P PALEOLAKES Reginald W. Herschy Hydrology Consultant, Reading, UK Introduction All lakes are subject to a variety of extrinsic and intrinsic forcing variables that regulate the subsequent history of the lake. This includes age, climate, catchment, bedrock composition, tectonic and volcanic activity, vegetation, aquatic biota, and human activities. Strictly it is the history of change in these variables and the paleolimnological records of very old or ancient lakes that eventually lead us to the age of the lake. Paleolimnological records found in three distinct types of archive Water Lake water itself and its contents have finite residence times, the time required for the average molecule of water to cycle through the system. In lakes with long residence time measured in say hundreds to thousands of years, the water itself may provide important paleolimnological clues to lake history. Geomorphology The geomorphology of the lake basin in its shoreline and shape characteristic features can persist for many thou- sands of years long after the lake has gone. In this respect, a lake basin evolution is a more useful concept than the static one of lake origin. It is therefore an essential element in the design of a paleolimnological study. Sediments Sediments provide the most durable feature since they may persist long after the lake itself, or its geomorphology ceased to exist. Content archives in paleolimnological are the physical sedimentary inputs to the lake’s record. These include terrigenous, chemical, and biogenic sediments; cosmo- genic and volcanogenic particles; and fossils that originate outside the lake, like pollen, or in the lake, like fish, aerosols, and water-borne pollutants. Formation and history of lakes The formation and history of lakes has intrigued earth sci- entists for over a century; Hutchinson (1957) recognized 11 major categories of lake origins and since then advances have been made in understanding basin evolu- tion using radiometric dating techniques, seismic stratig- raphy, and lake drilling. The following lake classification (after Cohen, 2003) incorporates major elements of Hutchinson’s scheme: Basin closure Temporal duration (years) 1. Glacial 10 4 –10 5 2. Tectonic 10 5 10 7 3. Fluvial 10 4 4. Coastal 10 4 5. Volcanic 10 4 –10 7 6. Wind 10 4 7. Solution 10 4 –10 7 8. Landslide 10 3 9. Meteorite 10 5 –10 7 10. Artificial 10 3 L. Bengtsson, R.W. Herschy, R.W. Fairbridge (eds.), Encyclopedia of Lakes and Reservoirs, DOI 10.1007/978-1-4020-4410-6, # Springer Science+Business Media B.V. 2012
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P
PALEOLAKES
Reginald W. HerschyHydrology Consultant, Reading, UK
IntroductionAll lakes are subject to a variety of extrinsic and intrinsicforcing variables that regulate the subsequent history ofthe lake. This includes age, climate, catchment, bedrockcomposition, tectonic and volcanic activity, vegetation,aquatic biota, and human activities. Strictly it is the historyof change in these variables and the paleolimnologicalrecords of very old or ancient lakes that eventually leadus to the age of the lake.
Paleolimnological records found in three distincttypes of archiveWaterLake water itself and its contents have finite residencetimes, the time required for the average molecule of waterto cycle through the system. In lakes with long residencetime measured in say hundreds to thousands of years, thewater itself may provide important paleolimnologicalclues to lake history.
GeomorphologyThe geomorphology of the lake basin in its shoreline andshape characteristic features can persist for many thou-sands of years long after the lake has gone. In this respect,a lake basin evolution is a more useful concept than thestatic one of lake origin. It is therefore an essential elementin the design of a paleolimnological study.
L. Bengtsson, R.W. Herschy, R.W. Fairbridge (eds.), Encyclopedia of Lakes and R# Springer Science+Business Media B.V. 2012
SedimentsSediments provide the most durable feature since theymay persist long after the lake itself, or its geomorphologyceased to exist.
Content archives in paleolimnological are the physicalsedimentary inputs to the lake’s record. These includeterrigenous, chemical, and biogenic sediments; cosmo-genic and volcanogenic particles; and fossils that originateoutside the lake, like pollen, or in the lake, like fish,aerosols, and water-borne pollutants.
Formation and history of lakesThe formation and history of lakes has intrigued earth sci-entists for over a century; Hutchinson (1957) recognized11 major categories of lake origins and since thenadvances have been made in understanding basin evolu-tion using radiometric dating techniques, seismic stratig-raphy, and lake drilling. The following lake classification(after Cohen, 2003) incorporates major elements ofHutchinson’s scheme:
MacedoniaTaho United States 1–20Tanganyika Burundi, Congo 2–20
(Democratic Republic)Tanzania, Zambia
Titicaca(Lago Titcaca)
Bolivia, Peru 2–20
Vostok Polar regions 1–20
Source: Lake Basin Management Initiative: LakeNet 2005
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Table 1 gives a selection of ancient lakes of the order of206 years.
BibliographyCohen, A. S., 2003. Paleolimnology: The History and Evolution of
Lake Systems. Oxford: Oxford University Press.Hutchinson, G. E., 1957.ATreatise on Limnology. NewYork:Wiley.
Cross-referencesPaleolimnology
PALEOLIMNOLOGY
Barbara WohlfarthDepartment of Geological Sciences, StockholmUniversity, Stockholm, Sweden
SynonymsLakes as archives of earth history; Limnogeology
DefinitionPaleolimnology is the study of lakes and lake sediments toreconstruct past climatic and environmental changes.
IntroductionLakes have formed and vanished throughout Earth’s his-tory (see Classification of Lakes from Origin Processes;Lakes on Earth, Different Types), but their traces in theform of shorelines, sedimentary rocks, and sediments areoften still preserved. The study of lake sediments andsedimentary rocks, to reconstruct environmental andclimatic changes through time is called paleolimnologyor limnogeology. No clear definition exists that woulddelimit these two terms, although paleolimnology is oftenused in the context of younger lake sediments (from pre-sent to ca. 2 million years ago), while limnogeology ismore used to define the study of older lacustrine sedimentsand sedimentary rocks.
Paleolimnology as a science beganwith the study of lakedevelopment, i.e., with the observation that lakes changeover time from oligotrophic (nutrient poor) to eutrophic(nutrient rich) conditions, as the lake fills with sediment,and the sediment–water interface becomes deoxygenated(Engstrom et al., 2000). The recognition of a “cultural”eutrophication later led to intensive studies of lake eutro-phication and lake water acidification connected to humanimpact; and presently, paleolimnology forms an importanttool for assessing natural reference conditions and restora-tion targets for lake ecosystems (Bennion et al., 2010;Bindler et al., 2010). Parallel with this development, lakesand their deposits have emerged as an important continentalarchive to reconstruct climatic and environmental changeson shorter (last 12,000 years) and longer time scales (last2 million years). Ancient lakes (see Paleolakes) moreoverare increasingly recognized as important evolutionaryarchives which allow assessing of the role of abiotic factorsas driving forces for generating biodiversity (Rossiter andKawanabe, 2000). Excellent overviews on paleolimnologyand limnogeology are provided by O’Sullivan (2004);Cohen (2003); Last and Smol (2001a, b, c); Last et al.(2001); Gierlowski and Kelts (2000).
The study of lake sedimentsLake sediments are composed of autochthonous (formedin the lake itself) and/or allochthonous (transportedinto the lake by water and wind) material which arecontinuously deposited on the lake bottom (see LakeSediments; Sedimentation Processes in Lakes) (Figure 1)(Bloesch, 2004). Anoxic bottom waters and absence ofborrowing organisms in certain lakes allow the preserva-tion of seasonal and annual layers (laminated or varvedsediments), but in most lakes, sediments have becomemixed and their original laminations have disappeared.Changes in the catchment and in the lake itself due tochanges in environmental and/or climatic conditionsand/or human impact are continuously registered in thesediments. Lake sediments are therefore sensitiverecorders of local, regional, and even global changeswhich can be reconstructed using a variety of physical,chemical, and biological methods, so-called proxies(see Lakes as Archives of Earth History) (Last and Smol,2001a, b, c; Last et al., 2001).
Paleolimnology, Figure 1 External and internal environmental factors influencing suspended sediments, sedimentation andsediment formation in a lake basin. 1 = sources of suspended particulate matter (SPM); 2 = transportation and transformation of SPM;3 = removal of SPM. (From Bloesch, 2004, Figure 8.1.)
PALEOLIMNOLOGY 595
Methods used in paleolimnology include bathymetricand seismic surveys to determine lake depth and morphol-ogy, sediment thickness, distribution and unconformities,and past lake-level changes. Limnological data are col-lected to assess the present lake status, catchment landuse and, nutrient supply, and to provide calibration datasets for down-core multi-proxy analyses. Sediment coresare obtained using a variety of different coring devices,ranging from gravity and freeze corers for the topmostand least consolidated sediments, to modified Russiancorers (for shallow lakes) and piston corers (for deeplakes) to obtain undisturbed sediment sequences. Physicalanalyses of the sediments include lithostratigraphicdescriptions to characterize the sediment type, structureand layer thickness, and mineralogy and mineral magneticproperties to assess the composition of the inorganicsediment fraction; these in turn provide information on,for example, sediment sources, transport mechanisms,depositional environments, and catchment erosion. Chem-ical sediment analyses comprise inorganic geochemistrywhich can give information regarding catchment erosionand lake status changes; organic geochemistry to assess,for example, lake productivity, aquatic/terrestrial inputs,
oxygen concentration, source of terrestrial material,biomarkers, and industrial pollution; and stable isotopechemistry to reconstruct changes in lake productivity,lake nutrient status, lipid biomarker sources, sources oflake waters, precipitation, lake hydrology, and lake watertemperature. Biological analyses include, for example,pollen, spores, and plant phytoliths to reconstruct catch-ment, lake and/or regional vegetation history, and humanimpact; plant macrofossils to assess lake basin vegetationhistory; charcoal analysis to reconstruct catchment firehistory; coleoptera to reconstruct ecosystem changesand temperatures; and limnic and terrestrial microfossils(diatoms, crysophyte cysts, ostracodes, cladocera, chiron-omids) to reconstruct changes in lake status (pH, salinity,nutrients, trophic state, temperature, precipitation).Chronological analyses (see Age Determination of LakeDeposits) provide an age frame for these reconstructionsand enable correlations to other geological archives.Modern data sets (e.g., diatoms, chironomids, plantmacrofossils, coleopteran, stable isotopes) and associatedtransfer functions are used to provide quantitativeestimates of lake status changes, temperature, andprecipitation.
BibliographyBennion, H., Battarbee, R. W., Sayer, C. D., Simpson, G. L., and
Davidson, T. A., 2010. Defining reference conditions andrestoration targets for lake ecosystems using palaeolimnology.Journal of Paleolimnology, doi:10.1007/s10933-010-9419-3.
Bindler, R., Rydberg, J., and Renberg, I., 2010. Establishing naturalsediment reference conditions for metals and the legacy oflong-range and local pollution on lakes in Europe. Journal ofPaleolimnology, doi:10.1007/s10933-010-9425-5.
Bloesch, J., 2004. Sedimentation and lake sediment formation.In O’Sullivan, P. E., and Reynolds, C. S. (eds.), The LakesHandbook. Oxford: Blackwell. Limnology and LimneticEcology, Vol. 1, pp. 198–229.
Cohen, A. S., 2003. Paleolimnology – The History and Evolutionof Lake Systems. Oxford: Oxford University Press. ISBN0-19-513353-6.
Engstrom, D. R., Fritz, S. C., Almendinger, J. E., and Juggins, S.,2000. Chemical and biological trends during lake evolution inrecently deglaciated terrain. Nature, 408, 161–166.
