GEOCHEMISTRY OF THE SURFACE AND GROUND WATERS OF THE UPPER BASIN OF THE RIVER LLOBREGAT

RESUMEN.En el presente estudio se presentan y discuten las principales características geoquímicas de las aguas superficiales y subterráneas de la Alta cuenca del río Llobregat hasta la entrada del río al embalse de La Baells. El conjunto de aguas analizadas presentan características muy contrastadas. Así, tanto en la subcuenca de las fuentes del Llobregat como en la del río Bastareny predominan las aguas bicarbonatadas calcicas poco mineralizadas. En la subcuenca del río Arija, sí bien las'aguas del curso alto y las de los principales afluentes también son bicarbonatadas calcicas, destaca el hecho de que en la confluencia con el río Llobregat el agua es sulfatada calcica. La subcuenca del río Saldes es la que presenta una mayor heterogeneidad, con aguas bicarbonatadas calcicas, cloruradas sódicas y sulfatadas calcicas, las cuales provocan que en la confluencia con el río Llobregat el agua sea bicarbonatada-sulfatada sódico-cálcica. El análisis de componentes principales ha permitido sintetizar estas características de forma muy clara. Los resultados se interpretan, esencialmente, a partir de las litologías drenadas por los distintos cursos de agua. .

RESUMEN.-En el presente estudio se presentan y discuten las principales características geoquímicas de las aguas superficiales y subterráneas de la Alta cuenca del río Llobregat hasta la entrada del río al embalse de La Baells.El conjunto de aguas analizadas presentan características muy contrastadas.Así, tanto en la subcuenca de las fuentes del Llobregat como en la del río Bastareny predominan las aguas bicarbonatadas calcicas poco mineralizadas.En la subcuenca del río Arija, sí bien las'aguas del curso alto y las de los principales afluentes también son bicarbonatadas calcicas, destaca el hecho de que en la confluencia con el río Llobregat el agua es sulfatada calcica.La subcuenca del río Saldes es la que presenta una mayor heterogeneidad, con aguas bicarbonatadas calcicas, cloruradas sódicas y sulfatadas calcicas, las cuales provocan que en la confluencia con el río Llobregat el agua sea bicarbonatada-sulfatada sódico-cálcica.El análisis de componentes principales ha permitido sintetizar estas características de forma muy clara.Los resultados se interpretan, esencialmente, a partir de las litologías drenadas por los distintos cursos de agua. .SUMMARY.-In this workthe main geochemical characteristics of the surface and ground waters of the Upper basin of the River Llobregat are described and,discussed.The luater samples analysed reveal sharply contrasting characteristics.In both the Fonts del Llobregat and River Bastareny catchments, calcium bicarbonated ivaters with a low mineral content clearly predominate.However, in the catchment of the River Arija, although the waters of the upper course and the main tributaries are also calcium bicarbonated, it is ivorth noting that at the confluence with the River Llobregat calcium sulphated water is found.The catchment of the River Saldes shoivs a greater heterogeneity, luith calcium bicarbonated, sodium chloridized and calcium sulphated loaters, and thus at the confluence with the River Llobregat the water is sodium-calcium bicarbonated-sulphated.Principal components analysis enables us to arrive at a synthesis which clearly explains these characteristics.These results are fundamentally interpreted on the basis of the lithologies drained by the different watercourses.

