Estimation of ground-water exchange with semi-arid playa ...hera.ugr.es/doi/16518251.pdfMajor...

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Journal of AridEnvironments

Journal of Arid Environments 66 (2006) 272–289

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Estimation of ground-water exchange with semi-aridplaya lakes (Antequera region, southern Spain)

M. Rodrıguez-Rodrıgueza,�, J. Benaventeb, J.J. Cruz-San Julianb,F. Moral Martosa

aUniversity Pablo de Olavide, Carretera de Utrera Km. 1, Seville 41013, SpainbWater Research Institute, University of Granada, C/Ramon y Cajal s/n, Granada 18071, Spain

Received 30 May 2005; received in revised form 25 October 2005; accepted 28 October 2005

Available online 9 December 2005

Abstract

Playa lakes occur in arid and semi-arid climates and have a significant economic, ecological and

cultural value. They are particularly vulnerable to changing hydrologic regimes due to climate change

or human activities. We determined the hydrological regime of 10 playa lakes in southern Spain

based on water budgets for a 5-year period (1997–2001). Surface runoff was measured in the

watersheds, precipitation and evaporation/evapo-transpiration estimated using local meteorological

data and ground-water flows assessed using a network of wells and piezometers. The examination of

seasonal variations in the lakes’ water levels and the water budgets indicated that ground-water

discharge plays a key role in the hydrological dynamics and the maintenance of the playa ecosystems.

Major inorganic ions and stable hydrogen and oxygen isotopes in lake water, ground-water and

springs were measured. Water samples from the lakes and ground-water were a mixture of cations

�SO42� and �Cl� type due to the aridity of the climate and lithologies of the basin. The high TDS

(63.4 g/l) content of some ground-water samples indicates regional geologic control on water quality

and the dissolution of gypsum and halite. Stable oxygen isotope ratios for lake water (�3.6 to 9.8%d 18OSMOW) were different from those of ground-water and springs (�6.8 to 1.1% d 18OSMOW)

suggesting different evolutional patterns. The results of this study provides evidence that the

combination of water budgets, hydrochemistry and stable isotope hydrology can lead to a better

understanding of wet playa’s hydrology. This approach could, thus, prove helpful to establish

hydrological regimes in this type of semi-arid environments.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Hydrological regime; Water chemistry; Environmental isotopes; Saline ground-water

see front matter r 2005 Elsevier Ltd. All rights reserved.

.jaridenv.2005.10.018

nding author. Tel.: +0034 954349524; fax: +0034954319151.

dress: [email protected] (M. Rodrıguez-Rodrıguez).

www.elsevier.com/locate/jnlabr/yjare

ARTICLE IN PRESSM. Rodrıguez-Rodrıguez et al. / Journal of Arid Environments 66 (2006) 272–289 273

1. Introduction

Seasonally to perennially filled playa lakes tend to occur in depressions whose floorsintersect the water-table (Duffy and Al-Hassan, 1988). These kinds of ecosystems areabundant in the Antequera region and all over southern Spain. These wetlands providehabitat for non-migrating and migrating birds (Cruz-San Julian and Benavente, 1996) aswell as a number of endemic and endangered species (Rodrıguez-Rodrıguez, 2002). Themost important of these habitats is Fuente de Piedra Playa Lake (Fig. 1), a Ramsar site(i.e. ‘‘Wetland of International Importance’’), which constitutes one of the main nestingplaces for the pink flamingo (Phoenicopterus rubber roseus) in southern Europe (Troya andBernues, 1992). The Antequera playa lakes are covered by grasses, sedges and rushes aswell as halophytic vegetation and, thus, support most of the region’s biodiversity.

The maintenance of these playa lakes or Salinas require an understanding of thehydrological processes involved, taking into account that the main difference betweenthe different types of playas is the elevation of ground-water in relation to the elevationof the surface of the playa (Rosen, 1994; Yechiely and Wood, 2002). During the summerthe lake area shrinks due to high evaporation rates and sedimentation of evaporites occurs.Ground-water resources in the area must be managed considering the volumes of ground-water involved in the water budgets of the playa lakes. Hydrological manipulations such asover pumping in the watershed of the playa lakes can further degrade these ecosystems.Irrigation lands are now increasing in many places of Andalusia, such as Antequera, due tothe irrigation of olive trees and other types of crops. Continuous depletion of the water-table may result in the modification of hydrological cycles in each system and could lead to

SalinosoSalinosostreamstream

SantillSantillán streamstream

stream

stream

ArenalesArenales

streamstream

AlbinaAlbina

streamstream

Sala

do

Sala

dostream

stream

Tinajas

Tinajas

Stream

Stream

GuadalhorceGuadalhorce riverriver

Serafina

Serafina

N

Fig. 1. Playa lakes in Antequera region (southern Spain). All of them are located in the Triassic of Antequera

unit, characterized by the dominance of clays, marls and evaporate materials (German– Andalusian facies). WS:

Cerro del Palo weather station.

