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Responses of a Saline Lake Ecosystem in a Semiarid Region to Irrigation and ClimateVariability: The History of Salada Chiprana, Central Ebro Basin, SpainAuthor(s): Blas L. Valero-Garcés, Ana Navas, Javier Machin, Tony Stevenson and Basil DavisSource: Ambio, Vol. 29, No. 6 (Sep., 2000), pp. 344-350Published by: Springer on behalf of Royal Swedish Academy of SciencesStable URL: http://www.jstor.org/stable/4315051 .

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Report Bias L. Valero-Garces, Ana Navas, Javier Machin, Tony Stevenson and Basil Davis

Responses of a Saline Lake Ecosystem in a Semiarid Region to Irrigation and Climate Variability The History of Salada Chiprana, Central Ebro Basin, Spain

To adequately manage the fragile and changing environ- ments of semiarid regions it is essential to disentangle human from climate or other environmental impacts over longer timescales than human memory. We investigated sediment cores from Salada Chiprana, a saline lake in the central Ebro basin in Spain, using pollen, charcoal, sedi- mentological, geochemical and radiometric dating tech- niques. The sequence indicates a rapid evolution from an ephemeral playa lake during the Late Holocene to a per- manent saline lake a few centuries ago. The limnological evolution correlates with changes in agricultural practices and provides evidence of the strong impact of irrigation on the lake's hydrological balance from the XVth century. The work demonstrates that the Salada Chiprana, the only permanent, relatively deep, hypersaline lake in Spain has been created by a long history of human interaction with the landscape.

INTRODUCTION The dominant semiarid climate in the Mediterranean and cen- tral regions of the Iberian Peninsula together with the presence of extensive endorheic areas has favored the development of a large number of small saline lakes. In Iberia, 4 closed-drainage areas contain most of these ephemeral and shallow lakes: the cen- tral Ebro Basin, northern Castille, La Mancha, and the Guadalquivir basin (1, 2). One of these lakes, Salada Chiprana, located in the central Ebro Basin, is the only permanent (4.2- 5.6 m deep) hypersaline lake in Iberia, containing a highly di- verse flora and fauna including a number of rare and endangered

Figure 1. Location of the Salada Chiprana in the central Ebro basin, Iberian Peninsula. Salada Chiprana (*) is located southeast of Zaragoza (Z), close to the village of Chiprana (CH), and near the Ebro river. Hundreds of saline playa lakes dot the

E bro steppe of Los Monegros, the most northerly area of semiarid

Basin climate in Europe.

IBERIAN PEN IN S U A ........ ^^^^ 011a +F

PENINSUA41030'N -MONEGROS,

~T~I Ebro River .. . .~~~~~~- . . . . . . . -.-------.a **** L?ViQuaternary deposits ....

Carbonate Units > .. .. A.... Li] Evaporite Units < . ..J.:: | . I

o ' CGuaalo -::- Claystone Units E I

Sandstone Units W 00 00' H 0 25 km

Limestone Unit JURASSIC

species (3-8). The lake's watershed has been altered by agricul- tural use over the last 150 years and irrigation returns form a significant component of the lake's hydrological balance. Given the lake's uniqueness in Iberia it is essential to better understand its evolution in the recent historic period by attempting to dis- entangle the role of climate from human and other environmen- tal impacts. In this paper, we investigate sediment cores from Salada Chiprana lake using sedimentological, pollen, charcoal, geochemical and radiometric-dating techniques. We also corre- late the limnological evolution of the lake to changes in agri- cultural practices and climate over the last centuries.

THE SALADA CHIPRANA

Geographic Location and Climate

The Ebro Basin is a large depression surrounded by the Pyrenees to the north, the Iberian Range to the southeast, and the Catalan Ranges to the east. It is mostly filled with Tertiary continental deposits (9, 10). The Salada Chiprana (41?14'30"N, 0?10'50"W, 150 m a.s.l.) lies on the Upper Oligocene Miocene Caspe For- mation (Fig. 1), composed of elongated sandstones (infilling of meandering palaeocanals) embedded in fine-grained siltstones deposited in a fluvial floodplain environment (10). The differ- ent erodibility of these rock formations has resulted in a 'nega- tive' relief with small topographically-low areas surrounded by palaeocanals. Climate is Mediterranean with a strong continen- tal influence, and is characterized by very hot summers, cold, dry winters, and low rainfall (300-350 mm yr-') (11, 12). Aver- age monthly temperature ranges from 5.3?C (January) to 27.7?C (August). The high insolation and evapotranspiration (1000-1500 mm yr '), and the prevalence of strong dry NW winds also con-

tribute to a water deficit throughout the year, especially during the sum- mer. Rainfall is irregularly distrib- uted, although spring and autumn precipitation accounts for more than 70% of the total annual rainfall.

Limnology

The Salada Chiprana (surface area = 13.25 ha) belongs to a group of wetlands and lakes hydrologically connected that includes: Las Roces, Clota de El Farol to the SW, Campo de Saladas, and Plana de San Marcos (Fig. 2). The watershed of the complex is about 516 ha, and 156 ha belongs to the Salada Chiprana. The Salada Chiprana waters are of (Sol-)- (Mg2+) (Na+) type, with low carbonate and cal- cium contents, high Mg/Ca ratios, and an average salinity of 40 mg L-l(8). Average water depth is 3.2

344 ? Royal Swedish Academy of Sciences 2000 Ambio Vol. 29 No. 6, Sept. 2000 http://www.ambio.kva.se

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m, and the volume about 700 000 hm3 (7, 8, 13). Brine salinity and composition do not vary greatly during the year, and chemi- cal and thermal water stratification have been documented (4, 7).

