Worldwide sulfur pollution of rivers. J. Geophys. P. G. Cook and A. L. Herczeg), pp. 195–231. Kluwer. Res. 76, 6597–6600. Ludwig Ch., Ranner H., Kavka G., Kohl W., and Humpesch U. (1990) Berner K. E. and Berner R. A. (1987) The Global Water Cycle. Prentice Long-term and seasonal aspects of the water quality of the river Hall. Danube within the region of Vienna (Austria). Water Sci. Technol. Bothar A. and Kiss K. T. (1990) Phytoplankton and zooplankton 22, 51–58. relationship in the eutrophicated river Danube. Hydrobiologia 191, Mayer B. (1998) Potential and limitations of using sulphur isotope 165–171. abundance ratios as an indicator for natural and anthropogenic en- Brehm J. and Meijering M. P. D. (1990) Flie␤gewa¨sserkunde. Quelle vironmental change. In Isotope Techniques in the Study of Environ- and Meyer. mental Change, pp. 423–435. International Atomic Energy Agency, Buhl D., Neuser A. D., Richter D. K., Riedel D., Roberts B., Strauss H., Vienna. and Veizer J. (1991) Nature and nurture: Environmental isotope Meybeck M. (1982) Carbon, nitrogen, and phosphorus transport by story of the river Rhine. Naturwissenschaften 78, 337–346. world rivers. Am. J. Sci. 282, 401–450. Burke W. H., Denison R. E., Hetherington E. A., Koepnick R. B., Meybeck M. (1996) River water quality: Global ranges, time and space Nelson H. F., and Otto J. B. (1982) Variation of seawater 87Sr86Sr variabilities, proposals for some redefinitions. Verh. Internat. Verein throughout Phanerozoic time. Geology 10, 516–519. Limnol. 26, 81–96. Claypool G. E., Holser, W. T., Kaplan I. R., Sakai H., and Zak I. (1980) Meybeck M. and Helmer R. (1989) The quality of rivers: From pristine Danube hydrochemistry 3853

stage to global pollution. Palaeogeogr. Palaeoclim. Palaeoecol. 75, Sakai H. and Krouse H. R. (1971) Elimination of memory effects in 283–309. 18O/16O determinations in sulfates. Earth Planet. Sci. Lett. 11, 369– Mu¨ller S. (1975) Sauerstoffhaushalt von Flie␤gewa¨ssern: Diskussion 373. der wesentlichen Einflussgro¨␤en. Schriftenr. Bayer. LA f. Um- Shakur M. A. (1982) ␦34S and ␦18O variations in terrestrial sulfates. weltsch. 1, 5–72. Ph.D. thesis. University of Calgary. Mu¨ller K. (1988) Untersuchungen zum Stickstoff-, Phosphor- und Siegenthaler U. (1979) Stable hydrogen and oxygen isotopes in the Kaliumeintrag in das Grundwasser nach Gu¨lledu¨ngung. Acta Hydro- water cycle. In Lectures in Isotope Geology(eds. E. Ja¨ger and J. C. chim. Hydrobiol. 16, 397–405. Hunziker), pp. 264–284. Springer. Mu¨ller D. and Kirchesch V. (1986) Zur Auswirkung der Stauregu- Stumm W. and Morgan J. J. (1996) Aquatic Chemistry. Wiley. lierung auf den Sauerstoffhaushalt von Mosel, Fulda, Saar und Tessenow U. (1966) Untersuchungen u¨ber den Kieselsaüregehalt der Donau: Mikrobiologisch-biochemische Untersuchungen und Gu¨te- Binnengewa¨sser. Arch. Hydrobiol. Suppl. 