ARTICLE IN PRESSM. Rodrıguez-Rodrıguez et al. / Journal of Arid Environments 66 (2006) 272–289274

the desiccation of the lakes or, at least, the alteration of the flooded term; furthermore, theestablishment of wetland vegetation and wetland processes is directly related to ground-water hydrology (Mitsch and Gosselink, 1993; Atekwana and Richardson, 2004).In wet playas’ ecosystems, both runoff and ground-water are important water sources.

Several studies show that the depth of the water-table determines the distribution and typeof vegetation (Margalef, 1983). Thus, the nature of degradation, as a result of hydrologicalalteration, is dependent on the water source that supports vegetation.Previous studies have shown that the maintenance of some of the ecosystems of the

Antequera region, such as Fuente de Piedra (Linares, 1990; Rodrıguez-Rodrıguez, 2002) orthe Campillos Complex (Benavente et al., 1998) is dependent on ground-water discharge.Chikita et al. (2004) examined how ground-water output and input contribute to a lake’schemistry by estimating the hydrological and chemical budgets of a volcanic caldera lakein Hokkaido, Japan. Atekwana and Richardson (2004) measured major inorganic ions andstable C and O isotopes in surface and ground-water of the Corral Canyon MeadowsComplex (Nevada, USA) to determine whether stream water or ground-water was thewater source supporting vegetation. These studies concluded that ground-water wasprimarily the source and that multiple chemical and stable isotope tracers were useful incarrying out these types of investigations.The conclusions about estimations of ground-water exchange obtained by Gurrieri and

Furniss (2004) using mass-balance methods state that this type of methodology provedrobust ground-water inflow values using Ca2+, Mg2+ or K+ as tracers, while success withstable isotopes (d 18O and d 2H) was more limited.In southern Spain, these types of investigations are scarce, but the number of semi-arid

playas is large. The majority of these closed-basin complexes are protected as NaturalReserves by the Autonomous Government, but most of them are in jeopardy due toground-water pumping in nearby areas. The frequent conflicts arising between the waterdemand for intensive agriculture and nature conservation are common in the semi-aridzones where saline lakes are located. The application of the recent European WaterFramework Directive also justifies the study of these water bodies as every lake, river oraquifer must be managed in the frame of a basin-wide perspective. In order to improvethe management of these ecosystems using scientific rather than political criteria, moreinvestigation is needed.The main goals to be addressed in this study are: (a) the estimation of the water budget

in 10 playa lakes of southern Spain in order to establish whether the water source thatsupports them is mainly runoff or ground-water and (b) the analyses of geological featuresas well as hydrochemical and isotopic tracers in order to develop a conceptualhydrochemical and hydrogeological model of the systems.The results of this work contribute to a better understanding of hydrological dynamics

of wet playas using major-ion chemistry, stable O and H isotope analysis and waterbudgets.

2. Methods

2.1. Site description

Ten playa lakes have been included in this study, all of them located within theAntequera region at elevations between 410 and 800m a.s.l. (Fig. 1). This area constitutes


a large karstic outcrop located in the so-called Subbetic Units of the Betic Cordillera(Lhenaff, 1981) and is known as the Triassic gypsum of Antequera unit (Calaforra andPulido-Bosch, 1999). Many authors have pointed out the occurrence of large-scale diapiricprocesses in other locations of the Triassic belt of the Betic Cordillera and its relation withthe formation of saline and hyper-saline lakes and springs (Rodrıguez-Estrella, 1983). TheTriassic of Antequera is considered as the ‘‘German–Andalusian’’ type Triassic facies and ischaracterized by the dominance of clays, marls and evaporitic materials. Evaporites aremainly constituted by gypsum and halite, the former outcropping at the centre of diapiricstructures and the latter deposited as subsurface layers, this corroborated by the existence ofnumerous sodium-chloride springs and cores. The exact depositional structure of the haliteis not yet clearly defined, as it may be massive or dispersed within the Triassic marls (Peyre,1974). The Grande and Chica lakes are located in the outer part of a diapiric structure thatconstitute a karstic triassic aquifer (Fig. 1) and were originated as collapse dolines(Calaforra and Pulido-Bosch, 1999). Fuente de Piedra aquifer is made up primarily ofUpper Miocene calcareous sands and of Quaternary alluvial materials. However, karstifiedJurassic carbonate materials (Mollina and Humilladero sierras, see Fig. 1) also outcrop overthe basin and are integrated in the hydrogeological system (ITGE, 1998; Heredia et al.,2004). Campillos Playa Lakes are as well placed above thin layers of Quaternary alluviumand Upper Miocene calcarenite. In both cases, karstified materials of the Triassic ofAntequera unit (mainly clays and gypsum) constitute the regional substratum.

Although vegetation is absent from the playa surface during the desiccation period,submersed angiosperms such as Druppia drepanensis colonize the flooded playa floorin some of these systems, such as Fuente de Piedra (Garcıa Jimenez, 1991). Moreover, inmost of the playas studied, terrestrial vegetation surrounds the maximum flooded areain the form of shrubs (Tamarix africana, Nerium oleander), reeds (Juncus sp., Phragmites

sp. and Typha sp.) and other species from the Quenopodiaceae family (Salicornia sp.,Sarcocornia sp. and Arthocnemum sp.).