The most conspicuous feature of Salada Chiprana is the pres- ence of very distinct lacustrine sub-environments defined by depth, physical and chemical water properties, and biological assemblages (4, 7): i) littoral areas; ii) sub-littoral charophyte meadows; iii) benthic cyanobacterial mat communities; and iv) an anoxic hypolimnion. The littoral sub-environments are domi- nated by Ruppia maritima L. var. maritima between 0-0.8 m water depth. The charophyte meadows composed of Lampro- thamium papulosum, develop in deeper sub-littoral waters. The benthic communities are mostly composed of the cyano- bacterium Microcoleus chthonoplastes which can develop in nu- trient-poor, transparent and oxygenated waters. These commu- nities form 2-3 mm thick mats, up to 1-1.5 m water depth. The deep anoxic waters are the habitat of green phototrophic sulfate- reducing bacterium (Chlorobium vibrioforme).

Hydrology Salada Chiprana is fed by rainfall, groundwater, runoff, and ir- rigation returns. The ultimate source of the solutes in groundwaters and playa lakes in the central Ebro basin is the dissolution of the carbonate and evaporite rocks in Tertiary for- mations (12-18). The quantitative contributions of the main wa- ter inputs for the Salada, particularly groundwater and irrigation returns, are still unknown (7, 8, 13). Most hydrological surveys do not favor a large groundwater input of high salinity waters and suggest that irrigation returns are large enough to maintain the actual hydrological levels. A study of the isotopic composi- tion of the rain, deep springs, and the Salada Chiprana waters (19), indicates that there is no deep groundwater recharge from the Iberian Range.

IRRIGATION AND WATER USE About 4100 ha of the Chiprana and Caspe areas are irrigated from the Civan Canal. This canal, a diversion of the Guadalope river, runs parallel to the Ebro river for about 52 km and ends in the surroundings of the Salada Chiprana (Fig. 2). The irriga- tion return flows are diverted to the Regallo Creek, to the Salada de Las Roces, and thence to the Salada Chiprana; the average annual flow is estimated as 2.5 L s-', and the total freshwater input during 1993 as 103 826 m3 (13). Currently, 43.8 ha are ir- rigated within the Salada Chiprana watershed. The main crops are barley, alfalfa, sunflowers and olive trees, irrigated by flood- ing.

Records of irrigation activities exist from 1838, when a com- mittee composed of the 40 landowners with the largest proper- ties was formed. The irrigated surface reached 3912 ha during the 1 950s and was reduced by the construction of the Mequinenza Dam in the Ebro river in 1967; about 400 ha of rich farm land was covered by the scheme. The construction of the Civan reservoir in the Guadalope river in 1992 has enabled the irrigation of an additional 200 ha. Olive trees formed the main crop until 1970 when a severe winter killed many trees and led many farmers to replace olives with corn and alfalfa. The higher water needs of these new crops, and the low efficiency of the irrigation techniques have subsequently resulted in an increase in water consumption.

METHODS A long core (Core I ) was collected using a combination of Mackereth and Livingstone corers in the deepest part of the ba- sin in 1991, and described and analyzed for sediment composi- tion and pollen content by Davis (5). Pollen analyses were de-

+ E

The Salada Chiprana Is a unique ecosystem In the Central Ebro valley. The lake is permanent (up to 5.6 m deep), waters are hypersaline (up to 50 g IL'), and anoxic conditions are frequent at the bottom. The Salada Chiprana contains several subbasins with steep margins separated by highs, as the one shown in the photo. Photo: B. Valero-Garces.

R IVER

Salada Chiprana HIPRANA Complex GUj3

1 ~~~~~~~~~~\River

1 km

Fgr 2 Th iriato syte In th Chprn -

Cap ara Watel*rs

Seerl susdir caal alo iriato of mos of th lan betwee

trie usn covetinl tehiqe 20 Tw lon core

were retievda ChithnaI a modiiqed 5ecytm dIamether Livngtone borvley. The lak insh depermnet (parto 54.2 m dep)awtersdph are thyersakle basi in April L1997 The twoi codiions cores werequn splt, pheottographed Slde- sCribed,and corrinelaeda subbsing lithostepmagicand sedimentologica marker s. the pre seonceo dishhto.nPhtive seimn layers-arenale.

detilued coThrrelation sytefi the treCoiresana- ofaspe logrea. Waters are diverte from seethed GudaopeRiverm allug the seimentologial.an

geohemClanCaal analyses Ebro rier1. LTholg CviCanal seiends fertea Salada ChpaaCope,were alorrigoofeatetisonore wthurn fonsae diesribed.

byeDaisned useimgcnentarynaltcinqes were ieTifie baedong colres

were ~ ~ ~ ~ ~~~AP rtivdwtamoiid5cdimtrLingtncoe

321 5ntedeetpat(.4)aerdph fteaebsni

Fetigued 2.Thorrigation systhemi thre chirasna of Case area. Watres(7 are divera sleted frmteGaaopeRvrfthroughl the CeiventoCanial.an Sevceral sbiarcanalyss allowrreI)igtionlof y moto hand betweentfa thres Civan Caals aned thEbo rivr.lathe Chisvcor Canal tend onea thesie Saad Chviprn Co.edmpex,ar whie ere irrgtodetuntiflows baredivecolr,ed lthelgy Saanda Chdipranatomleonsicstrutrs.o sevrgal laktes andent depresseerions: 1. Slada-oChipratina,2 Lagnalydes las Ro0Ces. PRandomde Fawdrof, 4.l Campo elas aedas aned 5. PhanaderSaneMaros.sei

tertminedrusigyb cnetoal tieecniqe (20)0 difatwomelong Coresn adsluanlsswere retrieved with a modfiei5-m-dame er Liigsoe 0oe (2)Analther deepes parmet (4.2mpwaer depthg) ofete lakebsind winh hapril 1997.thre tof Hloangdoe were spit,3: photiographteed, ade scribzed, anforterelaedmusngithcompogicalond sedtoimenooicalo

bypDavism(5). Seimentar faie wer Idcidentifiuped blased. oncoothr,

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50-cm-long core (Core III ) was collected in the same site of Core II with the sediment/water interface undisturbed and sam- pled every half cm for 2"0Pb analyses. The chronology of the Chiprana sediment sequence is constrained by three AMS 14C dates from sediment Core I (5), one from Core II, and by210Pb radiometric techniques (Core III). The 210Pb content was meas- ured at the St. Croix Watershed Research Station, Minnesota, USA.