Introduction
When studying the chemical properties of the water of a river, it is essential to remember that its hydrogeochemical characteristics are the result of the spatial and temporal integration of all the water flows that carry rainwater to the river.It is therefore evident that one cannot seek to explain the chemistry of the water of a river by referring solely to the dissolution processes in the river-bed (WALLING and WEBB,1986).In fact, much of the interaction between rainwater and the substratum takes place in the ground (DREVER, 1982).A number of authors have undertaken to study the influence of lithology on the chemical quality of continental waters.In this respect, MEYBECK (1984) analyses the geochemical characteristics of waters with reference to lithology on the basis of the concentrations of the major elements and the ionic relationships Ca2+/Mg2+, Ca2+/Na+ and Si02/Xcations.
Various studies have been made of the River Llobregat and its tributaries which have made it possible to define the main limnological characteristics of the basin as a whole (GONZALEZ et al. 1985;MUÑOZ andPRAT 1992, 1994;PRAT et al. 1984).
The aim of this work is to define the geochemical characteristics of the surface and ground waters of the Upper basin of the River Llobregat, and to attempt to establish a possible link with the lithological nature of the different catchments concerned, and also the role played by human activities.
This characterization has been based on the major elements.The sampling points extend from the sources of the Bastareny and Llobregat rivers, which provide the most important volumes of groundwater to the basin, to the entrance of the river to the Baells reservoir.This research has been undertaken v^ith the support of the Lucdeme Project: "Dynamics of degraded geosystems in mountainous areas: Upper Llobregat Basin.Evolutionary action of the natural and human processes of degradation.Quantification of these in order to propose guidelines for their control", and within the framework of the collaboration between the "Jaume Aimera" Earth Sciences Institute of the C.S.I.C. and the Geological Survey of the Autonomous Government of Catalonia (FREIXES, 1988(FREIXES, , 1989(FREIXES, , 1990)).Dr. Nuria Clotet, the director and coordinator of the project, died while the research was in progress, and we dedicate this work to her memory.