In relation to hydrology, the flooded season extends from December to June. Lake levelsdecline from May in response to higher evaporation rates, lack of rainfall and a decrease indischarge. In the case of Grande Lake, the system is flooded throughout the entire year,and no historical evidence of total desiccation has been found. Nevertheless, a greatoscillation (ca. 5m) in water levels can be observed from summer to winter, this situationtaking place during exceptionally rainy years. The rest of the playa lakes usually desiccateduring the summer. Only if total precipitation of the previous year is more than 700mm,the playa lakes do not desiccate.

The region experiences a Mediterranean climate with semi-arid trends; consequently,inter-annual variations in climatic conditions can be considerable, some years experiencingextremely dry summers and other years being moderately humid (ITGE, 1998). Meanannual precipitation totals 500mm (Linares, 1990) most of it taking place from October toFebruary. On the basis of water balance calculations, mean annual evapo-transpiration inthe area is estimated to be around 380mm. Consequently, mean annual infiltration/runoffof ca. 120mm is to be expected in the catchments of the different playa lakes.

2.2. Description of the playa lakes

The main morphometric characteristics of the lakes studied are shown in Table 1.Fuente de Piedra Playa Lake is the largest Spanish saline lake, although the values

ARTICLE IN PRESS

Table 1

Morphometry of lakes in the study area

Area

(km2)

Watershed

area (km2)

Max.

depth (m)

Mean

depth (m)

Relat.

depth (%)

Volume (m3)

Fuente de Piedra Playa Lake 13.50 152.30 4.4 2.4 0.1 37.23� 106

Ratosa Playa Lake 0.36 3.30 2.7 1.6 0.4 57.38� 104

Grande Lake 0.09 0.15 13.2 5.9 3.8 56.76� 104

Chica Lake 0.08 0.17 8.3 2.9 2.6 22.91� 104

Dulce Playa Lake 0.78 1.04 2.6 1.3 0.3 98.20� 104

Salada Playa Lake 0.18 0.72 2.6 1.3 0.5 24.23� 104

Cerero Playa Lake 0.06 0.28 2.4 1.0 0.8 6.75� 104

Camunas Playa Lake 0.05 0.22 0.4 0.2 0.6 4.40� 104

Capacete Playa Lake 0.13 0.25 1.7 0.6 0.4 8.58� 104

Marcela Playa Lake 0.12 0.22 2.1 0.9 0.4 7.52� 104

M. Rodrıguez-Rodrıguez et al. / Journal of Arid Environments 66 (2006) 272–289276

expressed in Table 1 have been calculated in relation to the maximum flooded surface, sothey have to be considered cautiously. The rest of the playa lakes are relatively small, theirmaximum flooded surface ranging between ca. 0.8 km2 (Dulce Playa Lake) and less than0.1 km2 (Camunas and Cerero playa lakes). Watershed area ranges between more than150 km2 (Fuente de Piedra Playa Lake) to less than 0.2 km2 (Grande Lake). The relativedepth (Hutchinson, 1957) is the maximum depth as a percentage of mean diameter. Formost lakes, relative depth is less than 2%. Deep lakes with small surface areas exhibitgreater resistance to mixing and usually have a relative depth greater than 3.5%. This is thecase of Grande Lake (3.8%) and for that reason is less vulnerable to externalenvironmental changes, whereas Fuente de Piedra Playa Lake amplifies any change inexternal conditions (0.1%).

2.3. Water sampling and analysis

Surface (lake water) and ground-water samples were collected in 2–3 months intervalsfrom 1997 to 1999, which was an exceptionally humid period. Playa lake water sampleswere collected at a distance of 5m from the shore of the playa lake and at a depth of 0.5m.Some depth profiling of lake chemistry was done on the deeper systems (Grande and Chicalakes) in August of 1998 and March of 1999.Ground-water samples were collected from an existing network of piezometers and

pumping wells (Fig. 1). The piezometers consisted of a perforated 30-m PVC tube and wereinstalled on the shore of the playa lakes. Ground-water was sampled from the piezometersusing a foot pump, removing stagnant water by pumping until stabilizing the temperatureand the electric conductivity at 25 1C (EC25).In some piezometers, depth profiling was also done using a multilevel sampler device.

In order to examine the chemical composition of surface and ground-water, major ionswere analysed in samples that passed through 0.45 mm filters. Filtered samples wereanalysed for Ca2+, K+, Mg2+, Na+, NH4+, Cl�, NO3

�, PO43� and SO4

2� by ionchromatography and spectrophotometry at the Water Institute Laboratory (University ofGranada). Cation–anion balance and conformity between calculated and measuredconductivity shows acceptable data quality. The charge imbalance observed among


samples ranged from 0.8% to 4.5%. Heavy metals were measured using atomic absorptionprocedures.

Stable isotopes of oxygen and hydrogen (d 18O and d 2H) are normally shown as ratiosfrom the heavier to the lighter one, relative to the standard mean ocean water (RSMOW).The isotope ratios are reported in the d notation:

d ð%Þ ¼ 103Rs � RSMOW

RSMOW.