RESULTS The sediment sequence (Core II) is composed of: i) massive grey muds with abundant isolated gypsum crystals at the base; ii) massive red clays; and iii) finely laminated, organic-rich black sediments at the top (Fig. 3). Six sedimentary units were defined, based on the sedimentary facies and all the measured compositional and geochemical parameters. Distinctive depo- sitional sub-environments have been identified based on sedi-

mentary features of modem evaporitic settings and diagnostic sedimentary facies (22, 23). Although the boundaries between units are not located at the same depths, the main units are present in both cores and are easily correlated. Davis (5) distin- guished in Core I: (Fig. 4) i) a basal unit (206-192 cm - SC-6) composed of grey lacustrine playa clays that correlates with sedimentological Unit 6 (175-148 cm, Core II); ii) a unit com- posed of red clays (192-130 cm - SC-5) that correlates with Unit 5 (148-95 cm, Core II); iii) a unit composed of grey/blue lacustrine clays (130-45 - SC-4) that corresponds to sedimentological Unit 4 (95-55 cm, Core II); and iv) a laminated organic mat and lacustrine clays unit (unit 4: 45-0 cm - SC 1-3) that corresponds to Units 3 to 1 (55-0 cm, Core II).

Accurate dating of saline lake sequences in the Ebro Basin is hindered by the scarcity of terrestrial organic material in the sediments and the presence of numerous hiatuses (5, 6, 19, 24- 28). Davis (5) provided a chronology for Salada Chiprana sedi-

Figure 3. Sedimentary facies, sediment composition (percentages of organic matter, total carbon, and sulfur), chemical composition (Al, Fe, Na and Sr) of the Chiprana Core 1.

DEPTH 14CAGE (cm) (yr BP) UNITS FACIES % O.M. % C % S Al (%) Fe (%) Na (%) Sr (ppm)

20- iA 20

~~2 40 4 0 - -~~~~~ ~ A ..._.=-_._._._

(*)315 * 60 B 60 A

80 (*)420 ? 50 ------B -

100-

120- 5

140 -

3410 150 I

160 -6 -KE572560

K K

1015200 2 4 60 5 10 00.5 1.520.5 15 2 0 0.51 1.520 1000 2000

SEDIMENTARY FACIES

Black, laminated mud Cyanobatenal mats E11 Gray, banded muds Red, massive fine silt

I Gypsum laminae F Gray- greenish laminated muds E Gray, massive fine silt x Gray, green gypsum-rich silt

/'-""""' Sedimentary unconformity

Figure 4. Summary Selected trees and shrubs Selected herbs

pollen and charcoal /e diagram of the Chiprana R /A

sequence (Core 11). The 9\\ 1 depicted zones are & * /? provided to depict the tS 0 Z

lithostratigraphical ?... 1 ,.. _. ...... ... ..........

correlation with Core I Zone

(right column). Only 20- SC 1-3 selected plant taxa are shown. 40'

315 * 60 BP - -

420 *50 BP. 60-

SC 4 E

100-

()-120-

140-

160- SC 5

5725 * 60 BPI - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

200- r SC 6

20 20 460 01 'i 2 20 20 2040 20 20 4 204'0 6 20406 220 %% % % % % % % % %% %

Anal. B.A.S.Davis - Dept. Geography, University of Newcastle

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mentary sequence, based on 3 AMS radiocarbon dates (Core I) from a mixture of Chenopodiaceae plant remains and Carophyllaceae seeds at 50-51 (315 ? 60 14C yr BP) and 73-75 cm (420 ? 50 14C yr BP), and charcoal from 191-194 cm (5725 ? 60 14C yr BP). He suggested the presence of several hiatuses in the lower part of the record, most likely between units SC-6 and SC-5 and SC-5 and SC-4. We improve the chronological framework for Salada Chiprana with another AMS 14C date from charcoal at 145 cm (Core II) and a 2l0Pb chronology for the up- per sediments (Core III).

Unit 6 is composed of massive grey-green muds with abun- dant isolated gypsum crystals (< 1 mm), and calcite as the only carbonate mineral. Displacive textures and matrix mud inclu- sions in the crystals suggest that the gypsum crystals were formed as a result of intrasediment growth in a saline mudflat environment. This is confirmed by the palynology which is sug- gestive of a playa type environment (Fig. 4). Salada Chiprana

5- c I / 0- A\I 10

ElS ~01 E 15- _ _.; C,~~~~C 20 C

0.

o25

80 30

35

40

45-

0.1 1 2 P ig1 5 Total 210Pb Activity (pCi 91)

0 -

2 B

4

6

o8

12

14

16

18-r., 2000 1950 1900 1850 1800

21 Pb Age (Calendar yr)

0

15

25

__35

E 2. 45

a- 55

65

75

85

95, .. .. 1400 1500 1600 1700 1800 1900 2000

Calendar Years (A.D.)