32, 1–128. modellrechnungen—Teil I. Dt. Gewa¨sserkdl. Mitt. 30, 152–162. Mu¨ller D. and Kirchesch V. (1990) Algenwachstum in Flie␤gewa¨ssern: Trimborn P. (1993) Messungen des Deuterium- und Sauerstoff-18- Gu¨temodellaussagen zum Einfluss von Tiefe, Zooplankton und Gehalts von Niederschlagswasser,pp. 170–173. Jahresbericht Insti- Na¨hrstoffgehalt. Dt. Gewa¨sserkdl. Mitt. 34, 66–75. tut fu¨r Hydrologie, GSF-Forschungszentrum fu¨r Umwelt und Ge- O’Neil J. R., Adami L. H., and Epstein S. (1975) Revised value for the sundheit. 18 Varga P., Abraham M., and Simor J. (1990) Water quality of the O fractionation between CO2 and H2Oat25°C. J. Res. Geol. Surv. 3, 623. Danube in Hungary and its major determining factors. Water Sci. Palmer M. R. and Edmond J. M. (1989) The strontium isotope budget Technol. 22, 113–118. of the modern ocean. Earth Planet. Sci. Lett. 92, 11–26. Veizer J., Ala D., Azmy K., Bruckschen P., Buhl D., Bruhn F., Carden Pastorelli S., Marine L., and Hunziker S. (2001) Chemistry, isotope G. A. F., Diener A., Ebneth S., Godderis Y., Jasper T., Korte C., ␦ ␦18 ␦34 87 86 ␦13 values ( D, O, SSO4) and temperatures of the water inflows in Pawellek F., Podlaha O. G., and Strauss H. (1999) Sr/ Sr, C two Gotthard tunnels, Swiss Alps. Appl. Geochem. 16, 633–649. and ␦18O evolution of Phanerozoic seawater. Chem. Geol. 161, Pawellek F. (1995) Geochemie und Isotopengeochemie von 59–88. ␤ Flie gewa¨ssern am Beispiel der oberen Donau und einiger ihrer Wadleigh M., Veizer J. and Brooks C. (1985) Strontium and its Nebenflu¨sse. RNDr thesis. Ruhr-University, Bochum. isotopes in Canadian rivers: Fluxes and global implications. Pawellek F. and Veizer J. (1994) Carbon cycle in the upper Danube and Geochim. Cosmochim. Acta 49, 1727–1736. its tributaries: ␦13C constraints. Isr. J. Earth Sci. 43, 187–194. DIC Walter R. (1992) Geologie von Mitteleuropa. Schweizerbart. Rank D. (1986) Isotopenverha¨ltnisse und Radionuklide—Spuren in der Yanagisawa F. and Sakai H. (1983) Thermal decomposition of barium Umwelt. Mitt. O¨ sterr. Geol. Ges. 79, 343–357. sulfate–vanadium pentoxide–silica glass mixtures for preparation of Regionale Zusammenarbeit der Donaula¨nder. (1986) Die Donau und ihr Einzugsgebiet—Eine hydrologische Monographie. Selbstverlag. sulfur dioxide in isotope ratio measurements. Anal. Chem. 55, 985– Roy S., Gaillardet J., and Alle´gre C. J. (1999) Geochemistry of dis- 987. solved and suspended loads of the Seine river, France: Anthropo- Yang C., Telmer K., and Veizer J. (1996) Chemical characteristics of ␦ ␦13 ␦34 genic impact, carbonate and silicate weathering. Geochim. Cosmo- the “St. Lawrence” riverine system: DH2O, CDIC, Ssulfate and chim. Acta 63, 1277–1292. dissolved 87Sr/86Sr. Geochim. Cosmochim. Acta 60, 851–866. Rozanski K., Aaragua´s-Aragua´s L., and Gonfiantini R. (1993) Isotopic Yurtsever Y. (1975) Worldwide Survey of Stable Isotopes in Precipi- patterns in modern global precipitation. In Continental Isotope In- tation: Report of the Section of Isotope Hydrology. International dicators of Climate, Vol. 78, pp. 1–36. American Geophysics Union. Atomic Energy Agency.