Gierlowski-Kordesch, E., and Kelts, K. (eds.), 2000. Lake BasinsThrough Space and Time. Tulsa: American Association ofPetroleum Geologists Studies in Geology, Vol. 46.
Last, W. M., and Smol, J. P. (eds.), 2001a. Tracking EnvironmentalChange Using Lake Sediments: Basin Analysis, Coring andChronological Techniques. Dordrecht: Kluwer, Vol. 1. 548 p.
Last, W. M., and Smol, J. P. (eds.), 2001b. Tracking EnvironmentalChange Using Lake Sediments: Physical and GeochemicalMethods. Dordrecht: Kluwer, Vol. 2. 504 p.
Last, W. M., and Smol, J. P. (eds.), 2001c. Tracking EnvironmentalChange Using Lake Sediments:Terrestrial, Algal, and SiliceousIndicators. Dordrecht: Kluwer, Vol. 3. 371 p.
Last, W. M., Birks, H. J. B., and Smol, J. P. (eds.), 2001. TrackingEnvironmental Change Using Lake Sediments: ZoologicalIndicators. Dordrecht: Kluwer, Vol. 4. 217 p.
O’Sullivan, P., 2004. Palaeolimnology. In O’Sullivan, P. E., andReynolds, C. S. (eds.), The Lakes Handbook. Oxford: Blackwell.Limnology and Limnetic Ecology, Vol. 1, pp. 609–666.
Rossiter, A., and Kawanabe, H. (eds.), 2000. Ancient Lakes: Biodi-versity, Ecology, and Evolution. London: Academic. Advancesin Ecological Research, Vol. 31. 624 p.
Cross-referencesAge Determination of Lake DepositsBaikal, LakeCaspian SeaDead SeaLakes as Archives of Earth HistoryRussian LakesRussian Lakes, Geographical ClassificationTiticaca Lake
PEIPSI LAKE IN ESTONIA/RUSSIA
Külli Kangur1, Andu Kangur1, Anto Raukas21Centre for Limnology, Estonian University of LifeSciences, Tartu, Estonia2Institute of Ecology, Tallinn University, Tallinn, Estonia
IntroductionLake Peipsi is located south of the Gulf of Finland on theborder between the Republic of Estonia and RussianFederation, being the largest international lake in Europe.
By its surface area (3,555 km2), Lake Peipsi is the fourthlargest lake in Europe after Ladoga, Onego, and Vänern.Peipsi is a very old geographical name of Finno-Ugricorigin in the northern part of the Eastern European Plain,but its etymology is uncertain (Jaani, 2001a). In old maps,the lake is depicted since the sixteenth century (Varep,1995). At different times, the lake is known in slightly dif-ferent forms: Peibes, Peibas, Peybass, Beibessee, Beibs,and Peips. Ancient name Peipus has persisted mainly inGermanic language literature. In recent literature andgeographical maps, the lake appears under two names:Peipsi and Chudskoe (or Chudsko-Pskovskoe) of Russianorigin. Slavic people called Fenno-Ugric people livingto west from Lake Peipsi “tšuuds” (from “tsuzoi”meaning“foreign” in Russian).
LocationLake Peipsi (Figure 1) is situated in the East EuropeanPlain between 57�510�59�010 N and 26�570�28�100 E at30 m above the sea level. The surface area of Lake Peipsiis 3,555 km2 (at the mean water level of 30 m a. s. l.),of which 1,570 km2 (44%) belongs to Estonia and1,985 km2 (56%) to Russia (Jaani, 2001a). The lake isshallow with a mean depth of 7.1 m, a maximum depthof 15.3 m, and a volume of 25 km3. These characteristicsdepend greatly on the overall natural water level fluctua-tions of 3.04 m over the last 80 years, with an averageannual range of 1.15 m (Jaani, 2001b). During the highestwater level on May 12, 1924 (31.76 m a.s.l.), the surfacearea was estimated at 4,330 km2 and the volume of waterat 32.128 km3. At the lowest water level on November 7,1994 (28.72 m a.s.l.), these values were 3,480 km2 and20.98 km3, respectively. Thus, the surface area of the lakemay vary by 850 km2 and the water volume by 11.15 km3.
Lake Peipsi, elongated in the north–south direction, israther a lake system, consisting of three limnologicallydifferent parts (Figure 1). The northern part, Lake Peipsis.s. (sensu stricto, Chudskoe in Russian), is the largest(2,611 km2) and deepest (average depth 8.3 m). The south-ernmost part, Lake Pihkva (Pskovskoe), measures708 km2 and is 3.8 m deep on average. The strait betweenthem is Lake Lämmijärv (Teploe) (236 km2; mean depth2.5 m). The names Lämmijärv and Teploe (“lämmi” inEstonian and “teploe” in Russian means “warm”) arehydrologically motivated because in spring and winter,its water is much warmer than in Lake Peipsi s.s. and LakePihkva.
The first inhabitants of the area were Stone Age huntersand fishermen. At the end of the third millennium B.C.,cattle breeding and agriculture started to develop. Perma-nent agricultural settlements were founded in the firstmillennium A.D., at the end of which period, the Slavsreached the eastern coast of the lake. From the fifteenthto sixteenth centuries, fishing villages appeared on itscoasts. At present, the sparsely distributed population(8–9 inhabitants per square kilometers) is mainly engagedin fishery and agriculture. Only 19% live in towns, and thenumber of habitants is decreasing.
Peipsi Lake in Estonia/Russia, Figure 1 Location of Lake Peipsi.
PEIPSI LAKE IN ESTONIA/RUSSIA 597
Islands and coastlineLake Peipsi has 35 islands and islets with total area of29 km2, which forms 0.8% of the surface area of the lake.The islands are concentrated in the southern part of thelake. The biggest islands are Kolpino (11.1 km2),Piirissaar (7.5 km2), and Kamenka (4.0 km2). In LakePihkva, the Talabskij Archipelago consists of three smallbut high islands. Those were formed along the margin ofthe ice tongue which penetrated into Lake Pihkva basinduring the Otepää Stade of the last glaciation. IslandPiirissaar is a natural boundary between Lake Peipsi s.s.and Lake Lämmijärv. The threshold between the two lakesis cut by wide but shallow straits, which are located westand east of the Island Piirissaar and called the Estonianand Russian Gates, respectively. The 520-km coastlineof Lake Peipsi is rather straight, without many disjunc-tures. In the southeastern corner of Lake Peipsi s.s.,Raskopel Bay forms a small separate lake.
The catchmentLake Peipsi belongs to the Baltic Sea watershed and islinked with the Gulf of Finland via the River Narva(Figure 2). The submeridionally elongated catchment areaof Lake Peipsi (47,800 km2 including lake surface)extends from 59o13` to 56o08` N and from 25o36` to30o16` E and is shared by Russia (27,917 km2), Estonia(16,323 km2), Latvia (3,560 km2), and, for a negligiblepart, by Belarus (Jaani, 2001a). The drainage basin is flat,with a highest point of 318 m above sea level. The lakecatchment is mainly a gently undulating glaciolacustrineor till-covered plain. Forests and seminatural areas domi-nate in the lake drainage basin. Agricultural areas coveraround 14% of the basin. The total population of the basinprovides ca. 1,000,000 inhabitants.
The catchment area of L. Peipsi holds more than 4,500lakes, the largest of which is a shallow, highly eutrophicLake Võrtsjärv (270 km2). About 240 rivers and streamsflow into Lake Peipsi. Catchment areas of the largestrivers are the following: the Velikaya (25,200 km2), the
Emajõgi (9,745 km2), the Võhandu (1,423 km2), and theZhelcha (1,220 km2) which account for 80% of the totalinflow, thus controlling the water regime of the lake. TheVelikaya River drains the largest portion of the Russianand Latvian parts of the basin and discharges into LakePihkva. Close to the river mouth is situated the major townof the area Pskov (191,961 inhabitants after World Gazet-teer, 2010) which is the main point source of nutrients toLake Pihkva. The Emajõgi River drains the majority ofthe Estonian part of the basin and discharges into LakePeipsi s.s. The major town at the Emajõgi River is Tartu(102,455 inhabitants after World Gazetteer, 2010), whichis situated about 50 km from the river mouth. The otherbigger rivers include the Piusa (796 km2), theRannapungerja (601 km2), and the Chernaya (530 km2).The outflowing River Narva (77 km long) is the secondlargest river after the River Neva flowing into the Gulfof Finland. The annual mean runoff through the RiverNarva is more than 12.5 km3, which makes about half ofLake Peipsi’s water volume (25 km3) and about 3% offresh water flowing to the Baltic Sea (Haberman et al.,2008). The average water retention time in Lake Peipsiis about 2 years. The water level is not regulated.A strong dependence of the water level on precipitationis characteristic of the hydrological regime of Lake Peipsi.Long-term variability of water level in Lake Peipsi has anexpressive cyclic nature (Figure 3).
The geological settingThe thickness of the crust in the Lake Peipsi area increasesgradually from about 45 to 50 km toward the south. Thesedimentary cover is rather thin, ranging from 300 m inthe north to 600 m in the south. Three sedimentarymacrounits are recognized: Upper Vendian – LowerOrdovician siliciclastics, Middle Ordovician – Siluriancarbonates, and Devonian, mainly siliciclastics (Miideland Raukas, 1999). Most of Lake Peipsi belongs to theDevonian outcrop area. In the northern part of the lake,dolomitic marls with interlayers of dolostone, siltstone,
56° 08' N30° 16' E
Velikaya
Velikaya Alo
lya
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Emajõgi Chernaya
Ahj
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Lake Võrtsjärv
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RUSSIA
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59° 28' N
59° 13' N25° 36' E
ESTONIA
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0 20 40 60 80 km
Peipsi Lake in Estonia/Russia, Figure 2 Catchment area of Lake Peipsi and the River Narva (after Jaani 2001a).
Peipsi Lake in Estonia/Russia, Figure 3 Mean annual water level in Lake Peipsi in 1920–2010.
PEIPSI LAKE IN ESTONIA/RUSSIA 599
and sandstone crop out. In the south, sandstones andsiltstones with interbeds of claystones occur with dolo-mitic marls, dolostones, and limestones.
Peipsi is a natural lake and started about 13,000 radio-carbon (14C) years ago as a big ice-dammed water basin.The Peipsi depression formed as a result of glacial erosion.The gently sloping bedrock surface is about 40 m abovethe sea level and is at its deepest (15–20 m b.s.l.) in theancient valleys that were overdeepened by the glacier.The Quaternary cover is relatively thin, mostly less than10 m. Several stadial till beds of the last glaciation havebeen found in the depression, differing in color andmineral composition (Raukas, 1978). Older tills have beenidentified only in the buried valleys. Two well-developedice marginal belts are recorded by interrupted endmoraines via Talabskij Islands in Lake Pihkva andMehikoorma-Pnevo in Lake Lämmijärv.
Tectonic movements have exerted a strong influence onthe formation of the lake. As the northern coast of the lakeis lifting more rapidly, there is a gradual southward move-ment of the lake waters as a result of crustal tilting, whichhas led to the submergence of several Neolithic settle-ments in the vicinity of the lake. The chronicle of Pskovrecords that in 1458, a church was built on the Island ofOzolitsa. The remains of this church are now submergedbeneath 0.4–2.5 m of water, and two small islets(Lezhnitsa and Stanok) are all that remains of the formerisland (Tyumina, 1966). During the last 10,000 years,the uplift in the northern part of the lake basin has been10 m greater than in the southern portion of the lake(Miidel and Raukas, 1999).