Area studied
Geochemical analysis was undertaken in the Upper basin of the River Llobregat, that is to say, in the catchments of the Llobregat, Arija, Bastareny and Saldes rivers as far as the Baells reservoir (figure 1).This basin has been the focus of studies concerned with erosive processes cind the quantification of the flux of solids into the river (CLOTET, 1984 a) and b); CLOTET and GALLART, 1986;BALASCH et al., 1992;CASTELLTORT, 1995).
In terms of its structure, the Upper basin of the River Llobregat is situated between two important geological units: the Cadi thrust sheet and the Southern Pyrenean unit.In the Cadi thrust sheet, situated further north.Palaeozoic and Tertiary materials can be observed in particular; although the proportion of Mesozoic materials is smaller, the garumniem facies can be found with important outcrops.
The Southern Pyrenean unit, situated to the south of the Cadi thrust sheet, is mainly composed of Mesozoic and Tertiary lithologies, with an important development of the garumnian materials.
The catchments of the Bastareny and the Llobregat rivers have mainly developed in material belonging to the Cadi thrust sheet.The River Bastareny, however, crosses the Southern Pyrenean unit froin Bagá village, and from Guardiola de Bergadà village, where it meets the Llobregat river, the watercourse develops in the Cretaceous limestones of the South Pyrenean unit and flows to the Baells reservoir.
The hydrographie basin of the head of the River Llobregat is situated on the southern slopes of the Eastern Pyrenees (figure 1); to the N-NW of the basin lies the Cadí-Moixeró range, to the N-NE the relieves of Tosa d'Alp, Puigllançada and PletaRoja, to the W-SW the Pedraforca massif and the ranges of Ensija and Serrât Negre, to the south the Baells reservoir, to the southeast the Catllaraàs range, to the east the col of Merolla and to the north-east the Barraca range.The total area of the basin is abotit 345 km^.
PIRINEOS [147][148] The following is a description of the main catchments which contribute to the basin: The catchment of the River Arija drains the waters of the western part of the Mogrony range, the relieves of Pedra Picada and Emperadora, the southern and eastern slopes of the Meranges range, the north-west area of the Tubau plains, the northern slopes of the Fajabranca range and the eastern slopes of the CatUaras range.The Arija system evolved principally in Tertiary materials, to be exact in marls, gypsums and limestone intercalations of the llerdian-Cuisian period (Sagnari formation), marls, red sandstones and limestones of the Cuisian period (Corones formation), marls and marlycalcareous material (Armàncies formation) and in Cuisian-Lutetian turbidites (Campdevànol formation); notwithstanding this, the highest part of the head is situated in Devonian limestones, in the foothills of the Mogrony range; it crosses Permian sandstones cind lutites, as well as the entire group of Mesozoic materials formed by Buntsandstein sandstones and lutites, and limestones and arkosic sandstones of the Late Cretaceous; but above all, mention should be made of the versicoloured clays and Keuper evaporites (gypsums) which constitute an important outcrop crossed east to west by the River Arija just before Pobla de Lillet village.
The River Arija runs for 12.1 km before it joins the River Llobregat at Pobla de Lillet and its basin covers an area of 50.3 km^.
The catchment of the River Bastareny is bordered to the north by the relieves of Moixeró, la Moixa émd MoLnells, to the W-NW by the Muga, Comabona and the Pedregosa ranges, emd to the south by the Gisclareny range.The River Bastareny receives a notable volume of ground water through the Adou del Bastareny karstic system, whose main outflow points are the Adou spring emd its own importcmt overflow points, in addition to other permcment springs in the same system, such as the Bullidor de Sant Esteve spring cmd the Violi spring (FREIXES et al, 1995).The nature of the materials of the Bastareny basin is relatively comparable to that observed in the case of the River Arija.Tertiary materials predominate throughout most of the watercourse from the Muga cind Murcurols streams and from Adou spring.The lithological units are: marls and marlycalcareous material of the Sagnari formation (llerdian-Cuisian), marls, limestones and red sandstones of the Corones formation (Late llerdian-Early Cuisian), limestone and marly-calcareous materials of the Penya formation (Cuisian) and calcareous sandstones, marls and lutites of the Armàncies formation (Cuisian); the southern slopes of the relieves of La Moixa, Moixeró and Tosa d'Alp are also drained by tributaries of the Carboniferous slates, Cretaceous limestones, and limestones, sandstones and lutites of the Garumnian period); however, the drainage channel of both these streams crosses the different Tertiary units.To be precise, the Gréixer stream rises in the southern foothills of Tosa d'Alp; the head is located in Devonian limestones and Carboniferous slates, and downstream it cuts through Stephcino-Permian riolites, Buntsandstein sandstones and lutites.Cretaceous limestones (Santonian mid-Campanicin) and materials of the garumnian facies (which is notably developed: conglomerates, sandstones, lutites and limestones); before reaching the Bastareny, the Gréixer stream cuts through Tertiary units: limestones of the Cadi formation and marly-calcareous materials, limestones and marls of the Sagnari, Corones and Armàncies formations.
The relief of the Cadi range is largely drained below the surface by the Adou del Bastareny karstic system.The karstified materials are mainly limestones and marly-calcareous of the Armàncies and Penya formations.
The River Bastareny runs 14.8 km to join the River Llobregat at Guardiola de Berguedà village; its basin covers an area of 79.2 km^.
The catchment of the River Saldes is surrounded to the north by the Gisclareny range and the cliffs of Gresolet and La Bola, to the west by the Pedraforea massif, and to the south by the Ensija range and the cliffs of Vallcebre.The basin has mainly developed in Mesozoic and early Tertiary lithologies, which may be summarised as follows: versicoloured clays and Keuper evaporites.Cretaceous limestones (Santonian mid-Campanian) and limestones, conglomerates, sandstones and lutites with intercalations of Garumnian lignites.
The River Saldes, which flows into the River Llobregat at Collet, is 19.2 km long and has a basin of 102 km2.
The catchment of the sources of the River Llobregat drains the southern slopes of the Barraca, Rus and Puigllançada ranges, the Catllaras range and the ranges of Colobre and Falgars.This catchment mainly receives groundwater flow originating from the karstic system that has been given the name of its main oufflow point: the Llobregat springs, the source of this river course.In this catchment, the river cuts through Palaeozoic, Mesozoic and Tertiary materials; the head is located mainly in Devonian limestones (Monell and Fontetes streams), while downstream the river crosses Permian sandstones and lutites, Buntsandstein conglomerates, sandstones and lutites, -CATCHMENT OF THE RIVER SALDES: . SI = Salada stream, which drains the northern sector of the Ensija range.Cretaceous arkosic sandstones (Coniacian-Early Santonian) and also an important Garumnian outcrop with limestones, conglomerates, sandstones and lutites (Clot del Moro).In the final course, running to la Pobla de Lillet village, it crosses Tertiary marly-calcareous materials, limestones and marls of the Sagnari, Corones and Armàncies formations.
In the course from la Pobla de Lillet to Guardiola de Berguedà villages, the River Llobregat crosses the turbidites of the Campdevànol formation, Jurassic and Cretaceous limestones and Keuper versicoloured clays and evaporites.
Between Llobregat springs and the Baells reservoir the river runs for 14.7 km, and its basin covers an area of 113.2 km2 (this figure does not include the areas of the catchments of the main tributaries).
The average volume of water m the River Llobregat where it passes the Collet station is 167.5 hm^ (average taken over the period 1975-1990) (JUNTA D'AIGÜES, 1995).