The origin and subsequent evaporative process that occurs in natural waters can bedetermined by examining the relationships between these isotopes (Craig and Gordon,1965; Zimmerman, 1979). In precipitation, rivers and lakes measured worldwide showedthat the d-values of the stable isotopes fit along a straight line on a d 2H–d 18O plot. Thisline, termed the ‘‘Global Meteoric Water Line’’ is characterized by the relation: d 2H ¼ 8d 18O+10.

During evaporation, and as a result of both kinetic and equilibrium processes, the watervapour becomes poor in heavy isotopes of oxygen and hydrogen, d 18O and dD (i.e. 2H).This impoverishment, and its magnitude, depends on the relative humidity of theatmosphere in which the water is evaporating, the composition of the water vapour in theatmosphere and ionic strength (Swart et al., 1989). In this sense, the main effects caused bythe dissolved salts (ions) in the isotopic composition of evaporating water are:

(1)
The dissolved salts decrease the thermodynamic activity of the water, as well as theevaporating rate.
(2)
The water molecules get distributed in the hydration spheres of the dissolved ions, andthe evaporating rates (as well as the ionic compositions) differ from those of thedistillate water. This effect may be different in each salt.
(3)
Salts could reach saturation at some stage of the evaporation process, including in theirwebs water molecules on crystallization. This process removes water with a differentisotopic composition from that of the liquid water.
Oxygen stable isotope ratios were determined using the CO2 equilibration technique ofEpstein and Mayeda (1953) from a series of samples collected from 1991 to 1994.Hydrogen was prepared from 1 to 5 ml samples by reduction over Zn at 550 1C (Tanweeret al., 1988). The isotopic ratios of both gases were determined using a Finnigan Mat 251at the Stable Isotope Laboratory of the Zaidin Experimental Station (Granada, Spain).Analytical uncertainties are 0.2% for d 18O and 1% for d 2H.

2.4. Water budget

The water budget of a playa lake is given as

DV ¼ P� E þ Si � So þ Gi � Go, (1)

where Gi is the ground-water inflow to the lake (discharge), Go the ground-water outflow(recharge), DV the change in playa lake storage, P the precipitation, E the evaporation, Si

the surface water inflow and So the surface water outflow; being that the lakes are terminal,So equals zero. Surface water inflow has been estimated using the SCS Curve Number


Method (Chow et al., 1994). The method is based in the following general equation:

Q ¼ðP� IaÞ

2

ðP� IaÞ þ S, (2)

where Q is the runoff, P the rainfall, S the potential maximum retention after runoff beginsand Ia the initial abstraction before ponding (so the potential runoff is P�Ia). By study ofresults from many experimental watersheds, the following empirical relation was obtained:

Ia ¼ 0:2S (3)

with this assumption, the general equation could be written in a more simple way:

Q ¼ðP� 0:2SÞ2

ðPþ 0:8SÞ(4)

plotting the data for P and Q from many watersheds, and transforming S to the parameterCN ðS ¼ ð1000=CNÞ � 10Þ, several curves can be used to estimate the runoff generated bya single storm event. Soil classes where assigned from the analysis of aerial photo and fieldverification. Totalizing daily runoff to a monthly scale, Si was obtained.Daily evaporation data have been obtained from a ‘‘Class A’’ evaporation tank located

at Cerro del Palo weather station (WS), see Fig. 1, corrected and multiplied by theaveraged flooded area on each time interval to obtain E (hm3). Ground-water flowsobtained (Gi and Go) were confirmed using a network of wells and piezometers.

3. Results and discussion

3.1. Hydrochemistry

Sulphate, Cl� and Na+ are the dominant components of surface water and ground-water (Table 2). Elevated levels of SO4

2� and Ca2+ in Grande Lake may be due to theexistence of gypsum in the substratum. On the other hand, Cl� and Na+ dominatedFuente de Piedra Playa Lake, this being due to concentration by evaporation. The relativeconcentrations of ions in each water sample are shown in a Piper diagram (Figs. 2 and 3).Surface waters from the playa lakes suggest a mixture of cations ranging from SO4

2� typeto Na+ Cl� type depending basically on the substratum’s lithology and its degree ofevaporation. Ground-water is dominated by Na++K+ and Cl� ions, the salinityincreasing with depth (Fig. 4). EC25 profiles in several piezometers of Fuente de Piedra,Dulce, Salada and Cerero playa lakes confirm this behaviour, and suggest that ground-water in these systems is undergoing a similar chemical evolution (Rodrıguez-Rodrıguez etal., 2005). The formation of a salinity interface below the playa surface has been reportedmany times in several arid-zone environments (Duffy and Al-Hassan, 1988; Yechiely andWood, 2002). This is noteworthy due to the fact that an abundance of such environmentsexist throughout southern Spain (Rodrıguez-Rodrıguez, 2002). A possible explanation isrelated to the abundance of Triassic evaporites in the area (Subbetic formations) as thedepressions hosting the playa lakes originated from the dissolution of these evaporites(Andreo y Duran, 2004). Variations in cation–anion proportions within each system areexplained by the differences in residence time and the degree of rock–water interactions, asexplained above.