Figure 5. Chronology of the Salada Chiprana core. A. Total 210Pb activity in the upper 40 cms (Core ll). B. The 210Pb chronology for Salada Chiprana core based on a supported 210Pb activity of 0.29 pCi g1 and a constant flux:constant sedimentation model. C. A proposed chronology for the main limnological changes in the Salada during the last 600 years based on the 210Pb chronology (squares, Core ll) and two 14C dates (dots) from Core 1(5).

during deposition of unit 6 was an ephemeral, shallow saline lake similar to the current lakes in the Central Ebro Basin. Accord- ing to the basal date of 5725 ? 60 14C yr BP provided by Davis (5), and our AMS date from the overlying Unit 5 at 145 cm (3410 ? 150 14C yr BP, Woods Hole Laboratory number: OS 16936), the deposition of Unit 6 took place during the mid- Holocene (6000-4000 14C yr BP).

The sharp change to the reddish massive fine muds of Unit 5 (148 cm) indicates that an abrupt change in the depositional en- vironment took place prior to 3500 14C yr BP. This abrupt bound- ary is located at 130 cm depth in Core I. Sediments of Unit 5 are characterized by higher clay mineral and lower gypsum con- tents. Higher concentrations in aluminum and iron also reflect the higher clay content. The oxidized, detrital nature of the sediments, together with lack of aquatic pollen and seed types and Chenopodiaceae pollen suggest frequent desiccation stages with accumulation of windblown material in the small surface depressions of a dry playa lake (23). These features suggest that Salada Chiprana was a dry mudflat with the local watertable be- low the surface during most of the Late Holocene. The sharp changes in lithology indicate that Unit 5 is bounded by erosive unconformities. The upper boundary at 95 cm depth represents a sedimentary hiatus of unknown age developed during periods when the lake dries out.

The deposition of massive, coarser brown and grey silts with more abundant gypsum crystals and lower clay content (Unit 4B) indicates an increase in the water balance, and the re-establish- ment of a shallow ephemeral saline lake. Periods of more fre- quent desiccation are indicated by increases in the clay content, and related elements (Al, Fe). The increases in organic matter and Na contents at the top of Unit 4A suggest deposition in a shallow saline lake with the water-table close to the surface even during desiccation stages. This is confirmed by the pollen re- sults, which show increases in Ruppia and Potamogeton pollen together with high levels of Chenopodiaceae pollen. An AMS '4C date from this unit provides an age of 420 ? 50 yr BP, which indicates that the watertable rise in Salada Chiprana at the base of Unit 4 occurred around 600 years ago, in the XJVth century. The boundary between SC-5 and SC-4 evidences a marked de- forestation as pine woodland gives way to Juniperus and other steppe like plants (e.g. Artemisia). Another abrupt sediment change inaugurates Unit 3 (Fig. 3).

The upper units 3, 2 and 1 are composed of organic gypsum and aragonite-rich finely laminated sediments. Both, clay min- eral and aluminum contents decrease reflecting a lower detrital input. The presence of aragonite indicates waters with higher Mg/ Ca ratios. Strontium preferentially substitutes Ca2" in aragonite and, consequently, it is also more abundant in the upper units. The preservation of lamination, the increase in organic matter and Na contents, and the change in the carbonate mineralogy, together with high levels of Ruppia maritima var. maritima seeds, Ruppia pollen and Lamprothamnium papulosum oospores point to deposition in a permanent, deep saline lake (Fig. 4).

Unit 3B is composed of an alternation of organic-rich grey muds and gypsum laminae; Unit 3A groups organic-rich muds and bacterial mats not very well developed that grade upwards into the same alternation of facies characteristic of Unit 3B. Or- ganic-rich muds and gypsum laminae indicate hypersaline, an- oxic conditions and the development of water stratification in Salada Chiprana. During lower lake levels, meromixis was dis- rupted and oxygenated bottom waters allowed development of bacterial mats in the deepest part of the basin. According to the chronological framework, the sharp increase in water levels rep- resented by the onset of sedimentation of Unit 3 occurred in the XVJJth century (315 ? 60 14C yr BP; Figs 3, 4, and 5). These limnological changes correlate with the onset of an increasing trend in Olea and decrease in Pinus pollen.

Unit 2 is composed of well-developed finely laminated cyano-

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bacterial mats and some intercalated black, organic- and gyp- sum-rich laminae (Fig. 3). Lower sodium content indicates rela- tively lower salinities. The dominance of well-developed cyanobacterial mats favors an interpretation of stable conditions in the hydrological balance of the lake. According to the cur- rent ecological conditions of bacterial mats in Chiprana, we es- timate the water depth to be up to 2 m. During short periods of higher lake levels, anoxic bottom conditions developed and thin black, gypsum- and organic matter-rich laminae deposited.

The 210Pb chronology helps constrain the main limnological changes occurring in Salada Chiprana during the last centuries. The 2'0Pb content in Core III shows an irregular decline to about 17 cm, below which supported (background) values are reached (0.29 pCi g-', Fig. 5). The 2l0Pb at depth is somewhat variable, so it is difficult to decide where unsupported 2l0Pb levels off. Another problem in establishing a detailed chronology arises from the very low 210Pb activities at the top of the core, so the variability at depth produces even greater dating uncertainty. The unsupported 2l0Pb flux of 0.14 pCi cm-2 yr-l is relatively low compared to north temperate mid-continental regions. However, similar low values occur in another saline lake in the Ebro Ba- sin (Salada Mediana; 28), and are coherent with low regional atmospheric fluxes of 210Pb as expected in an arid region. Tak- ing all this into consideration, the chronology shown in Figure 5 has been calculated using the constant rate of supply model (29). For the estimation of the sedimentation rates, the cf:cs (con- stant flux:constant sedimentation) model is more robust. We con- sider that given the uncertainties in the data, this conservative approach is more appropriate, because we are not interpreting each inflection in the 210Pb profile; instead we drive a regres- sion line through the data to obtain an average sedimentation rate. On the other hand, the different sediment laminae present in the core (bacterial mats, gypsum laminae, organic-rich sediments) have different accumulation rates, and the 210Pb chro- nology lacks the adequate resolution to detect such fluctuations in sedimentation rate. These results give a mean sedimentation rate of 0.10 g cm-2yr 1' (e.g. the upper 17 cm represent about 80 years). Assuming a similar average accumulation rate for the upper Units 1 and 2, the spread of cyanobacterial mats in the lake (Unit 2) would have occurred at the beginning of the XIXth century, and the transition to the finely laminated, organic-rich sediments of Unit 1 at the beginning of the XXth century.