A significant role in the sedimentation andresedimentation of bottom and coastal deposits is playedby the lake ice. Almost every spring, ridges of pressureice, up to 10 m high, are pushed forward against the shore,shaping the coast, redepositing older sediments,transporting huge boulders, and endangering the buildings.
Bottom sediments and shoresBottom sediments are variegated. In the shallow coastalregions, sediments are relatively coarse-grained
(prevailingly sands), whereas in sheltered areas (behindislets and in bays) and in the deep central part of the lake,fine-grained sediments (clayey silts and clays) dominate(Raukas, 1999). Usually, the sedimentary material iscarried into the lake by the rivers and as a result of the ero-sion of the coast and lake bottom; it is then distributedunder the influence of waves and streams according tobottom topography. The thickness of deposits is mainly1–2 m and rarely over 10 m. The mineral and chemicalcomposition of sand, silt, and clay fractions and thecontent of organic matter (up to 40% in Lake Peipsi s.s.,85% in Lämmijärv, and 35% in Lake Pihkva) as well asmicroelements is different in various parts of the lake.Fine-grained organic-rich sediments are very cohesive,playing the main role in the circulation of various inor-ganic and organic pollutants like nutrients and xenobiotics(Punning et al., 2009).
The abrupt cliffed shores (an abrasional escarpments inDevonian sandstone), scarp (an abrasional bluffs in sand,till, or peat), and erosional and flat erosional-accumulationshores are distinguished in Lake Peipsi (Tavast, 1999).The flat erosional-accumulation shores are divided into(1) till shore – an abrasional shore with a protective coverof boulders; (2) gravel shore – an accumulation shore withpebbles and gravelly sediments; (3) sandy shore – anaccumulation sandy beach with a ridge of foredunes;(4) silty shore – an accumulation shore with silty-clayeysediments; and (5) artificial shore with manmade struc-tures. During high stand of water, serious damages to theshores are registered. So in the 1920s, the people fromNina village were resettled. In 1987, at the northern coast,the sandy scarp retreated several meters, and near Alajõe,a 4-m-high new bluff formed into dunes. In 2010, seriousdamages were registered also on the western shore nearRanna.
Climate conditionsLake Peipsi is situated in the northern region of the tem-perate zone with variable weather conditions. Summertemperatures can reach high extremes in the Peipsi area.Since 1924, the highest surface water temperature
600 PEIPSI LAKE IN ESTONIA/RUSSIA
(28.8�C) was measured in June 27, 1988. Water tempera-ture commonly reaches its maximum in July, but it canhappen from the beginning of June to the end of August.The lake belongs to polymictic type of lakes, where thecomplete mixture of water body takes place several timesa year. Due to the lake’s large surface area and relativeshallowness, waves affect the bottom during the ice-freeperiod. Therefore, thermal stratification is usually epi-sodic and unstable and can be disturbed already bya moderate wind or undulation. Due to mixing, the waterof the lake is usually rich in oxygen during the open waterperiod. Lake Peipsi is, as a rule, covered with ice fromDecember till April; however, the start dates of ice-coverand ice-off dates have been highly variable during recentyears. Both the formation of ice and the melting processin Lake Peipsi normally take 2–3 weeks, but they can lastup to a month. The first ice near the coast is usually formedin early November. In some years, the ice-cover periodmay last even to the beginning of May. Winter 2007/2008 was the warmest recorded during the whole periodof measurements (142 years) in Estonia (Jaagus, 2008).According to measurements by the Estonian Institute ofHydrology andMeteorology, ice-cover destruction startedalready on January 19, 2008. Furthermore, the ice-coverthickness varies from year to year; the maximum thicknessof ice can reach 75 cm and even more in some years.The near-bottom water frequently suffers from oxygendeficiency when the lake is ice-covered.
Lake type and limnetic variabilityLake Peipsi belongs to the shallow unstratified polymictictype of lakes with light water of medium hardness
Peipsi Lake in Estonia/Russia, Table 1 Selected morphometric, chthree parts (Lake Peipsi s.s., Lake Lammijarv, and Lake Pihkva). Wa90% tolerance limits are given in brackets. These estimates correspyear) between 2006 and 2010 (After Kangur et al., 2011 submitte
CharacteristicLake LakePeipsi s.s. Läm
Surface area, km2 2,611 236Maximum depth, m 12.9 15.3Mean depth, m 8.3 2.5Water volume, km3 21.79 0.6TP, mg P m�3 37.5 66.7
(17.1�82.0) (31.9PO4-P, mg P m�3 5.8 10.5
(1.1�32.7) (2.0�TN, mg N m�3 703 896
(417�1,188) (573aDIN, mg N m�3 122 127
(31�470) (30�Chlorophyll a content, mg m�3 17.9 33.3
aDIN is the sum of ammonium ion, nitrate ion, and nitrite ion concentr
(average 2.3 m Eq L�1) located on mineral land. The con-siderable dimensions of the lake and relatively slow waterexchange (the ratio of the volume to annual inflow) deter-mine that the retention time for Lake Peipsi is about2 years. The variability of limnetic parameters, typicalfor the large lakes, is characteristic for Lake Peipsi. Thethree lake parts have different morphometry, hydrology,trophic state, and humic content which provide a greatvariety of biotopes and support organisms with dissimilarecological requirements. Most of the lake aquatory haslately been mesotrophic, which favors coexistence of theindicators of the meso- and eutrophic state as well as thespecies preferring a higher trophic state. Total speciesnumber of vascular plants and bryophytes is 140, algaeare presented by 1,000 species, zooplankton containsabout 300 species, macrozoobenthos has more than 400species, and ichtyofauna includes 37 species.
At present, the lake as a whole is eutrophic, with a clearsouth-north gradient. The northern and deeper part, LakePeipsi s.s., is significantly poorer in nutrients than thesouthern, very shallow part, Lake Pihkva (Table 1).
Using the OECD (1982) classification system, thepresent-day conditions characterize Lake Peipsi s.s. asa eutrophic water body, while the trophic status of LakeLämmijärv is close to hypertrophic and Lake Pihkva isa hypertrophic basin (Kangur and Möls, 2008). Differ-ences in the water quality between the northern and south-ern parts of the lake (polarity) is caused, on the one hand,by the differences of natural environmental conditions, buton the other hand, it is determined by local human impact.The catchment area of Lake Pihkva is 2.5 times biggerthan that of Lake Peipsi s.s. in relation to the surface area
emical, and phytoplankton characteristics of Lake Peipsi and itster quality parameters are presented as geometric means, andond to the open water periods (Julian days 100–310 within eachd)
and 5 times bigger in relation to the volume of the lake. Itmeans that natural nutrient load to Lake Pihkva is signifi-cantly higher than in Lake Peipsi s.s. Although LakePeipsi has been a center of human activities for centuries,the nonuniform anthropogenic impact to the different lakeparts has especially intensified during the last decades.The loss of resilience and stability of Lake Peipsi ecosys-tem poses a risk to biodiversity and ecosystem function-ing, as well as to human livelihoods dependent on waterecosystem services.
Multiple stressorsThe wide diversity of coexisting human impact (e.g.,eutrophication, pollution, overexploitation, introductionof nonindigenous species) and natural (e.g., extremeweather events, fluctuations in water level and tempera-ture, changes in ice conditions and water retention time)stressors are affecting the Lake Peipsi ecosystem dynam-ics. Multiple stressors are causally linked to socioeco-nomic and natural processes in the large catchment areaof the lake located in different landscapes.
EutrophicationAs in many shallow lakes, eutrophication (nutrient enrich-ment from human activity) remains the most seriousenvironmental problem for Lake Peipsi triggering changesin the whole ecosystem. Lake Peipsi receives pollutionmainly through river water and precipitation directly intothe lake. Riverine transport is the most important pathwayfor input of nutrients from both point and nonpoint sourcesto Lake Peipsi (Loigu et al., 2008). The majority of phos-phorus (P) and nitrogen (N) compounds are carried intothe lake by the Velikaya River in the Russian Federationand by Estonian Emajõgi River. These two rivers accountfor 74% of the total nitrogen load and of total phosphorusload in Lake Peipsi (Loigu et al., 2008). The VelikayaRiver alone accounted for approximately 52% and 41%of the total phosphorus and nitrogen load, respectively.According to assessments for 2001–2005, Lake Peipsireceived 8,324 t N year�1 and 96.5 t P year�1 and 8,532t N year�1 and 171 t P year�1 from Estonian and Russianparts of the catchment, respectively (Loigu et al., 2008).According to estimates by Buhvestova et al. (2011), theaverage annual load of nutrients discharged into LakePeipsi s.s. by major Estonian rivers during the period1992–2007 comprised 5,600 t of N and 179 t of P. How-ever, the major part of the loading from the south reachesLake Peipsi s.s. through Lake Lämmijärv. According tocalculations of Rumyantsev et al. (2005), average annualload of P to Lake Peipsi s.s. both through the rivers ofthe Russian part of the catchment and the waterflow fromLake Pihkva during the time span 1992–2003 comprised280 t. Thus, the value significantly exceeded our calcu-lated average annual Estonian riverine load for the period1992–2007 (179 t of phosphorus). The average annualarea-specific Estonian riverine export of TP to lake Peipsis.s. was estimated at 0.16 kg P ha�1 year�1, while thevalue of TN was 5.1 kg N ha�1 year�1 (Buhvestova et al.,
2011). However, the estimates of external load to LakePeipsi from the Russian part of the catchment area havebeen scarce. Nutrient concentrations in rivers discharginginto Lake Peipsi are probably still influenced by nutrientstores from the period of intensive fertilization. The load-ing of N into Lake Peipsi s.s. from the Estonian catchmentdecreased substantially from the period of intensive agri-cultural activity in the 1980s to the present time, whereasthe loading of P decreased much less. Especially the accu-mulation of phosphorous in soils will influence P losses onlong-term, and the leaching of nutrients can continue fordecades after reduced fertilization because of the soil’scapacity to retain nutrients.
The increasing difference in total phosphorus (TP)concentrations between the northern and southern partsof the lake (polarity) clearly shows that the input ofP from the south is increasing (Kangur and Möls, 2008).This can be considered as an indication of lake eutrophica-tion. In the case of Lake Pihkva, a critical threshold levelof P seems to have been exceeded and the lake is “full”of P (Kangur and Möls, 2008). Evidently, Lake Pihkva islosing its resilience. Also, Nõges et al. (2007) supposedthe growth of phosphorus loading from the Russiansubcatchment in the period 1992–2002, in comparisonwith loading of 1980s. In contrast, the polarity total nitro-gen (TN) concentration in lake water remained relativelystable over the years and can be related to differences innatural conditions between different parts of the lake.Moreover, it refers to the resilience of the lake to year-to-year changes in riverine loads of nutrients. This mightbe due to in-lake processes: N2 fixation and denitrifica-tion. Moreover, owing to lake’s shallowness and relativelylong water residence time (about 2 years), the naturalprocesses, especially fluctuations of water level andtemperature, can have influenced the lake water quality.As there is a big storage of phosphorus in the sedimentsof Lake Peipsi (Punning and Kapanen, 2009), lowervalues of water level in combination with higher summertemperatures could have enhanced the internal nutrientloading, which was followed by increase in TP concentra-tion in lake water. It is especially evident in shallowerLake Pihkva, which is characterized by greater temporalvariation of water quality, while the larger, deeper north-ern part, Lake Peipsi s.s., is more resilient to naturalenvironmental changes. Thus, in-lake TP concentrationscan be more sensitive to natural changes in water leveland temperature than to year-to-year changes in riverinenutrient loads.