ARTICLE IN PRESS

Table

2

Meanconcentrationofchem

icalconstituents

intheplayalakes

andground-w

ater(samplescollectedover

theperiod1997–2000)

Chem

icalconstituent

Fuente

dePiedra

aRatosa

Grande

Chica

Dulce

Salada

Cerero

Camunas

Capacete

Marcela

Ground-w

aterb

pH

(s.u.)

9.0

8.9

8.6

8.3

8.9

8.5

9.1

8.3

9.1

8.9

7.1

Conductance

(mS/cm)

29.5

7.3

3.0

3.7

2.8

17.6

6.1

17.7

7.1

8.5

76.6

TDS(g/l)

17.6

4.2

2.8

3.1

1.9

12.0

4.4

19.9

4.6

5.5

63.4

TS

19,682.5

4944.4

3452.2

3596.0

2031.9

13,673.3

452.2

22,778.6

5443.3

5862.2

—

SS

179.2

43.7

431.7

275.7

35

183.6

48.2

507.7

117.5

55.5

—

O2

68.8

5.9

10.2

9.0

6.8

6.9

7.1

6.4

7.3

7.7

—

CO

3H

(mM)

1.4

1.6

2.0

2.5

1.5

1.9

0.9

3.3

3.1

1.6

3.7

Cl

9077.3

2075.5

291.1

398.9

473.1

5226.4

2057.4

3801.0

1597.6

2120.7

36,962.0

SO

42183.1

594.9

1640.9

1617.1

716.1

2599.4

722.6

10,329.5

1280.1

1427.2

3894.0

NO

2(mM)

0.6

0.4

0.6

0.5

0.3

1.8

0.3

0.8

3.2

1.9

—

NO

3(mM)

14.8

10.3

18.8

17.5

27.7

50.0

21.6

30.7

38.9

55.3

1628.0

Ca

643.0

202.0

507.3

540.0

233.7

731.1

326.9

7289.49

302.7

289.4

916.9

Mg

711.6

212.2

126.3

99.9

59.6

832.5

231.02

1787.0

226.9

231.0

2733.2

Na

4815.9

1010.6

132.0

258.9

297.4

2424.0

132.0

3180.5

905.9

1288.6

18,303.2

K103.0

14.3

5.7

14.2

17.1

55.8

27.7

28.1

63.7

12.5

—

NH

4(mM)

3.5

19.8

3.6

3.6

7.3

7.9

7.1

10.4

14.2

11.5

—

Chlorophyll

a(m

g/m

)17.8

5.6

9.4

3.9

3.1

6.3

1.4

11.9

4.0

3.3

—

Cu(ng/1)

63.7

5.0

3.2

3.4

3.4

19.0

3.9

7.5

10.8

11.6

—

Zn(ng/1)

9.9

21.3

15.5

921

14.9

8.4

10.2

114.3

12.0

15.5

—

Mn(ng/1)

191.2

166.5

83.3

243.4

298.4

255.4

160.9

432.5

416.9

165.4

—

PO

4(nM)

0.3

0.2

0.2

0.2

0.2

0.8

0.2

0.9

17.4

0.3

—

SiO

2(mM)

42.4

27.8

278.1

155.3

16.1

22.2

11.9

48.9

44.8

16.9

2753.0

Nt(mM)

283.9

97.8

58.2

82.0

94.0

236.1

87.2

363.8

263.5

241.3

—

Pt(mM)

2.4

2.3

0.8

1.5

2.7

3.7

2.1

6.9

35.7

17.8

—

Unitsin

mg/lunless

otherwisespecified.

aData

from

Linares(1990),Alm

ecija(1997)andRodrıguez-R

odrıguez

(2002)(84samples).

bMeanconcentrationfrom

piezometerslocatedin

lakes’basin.

M. Rodrıguez-Rodrıguez et al. / Journal of Arid Environments 66 (2006) 272–289 279

ARTICLE IN PRESS

HCO3 Cl SO4 Ca Mg Na1.0

10.0

100.0

1000.0Concentration (meq/l)

80 60 40 20 20 40 60 80

20

40

60

80 80

60

40

20

20

40

60

80

20

40

60

80

Ca Na HCO3 Cl

Mg SO4

Legend:

DulceSaladaCereroCamuñasCapaceteMarcela


10.0

100.0


80 60 40 20 20 40 60 80

20

40

60

80 80

60

40

20

20

40

60

80

20

40

60

80

Ca Na HCO3Cl

Mg SO4

Legend:

Fuente de PiedraRatosaGrandeChica

(A) (B)

Fig. 2. Major-ion composition of surface water, samples collected bimonthly during a humid period, 1997–2000.

(A) Fuente de Piedra and Ratosa playa lakes: sodium-chloride water facies. Grande and Chica lakes: calcium-

sulphate water facies. (B) Campillos Playa Lakes: sodium-chloride and mixed-sulphate water facies.