According to the extrapolated 2"0Pb chronology (Fig. 5), depo- sition of Unit 2 occurred in the late XVIIJth and the XIXth cen- turies. This period of stable and relatively low lake levels char- acterized by the dominance of the cyanobacterial mats ended with a period of fluctuating and generally increasing lake levels at the end of the XIXth century conducive to more frequent an- oxic bottom conditions (Unit 1B). Presence of indurated gyp- sum and charophyte-rich laminae indicates periods of concen- trated waters and likely lower lake levels; black, organic-rich laminae indicate deposition during deeper lake waters. The up- per sediments (Unit IA) are mostly composed of charophyte and organic-matter-rich, black, laminated muds suggesting higher lake levels since 1950. An encrusted, gypsum-rich interval in- tercalated at 5-7.5 cm represents higher salinities, and likely lower lake levels. According to the 2"0Pb chronology, this pe- riod would have occurred during the mid- 1960s through mid- 1 970s. Since then, organic-rich laminated muds have deposited in the deepest areas of Salada Chiprana lake.

DISCUSSION Climate and human-induced changes have been interplaying fac- tors in landscape transformation and degradation over the last millennia in the Central Ebro Basin. Davis (5) provides the most up-to-date account of vegetation and lake-level changes in the area during the Late Holocene. Early deforestation correlates

with early Bronze Age settlement about 5000 yr BP. Moderate lake levels during the period 4000-3500 yr BP correlate with higher watertables in Salada Chiprana (Unit 6). An arid episode in the Ebro basin at about 3400 yr BP described by Davis (5), coincides with the development of a dry mudflat in Chiprana (Unit 5), and the decline of Bronze Age settlements in the cen- tral Ebro Basin (30-32). Erosion during this and/or other arid periods has resulted in a long sedimentary hiatus, and the Late Holocene sequence is not complete. The decline of the Pinus for- est had occurred in the area during this period, prior to histori- cal times (Fig. 4) The next sediments accumulated in Salada Chiprana (Unit 4) were deposited during the XIVth century. This period of increased watertable correlates with changes in both, climate and land use.

The watertable increase in Salada Chiprana at the onset of Unit 4 correlates with large agricultural changes in the area and also the climatic fluctuations at the end of the Medieval Warm Pe- riod (33). The use of the Guadalope river water for irrigation purposes in the Caspe and Chiprana area is likely to have started during the Arab epoch (VIIth_XIIth centuries). No archaeologi- cal or historical studies have been conducted, although some stonework close to the beginning of the Civain Canal, date from the XIIthXIIjIth centuries (Civan Committee Manager, pers. comm.). The first historic document dated from 1413 when King Ferdinand of Antequera gave privilege of the use of the Civa'n channel to the city of Caspe, as a reward for his election as the new king of Aragon in Caspe. During the XVth century a tunnel was planned to eliminate 6 km of the channel, and to reduce the costs of annual cleaning, but was abandoned after structural prob- lems led to collapse of the tunnel roof.

On the other hand, the XIVth_XVth centuries were also a pe- riod of climate change in western Europe, after the end of the Mediaeval Warm Period (AD 900-1300; 33). Dendroclimat- ological reconstructions for the Central Ebro valley (34, 35) show a high climate variability (rainfall and temperature) since the XlIIth century, after the relatively low variability of the Medi- eval Warm Period. During the 1400s-1600s both droughts and floods were more frequent. Climate variability was particularly high during the period 1480-1520 AD when annual precipita- tion increased and temperature decreased (Fig. 6). Rainfall was higher during the XVI1h century than during the XV"h century. Although some irrigation returns could have been diverted to the Salada, those were likely to be small, and we consider that these climatic changes are enough to explain the hydrological changes in the Salada. Increased precipitation and lower evaporation brought by reduced temperatures during the XVt'-XVIth centu- ries could account for the small watertable rise experienced in Laguna Salada during the period of deposition of Unit 4 (Fig. 6).

The increase in lake level at the base of Unit 3 occurred dur- ing the XVJIIth century, a period of reduced rainfall in the cen- tral Ebro valley (34). Although extreme precipitation events oc- curred during the XVIIth and XVIIIth centuries, the increase in total annual precipitation was moderate in Iberia (36). The limno- logical changes in the Salada Chiprana are more coherent with the history of the agricultural use of the area. Modern agricul- ture was established in the XVth and XVIth centuries with increas- ing farm land, massive expansion of olive plantations and wide- spread introduction of irrigation. The Salada Chiprana pollen record clearly shows this expansion in olive cultivation about 300 yrs ago (Fig. 4). The decreasing values of pine and scrub components, similar values of the herbaceous elements, and the presence of a peak in charcoal prior to the olive expansion indi- cate some deforestation of the surrounding areas for olive culti- vation. More stable limnological conditions characterized by hypersaline waters and relatively lower lake levels favored the dominance of cyanobacterial mats during deposition of Unit 2 (XIXth century).

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Figure 6. Summary of environmental changes in the Salada Chiprana compared to the dendro- climatic reconstructions (34) and to the main historic events of the Civan Irrigation Canal.