A considerable effort has been invested to reduce exter-nal nutrient loads, primarily of P loading to Lake Peipsi.Since 1998, wastewaters of Tartu have been purifiedchemically, and the efficiency of P removal has beenabout 85–90%. Wastewaters from Pskov are purified onlybiologically, and most of phosphorus is not removedyet (Loigu et al., 2008). As Peipsi is situated on the borderof the EU, state and regional, economical, andpolitical interests are affecting the water managementplanning. The transboundary conditions complicate the
implementation of policies that might prevent or mitigateenvironmental damage in the Peipsi region.
The limnological time series data (from the 1950s to2010) indicate deterioration of lake water quality andadverse changes in the whole ecosystem of Lake Peipsi.A deterioration of the lake’s ecological status is indicatedby massive blooms of cyanobacteria, oxygen deficiency,and cyanotoxins in water, shifts in species compositionand dynamics of phytoplankton, expansion of reeds andloss of small-sized amphibious plant communities, massdevelopment of epiphyton, accumulation of organic sedi-ments, drastic decrease of zooplankton abundance,changes in the structure of fish community, silting ofspawning areas of fish, and summer fish kills. Eutrophica-tion has been the most rapid in the southern parts of thelake: in Lake Pihkva, which is directly affected by pollu-tion coming from Velikaya River in Russia. Doubled TP,dissolved inorganic phosphorus (PO4-P), silica (Si) andchlorophyll–a (Chl a) contents, increased total alkalinity(HCO3
�) and pH, as well as decline in water transparencyand oxygenation conditions during the last decades, indi-cate an increase in the trophic level of Lake Pihkva(Kangur et al., 2007b).
MacrophytesAmong the rich flora containing about 150 macrophytespecies, dominating have always been Potamogetonperfoliatus L. among the submergents and Phragmitsesaustralis (Cav.) Trin. ex Steud. among the emergents(Mäemets et al., 2010). Some species of mesotrophic stagebecame extinct in the 1980s (Isoëtes echinospora Durieuand Subularia aquatica L.) or are suppressed (Alismagramineum Lej., Potamogeton filiformis Pers., etc.)(Mäemets and Freiberg, 2004). In Lake Peipsi, the expan-sion of reeds has been the most evident result of eutrophi-cation during the last 40 years. Increase of reeds isespecially remarkable in Lake Peipsi s.s. where mesotro-phic status is replaced by eutrophic. Since the end of the1960s, the average biomass of reed per square meter hasincreased more than 70 times in the northern part of thelake (Mäemets, 2005). The success of reeds on LakePeipsi has three main causes: (1) high nutrient loading,especially in the 1970s and 1980s, (2) low-water periodat the end of the 1960s and beginning of the 1970s, and(3) diminishing or cessation of grazing (Mäemets andFreiberg, 2004). Expansion of reeds causes decrease offloristical diversity and increase of uniformity of lakeparts. The expanding reed belt provides favorable growthconditions for the wind-sensitive shade-tolerant species ofhypertrophic waters (Spirodela polyrhiza Schleid,Ceratophyllum demersum L.) (Mäemets, 2005). Tall reedshoots shadow the habitats of the light-demanding small-sized species, and slowly decomposing litter covers largeareas. Recent depth limit of reeds reaches mostly 1 m.Their expansion seems to be quite analogous to the resultof fertilization experiments on grasslands where additionof nutrients favored the decrease in species number andprevalence of large-sized graminaceous species (cit.
Mäemets et al., 2010). Eutrophication has expandednorthward along the longitudinal axis of the lake. So thereeds have occupied the northwestern shore of the lakeduring the 1980s and have appeared on the northerndyne shore during the last decade. Their establishmentthere is hindered by bottom conditions (moving sand)and changing water level. However, on the more flattenand sheltered shore stretches permanent stands exist nowalso in the northern shore. The growth rate of reed standsin eutrophic conditions may exceed 1 m per year.
In parallel with the direction of the eutrophicationnorthward, expansion of nutrient-demanding speciestoward the northern part has taken place already in1970s, when there appeared Zannichellia palustris L.,Elodea canadensis Michx., Ranunculus circinatusSibth., Ceratophyllum demersum L., Lemna trisulca L.,Spirodela polyrhiza (L.) Schleid., and Potamogetonpusillus L.
The richest flora of Lake Peipsi was characteristic forthe period of the coexistence of nutrient-demanding andnutrient-sensitive species in 1970–1980. Macrophytespecies richness has decreased in parallel with lake eutro-phication. Comparing the frequency of the 67 species inthe stations around the whole lake in 1970–1980 and in1997–2007, a statistically significant decline occurredin the case of 20 taxa, among them frequency decreasedtwofold for 15 species. The most obvious reason for thesechanges is the occupation of the littoral by reeds (Mäemetset al., 2010).
PhytoplanktonLake Peipsi is inhabited in all ecotopes (pelagial, littoral,periphyton, benthos) by more than 1,000 algal taxaidentified up to now: cyanobacteria (Cyanophyta) – 186;diatoms (Bacillariophyta) – 539; green algae(Chlorophyta) – 331 species; and other groups – 138species. Phytoplankton of open water area consists ofabout 500 algal species. The species composition in LakePeipsi is characteristic for large lowland lakes likeLadoga, Onego, Vänern, Vättern, and Mälaren andresembles also that of Ancylus Lake (Davydova, 1981).Diatoms prevailed in the plankton taxonomic compositionand biomass during most of the year; however,cyanobacteria exceeded them in summer and autumnseasons in the last decades. A drop in diatoms occurredin Lake Peipsi s.s. from 2000. The abundance of formerdominant species in cold seasons, mesotrophicAulacoseira islandica (O. Müller) Simonsen, is decreasedat present. At times, eutrophic Aulacoseira granulata(Ehr.) Sim. and A. ambigua (O. Müller) Sim. occupy animportant part in plankton. The unicellular centric species(genera Cyclotella, Stephanodiscus, Cyclostephanos)are also important. Among cyanobacteria, thegenera Microcystis, Anabaena, Aphanizomenon, andGloeotrichia echinulata (J.S. Smith) P. Richter causemassive water blooms in favorable weather conditions,particularly in nearshore areas as well as in the southernhypertrophic lake parts. Nuisance cyanobacterial blooms
are not a phenomenon of the modern industrial society.Massive development of cyanobacteria was noticed inLake Peipsi sometimes since 1895 (review Laugasteet al., 2001). The share of cyanobacteria in phytoplanktonbiomass increased during the last decades from 20% to60% in Lake Peipsi s.s., and from 30% to 90% in thesouthern parts of the lake in summer months (Habermanet al., 2010). In recent years, strong and long-lasting(up to November) algal blooms were repeatedly observedin the lake. Depending on weather conditions, the durationof algal blooms has increased. Along with continuous hotweather and decreasing water level, the abundance ofalgae increased in July–August 2002 and the Chl a con-tent in the nearshore water reached 400 mg m�3 and thephytoplankton biomass 250 g m�3 in July–August(Kangur et al., 2005). The ecological situation in the lakeworsened quickly and led to a strong fish kill. Highconcentrations of cyanotoxins were determined repeatedlyin Lake Peipsi water during cyanobacterial blooms.Microcystins were identified in bloom samples, whenAnabaena spp. and Microcystis spp. dominated in LakePeipsi (Tanner et al., 2005). Maximum concentrations ofmicrocystins in water were determined on September 8,2002 (586 mg L�1), and on July 5, 2005 (65 mg L�1). Nomicrocystins were found in the samples from massivebloom of mainly G. echinulata in summer 2002.
ZooplanktonIn zooplankton species composition and abundance,important changes have occurred during the last century.The species of oligotrophic waters Holopedium gibberumZaddach lived in Lake Peipsi from 1909 to 1964, but ithas not been encountered there later. Until the 1930s, nojuvenile Dreissena polymorpha (Pallas) were found inthe zooplankton of Lake Peipsi because adultD. polymorpha did not yet inhabit this water body. Thecladoceran species Daphnia galeata Sars is found in thelake since 1950 (Haberman, 2001).
At present, with respect to number, small rotifers(Rotatoria) dominate in Lake Peipsi zooplankton through-out the year, while with respect to biomass, considerablylarger cladocerans (Cladocera) and copepods (Copepoda)prevail, especially Eudiaptomus gracilis (Sars) and spe-cies of genera Daphnia and Bosmina. In spring (May),rotifers and copepod juveniles prevailed; in summer andautumn, the species of the genera Daphnia, Bosmina,and Eudiaptomus gracilis (Sars) were commonly domi-nating, but their biomass was different. In early summer(June) and in late summer (September), the role of thegenus Bosmina and copepods in the zooplankton biomasswas greater than in July when cladocerans, particularlyDaphnia cucullata Sars, were prevalent. Zooplankton bio-mass in summer (mean values for July–August, 1997–2006) was 2.23 mg L�1 and abundance was 510 ind. L�1.
In parallel with increasing cyanobacterial blooms, anessential decline occurred in zooplankton. A significantdecrease in the biomass of all zooplankton groups –cladocerans, copepods, and rotifers – occurred from
2001 (Haberman et al., 2010). The most essential declineaffected rotifers. The abundance of D. polymorphaveligers also decreased significantly in the whole lake.The decrease in the amount of zooplankton reflects deteri-oration of lake water quality. The effect of planktivorousfishes on the zooplankton was significant in the 1960swhen the fish community was dominated byplanktivorous vendace and smelt. However, the recentdecrease in zooplankton cannot be explained by theincreased pressure of fishes due to vanished populationsof planktivorous fish (Kangur et al., 2008a). However,cyanobacterial blooms and presence of cyanotoxins areprobably the main reasons for the significant decreasein the amount of zooplankton, particularly rotifers(Haberman et al., 2010).