Methodology
In order to make a geochemical characterization of the waters of the Upper Llobregat basin, samples were taken at 29 points dotted among the four catchments between June 1988 and December 1990 (table 1, figure 1).Of these 29 points, there were 11 from which samples were taken fortnightly during the 1988-89 cycle and then monthly during the 1989-90 cycle: these were the two mam karstic springs (LI-Llobregat springs cind B2-Adou del Bastareny spririg), the totals for each catchment (A4-River Arija catchment total, L5-rivers Llobregat and Bastareny total, L9-sources of the River Llobregat catchment total, B6-River Bastareny catchment total, Lll-rivers Llobregat and Bastareny total, S6-River Saldes catchment total and L14-Upper Llobregat basin total), and the two most noteworthy inflows from a geochemical point of view (S5-Vallcebre stream, tributary of the River Saldes, and Sr-stream at Cal Rodó, tributary of the Vallcebre).Three samples were taken from each of the remaining points during the same period.
With each sampling the water temperature, conductivity pH and aUcaünity (TAC) were measured in Ü' ie field.The remaining major ions (calcii.uTi,magnesirmi, chlorides, sodium, potassium and sulphates), the nitrates and the total hardness (TH) were analysed in the laboratory using Standard Methods inethodology To present the geochemical characteristics, we have used modified Stiff diagrams and tables with the basic statistics (mean, deviation and rcinge) corresponding to each point where water was sampled.Both the middle course of the river (Al) and the two main tributaries (A2 and A3) contain calcium bicarbonated water with a relatively low level of mineralization.On the other hand, water from the point representing the total of the catchment (A4) is calcium sulphated, with significantly higher concentrations of chlorides, sodium, calcium, magnesium and sulphates than water from the aforementioned points; thus the global mineralization of the water, expressed as electrical conductivity, is also markedly higher.This is due to the fact that in its lower course the River Arija crosses evaporitic levels (Keuper gypsums in this case) which bring about a change in its geochemical characteristics.Since the gypsums are much more soluble than the limestone materials, the water at point A4 is more highly mineralized than at the remaining catchment stations.

Catchment of the River Bastareny (figure 1; table 3)
The geochemical characteristics of the water from the points studied are very homogeneous: all the samples are calcium bicarbonated with a low level of mineralization.The only barely appreciable differences are found in the concentration of sulphates, which is higher at Bl (Murcurols stream) and B4 (River Gréixer) than at the remaining sampling points.This is explained by the passage of these two tributaries through substrata with more soluble materials, in this case Keuper gypsums.In this catchment the role of the ground waters is very important, due to the volume of water they bring to the river (15-18 hm^"^ a year) and to the geochemical characteristics, clearly calcium bicarbonated, they give the water.In fact, the main inflow to the catchment comes from the Adou karstic system, which drains into the River Bastareny through several permanent outlets (three of which are of special importance: the Adou spring (B2), the Bullidor de Sant Esteve spring and the Violi spring), and through numerous overflow points of a temporary nature (Freixes et al., 1995).There are other springs belonging to small hydrogeological units that are totally independent of the Adou karstic system; the most important of these are the Faig spring and the Bullidor de la Llet spring, which drain into the area of the Font del Faig stream (B3).