DEPOSITIONAL DENDROCLIMATOLOGY CHRONOLOGY UNITS EVOLUTION

I B

2 - 1800 - -

3B - 1700

____ .. 4A

s_ _ ~~~~~~~~~~~~... . .... .. .. . 1500- e

t7

4B _------- -1400HIATUS EROSION

200 400 600 M.W.P. (Annual Rulnfl.

Central Ebro wry Lab Holocene 5 mmyr1) (4 -?KaBP)

HIATUS EROSION

Mid Holocene A 1% A (6-5 Ka BP) 6

1 2 3 4 5

CIVAN CANAL IRRIGATION

Com and aifalfa crops 1970 Farm machinery 1960

Increased fann land XIX

Agrarian crisis xviii

Olive expansion Modem Agriculture XVII- XVIII centuries

Canal enlargement

Privilege of Caspe 1413

Canal constnrction VIIi-XII centudes

Depositlnal Envlronments

1. my MUWl 2. Ephmrat Stan Lake (Saline Pan) 3. Shaow Saline Lain 4. Perennial Seine La wthh Cyanobacedal mats

. Perennial, Marwont, Deep 8dm Lake

Increasing agricultural use of the land at the end of the XIX' century could be responsible for the increase in lake levels, and the frequent anoxic bottom conditions that characterize the tran- sition to Unit 1 (Figs 3 and 5). The abundance of gypsum lami- nae intercalated with the organic-rich black muds reflects sev- eral periods of increased water chemical concentration (and likely lower lake levels) during the early XXI" century (base of Unit 1). Several studies (4, 7, 8, 13) have documented large changes in limnological parameters during the last decades. Laguna de Las Roces was likely a saline lake 30 or 40 years ago, according to vegetation surveys (37). Increasing irrigation in the area produced a drop in water salinity in the Laguna Las Roces and flooding of the surrounding fields. Higher lake lev- els in Chiprana during the 1950s correlate with the introduction of farm machinery. After a short period (mid-1960s through mid- 1 970s) of higher salinities, the water depth increased again (Fig. 6). The change from olive trees to corn and alfalfa crops in the 1970s resulted in an increase in irrigation water consumption from the Civan Canal, and larger return inflows into the Salada Chiprana. The impact of irrigation returns on the hydrology and water quality has also been clearly documented in other areas of the Ebro Basin (38).

The Aragon Regional Government has been monitoring the Salada Chiprana for the last 2 decades, including measurements of the water quality and the lake level during the period 1993- 1996 (7, 8, 13). During low salinity periods, triggered by increas- ing irrigation returns, Artemia salina disappeared and the lake was colonized by a brackish fauna. The waters were anoxic be- low 3 m, and benthic microbial communities were not very well developed. During the summer of 1995, the lake reached a low lake level stage that isolated one of the bays, and a hypersaline brine developed (73-100 g L-'). Waters were more transparent, anoxic bottoms reduced, and cyanobacterial mats expanded to deeper areas. These qualitative observations demonstrate that the main lake level fluctuations and lake water compositions are re- lated to the changes in the irrigation return flows.

A recent rise in lake levels has also been documented in other

sites in the Ebro basin (5, 19, 26-28), but the studies lack the chronological control to solve the precise timing and the possi- ble causes. However, more detailed dendroclimatological recon- structions for precipitation and temperature do not show trends comparable to the Chiprana record (34). The XXth century is characterized by reduced rainfall, but sedimentological evidence indicates that lake levels during deposition of Unit 1 were gen- erally higher than during Unit 2. Finally, meteorological records for the last decades do not correlate with the increasing lake lev- els in Chiprana Salada; a humid period with annual rainfall higher than 350 mm (1969-1976) and an arid period since then punctuated with some humid years (1983, 1986, 1987, 1988). To summarize, the limnological features of Salada Chiprana during the last decades are mostly controlled by the amount of irrigation returns diverted to the lake. Therefore, the hydrologi- cal changes in the Salada Chiprana do not correlate with the re- constructed or measured rainfall because they are obliterated by the direct impact of irrigation returns.

CONCLUSIONS The saline lakes and steppes in the Central Ebro valley are unique in Europe. Human activities have played a dynamic role in the transformation of these ecosystems, and landscapes have provided natural resources (wood, salt from the lakes, soils, hunt- ing grounds) during the long 7000 year history of human occu- pation in the region. However, because of the small population, landscape degradation due to human impact has been low until modern historic times. Several vegetation changes in the area (early Neolithic, 4000 yrs BP, early Mediaeval) seem more re- lated to climate variability than to anthropogenic deforestation. In the Central Ebro valley, large environmental changes during the Late Holocene have been aggravated, but not generated, by human action.

During the last millennium, human activities became a more significant force in landscape and ecosystem transformation in the Central Ebro valley than are climate-induced changes. Mod-

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em agriculture was established in the XVIIth and XVIIIth centu- ries with increasing farmland, massive expansion of olive plan- tations and widespread introduction of irrigation. Close to the Guadalope and Ebro river valleys, extensive irrigation resulted in a greater transformation of the landscape. Major changes oc- curred in the 1 950s when mechanization of agricultural practices was responsible for ploughing many of the saline lakes water-

sheds, and when new modem irrigation plans were implemented. The limnological changes in the Salada Chiprana are coher-

ent with the history of the agricultural use of the area. Currently, the Salada Chiprana is the only permanent, deep hypersaline lake in Spain, a unique ecosystem in the Central Ebro valley created by a long history of human interaction with the landscape.

References 1. Comin, F.A. and Alonso, M. 1988. Spanish salt lakes: their chemistry and biota.