ZoobenthosThe three main groups of macrozoobenthos in Lake Peipsiare Chironomidae (with 111 taxa), Mollusca (83), andOligochaeta (59) which formmore than half of the speciesnumber (Kangur et al., 2008b). The abundance andbiomass of macrozoobenthos (average without largemollusks 2521 � 96 ind. m�2 and 12.3 � 0.5 g m�2 in1964–2006) as well as species diversity are continuouslyhigh in Lake Peipsi. Excluding large clams, chironomidsand oligochaetes are dominating in the bottom fauna.The typical community of eutrophic lakes dominated byChironomus plumosus (L.) (Chironomidae) andPotamothrix hammoniensis (Mich.) (Tubificidae) hasinhabited the profundal of Lake Peipsi presumably duringhundreds of years. Small bivalves of the familiesPisidiidae and Sphaeriidae are still abundant in theprofundal. Several oxyphilous species characteristic ofmesotrophic or oligotrophic lakes, as chironomid larvaeof Monodiamesa bathyphila (Kieffer) and oligochaetesLamprodrilus isoporus Mich., Tasserkidrilus acapillatus(Finog.), Peipsidrilus pusillus Timm, and Limnodrilusprofundicola (Verrill), are present in Lake Peipsi.However, the introduction/invasion of alien species hasirreversibly changed the benthic invertebrate communityof Lake Peipsi. The zebra mussel D. polymorpha thatinvaded Lake Peipsi in the 1930s (Mikelsaar and Voore,1936) forms now the most significant animal populationof the lake in terms of biomass. The biomass of zebra mus-sel exceeds the biomass of all other bottom animals about20 times. The impact of zebra mussel on water quality inLake Peipsi, through the filtration of phytoplankton andincreasing the sedimentation rate of suspended matter, issignificant. However, zebra mussels and also zooplanktoncannot feed on large colonies of cyanobacteria. TheBaikalian amphipod Gmelinoides fasciatus (Stebbing),a successful invader in Europe, was introduced into LakePeipsi with the intention to improve the feeding base offish in the 1970s. The newcomer was at first explosivelydistributed near the site of introduction in the eastern shoreof the lake and followed by the distribution in the westernshore in the 1980s (Timm and Timm, 1993). Until the1970s, only two gammaridean species occurred in Lake
Peipsi:Gammarus lacustris Sars, among macrovegetationand stones in the littoral, and Pallasiola quadrispinosaSars, in open sand bottom habitats. Intentional introduc-tion of G. fasciatus from Siberia has irreversibly alteredlittoral benthic communities in Lake Peipsi. At present,G. fasciatus is the most abundant macroinvertebratespecies in the nearshore area, while the native gammaridsG. lacustris and P. quadrispinosa appear to be extinct andoligochaetes have declined (Kangur et al., 2010). Thedistribution pattern of the invader close to water edge insummer makes it mostly inaccessible for adult fish. Beinghighly mobile, G. fasciatus is not sensitive to water levelfluctuations in shallow lakes. These characteristicsincrease its success.
Fish community characteristicsLake Peipsi is inhabited by 37 fish species (Kangur et al.,2008a). Over the past 80 years, no species have been lostfrom Lake Peipsi; on the other hand, there is neither anyinformation about invasion of new species into the fishcommunity. Lake Peipsi has been rich in fish production,where smelt, Osmerus eperlanus eperlanus m. spirinchusPallas; vendace, Coregonus albula (L.); and pikeperch,Sander lucioperca (L.) have been the main commercialfishes in the lake at different times. However, despite thesame species composition and interannual variations, thecommercial fish catch was seen to decline to about halfof the catches taken 80 years ago. According to commer-cial statistics, the average annual catch of fishes was11,650 t (33 kg ha�1) in 1931–1940 and 5,593 t (e.g.,16 kg ha�1) in 2005–2009. In addition, substantial alter-ations in relative species dominance have been noted. Inthe 1930s, the main commercial fish were smelt (43% oftotal catch); roach, Rutilus rutilus (L.) (16%); perch, Percafluviatilis L. (7%); and bream, Abramis brama (L.) (7%).In 2005–2009, most of the commercial catches comprisedpikeperch (34%), bream (17%), roach (14%), and perch(13%). Less abundant commercial fish species were pike,Esox lucius L.; burbot, Lota lota (L.); and ruffe,Gymnocephalus cernuus (L.). Peipsi whitefish,Coregonus lavaretus maraenoides Poljakow; vendace;eel, Anguilla anguilla (L.); rudd, Scardiniuserythrophthalmus (L.); ide, Leuciscus idus (L.); tench,Tinca tinca (L.); and white bream, Blicca bjoerkna (L.)have been occasionally represented in catches. The RedBook of Estonia (2011) includes wels, Silurus glanis L.;grayling, Thymallus thymallus (L.); bullhead, Gottusgobio L.; asp Aspius aspius (L.); mud loach, Misgurnusfossilis (L.); vendace; and Peipsi whitefish.
Fish stocks of Lake Peipsi are mainly affected by(1) overexploitation, by (2) ecosystem changes (e.g.,eutrophication, degradation in water quality, siltation ofspawning grounds, shifts in food webs), and also by(3) natural processes (e.g., heat waves, increases in watertemperature, changes in ice conditions, fluctuations inwater level). Concurrent worsening ecological conditionsin Lake Peipsi and high fishery pressure (includingpouching, unregistered caught quantities, excessive
number of professional fishermen) is threatening fishstocks, causing a substantial decrease in catches and trig-gering changes in community structure. The effect of fish-ing is the most important human impact on the fishcommunity in Lake Peipsi. Even though the fisherymethods have changed, the fish stocks of the lake haverepeatedly suffered from the overfishing (Kangur et al.,2007a). Investigations made by von Baer (1852) in themiddle of the nineteenth century targeted the reasons forthe declining stocks and catches of main commercial fishspecies (mainly bream) in Lake Peipsi and concluded thatthe main reason was the intensive use of fine-meshedtowed fishing gear as well as the blocking of the spawningmigration routes of bream by large traps. In the 1950s,fishing was markedly intensified in Lake Peipsi due tohigh demand for food after WW II. Therefore, trawlingwas reintroduced in the lake and expanded drastically.Extensive use of fine-meshed towed fishing gear (e.g.,trawls replaced later by bottom seines) affected mostlyrecruitment of pelagic predator, pikeperch, killing youngspecimens of this fish in large quantities. The next drasticincrease in fishing pressure was caused by the sociopolit-ical changes brought along with the collapse of SovietUnion. At the beginning of 1990s, fishing becamea highly significant source of employment. Therefore,the number of fisherman doubled in comparison with theend of Soviet period. During the last decade, the fisheryin the lake is regulated according to the Estonian–RussianFisheries Agreement from 1994, whereas since 2000,quotas are established for all commercial species.
Fishery has direct negative impact on the total stock andon the size composition of the fish community. Particu-larly, pikeperch population is affected because largerspecimens are almost completely removed leaving anunbalanced population of only a few young year-classes.Substantial decrease in the abundance of larger specimensof pikeperch in L. Peipsi means that the predatory pressureof its stock has changed and directed to smaller prey.Human-induced imbalance within fish stocks (e.g.,change of predator versus prey proportions) has cascadingeffect through food webs. The ecological role of toppredators as the main regulators of the abundance ofcoarse fish has diminished.
Although the population dynamics of several fishspecies, especially of big predators, is to a large extentcontrolled by fishery, the long-term effects of concurrenteutrophication and environmental extremes (e.g., heatwaves, water level fluctuations, changes in ice conditions)on the fish community are considerable. Since the 1930s,several marked changes occurred in the composition offish community. By the turn of the decade 1980/1990,a sharp decline in vendace population coincided witha major increase of pikeperch. The abundance changesin the Lake Peipsi fish community have gone in oppositedirections for cold-adapted as compared with warm-adapted species (Kangur et al., 2011 submitted). The fishcommunity has shifted on a long-term scale from clean-and cold-water species like smelt, vendace, whitefish,
and burbot toward more pikeperch and bream, whichprefer productive warmer and more turbid waters. LakePeipsi is no longer a suitable habitat for smelt, vendace,whitefish, and burbot, which prefer colder oligotrophicwater and that richer in oxygen. However, the new condi-tions are suitable for pikeperch and bream, which aregenerally classified as warm-water-tolerant speciesfavored by eutrophic conditions. Although the fish specieslist has not changed in Lake Peipsi during the last decades,there have been significant shifts in relative dominanceand in the prevalent feeding habits of the fish species.A major decrease in pelagic planktivores (e.g., smelt,vendace, Peipsi whitefish) can be considered as the mainindicator of such significant shifts.
Besides small, systematic trends that have becomeimportant in the longer term, major abrupt changes haveoccurred repeatedly during the last half century in theLake Peipsi fish community. Concurrent eutrophicationand sudden environmental extremes (e.g., heat waves)can cause long-lasting and irreversible changes in the fishcommunity of the lake. In Lake Peipsi, the effects of eutro-phication have seemed to increase dramatically in hot anddry summers, when water level decreases sharply, and allthe usual water quality parameters (e.g., water transpar-ency, nutrient content) have demonstrated the worseningof the lake’s ecological health (Kangur et al., 2005). Thus,the lake’s status can shift abruptly, e.g., in response todrought, causing unexpected catastrophes in its biota(e.g., fish kills). Current data indicate that recent climatewarming in summer time (together with severe heatwaves) and nutrient enrichment in the Lake Peipsi ecosys-tem are acting in the same direction: both are increasingthe probability of fish kills, which have become more fre-quent and extensive. In the summers when cyanobacterial(blue-green algae) blooms, hot and calm weather, andconsistently high water temperature (up till 26–28�C)co-occur, fish kills have been repeatedly observed in LakePeipsi over the past five decades. Although mass growthof cyanobacteria has been documented in the lake sincethe nineteenth century (Laugaste et al., 2001), eutrophica-tion (the addition of the nutrients to the lake) appears tohave raised the intensity of the blooms. A fish kill duringa bloom of Aphanizomenon sp. was first described in1959, when a sudden large-scale smelt mortality occurredin the southern part of the lake, Lake Pihkva (Semenova,1960). The next massive smelt kill in summer 1972,during a calm warm period and strong cyanobacterialbloom, affected the entire lake. In the following years(1973–1974), no smelt were caught; however, a quickrecovery of stock occurred in the following 2–3 years.In a similar fashion, subsequent hot summers withcyanobacterial blooms had long-term negative effects onthe smelt population. In recent years, the abundance ofsmelt population has reached a historically minimumlevel. After extreme weather events and fish kill in 1988,the vendace population collapsed and has not yet returnedto its previous levels. Recently, however, besides cold-water fish (smelt, vendace), other fish species, especially
bottom-dwelling fish such as ruffe and juvenile fish ofseveral species, were also seriously affected by concurrenteffects (Kangur et al., 2011 submitted). During the fishkills in 2002 and 2010, ruffe has been seriously affected.This may be due to the fact that the heat waves andcyanobacterial blooms can lead to the bottom layers ofthe lake water becoming oxygen-deficient. As environ-mental extremes have become more frequent and summerfish kills have involved larger area, there was serious dam-age to the fish populations which eventually may lead tothe extinction of some fish species (Kangur et al., 2011submitted). This has already been proven to be correctfor smelt, a previous key species in the fish community.
Socioeconomic significanceLake Peipsi is of great economic significance, first of all asthe drinking water source for the Estonian industrial townNarva and its sister town Ivangorod on the Russian side ofthe border, but also in terms of water transport, fishery, andenergy production. Its bottom deposits hold great reservesof curative mud and building materials, and its waters coolthe huge kettles of the Baltic and Estonian Thermal PowerPlants and drive the turbines of the Narva HydropowerStation. The beaches of the lake, especially in the northernand eastern parts, have a big recreational value. Fishing isan important sector of rural employment in the Peipsiregion and an essential part of the lifestyle in the lake’scoastal villages. Fish stocks of the lake have been remark-ably high, whichmakes it economically important for bothcommercial and recreational fishermen.
History of researchHydrobiological studies on Lake Peipsi have a long tradi-tion; fishery investigations began already with the work ofKarl-Ernst von Baer in 1851–1852. Since 1950, system-atic hydrochemical studies are carried out on the lake.Annual hydrobiological monitoring of Lake Peipsi hasbeen carried out by the Institute of Zoology and Botanysince 1962 and monitoring of coasts by the Institute ofGeology since 1981. Today, this work is part of the Esto-nian State Environmental Monitoring Programme, whichgained legal ground in 1993. The results of the monitoringconstitute the main scientific base for political decisions tobe passed by the state and local authorities. Unfortunately,most studies since 1992 have been on the Estonian part ofthe lake. However, regular joint Estonian–Russian expe-ditions to the whole lake have been arranged since 2001.Several monographs about Lake Peipsi have beenpublished during the last decade (Miidel and Raukas(1999); Nõges (2001); Pihu and Haberman (2001);Haberman et al. (2008)).