3.2. Oxygen and hydrogen isotopes

Isotopic composition of surface water in the playa lakes studied range from 9.7% to�3.6% for d 18O and from 40.3% to �25.4% for dD (Fig. 5). Likewise, isotopiccompositions of ground-waters range from 1.1% to �7.0% for d 18O and from �20.0% to�48.1% for dD (Table 3). d 18O and dD surface water data align to the right of the GlobalMeteoric Water Line, following the equation dD ¼ 4.54 d 18O–11.03. The origin of playalake water is clearly meteoric, evaporative processes in surface water cause variation in theconcentration of d 18O and dD in the different playa lakes. Results are close to the localmeteoric water line obtained from rainfall data: dD ¼ 6.66 d 18O+0.67 (Almecija, 1997).This is in accordance with the fact that clouds producing precipitation over the areaoriginate from the Atlantic Ocean.

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1.0

10.0

100.0

1000.0


80 60 40 20 20 40 60 80

20

40

60

80 80

60

40

20

20

40

60

80

20

40

60

80

Ca Na HCO3Cl

Mg SO4

Legend:

FP lake shoreCampillos wellsFP lake basinArchidona spring

Fig. 3. Major-ion composition of ground-water, samples collected bimonthly during a humid period, 1997–2000.

Notice the geochemical evolution path in the upper part of the Piper diagram indicating increasing concentration

of Cl� and Na+ in ground-water, from the lake basin to the lake shore.


There seem to be a correlation between increasing salinity (notice dot size in Fig. 5) andthe evaporation that occurs in Fuente de Piedra Playa Lake. Variations in the d 18O valuesin ground-water can also be related to the evaporation processes, as the ground-watersamples plotted in Fig. 5 derived from the same piezometer located at different depths.

Isotopic data derived from water samples of Fuente de Piedra, Ratosa, Salada, CereroGrande and Chica lakes (Table 3) seem to exhibit a seasonal pattern, with lowest d 18Ovalues occurring during the discharge period and higher values during the summer.Moreover, surface water from the above-mentioned playas exhibit greater variations ind 18O values than the spring water and surface water from Grande Lake. This could implythat mixing processes due to input water (i.e. runoff and ground-water discharge) on theshores of the playa lakes attenuate variations in the d 18O values. On the other hand, aclearly meteoric origin is attributed to the water from Grande Lake Spring whereas thelake water has a higher d 18O and dD content, this indicating several evaporative cycles

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-8 -6 -4 -2 0 2 4 6 8 10 12

-60

-40

-20

0

20

40

60

δ D=

8

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Fuente de Piedra playa lakeFuente de Piedra playa lake

Fuente de Piedra piezometerFuente de Piedra piezometerGrande springGrande spring

18O (°/ )δ

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/)

δ

Cerero playa lakeCerero playa lakeSalada playa lakeSalada playa lake

Ratosa playa lakeRatosa playa lakeGrande lakeGrande lake

GMWLδO

LMW

L

δ D=6.6

δO0.6

Fig. 5. Isotopic composition of surface and ground-water. Dot size proportional to water salinity.

HCO3 Cl SO4 Ca Mg Na

1.0

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1.0

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Legend:

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10 m

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1 2

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160 0 50

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EC (mS/cm)

Dep

th(m

)

Fig. 4. Shoeller plots indicating major-ion composition of ground-water samples in piezometers 1 and 2. In the

lower part of the figure (#1), EC25 profiles are also shown.


(see Table 3). This behaviour may imply a greater ground-water component related to itsdischarge; otherwise, the lake should desiccate during the summer.

3.3. Water budgets

Monthly runoff and ground-water discharge patterns for three of the studied lakes,Fuente de Piedra Playa Lake (Fig. 6A), Dulce Playa Lake (Fig. 6B) and Grande Lake(Fig. 6C), can be observed in Fig. 6. Data were obtained at 1-month intervals from January1997 to May 2001. Surface runoff fluctuates in high response to rainfall and, subsequently,the predominant volumes recharging each system depend basically on the shape and size of

