HYDROLOGICAL PROCESSESHydrol. Process. 17, 1267–1277 (2003)Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/hyp.1283

The geochemical characteristics of the Parana Riversuspended sediment load: an initial assessment

Pedro J. Depetris,1* Jean-Luc Probst,2 Andrea I. Pasquini1 and Diego M. Gaiero3†

1 Centro de Investigaciones Geoquımicas y de Procesos de la Superficie (CIGeS), F.C.E.F. y N., Universidad Nacional de Cordoba, Avda.V. Sarsfield 299, 5000 Cordoba, Argentina

2 Laboratoire des Mechanismes de Transfer en Geologie, CNRS/U. Paul Sabatier, 38 rue des 36 Ponts, 31078 Toulouse Cedex, France3 Centre de Geochemie de la Surface, CNRS/U. L. Pasteur, 1 rue Blessig, 67084 Strasbourg Cedex, France

Abstract:

Most water in the Parana River drainage basin is supplied by the tropical Upper Parana (over 60% of the total annualwater discharge, 550 km3�. The total suspended solids (TSS) load (c. 80 ð 106 t year�1�, however, is essentiallyfurnished (50–70%) by the mountainous, arid and mostly sediment-mantled upper Bermejo River drainage basin. Thischaracteristic suggests that the Parana River solid load (TSS, 600 km upstream from the mouth) is largely recycledsedimentary material, whose discharge-weighted mean chemical index of alteration is c. 71. The extended UCC-normalized multi-elemental diagrams are similar to those of other world rivers. Nevertheless, the detailed inspectionof UCC-normalized rare earth element (REE) ‘spidergrams’ reveals a lithological source for the Parana River TSSthat might be compatible with either tholeiitic flood basalts (widespread in the upper drainage) or with young Andeanintermediate volcanic rocks. In view of the Bermejo River’s dominant role as a sediment contributor, we feel that thesignature preserved in the Parana’s TSS is the latter. Conversely, the Uruguay River TSS REE signature is certainlydetermined by the extensive weathering products of Jurassic–Cretaceous tholeiitic basalts. Copyright 2003 JohnWiley & Sons, Ltd.

KEY WORDS geochemistry; suspended sediment; Parana River; REE; CIA; sediment sources

INTRODUCTION

The composition and concentration of the total suspended sediment (TSS) loads of world rivers are determinedby the characteristics of their respective drainage basins; including geology, climate, relief and biota. Humanactivities also affect riverine TSS concentrations and composition.

Thanks to several studies, the factors governing continental erosion and sediment yield are nowadays moreclearly understood (e.g., Milliman and Syvitski, 1992; McLennan, 1993; Ludwig and Probst, 1996; Wallingand Webb, 1996). There is still interest in gathering data on the geochemical nature of the world’s large riversTSS load and, moreover, in comprehending better the role of factors controlling the composition of suspendedloads of world rivers (Gaillardet et al., 1999). This concern is mostly linked to the evaluation of chemicalweathering and the associated CO2 consumption fluxes (Amiotte-Suchet and Probst, 1993) in order to assessthe role of this mechanism in controlling the Earth’s climate (Berner et al., 1983; Raymo and Ruddiman,1992).

In this contribution, we have used geochemical data obtained from a TSS sample suite collected in theParana River drainage basin. Some of the samples were collected in the early 1970s; other TSS samples wererecently collected within the framework of a project initially sponsored by the European Commissions, and

* Correspondence to: Pedro J. Depetris, Centro de Investigaciones Geoquımicas y de Procesos de la Superficie (CIGeS), F.C.E.F. y N.,Universidad Nacional de Cordoba, Avda. V. Sarsfield 299, 5000 Cordoba, Argentina. E-mail: pdepetris@com.uncor.edu† Centro de Investigaciones Geoquımicas y de Procesos de la Superficie (CIGeS), F.C.E.F. y N., Universidad Nacional de Cordoba, Avda.V. Sarsfield 299, 5000 Cordoba, Argentina

Received 20 August 2001Copyright 2003 John Wiley & Sons, Ltd. Accepted 28 January 2002

1268 P. J. DEPETRIS ET AL.

currently supported by Argentina’s CONICET and FONCYT. The objective of this paper is to determine theTSS geochemical fingerprint of the Parana River and to assess the relative role of diverse lithological sourcesin controlling the TSS geochemical composition.