Catchment of the River Saldes (figure 1; table 4)
. The most notable feature is the great geochemical heterogeneity of the different tributaries of the River Saldes, clearly linked with the different litholo-PIRINEOS 147-148 gical substrata that make up the catchment.The waters of the Salada stream (SI) are sodium chloridized with high concentrations of sulphates and potassium, and they impose these characteristics on the water in the upper course of the river (S2); it is therefore clear that this stream drains highly soluble evaporitic material, where sodium chloride salts (halites) are present.The Gresolet stream (S3), which drains terrain which is basically limestone and' marly-calcareous, provides calcium bicarbonated waters with a low level of mineralization and relatively high sulphate levels.The water of the Esquers-(S4), Vallcebre (S5) and Cal Rodó (Sr) streams is calcium sulphated and highly mineralized, originating in Keuper and Garumnian gypsums.
The extremely diverse geochemical characteristics of these main tributaries have the effect that the water of the lower course of the river (S6), just before it joins the River Llobregat, is sodium-calcium chloridized-sulphated with a high level of mineralization (giving conductivity readings of between 700 and 1,700 |aS/cm at 20° C). 4.1.4.Catchment of the sources of the River Llobregat (figure 1; table 5) AU the water from the points included in this catchment is calcium bicarbonated with a low level of mineralization, except for that of the Regatell stream (L6) and the River Llobregat after the confluence with the River Bastareny just outside Guardiola de Berguedà village (LU), which have a comparatively higher concentration of sulphates, due to their passage through Keuper evaporitic materials.Karstic waters also play a very important role in this catchment: the most significant in terms of volume are the waters that come from the karstic system of Llobregat springs (LI), which provide some 25 hm^ a year; there are also some notable springs related to the streams of Monell, la Molina, Riutort and Sant JuUà de Cerdanyola, although these are considerably smaller in volume.4.1.5.Upper Llobregat basin total: River Llobregat just before the Baells reservoir (figure 1; table 6) Overall, the water that arrives at the Baells reservoir (L14) is calcium bicarbonated with a relatively low level of mineralization (between 300 and 700 )j.S/cm at 20° C) and of some significance with respect to chloride, sodium and sulphate concentrations.At all events, the mineralization of the water at this point is higher than upstrecim; this is due, at least in part, to the fraction of water in the River Saldes which flows into the River Llobregat (although before joining the River Llobregat part of the water in the River Saldes is channeled to Berga to supply industries), and also to its passage through Keuper gypsums.Following analysis of the variation in the concentration of some major ions in the water along the course of the River Llobregat, certain observations may be made: It can be noted that the concentration of sulphates shows a marked increase at the point corresponding to la Pobla de Lillet village (L5), at the station situated just after Guardiola de Berguedà village (Lll) and just before the reservoir (L14); in the first case, this increase is mainly due to the incorporation of water from the River Arija arid possibly to the effect of a certain volume of waste water.In the second case, the increase in the concentration of sulphates coincides with the river's passage through Guardiola, which suggests the incorporation of a significant fraction of waste water; furthermore, it should be pointed out that at this sampling point the water from the River Bastareny, which has a low sulphate content, has already joined the River Llobregat.Finally, the increase detected just before the reservoir appears to be attributable to the volume of water from the River Saldes which has joined the River Llobregat.
The concentration of chlorides shows a notable increase at la Pobla de Lillet (L5) and, particularly, just before the reservoir (L14).The first increase  is due to the addition of water from the River Arija and to a certain volume of waste water, while the second increase is very probably due to the addition of water from the River Saldes at the Baells reservoir.
There is a relatively low concentration of nitrates throughout the entire course of the River Llobregat, although a certain increase is detected where the river flows through Guardiola (Lll), due in all probability to discharges from the town.Finally, the conductivity variations indicate the overall effect of the River Arija, possible traces of pollution of human origin at la Pobla de Lillet and Guardiola, and the result of a volume of water from the River Saldes entering the River Llobregat shortly before the Baells reservoir.