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Table 3

Values of d 18O and d 2H for ground-water and lake water

Sample location Date of sample d 18O d 2H EC (mS/cm) TDS (g/l) Type

Fuente de Piedra lake Natural reserve

Fuente de Piedra 3/4/91 �1.74 �23.10 67.30 47.62 Lake brine

Fuente de Piedra 5/2/91 5.28 16.40 108.80 85.56 Lake brine

Fuente de Piedra 6/23/91 7.00 15.50 216.00 326.56 Lake brine






Fuente de Piedra 5/15/93 2.97 �0.10 140.30 117.21 Lake brine

Fuente de Piedra 3/8/94 0.74 �4.10 90.00 75.13 Lake brine

Piezometer 10m 10/17/94 �2.50 �36.00 71.00 44.18 Transition zone

Piezometer 20m 10/17/94 �0.80 �29.00 171.00 148.85 Transition zone

Campillos’s lakes Natural reserve

Salada 2/1/92 �0.92 �17.30 102.40 99.57 Lake brine

Salada 4/5/92 0.93 �9.40 101.10 93.85 Lake brine

Salada 6/13/92 2.06 �14.00 184.60 206.78 Lake brine




Salada 4/12/94 1.80 1.90 89.90 88.13 Lake brine

Cerero 5/1/93 4.84 11.90 45.80 32.76 Lake brine

Cerero 4/12/94 3.31 11.70 14.40 10.12 Lake brine

Piezometer 10m 10/1/94 0.20 �20.00 80.00 57.70 Transition zone

Piezometer 20m 10/1/94 1.10 �38.00 162.00 181.20 Transition zone

La Ratosa lake Natural Reserve

Ratosa 5/5/93 �0.43 �13.10 59.70 44.86 Lake brine

Ratosa 4/18/94 3.95 15.20 65.80 56.47 Lake brine

Piezometer 10/24/94 �5.43 �38.00 8.70 6.00 Transition zone

Archidona’s lakes Natural Reserve

Grande 2/10/92 5.55 5.10 3.93 4.27 Lake brine








Spring 4/9/92 �6.69 �45.10 3.01a 2.88 Ground-watera

Spring 9/1/92 �7.05 �47.10 3.01a 2.88 Ground-water




aMean value over the period 1992–1994.


the basin. In the case of Grande Lake, a small catchment area (see Table 1) induceslittle runoff into the lake. Fuente de Piedra catchment area is greater and three temporaryrivers contribute to its surface discharge. In any case, the total amount of ground-water

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m3

Hm

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m3

RunoffG.Discharge

(A)

(B)

(C)

Fig. 6. Monthly runoff and ground-water discharge on to the lakes: (A) Fuente de Piedra Playa Lake, (B) Dulce

Playa Lake and (C) Grande Lake.


discharge in this playa lake is very similar to its surface discharge, as can be deduced fromFig. 6. This behaviour may be attributed to the fact that the catchment area and theaquifer limits are very similar, as stated by Linares (1990). Thus, episodes of ground-waterdischarge normally occur after the contribution of its tributaries. Statistical analysesof the time series have also been made. Cross-correlation of precipitation/river inflowand precipitation/ground-water discharge, revealed that the time lag for the variablesmentioned is ca. 0.3 and 4 months, respectively.In Campillos Playa Lakes, the relationship between catchment areas and aquifer limits

are not as obvious. The piezometric level appears to be continuous and connectedthroughout the Campillos area and, thus, surface catchment’s areas may be much smallerthan the area of the associated alluvial aquifer (Rodrıguez-Rodrıguez and Moral, 2005).As a consequence, during periods with scarce or no precipitation, like the year 1998–1999(precipitation o200mm), Dulce Playa Lake maintains its water level without runoff(Fig. 6B) because there is net ground-water discharge (0.34 hm3). On the other hand, inyears with precipitation of approximately 400mm, surface runoff is considerable but there


is a net ground-water recharge (�0.49 hm3), keeping the playa’s floor dry from March toDecember 2000.

Grande Lake’s level fluctuations are not significant in relation to its maximum depth;moreover, surface runoff is scarce due to the superficial basin’s small area, whichoriginated as a collapsed doline (Pezzi, 1977). As a result, the calculated net ground-waterdischarge is continuous throughout the year and varies greatly. Variations seem to berelated to evaporation patterns rather than to rainfall or surface runoff. In this case, thehydrological budget may be dominated by ground-water discharge. The karstic aquifer inwhich this doline is settled, occupies a huge area, although the limits of the aquifer arepoorly defined due to the lack of hydrogeological investigation. Similar behaviour has beendetected in Chica Lake, although this system has undergone complete desiccation duringexceptionally dry periods.

Some negative results derived from the water budget during the study period suggestthat the playa lake could be recharging the aquifer. This is the case of five out of nine playalakes during, at least, two hydrologic years 1999–2000 and 2000–2001. The relatively largerecharge is probably due to leakage through permeable materials just below the playa lake.It is important to note that this situation occurs during dry years in which annualprecipitation is less than ca. 450mm. In this situation, precipitation and rainstorms, veryfrequent in a Mediterranean climate, and the subsequent runoff onto the playa lakes arenot sufficient enough to maintain the lakes’ water levels. In these circumstances, the playalakes could not be hydraulically connected to the aquifer system because the water-tabledepletion is due to low infiltration and increasing extractions. If this situation is in factoccurring and assuming disconnection between the surface water and the aquifer, negativevalues may coincide with ground-water extraction in each system, a term not included inthe water budget.

According to the results obtained, three main hydrological regimes are proposed in thisstudy. The first one is represented by Fuente de Piedra Playa Lake (Fig. 7A). In thissituation, the catchment area and the aquifer have more or less the same limits and surfacerunoff, river inflow and ground-water discharge into the playa lake are centripetal. Thismeans that the playa floor constitutes the base level of the aquifer. The only possibility oftemporal maintenance of this playa is tectonic subsidence. Thick layers of evaporites aredeposited every year on the playa floor and the only way out for these salts is eoliandeflation. Ground-water flow is conditioned and favoured by intense evaporation in thelake basin during most of the year. Similar results have been reported for this system inprevious studies (Linares, 1990; Almecija, 1997).