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Jaani, A., 2001b. Water regime. In Nõges, T. (ed.), Lake Peipsi.Meteorology, Hydrology, Hydrochemistry. Tartu: SulemeesPublishers, pp. 41–46.
Kangur, K., and Möls, T., 2008. Changes in spatial distribution ofphosphorus and nitrogen in the large north-temperate lowlandLake Peipsi (Estonia/Russia). Hydrobiologia, 599, 31–39.
Kangur, K., Kangur, A., Kangur, P., and Laugaste, R., 2005. Fishkill in Lake Peipsi in summer 2002 as a synergistic effect ofcyanobacterial bloom, high temperature and low water level.Proceedings of the Estonian Academy of Sciences: BiologyEcology, 54, 67–80.
Kangur, K., Park, Y.-S., Kangur, A., Kangur, P., and Lek, S., 2007a.Patterning long-term changes of fish community in large shallowLake Peipsi. Ecological Modelling, 203, 34–44.
Kangur, M., Kangur, K., Laugaste, R., Punning, J.-M., andMöls, T.,2007b. Combining limnological and palaeolimnologicalapproaches in assessing degradation of Lake Pskov.Hydrobiologia, 584, 121–132.
Kangur, A., Kangur, P., Pihu, E., Vaino, V., Tambets, M., Krause, T.,and Kangur, K., 2008a. Fishes and fishery. In Haberman, J.,Timm, T., and Raukas, A. (eds.), Peipsi. Tartu: Publishing houseEesti Loodusfoto, pp. 317–340 (in Estonian).
Kangur, K., Timm, T., Timm, H., Mälton, E., Kumari, M., andMelnik, M., 2008b. Zoobenthos. In Haberman, J., Timm, T.,and Raukas, A. (eds.), Peipsi. Tartu: Publishing house EestiLoodusfoto, pp. 291–315 (in Estonian).
Kangur, K., Kumari, M., and Haldna, M., 2010. Consequences ofintroducing the invasive amphipod Gmelinoides fasciatus intolarge shallow Lake Peipsi: present distribution and possibleeffects on fish food. Journal of Applied Icthyology, 26, 81–88.
Kangur, K., Kangur, A., Kangur, P., Ginter, K., Orru, K., Haldna, M.,Möls, T., 2011. Long-term effects of concurrent eutrophicationand environmental extremes on the fish community of LakePeipsi (Estonia/Russia). Fisheries Management and Ecology(Submitted).
Laugaste, R., Nõges, T., Nõges, P., Jastremskij, V. V., Milius, A.,and Ott, I., 2001. Algae. In Pihu, E., andHaberman, J. (eds.), LakePeipsi. Flora and Fauna. Tartu: Sulemees Publishers, pp. 31–49.
Loigu, E., Leisk, U., Iital, A., and Pachel, K., 2008. Peipsi järvevalgla reostuskoormus ja jõgede veekvaliteet. In Haberman, J.,
Timm, T., and Raukas, A. (eds.), Peipsi. Tartu: Publishing houseEesti Loodusfoto, pp. 179–199 (in Estonian).
Mäemets, H., 2005. Relationships of the macrophyte vegetation ofEstonian lakes with environmental conditions and changes inthe course of anthropogenic eutrophication. A thesis for applyingfor the degree of Doctor of Philosophy in Hydrobiology. Tartu
Mäemets, H., and Freiberg, L., 2004. Characteristics of reeds onLake Peipsi and the floristic consequences of their expansion.Limnologica, 34, 83–89.
Mäemets, H., Palmik, K., Haldna, M., Sudnitsyna, D., andMelnik, M., 2010. Eutrophication and macrophyte speciesrichness in the large shallow North-European Lake Peipsi.Aquatic Botany, 92, 273–280.
Miidel, A., and Raukas, A., (eds.) 1999. Lake Peipsi. Geology.Talinn: Sulemees Publishers. 148 p.
Mikelsaar, N.-Õ., and Voore, R., 1936. New data about appearanceof zebra mussel Dreissena polymorpha Pall. in Estonia. EestiLoodus 4, 142–145 (in Estonian)
Nõges, T. (ed.), 2001. Lake Peipsi. Meteorology, Hydrology,Hydrochemistry. Tartu: Sulemees Publishers, 167 p.
Nõges, T., Järvet, A., Kisand, A., Laugaste, R., Loigu, E.,Skakalski, B., and Nõges, P., 2007. Reaction of large andshallow lakes Peipsi and Võrtsjärv to the changes of nutrientloading. Hydrobiologia, 584, 253–264.
OECD, 1982. Eutrophication of water, monitoring, assessment andcontrol. Paris: Organization for economic Cooperation andDevelopment (O.E.C.D.), 150 pp.
Pihu, E., and Haberman, J. (eds.), 2001. Lake Peipsi. Flora andFauna. Tartu: Sulemees Publishers, 152 p.
Punning, J.-M., and Kapanen, G., 2009. Phosphorus flux in LakePeipsi sensu stricto, Eastern Europe. Estonian Journal Ecology,58, 3–17.
Punning, J.-M., Raukas, A., Terasmaa, J., and Vaasma, T., 2009.Surface sediments of transboundary Lake Peipsi: composition,dynamics and role in matter cycling. Environmental Geology,57, 943–951.
Raukas, A., 1978. The Pleistocene deposits of the Estonian SSR.Tallinn: Valgus, 310 p (in Russian with English and Estoniansummaries).
Raukas, A., 1999. Lithology. In Miidel, A., and Raukas, A. (eds.),Lake Peipsi. Geology. Tallinn: Sulemees Publishers, pp. 67–79.
Rumyantsev, V. A., Kondrat’ev, S. A., Shmakova, M. V., Basova,S. L., Shilin, B. V., Zhuravkova, O. N., and Savitskaya, N. V.,2005. The external loading of Lake Peipsi and its response.Vodnoe hozyaistvo Rossii, 7, 569–585 (in Russian).
Semenova, N. I., 1960. The reasons of smelt kill in Lake Pskov inAugust 1959. Nauchno-teknicheskij byulleten GosNIORKH,10, 23–24 (in Russian).
Tanner, R., Kangur, K., Meriluoto, J., and Spoof, L., 2005. Hepato-toxic cyanobacterial peptides in Estonian fresh water bodies andinshore marine water. Proceedings of the Estonian Academy ofSciences. Biology, Ecology, 54, 40–52.
Tavast, E., 1999. Shores. In Miidel, A., and Raukas, A. (eds.), LakePeipsi. Geology. Tallinn: Sulemees Publishers, pp. 101–109.
Timm, V., and Timm, T., 1993. The recent appearance of a Baikaliancrustacean, Gmelinoides fasciatus (Stebbing, 1899)(Amphipoda, Gammaridae) in Lake Peipsi. Proceedings of theEstonian Acadamey of Sciences. Biology, Ecology, 42, 144–153.
Tyumina, T. Y., 1966. About nature conditions in XII century in thenorthern part of Lämmijärv. In Ledovoe Poboische in 1242.Trudy Kompleksnoi Ekspedicij Po Utochneniu Mesta LedovogoPoboistsa. Moskva-Leningrad: Nauka, pp. 103–122 (inRussian).
Varep, E., 1995. History of geographical research. 1. Vanimad teatedEesti kohta. Feodaalse killustatuse periood. In Raukas, A. (ed.),Eesti: loodus. Tallinn: Valgus, Eesti Entsüklopeediakirjastus,pp. 17–25 (in Estonian).
Cross-referencesClimate Change Effects on LakesClimate Change: Factors Causing Variation or Change in theClimateFinnish LakesNutrient Balance, Light, and Primary ProductionRussian LakesRussian Lakes, Geographical ClassificationVõrtsjärv Lake in EstoniaWater Balance of Lakes
trap watersediment
Phosphorus forms in sediment, settling and suspended particles
Lake Erken
NH4CI-RP
NaOH-RP
NaOH-nRP
HCI-RP
Phosphor Exchange Sediment-Water, Figure 1 Phosphorusforms in sediment, settling, and suspended particles in LakeErken, Sweden.
PHOSPHOR EXCHANGE SEDIMENT-WATER
Kurt PetterssonDepartment of Ecology and Genetics, EBC, UppsalaUniversity, Norrtälje, Sweden
IntroductionLake sediments play a crucial role in the phosphorusmetabolism in lakes. The impact depends on the capacityto retain and thereby decrease the phosphorus availabilityin the lake water and secondly, on the ability to releasephosphorus when environmental conditions change. Theparticle composition, prehistory, and binding capacity ofthe sediment govern its behavior. The general view untilthe 1970s was that sediments acted as sinks for phospho-rus with the exception of periods with anoxia in the bottomwaters, when iron-bound phosphate is released to thehypolimnion of stratified lakes (Einsele, 1936; Mortimer,1941, 1942). During the last decades, more knowledgehas been gathered (Boström, 1982; Löfgren, 1987; Rydin,1999) and a much more complicated picture has devel-oped, emphasizing the important role of internal loadingfor lake water quality and especially for the summerblooms of cyanobacteria in lakes.
The internal loading from lake sediments will oftendetermine the level of eutrophication of the lake and thetime lag for recovery after reduction of the external load-ing. Internal loading is most important during summerwhen the water temperature is high, speeding up the lakeprocesses. The pool of phosphorus bound to particles inthe surficial sediments (10 cm) is vast (100 fold) in com-parison to the phosphorus pools in the water column.Phosphorus can leave the sediment in a dissolved statemainly as phosphate or as particles. In the latter case, thereare two major ways: as resuspended sediment particles(detritus) or by migration of resting stages of phytoplank-ton. Even if a very small share is released, it will have sig-nificant impact on the phosphorus concentration in thelake water.
The distribution of phosphorus forms in sediments hasbeen investigated since the 1950s. Generally, vertical pro-files of sediment phosphorus concentration, expressed ona dry weight basis, show an increasing concentrationtoward the sediment surface in eutrophic lakes. Thisincreasing vertical profile continues into the water, whenlooking at sedimenting particulate matter (sedimentation
traps) and suspended matter. The different phosphorusforms are determined by sequential extraction and labile,aluminum-, iron-, and calcium-bound phosphorus can beseparated. The residual is mainly organically bound phos-phorus. Organic as well as iron-bound and labile phospho-rus are the three fractions increasing in the vertical profilementioned above. An example of the fractional phospho-rus composition from Lake Erken, Sweden illustrating thisis shown in Figure 1.
A number of environmental factors are important in themobilization process. To leave the sediment in a dissolvedstate, phosphorus must be mobilized by physical, chemi-cal, or biological processes and then transported to thelake water. The splitting mechanisms includes desorption,dissolution of precipitates and complexes, ligandexchange, and enzymatic hydrolysis of organic esterbonds. Most studies indicate that sediment bacteriahave a significant role in uptake, storage, and release ofphosphorus including anaerobic release of iron-boundphosphorus. The redox potential in the sediments affectsreduction of iron (III) to iron (II) and a subsequent releaseof phosphate. At higher pH levels (i.e., in shallow lakeswith high primary production), hydroxide ions replacephosphate causing ligand exchange. A high water temper-ature increases the bacterial activity giving lowerredox potential and a higher production of enzymes.This means that phosphorus can be released from lakesediments although the oxygen concentration in thewater is high when the water temperature is high duringsummer.