DATA SOURCES

This paper is partially based on a set of depth-integrated TSS samples, collected in the Parana River drainagebasin (Argentina) between 1971 and 1973 by the UNDP/Argentine Government ARG 31 project. The sampleswere collected in high-relief tributaries, mainly from the Bermejo River drainage basin (San Francisco andPescado rivers), in the Bermejo and Pilcomayo rivers, and in the Parana main stem (at Corrientes, 1208 kmupstream from the mouth, and at Parana, 601 km upstream from the mouth) (Figure 1). The remaining TSSsamples were collected within the framework of a project supported by Argentina’s CONICET and FONCYT,initiated with the aid of the European Commissions. Such sample collection took place at Parana and Rosario(420 km upstream from the mouth) in the Parana River, and at Gualeguaychu (c. 90 km upstream from themouth) in the Uruguay River.

Depth-integrated suspended sediment samples collected in the early 1970s were initially flocculated with alanthanum nitrate [La(NO3�3ÐxH2O] solution and then centrifuged, washed, dried, weighted and stored. Thisprocedure, therefore, precluded the determination of rare earth elements in that particular sample set. TheTSS samples recently collected at Parana and Rosario (in the Parana River) were obtained from 0Ð5 m belowthe water surface, at different points across the river section. The same scheme was followed for the samplescollected in the Uruguay River, near Gualeguaychu. TSS were pre-concentrated by pressure filtration under1Ð5 atm N2 on GS type Millipore 0Ð45 µm filters (; 142 mm) and subsequently dried at 50 °C for 24 h.

The sample set was recently analysed by means of ICP-AES and ICP-MS for major components and traceelements at the Centre de Geochimie de la Surface (CNRS/ULP, Strasbourg, France). Analytical precision was2% for major oxides and 5% for trace elements; standards analysed are included in the corresponding table.

WATER DISCHARGE, TSS TRANSPORT AND MINERALOGY

With a basin area of 2Ð8 ð 106 km2, the Parana River is the second largest drainage system in South America(Figure 1). The long-term (1904–1994) mean annual discharge of the Parana River at the Corrientes gaugingstation (75% of the total drainage basin) is close to 550 km3 (EVARSA, 1994). The tropical Upper Paranacontributes about 80% of the total discharge during high flow (January–April) and about 65% during thelow discharge period (June–August). The remainder is mostly supplied by the Paraguay River, which drainsBrazil’s Mato Grosso and the Gran Pantanal as well as the Andean eastern slope through the Bermejoand Pilcomayo rivers. Figure 2A shows the water discharge variability during 1971–1973 as well as thecontribution to the total discharge from major tributaries. The Parana River flow anomalies have a significantcoherency with the El Nino phenomena occurring in the Equatorial Pacific (Depetris et al., 1996). Thisteleconnection, which was originally suggested in the 1920s by Sir Gilbert Walker’s group (e.g., Mossman,1924; Bliss, 1928), was the likely cause of the increased discharge observed during early 1973, inasmuch as1972 was an El Nino year (Figure 2A).

Current estimates attribute to the Parana River a mean TSS load of c. 80 ð 106 t year�1 (e.g., Depetris andPaolini, 1991; Milliman and Syvitski, 1992). By means of rating curves it has been possible to approximatethe TSS flux at the Parana cross-section and estimate the contribution from each of the major tributaries,namely the Upper Parana and the Paraguay rivers (Figure 2B). The Paraguay River TSS flux includes theBermejo River sediment load. Thus, during the period January 1971–June 1973, the Parana delivered a TSSload of over 89 ð 106 t year�1, of which the Paraguay River drainage basin supplied about 70% (includingthe Bermejo River contribution) and the Upper Parana River delivered the remnant. There are indications,

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

TSS GEOCHEMISTRY IN THE PARANA RIVER 1269

Precambrian metamorphic rocks

Continental sedimentary rocks (Carboniferous–Jurassic–Permian)

Tholeiitic basalts (Jurassic–Cretaceous)

Continental sands and sandstones (Cretaceous)

Sedimentary rocks (Devonian–Carboniferous)

Sedimentary rocks (Cambrian), metasediments (Precambrian)

Undiferentiated Precambrian, sedimentary rocks (Cambrian–Devonian)

Marine sediments (Paleozoic, Mesozoic), Tuffs and sandstones (Cenozoic),Volcanic rocks (Cenozoic)