Hydrobiologia 158, 237-246. 2. Pueyo-Mur, J.J. and De la Pefia, J.A. 1991. Spanish saline lakes. Sedimentology,

hydrochemistry and diagenesis (In Spanish, summary in English). In: Evaporite For- mation: Andean and Iberian Models. Pueyo, J.J. (ed.). Universidad de Barcelona, Bar- celona, pp. 163-192.

3. lbaniez, M.J. 1975. Endorheic drainage in the central Ebro depression. Cuad. Invest. Geogrdfica 7, 35-48. (In Spanish, summary in English).

4. Vidondo Curras, B. and Guerrero Sanchez, M.C. 1992. The Chiprana Saline lake: De- scription of its physical-chemical features as habitat for unique phototrophic bacterial communities. Cuadernos de Estudios Caspolinos 18, 117-246. (In Spanish).

5. Davis, B.A.S. 1994. Paleolimnology and Holocene Environmental Change from Endoreic Lakes in the Ebro Basin, North-east Spain. Ph. D. Dissertation, University of Newcastle Upon Tyne, UK. 317 pp.

6. Stevenson, A.C. 1995. Monitoring, modelling, paleoecology and wetland dynamics. In: Bases ecolgicas para la restauracion de humedales en la cuenca mediterranea. Montes, C., Oliver, G., Molina, F. and Cobos, J. (eds). Consejeria de Medio Ambiente, Junta de Andalucia, Sevilla, pp. 79-94.

7. LIMNOS - DGA 1996. Limnological Data for Natural Resources Management of the Las Saladas and Chiprana Wetland Complex. Diputacion General de Arag6n, Zaragoza. (In Spanish).

8. EPTYSA - DGA 1997. Bases for the Management of the Natural Resources in the Wetland Complex of the Saladas of Chiprana. Diputation General de Arag6n, Zaragoza. (In Spanish).

9. IGME, 1971. Geologic Map of Spain 1:200000. Huesca n? 23. Instituto Geologico y Minero de Espafia, Madrid.

10. Quirantes, J. 1978. Sedimentologic and Stratigraphic Study of the Continental Tertiary of Los Monegros. Instituto Femando el Cat6lico, Zaragoza, 200 pp. (In Spanish, sum- mary in English).

11. Lines Escardo, A. 1970. The climate of the Iberian Peninsula. In: Climates of North- ern and Western Europe. Wallen, C.C. (ed.). World Survey of Climatology 5, Elsevier, pp. 195-242.

12. Garcia-Vera, M.A. 1996. Hydrogeology of Endorheic Areas in Semi-arid Climates: The Monegros Case Study (Zaragoza and Huesca provinces). Publicaciones del Consejo de Proteccion de la Naturaleza de Arag6n, Zaragoza, 297 pp. (In Spanish).

13. ESHYG - DGA 1994. Hydrologic -Hydrogeologic Study of the Endorreic Basin of Las Saladas de Chiprana. Diputati6n General de Arag6n, Zaragoza, 128 pp. (In Spanish)

14. Pueyo-Mur, J.J. 1979. Modem evaporite formation in the saline lakes of the Bujaraloz, Sastago, Caspe, Alcafiiz and Calanda areas (Zaragoza and Teruel provinces). Rev. Inst. Invest. Geol. Diput. Provinc. Barcelona 33, 5-56. (In Spanish, summary in English).

15. Mingarro, F., Ordofiez, S., Lopez de Azcona, M.C. and Garcia del Cura, M.A. 1981. Sedimentology and chemistry of the Los Monegros saline lakes and their geological context. Bol. Geol. Minero 92, 171-195. (In Spanish, summary in English).

16. Sanchez-Navarro, J.A., Perez, A., Coloma, P. and Martinez-Gil, F.J. 1998. Combined effects of groundwater and aeolian processes in the formation of the northemmost closed saline depression of Europe, North -East Spain. Hydrol. Proces. 12, 813-820.

17. Navas, A. 1991. The pattem of gypsum transport in the Ebro river network. Catena 18, 45-49.

18. ITGE 1992. Use of Isotopic Techniques to Study Hydrological Problems (2nd phase). ITGE, Madrid, 34 pp. (In Spanish).

19. Valero-Garces, B.L., Delgado-Huertas, A., Navas, A.. Machin, J. Gonzalez, P., and Kelts, K. Quatemary sedimentologic and isotopic evolution of a playa lake: Salada Mediana, central Ebro Basin, Spain. Sedimentology. (In press).

20. Moore, P.D., Webb, J.A. and Collinson, M.E. 1991. Pollen Analysis. Blackwell, Ox- ford, 216 pp.

21. Wright, H.E. 1967. A square-rod piston sampler for lake sediments. J. Sed. Petrol. 37, 975-976.

22. Hardie, L.A., Smoot, J.P. and Eugster, H.P.1978. Saline lakes and their deposits: a sedimentological approach. In: Modern and Ancient Lake Sediments. Matter A. and M.E. Tucker M.E. (eds.). Int. Ass. Sed. Spec. Publ., 2, pp. 7-42.

23. Smoot, J.P. and Lowestein, T. 1991. Depositional environments of non-marine evaporites. In: Evaporites, Petroleum and Mineral Resources. Developments in Sedimentology, 50. Melvin, J. (ed.). Elsevier, pp. 189 -348.

24. Macklin, M.G., Passmore, D.G., Stevenson, A.C., Davis, B.A. and Benavente, J.A. 1994. Responses of rivers and lakes to Holocene enviromental change in the Alcafiiz Region, Teruel, North-East Spain. In: Environmental Change in Drylands: Biogeo- graphical and Geomorphological Perspectives. Millington A.C. and K. Pye K. (eds). John Wiley & Sons, pp. 11 3-130.