Several phytoplankton species have resting stagesoverwintering in the sediment. When growth is induced,they leave their habitat in order to shift their life form toa pelagic one. In Lake Erken, Sweden, the cyanobacteriaGloeotrichia echinulata has been shown to contribute to
Phosphor Exchange Sediment-Water, Figure 2 Increase of total phosphorus concentration in Lake Erken and the contribution ofmigrating Gloeotrichia echinulata.
608 PLAYA LAKE CHAINS: THE EXAMPLE OF THE YENYENING LAKES OF THE UPPER AVON RIVER CATCHMENT OF WESTERN AUSTRALIA
the internal loading of phosphorus during summer. Thefloating capacity of the colonies makes them able to passthe metalimnion and migrate to the epilimnion, transfer-ring phosphorus from sediments to the upper water strata(Figure 2).
BibliographyBoström, B., 1982. Recycling of Nutrients from Lake Sediments.
Uppsala Univeristy in Uppsala, Sweden, Vol. 659, 25 pp.Einsele, W., 1936. Uber die Beziehungen des Eisenkreislaufs zum
Phosphatkreislauf im eutrophen Seen. Archives of Hydrobiology,29, 664–686.
Löfgren, S., 1987. Phosphorus Retention In Sediments – Implica-tions for Aerobic Phosphorus Release in Shallow Lakes. UppsalaUniveristy in Uppsala, Sweden, Vol. 100, 21 pp.
Mortimer, C. H., 1941. The exchange of dissolved substancesbetween mud and water in lakes (part I and II). Journal of Ecol-ogy, 29, 280–329.
Mortimer, C. H., 1942. The exchange of dissolved substancesbetween mud and water in lakes (part III and IV). Journal ofEcology, 30, 147–201.
Rydin, E., 1999.Mobile Phosphorus in Lake Sediments, Sludge andSoil A Catchment Perspective. Uppsala Univeristy in Uppsala,Sweden, Vol. 426, 35 pp.
Cross-referencesCarbon Cycle in LakesEutrophication in Fresh Waters: An International ReviewLimnological Studies in Lake Erken SwedenMyponga Reservoir, South Australia: The Influence of Nutrients,Phytoplankton, Pathogens, and Organic Carbon on Water QualityNutrient Balance, Light, and Primary Production
PLAYA LAKE CHAINS: THE EXAMPLE OF THEYENYENING LAKES OF THE UPPER AVON RIVERCATCHMENT OF WESTERN AUSTRALIA
Jenny A. Davis1, Paul A. Carling21School of Biological Sciences, Monash University,Clayton, VIC, Australia2School of Geography, University of Southampton,Southampton, UK
IntroductionThe term “playa” or “pan” applies to individual arid zonebasins of varying size and origin that are subject to ephem-eral surface water flows (Shaw and Thomas, 1989) suchthat lakes may occur within playas as permanent orephemeral features. Playas in Australia are often geologi-cally young (Quaternary) features developed in aridenvironments and are often dry due to evaporation (Boggset al., 2006). Although playas are a response to tectonics, cli-mate change, and eolian and fluvial processes, the majorityof the scientific literature considers either their origin withina regional context, or the development dynamics of individ-ual playas (e.g., Bettenay, 1962). However, where playas aredeveloped within paleodrainage channels, they may exist asisolated features, but more often they exhibit a degree ofhydrological interconnectivity with other playas to form“playa chains” such that the development history of an indi-vidual playa cannot be addressedwithout consideration of itsneighbors.
PLAYA LAKE CHAINS: THE EXAMPLE OF THE YENYENING LAKES OF THE UPPER AVON RIVER CATCHMENT OF WESTERN AUSTRALIA 609
Dryland salinity is a major environmental issue ininland Australia, particularly in Western Australia andSouth Australia, and has been estimated to affect over2.2 million hectares (State Dryland Salinity Committee,1990). The Wheatbelt region of the southwest of WesternAustralia has the largest area of land affected by salinity,and this is predicted to increase to 8.8 million hectaresby 2050 (Australian Natural Resources Atlas, 2000). Iso-topic studies have shown that some salt in the soils areof marine origin and accumulate by winds transportingsalt inland from the sea (Chivas et al., 1991). However,in this region the replacement of deep-rooted perennialspecies with shallow-rooted annual cropping species(Wood, 1924; Mulcahy, 1978; Schofield et al., 1988)has resulted in waterlogging and extensive salinizationof rivers, streams, and valley floors. The reduction inevapotranspiration associated with widespread land clear-ing led to a rise in the level of the saline aquifer and mobi-lization of salt previously stored deep within the soilprofile.
Prior to clearing, Wheatbelt catchments were essen-tially completely vegetated with a diverse range of woodyplant communities whose distribution was controlled byclimate and soil type (Beard, 1981). The vegetation wascapable of using deeply infiltrated water during the dryseason. Most of the annual precipitation was evaporatedor transpired. However, there is anecdotal evidence thatthe drainage systems prior to the twentieth century werefresh or at least less saline than today (Cross, 1833;YLMS, 1996) with well-vegetated riparian zones. Withclearing, the water balance changed to one of reducedannual evaporation and interception and increased runoffand recharge (Hatton et al., 2003). Runoff onto andthrough valley floors is considered to have increased bya factor of 5, and increased groundwater recharge is fillingdeep sedimentary materials and bringing highly salinewater to the surface. Diffuse recharge has also increasedon slopes and ridges with additional hydraulic headsforcing groundwater toward the valleys and resulting inincreased discharge of water and salt to streams andwetlands. The changes in local climate due to forestremoval and the reduction in vegetation cover must alsohave implications for eolian processes. The YenyeningLakes and Salt River sections of the Upper Avon catch-ment (Figure 1) form a series of interconnected playa lakesand seasonally wetted salt pans confined withina paleochannel. The Yenyening Lakes are part ofa regional complex of playa lakes (Killigrew and Gilkes,1974) that only recently have received detailed scientificscrutiny (e.g., Boggs et al., 2006). The Yenyening Lakesare considered to be a very significant feature in thehydrology of the Wheatbelt (WRC, 2002) because all thedrainage of the Lockhart and Yilgarn catchments (whichcover a significant portion of the region) flows throughthem into the Avon–Swan system. Significantly, the mor-phology of the playa chains is a response to the geologyand the present climatic, topographic, and hydrographic
controls, but also the morphology has characteristicsinherited from prior climatic and hydrological systemsthat require elucidation.
Climate and hydrologyThe regional climate is characterized by hot, dry summersand warm, wet winters (Gentilli, 1971, 1993). The averageannual rainfall in the region is 350 mm, and the averageannual evaporation is approximately 2,100 mm (WRC,2002). Prevailing winds are strongest from the southwestduring summer but from the northeast during winter.
Although the name “Salt River” suggests that river hasalways been saline, this epithet probably referred to theepisodic pulses of salt that would have moved throughthe river when sufficient rainfall occurred in the upper-most areas of the catchment to move salt water throughfrom playas much further to the east and south, such asLake Deborah and Lake Grace.
A simple salt and water balance model for theYenyening Lakes System was developed by Bari (2002)from data available over the period 1973–2000. Duringthat period there was an average annual inflow of 39.5million cubic meters and outflow occurred in most years.Approximately 92% of the total annual input was lostby flow out to the Avon River and 8% by evaporationprocesses. Loss through seepage to the deep aquifer wasconsidered to be negligible. The median salinity of theplayas was 60,000 mg/L TDS, the annual average saltinput was 381,000 t, and 99% of the stored salt was lostdue to overflow.
The Yenyening Lakes Management Strategy (WRC,2002) suggested that the generalized description ofgroundwater hydrology in the Wheatbelt can be appliedto the Yenyening system. Prior to forest clearance, thehydrological system was in balance with the water tablemaintained at a constant depth and the native vegetationable to use all of the rainfall infiltrating the soil profiles.This situation was dramatically altered through land clear-ing. The water table has risen and the discharge of salinegroundwater to the surface drainage has increased.A substantial area with depth to groundwater from 0.5 to1 m adjoins the main drainage line, and the playas, chan-nels, and the Salt River are considered to be fully saturated(Smith, 2002). Land Monitor (2000) plots indicated thatthe area of salinized land in the region had increasedbetween 1989 and 1998 and would continue to increasesignificantly (Smith, 2002).
Geology and geomorphologyThe geology and geomorphology of Western Australiawas summarized byWhite (2000), who noted that satelliteimagery reveals that the modern landscape containsa mixture of ancient and modern features. Many modernrivers and playas are in the valleys of ancientpaleodrainage lines. The paleodrainage patterns of thestate were established by the end of the Cretaceous or earlyin the Tertiary (65–60 million years ago) (Van de Graaff
Playa Lake Chains: The Example of the Yenyening Lakes of the Upper Avon River Catchment of Western Australia,Figure 1 Location of the study area in southwestern Australia. The inset box shows the location of the Avon River tributaries andthe Yenyening Lakes. The inset circle shows the chain of playa lakes located between the south branch of the Avon River and theSalt River.
610 PLAYA LAKE CHAINS: THE EXAMPLE OF THE YENYENING LAKES OF THE UPPER AVON RIVER CATCHMENT OF WESTERN AUSTRALIA
et al., 1977; Zheng et al., 1998). White (2000) recognizedseven major paleodrainage provinces on the YilgarnCraton. The province in which secondary salinizationhas been particularly prevalent is that of south-to-northtrending valleys that drain into rivers flowing into theIndian Ocean (the Avon–Swan and Canning Rivers).
A comprehensive study of the geomorphology,geology, and paleohydrology of the Salt River system bySalama (1997), within the context of the regional develop-ment of the drainage system (Beard, 1999, 2000), notedthat the Salt River system connects the saline playas ofthe Yilgarn catchment in the eastern ancient zone withthe rejuvenated Avon–Swan system in the west and hasprobably occupied the same course since the earlyTertiary. At that time, the uplift of the Yilgarn Cratonand the formation of the Darling Scarp dammed the riverand caused the formation of a large inland lake. This largepaleolake at Yenyening (named Yilgarn Lake) persisteduntil the opening of the northern outlet of the Avon whichoccurred during exceptionally wet periods after denuda-tion reduced the height of uplifted areas (Salama, 1997).
Smith (2002) noted that the geology of the system wasmapped by Chin (1986a, b). Sand plain and laterite occurat higher elevations while the valleys contain Holocenealluvium and Cenozoic sediments. The basement com-prises medium to coarse adamellite, gneiss, rare dolerite,and quartz dykes some of which crop out as rocky knolls.
Today the Yilgarn and Lockhart Rivers merge at Caro-line Gap to form a broad valley floor containing the SaltRiver and, further downstream, the Yenyening Lakes.The two catchments comprise about 91,000 km�2 ofmainly cleared agricultural land (WRC, 2002). Overflowoccurs into the Avon River at Qualandary Crossing. Thecrossing was constructed in the early 1900s and acts asa weir to prevent backflow from the Avon River. Thecurrent gated culvert was completed in 1998; the gatesare opened under moderate flows while flood events passover the top of crossing (WRC, 2002).