Quaternary

40° S50° W60° W

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Buenos Aires

Rosario

Paraguay R

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0 200 400 km

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3 Sample sites

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Figure 1. Highly schematic geological map of the Rıo de la Plata drainage basin, showing the Parana and Uruguay rivers and major tributaries.Sampling sites: (1) Pescado River; (2) San Francisco River; (3) Bermejo River; (4) Pilcomayo River; (5) Uruguay River at Gualeguaychu;

(6) Parana River at Corrientes; (7) Parana River at Parana; (8) Parana River at Rosario

however, that due to accelerated dam construction and climatic change, the TSS relative contributions havechanged markedly in the last 20–30 years (Amsler and Drago, in press).

The distribution of clay minerals in recent marine sediments (Biscaye, 1965; Griffin et al., 1968) suggestedthat the clay-size sediment fraction delivered by the Parana River to the Atlantic Ocean was mostly illitic(½50%), with lesser proportions of smectites (20–30%), kaolinite and chlorite.

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

1270 P. J. DEPETRIS ET AL.

TS

S (

t mon

th−1

)

0

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Upper Paraná R. contribution

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A

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onth

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arge

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)

Figure 2. Tributary discharge contributions to the Parana’s outlet discharge (A). Major TSS contributions to the Parana River TSS load (B).Current mean annual discharge is c. 15 000 m3 s�1

The mineralogy of the Parana River suspended load was originally determined by Depetris and Griffin(1968). In the Parana’s lowermost reaches, the TSS < 2 µm size fraction also followed the relative order ofabundance (illite > smectite > kaolinite > chlorite) determined in adjacent off-shore marine sediments. Thecoarser size fraction (2–20 µm) showed K-feldspar, plagioclase, mica and quartz as abundant, indicatingacid igneous and crystalline basement rocks as the main source. Ensuing investigations further confirmed thedominance of micaceous materials in Parana’s TSS (e.g., Konta, 1988).

Consequently, it is not surprising that northern tributaries, like the Bermejo and Pilcomayo rivers, whichare major contributors to Parana’s sediment load, deliver a clay mineral suite (illite × smectite > chlorite >kaolinite) that closely resembles the one that ultimately reaches the ocean (Bertolino and Depetris, 1992).The upper Bermejo River TSS clay-size mineralogy showed trace amounts of a rare regular mixed-layerkaolinite/smectite (R1) (Bertolino et al., 1991).

THE CHEMICAL INDEX OF ALTERATION

Nesbitt and Young (1982) have derived the chemical index of alteration (CIA), which has proved useful toquantify the intensity of weathering. In molecular proportions, the index is:

CIA D 100[Al2O3/�Al2O3 C CaOŁ C Na2O C K2O�]

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

TSS GEOCHEMISTRY IN THE PARANA RIVER 1271

where CaOŁ represents the calcium in the silicate fraction only. During weathering, most of the aluminiumfrom primary minerals is transferred to clay minerals, whereas alkalis and alkaline earths are removed insolution from parental materials. Initially, CaO and Na2O will be removed more quickly from weatheredrocks than K2O. Therefore secondary phases exhibit higher CIAs than parental phases (e.g., the CIA ofplagioclase and K-feldspars is 50, whereas that of kaolinite is 100, and those of illite and smectite range from70 to 80). Values of 45–55 indicate essentially no weathering inasmuch as the average upper continentalcrust (UCC) has a CIA value of about 47 (McLennan, 1993). It follows that, although the proportions of clayminerals and primary minerals in a bulk sample will introduce substantial variation in the resulting CIA, ithas proved useful to characterize fine-grained TSS.

The CIA values of high-relief, high-sediment yield Andean tributaries range from 50 to 60 (San Franciscoand Pescado rivers), whereas the CIAs of Pilcomayo and Bermejo rivers range from 57 to 66. A discharge-weighted mean CIA value (N D 21) of 70Ð9 (Depetris and Probst, 1998) was calculated for the Parana, whichis considerably lower than an earlier estimate of 81 (McLennan, 1993).

As recently shown by Canfield (1997) for US rivers—where high runoff rivers transport the most heavilyaltered particulates and low runoff rivers carry the least altered—low runoff upper Bermejo and Pilcomayorivers exhibit the slightest leached TSS. As the suspended load moves downstream, CIA values increase. Thisis primarily due to the relative increase of fine-grained materials in the TSS load at downstream reaches oflarge rivers, in contrast with the coarser suspended load in high-energy upstream tributaries.