The principal components analysis (PCI) in order to synthesize the geochemistry results for the upper Llobregat
In order to obtain am overall picture of the geochemistry of the surface and ground waters of the Upper Llobregat basin, a PCA has been conducted with the mean values of all the samples taken at each station.Nine of the variables analysed have been included (conductivity, chlorides, sodium, potassium, calcium, magnesium, bicarbonates, sulphates and nitrates), for 29 statistical units corresponding to the 29 sampling stations.Due to the fact that factor 1 accounts for 50.3% of the variability and factor 2 accounts for 29.1 %, the discussion is centred on the factorial plane defined by these two axes.In the space of the variables (figure 5a), the chloride, sodium and potassium ions form one group, and the sulphates, calcium and magnesium ions form another, with very little correlation between the two.Conductivity is situated in the middle, and this is the variable which carries most weight in defining factor 1. This result indicates that in some waters the conductivity is basically determined by the chloride, sodivim and potassium variables, while in others it is the sulphate, calcium and magnesium ions which play a dominant role in mineralization.Overall, it is shown that in the Upper Llobregat basin the variability of the geochemical characteristics of the waters is mainly determined by differences in the concentrations of these two groups of ions.
In the space of the statistical i,mits (figure 5b) the sampling points are distributed so that four groups are outlined: -SI and S2, notable for the high concentrations of chlorides, sodium and potasium.
-Sr, S5, A4 and S4, notable for the high levels of sulphates and calcium -S6, which due to its special geochemistry (calcium-sodium chloridizedsulphated water) occupies an intermediate position on the factorial plane.
-The fourth group is formed by all the points of the sources of the River Llobregat catchment, those of the Bastareny catchment and the stations Al, A2 and A3 of the Arija catchment.Their significant characteristics are the typically calcium bicarbonated waters.
These four groups show the different types of water that determine the geochemistry of the River Llobregat where it flows into the Baells rsservoir, and the distribution of these types among the catchments.
This PCA therefore provides an effective synthesis of the geochemical characteristics of the waters drained by the River Llobregat in its upper course.

5, Conclusions
The results obtained show that waters of sharply contrasting chemical characteristics flow into the Upper Ltobregat basin.For although calcium bicarbonated waters with a low level of mineralization predominate in the basin as a whole, calcium sulphated and even sodium chloridized waters are of considerable importance in the basins of the Saldes and Arija rivers.
In all cases, there is a very close relationship between the chemical quality of the water and the lithology of the basin drained.In this respect, mention should be made of the role of the Keuper gypsums in the mineralization of the water in the lower course of the River Arija, emd of the Garumnian and Keuper gypsums in the mineralization of the Esquers, Vallcebre and Cal Rodó streams in the catchment of the River Saldes.At other points the water contains a certain concentration of sulphates (although considerably weaker than at the aforementioned points), which can also be linked with evaporitic facies in the basin, although the area covered by these is relatively small; this would be the case of the Murcurols stream at the head of the River Basf areny, the Junyent stream in the Arija catchment and the Regatell and Malanyeu streams, which are tributaries of the River Llobregat.The types of elements cinalysed make it difficult to evaluate the effects of humaii activity on the chemical quality of the waters.At all events, the concentrations of sulphates and chlorides appear to show evidence of certain urban waste discharges at Pobla de Lillet and Guardiola de Berguedà.

Fig. 2 .
Fig. 2. Variation in conductuvity and sulphate concentrations along the River Llobregat, from its source to the Baels reservoir.

Fig. 3 .
Fig. 3. Variation in chloride concentrations along the River Llobregat, from its source to the Baels reservoir.

Fig. 4 .
Fig. 4. Variation in nitrate concentrations along the River Llobregat, from its source to the Baels reservoir.

Fig. 5 .
Fig.5.Principal Components Analysis (PCA) with the mean chemical data from each of the water points sampled; a) space of the variables; b) space of the stadistical units, in wich the cluster of pionts situated between L14 and L12 represents aU the points in the River Bastareny catchment (B1-B6), all those of the sources of the River Llobregat catchment except the Sant Julia de Cerdanyola stream (LIO),the River Arija at Col of Merolla and the Junyet stream (Al and A3),and the Gresolet stream (S3).

Table 6 .
Geochemical characteristics of the River Llobregat just before the Baells reservoir (globalization point of the Upper Llobregat basin).