25. Burjachs, F., Giralt, S., Roca, J.R., Seret, G. and Julia, R.1997. Holocene palynology and desertification in the westem Mediterranean. In: Mediterranean Landscape through Space and Time. Implications for Desertification. Ibaiiez J.J., Valero-Garces B.L. and Machado C. (eds). CSIC, Geoforma Ediciones, Logrono, Spain, pp. 379-394. (In Span- ish).

26. Burjachs-Casas, F., Rod6, X, and Comin, F.A. 1996. Gallocanta: a case study of a pol- len sequence from an ephemeral saline lake. In: Estudios Palinol6gicos, XI Simposio de Palinologia. Ruiz Zapata, B. (ed.). Universidad de Alcala. pp. 25-29. (In Spanish).

27. Schutt, B. 1998. Reconstruction of palaeoenvironmental conditions by investigation of Holocene playa sediments in the Ebro Basin, Spain: preliminary results. Geomorphology 23, 273-283.

1g

28. Valero-Garces, B.L., Delgado-Huertas, A., G6nzalez, P., Navas, A.. Machin, J., and Kelts, K. Lateglacial and Late Holocene climate and environmental change in Salada Mediana, central Ebro Basin, Spain. Quat. Internat. (In press).

29. Olsson, 1. 1986. Radiometric Dating. In: Handbook of Holocene Palaeoecology and Palaeohydrology. Berglund, B.E. (ed.). John Wiley & Sons, pp. 273-312.

30. Harrison, R.J. 1994. Development and decline in the Mediterranean Bronze Age. In: Sheffield Archaeological Monographs 8. Mathers C. and Stoddart S. (eds). J.R. Collis Publications, pp. 73-97.

31. Sopena Vicien, M.C. 1998. The Bronze Age in the Middle Cinca Region. A Geoarcheological Study. Ph.D. Dissertation, University of Zaragoza, Spain. 811 pp. (In Spanish, summary in English).

32. Gutierrez-Elorza, M. and Pefia Monne, J.L. 1989. Upper Holocene climatic change and geomorphological processes on slopes and infilled valleys from archaeological dating (NE Spain). In: European Conference on Landscape Ecological Impact on Climatic Change. Mediterranean Region. Imeson, C. and De Groot, R.S. (eds). pp.1-20.

33, Pfister, C., Luterbacher, J., Schwarz-Zanetti. G. and Wegmann, W. 1998. Winter air temperature variations in westem Europe during the Early and High Middle Ages (AD 750 - 1300). The Holocene 8, 535-552.

34. Creus, J., Femrndez Cancio, A. and Manrique Menendez, E. 1996. Evolution of tem- perature and annual precipitation since 1400 A.D. in the Central Ebro Depression. Lucas Mallada 8, 9-27. (In Spanish, summary in English).

35. Creus Novau, J., F6rnandez Cancio, A. and Manrique Menendez, E. 1997. Dendrochronology and climate during the last milleniun in Spain. Methodological as- pects and preliminary results. In: Mediterranean Landscape through Space and Time. Implications for Desertification. Ibafiez J.J., Valero-Garc&s B.L. and Machado C. (eds). CSIC, Geoforma Ediciones, Logrofio, Spain, pp. 311-330. (In Spanish).

36. Barriendos, M. 1997. Climatic variations in the Iberian Peninsula during the late Maunder Minimum (AD 1675-1715): an analysis of data from rogation ceremonies. The Holocene 7, 105-111 .

37. Braun-Blanquet, J. and Bol6s, D. 1957. Plant communities in the Middle Ebro Basin and their dynamics. Ann. Aula Dei 5 (1-14), 1-266. (In French, summary in English).

38. Machin, J. and Navas, A. 1997. Impact of irrigation on the nitrate contamination of the surface waters in Bardenas. IAHS Publication 243, 109-116.

39. We appreciate the comments and criticisms by Dr. Gesa Weyhenmeyer and two anony- mous reviewers. The research in Salada Chiprana was partially funded by the National Science Foundation, United States of America, under the EAR 941-8657 programme, and by the Estacion Experimental de Aula Dei - CSIC project number Z-5-96.

40. First submitted 26 March 1999. Accepted for publication after revision 4 February 2000.

Blas L. Valero-Garces is a researcher at the Pyrenean Institute of Ecology. His major research interests are sedimentology, limnogeology, and the reconstruction of past climates and environments from lacustrine records. His address: Instituto Pirenaico de Ecologia CSIC, Apdo 202, 50080 Zaragoza, Spain. E-mail: blas@ipe.csic.es

Ana Navas is a researcher at the Department of Edaphology, Estaci6n Experimental de Aula Dei. She has particular interest in soils of semiarid regions. Her address: Estaci6n Experimental de Aula Dei - CSIC, Apdo 202, 50080 Zaragoza, Spain. E-mail: anavas@eead.csic.es

Javier Machin is the Head of the Department of Edaphology, Estacion Experimental de Aula Dei. His main research interests are saline soils in the Ebro valley, soil and water salinization problems in irrigation. His address: Estaci6n Experimental de Aula Dei - CSIC, Apdo 202, 50080 Zaragoza, Spain. E-mail: jmachin@eead.csic.es

Tony Stevenson is Dean of the Faculty of Law, Environment, and Social Sciences, University of Newcastle. His main research interests are the interaction between climate, vegetation and human society in the western mediterranean during the Holocene. His address: 4th Floor Claremont Bridge, University of Newcastle, Newcastle upon Tyne, NE1 7RU, United Kingdom. E-mail: tony.stevenson @ ncl.ac.uk

Basil Davis is a postdoctoral research fellow at the Max Planck Institute for Biogeochemistry, Jena. His main research interests are the impact of Holocene climate change on plant and human communities in the western Mediterranean. His address: Max Planck Institute for Biogeochemistry, Jena, Germany. E-mail: basil.davis@bgc-jena.mpg.de

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