Table I lists the discharge-weighted mean TSS chemical composition of the Parana as compared with otherlarge world rivers. Most large rivers integrate different lithologies, climates and soil types in their respectivedrainage basins. Consequently, the geochemical differences among the resulting TSS signatures of large riversare attenuated and are similar. Also, although we have not yet attempted the exercise proposed by Gaillardetet al. (1999), there is evidence that in the Parana, as in other world rivers, the TSS load is the result ofsubstantial sediment recycling. Clearly, 50–70% of the Parana’s total sediment load is supplied by the arid,mountainous and mostly sedimentary upper Bermejo River drainage basin (Figure 1).

TSS MULTI-ELEMENTAL DIAGRAMS

We have investigated the trace element composition of TSS in the Parana River and in several major tributariesby using multi-elemental normalization diagrams similar to the ‘spidergrams’ often employed in igneouspetrology. Figure 3 shows a series of TSS multi-elemental diagrams ordered according to their location in thedrainage basin. UCC-normalized diagrams for high-relief Bermejo River Andean tributaries (San FranciscoRiver and one sample of the Pescado River) exhibit ample variability in the ‘noisy’ diagram that, withenriched Sr, Ca and Mg, denotes the dominance of outcropping marine sediments in the basin (Figure 3A).Also, enriched alkaline earths, along with low levels of UCC-normalized Al, Ti and Fe in one conspicuoussample, depict a Mg-rich limestone or dolomite.

Downstream (Figure 3B), in the Bermejo and Pilcomayo rivers, UCC-normalized variability decreases.Enrichment peaks of soluble elements (Ca, Mg), which were prominent in the upstream San Franciscosediment load, are attenuated or simply become depleted (Sr) in Bermejo’s TSS. The Pilcomayo Riverbasin also delivers a TSS load which suggests the dominance of Mg-rich limestones as a significant sedimentsource.

We do not have, at this time, geochemical information on the TSS load of the Upper Parana River. However,the TSS load of the Parana River mainstream at Corrientes (Figure 3C) is the addition of the Upper Paranaand Paraguay rivers’ TSS loads. In this station, and at Parana (Figure 3D), the multi-elemental diagramsshow a clear pattern with significantly decreased variability. The UCC-normalized ‘spidergrams’ show thatBa has remained relatively constant whereas other soluble elements (Sr, Na, Ca, Mg) are significantly leachedin suspended phases. In general, the susceptibility of elements towards leaching is coherent with numerousprevious descriptions of element mobility on weathering. Potassium remained moderately depleted throughout

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

1272 P. J. DEPETRIS ET AL.

Table I. Parana River discharge-weighted mean (D.W.M.) TSS chemical composition as comparedto other world rivers: major oxides (%), trace elements (ppm)

Components Parana RiverTSS D.W.M.

Congo RiverTSSa

AmazonRiver TSSa

GangesRiver TSSa

SiO2 59Ð1 58Ð0 60Ð1 66Ð9Al2O3 16Ð7 25Ð0 22Ð8 16Ð0MgO 1Ð7 1Ð1 2Ð0 2Ð3CaO 1Ð0 1Ð4 2Ð3 4Ð1Na2O 1Ð3 0Ð32 1Ð2 1Ð5K2O 2Ð9 1Ð6 2Ð3 2Ð7Fe2O3 7Ð0 11Ð56 8Ð33 5Ð78TiO2 1Ð0 1Ð6 1Ð3 0Ð96MnO 0Ð11 0Ð20 0Ð14 0Ð14BaO 0Ð07 — — —P2O5 0Ð36 — — —Sr 129 61 309 —Ba 652 790 700 490V 147 163 232 —Ni 67 74 105 80Co 15 25 41 14Cr 163 175 193 71Zn 262 — — —Cu 90 — — —Sc 18 12 18 11Ð5Y 30 — — —Zr 212 — — —Mn 853 — — —

a McLennan (1993).

the sequence, probably due to the relative scarcity of acid, potassium-rich igneous rocks in the Parana basin.The UCC-normalized TSS composition at the Parana cross-section (Figure 3D) also shows a pronouncedsimilitude with UCC-normalized NASC (Gromet et al., 1984). Adsorption phenomena may also explain theenrichment with respect to NASC of metals like Ni, Cr and Cu (Figure 3D), whose enhanced concentrationsare most likely the result of anthropogenic inputs.