The second hydrological situation includes Campillos Playa Lakes: Dulce, Salada,Camunas, Capacete and Cerero (Fig. 7B). The aquifer systems related to these lakes seemto be more extense than each of the lakes’ catchment areas. Although more investigation isneeded to better define the aquifer limits, all the lakes forming the complex are ringing ahill or ‘‘cerro’’ (h ¼ 550m a.s.l.) consisting of permeable materials. The water-tablein the area is dome shaped and the ground-water flows from the centre to the limits ofthe complex, this recharging the playa lakes. Apart from this general behaviour, thehydrological regimes of these particular playa lakes depend on the geologic materials thatconstitute the substratum. This allows the differences between lakes to be distinguished.Campillos Playa Lakes are not terminal, as the final ground-water discharge of the alluvialaquifer is produced in nearby springs and streams (Canaveralejo spring and Tinajas stream,see Fig. 1). In this sense, they can be classified as through-flowing.

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Fig. 7. Hypothetical hydrological model proposed for the lakes studied.


The third hydrological regime proposed corresponds to Grande and Chica lakes(Fig. 7C). Results obtained from the cartography of the doline’s sinks and piezometricmeasurements over the area (Toledano, 2004) reveal that ground-water flow of a regionalkarstic aquifer tends to discharge the lakes throughout the year, as the water-table is, onaverage, 5m above the lake’s floor. In this sense, Grande and Chica lakes are the only truehypogenic lakes of the systems studied (i.e. ground-water discharge lakes).Finally, integrating hydrogeochemical data and geological observations, several factors

appear to be dominant in the formation and evolution of the playa lakes of Antequera.The existence of domes, due to the presence of subsurface deep-level halite, determines


both the hydrogeology of the area and the distribution of karstic forms (see Fig. 7, generalmodel). The karstification of the outcropping gypsum can lead to the formation of collapsedolines. The discharge areas of the karstic aquifers could be sulphate-water springs orperennial lakes. On the other hand, there exists the possibility of deep saline ground-waterflows with distant recharge areas that could discharge in sodium-chloride springs or hyper-saline lakes.

The results from water budgets and isotope analyses obtained in this study confirm thishypothesis.

4. Conclusions

In this study, the hydrological regime of the playa lakes studied in the Antequera regionhas been characterized. Dissolutions of evaporite materials of the Triassic belt ofAntequera have had a decisive influence on the hydrogeological evolution of the playalakes studied. The use of major-ion chemistry, isotopic analyses and water budgets hasallowed us to determine whether ground-water or runoff is the primary source of watersupporting the ecosystems of the playa lakes. The obtained results provide evidence thatground-water discharge plays a major role in the hydrological dynamics and maintenanceof such ecosystems. This study established that Grande Lake and Chica Lake are in directcommunication with the ground-water system and therefore constitute hypogenic ordischarge lakes. It seems apparent that during the study period the remaining playa lakesreceive inflowing ground-water during at least some months of the year, although the exactcalculated values for input and output fluxes must be viewed with some uncertainty.

Fuente de Piedra Playa Lake constitutes the second hydrological situation, in this casethe catchment area and the aquifer limits are the same and the flux is centripetal towardsthe lake that, consequently, constitutes the base level of the aquifer. Fuente de Piedra is,thus, a terminal playa lake, and becomes the discharge area for fluid from the underlyinglayers. A salinity interface below the playa lake suggests that part of the ground-waterdischarge could have a regional origin (high-salinity flows). The interface can be foundnear the shore at a shallow level. However, it sinks until the interface completely weakens,this occurring far from the playa centre.

Dulce, Salada, Camunas, Capacete and Cerero playa lakes constitute a closed-basincomplex in which the aquifer limits are indeterminate due to the variety of materials andthe complexity of the geological setting. In any case, the playa lakes are located around ahill consisting of permeable materials, and consequently ground-water discharge follows acentrifugal pattern. In this sense, they probably constitute through-flowing playa lakes.Nevertheless, ground-water inputs are discontinuous and could be zero due to lack ofprecipitation on an annual basis. Climate variations and overexploitation in nearby areasmay lead to water level depletion inducing changes in hydraulic gradients and ground-water flow paths. Consequently, modifications in hydrologic and ecological dynamics ofthese lakes can occur. In addition, this work illustrates the connection between playa lakesand their watershed and the need for basin-wide management.

Acknowledgments

We thank E. Caballero Mesa Ph.D. (CSIC, Spain) for the isotope analyses andM. Rendon Martos Ph.D., from the Fuente de Piedra board, for field assistance and the


concession of water level data from Fuente de Piedra and Campillos’ lakes. The criticalcomments of Dr. E. Jobbagy and the Editor D.A. Ravetta have helped us to improve thequality of this paper. Professor F. Gray revised the original manuscript and his suggestionsgreatly improve the text. This study was partly funded by the Project SINAMBA (CMA-98) (Environmental Council of Andalusia). M. Rodrıguez-Rodrıguez was supported by aMinistry of Education, Culture and Sports fellowship.

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