Changes in the multi-elemental diagrams, as the TSS load moves downstream, are interpreted as a majorconsequence of grain-size differentiation. The enhancement of metal adsorption (i.e., higher exchange capacity)may strengthen the notion of a relative increase of finer particles in downstream reaches.

Table II partly lists the data displayed in Figure 4, which again shows the geochemical consistency ofTSS in world rivers, already underlined by Gaillardet et al. (1999) and several other authors. The Parana(Figure 4A) and Uruguay (Figure 4B) rivers’ geochemical data have been added to their list. Aside fromrelative enrichments or depletions for certain elements, what is striking is the coherency of all the patterns,which basically reflects the geochemical laws governing the weathering of the Earth’s surface. The ParanaRiver TSS load is clearly enriched (as compared with the UCC) in Pb, Cu, Ni, Cr and Co, and significantlydepleted in the alkaline and alkaline earth elements, affected by the incongruent dissolution of silicates. Giventhe dominance of tholeiitic basalts in the Uruguay River drainage basin, its TSS load is richer than Parana’sin Fe, Co, Sc and Ti. The elements that remain basically unaffected and have concentrations similar to theupper continental crust are those that are less fractionated during weathering and transport (e.g., the REE).

UCC-normalized REE diagrams from the Parana River TSS exhibit an enrichment of REE (with respectto UCC) and a dominance of heavy and middle REE over light REE (Figure 5A). Tholeiitic basalts—alsoincluded in Figure 5A—show a REE pattern that resembles the UCC-normalized diagram for Parana’s and

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

TSS GEOCHEMISTRY IN THE PARANA RIVER 1273

0.01

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K Ba Zr Sr Na Y Al Ti Sc Ca Cu Fe Co Mg Cr Ni

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NASC

San Francisco R. Pescado R.

Pilcomayo R. Bermejo R.

Figure 3. UCC-normalized multi-elemental diagrams, arranged from upper basin tributaries to the lowermost sampling station: San Franciscoand Pescado rivers (A); Bermejo and Pilcomayo rivers (B); Parana River at Corrientes (C); Parana River at Parana (D). UCC-normalized

NASC included in D

Uruguay’s TSS. The relative abundance of tholeiitic basalts, however, is far more prominent in the Uruguaythan in the Parana River. Not surprisingly then, Uruguay’s Eu positive anomaly is closer to the one reportedby Haskin et al. (1968) for a composite sample of tholeiitic basalts (Figure 5A).

Figure 5B shows the UCC-normalized REE ‘spidergrams’ for major world rivers. The ‘spidergrams’ displaya characteristic that Goldstein and Jacobsen (1988) identified as typical of TSS from continental-class rivers

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

1274 P. J. DEPETRIS ET AL.

Table II. Major and trace element concentrations (ppm) in TSS (Parana and Uruguay rivers)

River: Parana Parana Parana Parana Uruguay Uruguay Referencea LaboratoryLocation: Parana Parana Rosario Rosario Gualeguaychu Gualeguaychu GEOPT 8Date: 06.10.98 11.15.98 06.12.98 11.28.97 11.27.97 06.11.98 OU-4b

Sample: PAR-7 PAR-8 PAR 7-1 PAR 6-1 URU-6 URU-7

Cs — — 11Ð45 — — 8Ð5 2Ð07 š 0Ð03 1Ð93Rb 104 98Ð1 152Ð2 133Ð5 53Ð9 91Ð9 98Ð5 š 0Ð8 94Ð6U 2Ð8 2Ð7 3Ð9 3Ð6 3Ð9 3Ð3 2Ð19 š 0Ð07 1Ð9Th 11Ð5 11Ð4 12Ð8 13Ð6 8Ð8 9Ð5 8Ð42 š 0Ð12 7Ð6Pb 45Ð5 23Ð7 29Ð0 97 61Ð5 76Ð4 14Ð1 š 0Ð4 12Ð8K 18 177 17 513 22 161 21 248 9 296 9 877 2Ð70 š 0Ð009Ł 2Ð7ŁBa 496 480 525 649 470 447 360Ð8 š 2Ð7 380La 34Ð7 35Ð0 39Ð2 39Ð3 31Ð3 34Ð0 24Ð96 š 0Ð35 22Ð9Ce 69Ð9 71Ð5 76Ð5 80Ð7 68Ð2 66Ð3 55Ð7 š 0Ð8 61Ta 1Ð3 1Ð3 1Ð3 1Ð4 1Ð3 1Ð2 1 š 0Ð03 0Ð94Pr 8Ð2 8Ð2 9Ð1 9Ð4 7Ð9 8Ð5 6Ð85 š 0Ð11 6Ð4Nd 31Ð1 31Ð2 34Ð2 35Ð6 30Ð8 33Ð3 27Ð9 š 0Ð4 26Ð4Hf 6Ð7 7Ð0 4Ð4 5Ð7 7Ð2 5Ð4 5Ð54 š 0Ð08 4Ð89Zr 278 299 171 225 309 218 195Ð1 š 1Ð7 180Sr 112 103 131 133 136 109 99Ð9 š 1 85Na 6 734 6 586 5 476 7 326 7 178 3 034 3Ð61 š 0Ð011Ł 3Ð63ŁSm 6Ð3 6Ð3 6Ð9 7Ð2 6Ð5 7Ð1 6Ð94 š 0Ð12 6Ð52Gd 5Ð1 5Ð1 5Ð8 5Ð9 5Ð7 6Ð5 7Ð39 š 0Ð12 6Ð36Tb 0Ð8 0Ð9 0Ð9 1Ð0 1Ð0 1Ð1 1Ð25 š 0Ð02 1Ð17Eu 1Ð4 1Ð4 1Ð5 1Ð6 1Ð7 1Ð8 1Ð64 š 0Ð02 1Ð53Ho 1Ð1 1Ð0 1Ð1 1Ð5 1Ð2 1Ð3 1Ð63 š 0Ð03 1Ð53Y 29 29 28 32 34 35 47Ð1 š 0Ð5 45Er 2Ð6 2Ð7 2Ð6 3Ð0 3Ð2 3Ð3 4Ð83 š 0Ð09 4Ð22Dy 4Ð8 4Ð8 4Ð9 5Ð5 5Ð9 6Ð1 7Ð81 š 0Ð11 7Ð43Yb 2Ð6 2Ð6 2Ð7 2Ð9 3Ð2 3Ð2 4Ð7 š 0Ð06 4Ð2Tm 0Ð4 0Ð4 0Ð4 0Ð5 0Ð5 0Ð5 0Ð72 š 0Ð01 0Ð68Lu 0Ð4 0Ð4 0Ð4 0Ð5 0Ð5 0Ð5 0Ð71 š 0Ð01 0Ð68Al 76 850 76 850 93 280 87 450 75 260 86 920 14Ð83 š 0Ð02Ł 15Ð5ŁTi 5 160 5 400 5 160 5 460 9 960 8 460 0Ð77 š 0Ð002Ł 0Ð78ŁSi 295 320 293 480 263 580 271 400 261 280 230 000 63Ð34 š 0Ð06Ł 61Ð8ŁSc 15 16 17 17 24 28 19Ð1 š 0Ð26 19Ð8Ca 5 219 4 647 6 435 6 220 9 438 9 867 4Ð48 š 0Ð013Ł 4Ð8ŁCu 48 83 57 134 112 117 27Ð3 š 0Ð51 25Fe 45 817 49 288 52 065 53 453 77 195 81 915 5Ð82 š 0Ð014Ł 6Ð2ŁCo 18 20 19 22 39 34 13Ð5 š 0Ð27 12Ð2Mg 7 020 6 600 9 780 9 000 5 280 7 860 2Ð3 š 0Ð008Ł 2Ð47ŁCr 93 72 76 96 60 75 54Ð7 š 1 55Ni 48 36 38 45 38 46 21 š 0Ð4 20

a International Proficiency Testing Scheme for Analytical Geochemistry.b Penmaenmawr microdiorite.c As oxides.

in NASC-normalized REE patterns: relatively uniform diagrams (although variable in absolute terms), anda prevalence of light REE over heavy ones. NASC-normalized (La/Yb)N of major rivers vary within thesmall range of 1Ð59 to 2Ð70 (Goldstein and Jacobsen, 1988), whereas using the same NASC values, (La/Yb)N

narrowly varies between 1Ð02 and 1Ð14 in the Parana River, and between 0Ð76 and 0Ð83 in the Uruguay River.The features shown by Parana’s TSS REE distribution are not only close to tholeiitic basalts, but are also

typical of relatively young volcanic rocks, of an intermediate to basic composition. Suspended sedimentsfrom major rivers draining large cratonic land masses have heavy REE depleted patterns relative to bothUCC and NASC. Characteristics similar to Parana’s were also observed in the TSS of medium-size or largerivers draining Andean terrain in Argentina’s Patagonia (Figure 5C), where the volcanogenic signature waspreserved on sediments essentially resulting from physical weathering, and less chemically altered than those

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

TSS GEOCHEMISTRY IN THE PARANA RIVER 1275

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Uruguay R. Changjiang R. Niger R. Mackenzie R.

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Figure 4. Extended UCC-normalized multi-elemental graph: Parana River TSS (A); Uruguay and other rivers (Gaillardet et al., 1999) (B).Elements are ranked on the X-axis in order to obtain a monotonic decrease of UCC abundances when normalized to Primitive Mantle

abundances (Gaillardet et al., 1999)

of the Parana River (Pasquini, 2000). NASC-normalized (La/Yb)N in Patagonian TSS fluctuate between 0Ð71and 0Ð85.

CONCLUDING REMARKS

Although most of the water in the Parana River drainage basin is supplied by the tropical Upper Parana (over60% of the annual water discharge), the TSS load is largely supplied (50–70%) by the mountainous, arid andmostly sedimentary upper Bermejo River reach. Hence, the load is mainly composed of recycled sedimentsthat, in the upper catchments, exhibit CIA values ranging from 50 to 60, close to the mean UCC. As thesuspended load moves downstream, its CIAs gradually increase to reach, near the mouth, a discharge-weightedmean of c. 71.

The downstream increase of the CIA is the response to grain-size differentiation, as UCC-normalized multi-elemental diagrams suggest. Soluble elements (Na, Ca, Sr, Mg) are progressively lost as the TSS load movestowards the riverine outfall. The gradual enrichment of clays in the TSS enhances adsorption phenomena (i.e.,higher exchange capacity), as revealed by the concentrations of Ni, Cr and Cu.

The broad picture that extended UCC-normalized ‘spidergrams’ project for the Parana River is similarto that of other world rivers. The inspection of the REE distribution, however, indicates that the overridingsignature preserved throughout the weathering process could be attributable to either the weathering products oftholeiitic flood basalts or to young volcanic arc rocks of intermediate compositions. A significant contributionfrom old crustal rocks is not evident in the ‘spidergrams’. Given the conspicuous role of the Bermejo Riverdrainage basin as the system’s major source of recycled sediments, we feel that the Parana River TSS load

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

1276 P. J. DEPETRIS ET AL.

A

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Changjiang R. Niger R. Amazonas R. Mississippi R.Indus R.

Figure 5. UCC-normalized REE diagram for the Parana and Uruguay rivers; data for tholeiitic basalt from Haskin et al. (1968) (A); forselected world rivers (Gaillardet et al., 1999; Goldstein and Jacobsen, 1988) (B); for Patagonian rivers (Colorado, Negro, Chubut, Deseado,

Coyle, Santa Cruz, Chico) (Pasquini, 2000) and mean andesite (Taylor and McLennan, 1985) (C)

has preserved a dominantly Andean REE signature rather than one determined by tholeiitic basalts, abundantin the Upper Parana upper catchments. In the Uruguay River drainage basin, on the other hand, there is littledoubt that its TSS UCC-normalized REE pattern is the one determined by the extensively distributed tholeiiticflood basalts and their weathering products.

ACKNOWLEDGEMENTS

We wish to acknowledge the sustained support of the ECOS/SETCIP Program, promoting scientific coop-eration between France and Argentina. The work completed has been partially financed through a projectsupported by Argentina’s CONICET (PIP 4829/96) and FONCYT (PICT 97-00966), which will continue to

Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 1267–1277 (2003)

TSS GEOCHEMISTRY IN THE PARANA RIVER 1277

support sampling and analytical work in the Parana and Uruguay rivers until January 2002. The study wasoriginally initiated within the framework of the European Commissions’ Project PARAT (Contract CI1Ł-CT94-0030), which studied the nature and dynamics of the transfer of particulate and dissolved phases fromsouthern South America to the SW Atlantic Ocean. P. J. Depetris and D. M. Gaiero are members of theCICyT in Argentina’s CONICET.

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