A series of oblique color aerial photographs of theYenyening Lakes were available from ten low-level flightsundertaken by one of us (JD), in different seasons,between October 2002 and May 2004. The photographs
PLAYA LAKE CHAINS: THE EXAMPLE OF THE YENYENING LAKES OF THE UPPER AVON RIVER CATCHMENT OF WESTERN AUSTRALIA 611
were used to determine the patterns of inundation in thesalt playas and across the Salt River valley floor, the shapeof the playas and the degree of interconnectivity, and thepresence and extent of retentive features, such as sandybanks and lunettes. Lunettes are the windblown ridges offine sediment that often accumulate on the downwindmargins of seasonally dry lakes due to deflation of thedry lake bed (Bowler, 1973). Remotely sensed imageryrevealed the extent of inundation following a majorepisodic rain event throughout most of the catchment inJanuary, 2000. A field visit which followed the Salt River,upstream, from Yenyening Lakes to Caroline Gap wasundertaken in May 2004 to ground truth aspects of theaerial photographs.
A series of channels and playas of various sizes occurimmediately upstream of Qualandary Crossing fora distance of approximately 30 km. Sandy or clay banksand “lunettes” are present. The lunettes are relativelybright on air photography; rise between 1 and 3 m abovethe dry season water level (DSWL – as noted in 2004)are arcuate in planform and usually are best developedon the downwind side of a given playa. The sandy banks,usually rising less than 2 m above the DSWL, often occuras a collection of several subparallel ridges that are partic-ularly obvious at low water levels. Those within the lakesappear to be lunettes that formed during lower lake levelsbut have been submerged by a rise in the water level. Boththe sandy banks and lunettes are actively developing aswitnessed by blowing sand and the presence of recentwind ripples on their surfaces in 2004. However, theeffects of river flow and wind-driven water circulationmust also play a role in the formation and morphologicalevolution of these banks as often they are more linear inplan view than neighboring lunettes. Figure 2a revealsthe presence of both banks and lunettes within lakesand channels throughout the system. A number of well-defined linear banks are present within The Channelsand adjoining unnamed lakes (Figure 2b). Thelower banks and lunettes are devoid of plant life or aredominated by samphires, but some of the higher ones,for example, those at Ossig’s Lake, contain shrubs andtrees.
The pattern of bank and lunette formation evident atOssig’s Lake under low water conditions, in March2004, revealed the influence of both eolian and fluvial pro-cesses (Figure 3a). The direction of water flow is from bot-tom right to top left, the northeast, while the predominantwind direction in summer (Figure 3b) is from top left tobottom right, the southwest. Thus wind-driven mixing,acting against the direction of any residual river flow, willpredominate during summer. High river flows will be inthe same direction as the dominant winds (northeasterly)during winter. Further upstream the geomorphology ofthe valley floor changes to that of fewer and smaller poolsand finally to a network of complex, shallow channels. Itis likely that the rise in the saline water table has resultedin greater definition of the shallow, diffuse channels.Under previous, less waterlogged conditions, many of
these shallow channels may have been predominantlydry and would have supported low, terrestrial plantcommunities.
The evaporation from the shallow water table whichconcentrates the salts in groundwater near the surfaceand accumulates them in the soil, as described by Smith(2002), is demonstrated by the white areas of salt promi-nent on the valley floor margins in Figure 2b.
Under conditions of high flow, many of the banks aresubmerged; however, those banks and lunettes containingwell-developed plant communities are likely to be rarelyflooded. A field visit in May 2004 demonstrated thatalthough many banks and lunettes are submerged duringhigh river flows, their morphology should still exerta major control on the direction of water flow, mixingprocesses, and retention times. Whereas small banks tendto be approximately parallel to the direction of flow, highbanks also occur that are transverse to the directionof stream flow. These few very high banks are stablefeatures, with good soil development and relict woodland,and occur as breached barriers between successive majorsalt lakes. These banks appear to consist of amalgams oftwo or more “fossil” lunettes, developed on a scale inexcess of the smaller, active lunettes within the lakes; theyrise to around 20m above theDSWL. In each case, a singlechannel cuts through each bank, thus connecting contigu-ous lakes. These high banks were not inundated by theexceptional flood of January 2000. This conclusion maybe drawn from the evidence of water levels in the satelliteimages and also from wrack marks consisting of accumu-lations of shells of the gastropod Coxiella, which arearound 2 m above the DSWL.
Large lunettes developed in SE Australia between17,000 and 15,000 B.P. (Bowler, 1973). No dates areavailable for the Yenyening banks, but it is hypothesizedthat these fossil lunettes developed in the late Quaternaryand/or Holocene and are evidence for seasonal desiccationof these chains of lakes, even if the water flow at that timewas less saline. The presence of these large banks separat-ing individual lakes affords a considerable degree of reten-tion to water flow down through the system, both throughconstraining surface flow to a single connecting channelbut also almost certainly inducing shallow groundwaterseepage between adjacent lakes.
Small lunettes and the lake margins are visibly subjectto wind action as wind-blown sand and eolian ripples wereobserved in 2004. Nevertheless there is no clear morpho-logical relationship between the lunette and lake planviews and the prevailing wind direction. Thus a moredetailed analysis of the orientation, morphology, stratigra-phy, and sedimentology of the smaller lunettes and linearbanks with respect to the prevailing winds is needed tofully elucidate the processes by which these structureshave formed. Similarly the large wooded banks separatingmany of the lakes are one order of magnitude higher thanthe small active lunettes and of considerable bulk. Theseare hypothesized to be lunettes that formed under priorwind and hydrological regimes.
Playa Lake Chains: The Example of the Yenyening Lakes of the Upper Avon River Catchment of Western Australia,Figure 2 (a) Right to left: Racecourse Lake (dry with white salt crust), Ossig’s Lake, The Neck, and Mud Lake (dry). Morbinning Gullyin the foreground. Direction of flow is from left to right. Oblique view from the northeast, December 22, 2003. (b) The Channels.Flow in this region is diffuse but overall direction is from left to right. Oblique view from the north, December 22, 2003.
612 PLAYA LAKE CHAINS: THE EXAMPLE OF THE YENYENING LAKES OF THE UPPER AVON RIVER CATCHMENT OF WESTERN AUSTRALIA
Notwithstanding the lack of detailed data, the informationrevealed by aerial photography and ground survey is suffi-cient to indicate that the lunettes and banks are an importantstructural component of the Yenyening Lakes system thatrecords the history of lake and drainage network develop-ment as well as controlling modern-day retentiveness.
Evidence of freshwater seeps along the margins of thevalley floor were also evident (through distinctive colorchanges) in some aerial photographs. The healthy plantcommunities present on the southwestern corner of TheChannels indicated the presence of freshwater dischargingfrom the adjacent slope. Whether this area will be
enhanced or degraded by the recent planting of maritimepines (Pinus pinaster) on the privately owned adjoiningslope is not known. This area appeared to contain the bestexample of healthy vegetation within the entire reserveand deserves further investigation. Freshwater seeps werenoted elsewhere using aerial photography and one,at Yenyening Lake, had a considerable surface flow. Theseseeps are of considerable nature conservation value, havelocal agricultural value, and have a currently undefinedeffect on dilution of low-flow saline waters in the valley.
The dry, salt-encrusted states of two lakes (RacecourseLake andMud Lake) were found to be due to the diversion
a
b
Playa Lake Chains: The Example of the Yenyening Lakes of the Upper Avon River Catchment of Western Australia,Figure 3 (a) Ossig’s Lake and The Neck under low-water conditions. Direction of flow is from bottom right to top left. Obliqueview from southeast, March 19, 2004. (b) Wind roses showing seasonal wind data for Beverley (lat: 32� 06’30”S, long: 116�55’29”E), thenearest weather station to Yenyening Lakes. The period of recording was from January 1985 to December 2006. Source of data:Commonwealth of Australia – Bureau of Meteorology.
PLAYA LAKE CHAINS: THE EXAMPLE OF THE YENYENING LAKES OF THE UPPER AVON RIVER CATCHMENT OF WESTERN AUSTRALIA 613
of water undertaken by a local resident in an attempt topromote flow through the main system. This was under-taken with the expectation that such action would preventan increase in the salt load in the large lakes used forrecreational activities (water-skiing) (T. McLean, perscomm.). This approach to “disconnecting” some lakesfrom the rest of the hydraulic system to decrease the reten-tion time of water in the rest of the reserve is an unproventechnique that might have unforeseen repercussions on the
nutrient status of the water and the ecology of the lakesthat remain connected.
Nature conservation, cultural, and recreationalvaluesThe nature conservation and recreational values of thelake were described by the Yenyening Lakes ManagementStrategy (1996). The lakes are recognized as an importantarea for waterbird habitat and breeding, with 41 species
614 PLAYA LAKE CHAINS: THE EXAMPLE OF THE YENYENING LAKES OF THE UPPER AVON RIVER CATCHMENT OF WESTERN AUSTRALIA
recorded using the lakes, and 10 species are known tobreed there (YLMS, 1996). Forty-six land species havebeen recorded in the lakeside bushlands. The lakes areencompassed by two Nature Reserves; these are vestedin the Conservation Commission of Western Australiaand managed by the Department of Conservation andLand Management. The main series of lakes lies withinReserve 31837 which was created for the purposes of“Recreation and Conservation of Flora and Fauna.”Further upstream is Reserve 28088 which was createdfor the “Conservation of Flora and Fauna” and containsThe Channels and adjoining flats and banks (YenyeningLakes Management Strategy, 1996).
The first sighting of the numbat (Myrmecobius fasciatus),a now rare and endangered marsupial, was recorded fromthe lakes’ area by Ensign Dale (1831) in a letter to the Sur-veyor-General, J.S. Roe (Cross, 1833). Dale also noted thepresence of “an inland lake of freshwater or perhapsa reservoir of the river”. . . “varied in its breadth from 60 to70 yards, and 5 or 6 miles in length.” Upon reaching this,he described seeing “an immense number of ducks, swansand other waterfowl” (Cross, 1833, p. 156).
The Yenyening Lakes Management Strategy(1996) noted that older local residents remembered thelakes teeming with birdlife and the surrounding wood-lands supported native animals and wildflowers. The areawas first settled in the 1890s, and degradation due to risingsaline groundwaters was observed from the 1930s onwardtogether with the spread of exotic weeds and the arrivalof exotic fauna including rabbits, foxes, and feralcats. Although the bushland adjoining the lakes isnow considered to be extremely degraded, the numeroussandy banks within the lakes’ system appear to be unaf-fected by salinization, and although weedy, stillsupport a range of local plant species including the salt-tolerant Salt River gum (Eucalyptus sargentii) and theYenyening mallee (E. vegrandis). Seed is collected fromE. sargentii for land rehabilitation programs throughoutthe southwest (Yenyening Lakes ManagementStrategy, 1996).
Ensign Dale noted that numerous aboriginal groupswere seen in the area (Cross, 1833). Although littlespecific information appears to have been recorded, thepresence of freshwater and abundant wildlife suggests thatthe lakes were important for indigenous groups.
Early settlers hunted, swam, and picnicked by the lakes,but the current most popular form of recreation at the lakesis water-skiing (Yenyening Lakes Management Strategy,1996). As a consequence, some of the current manage-ment of water levels in the lakes, via the gates atQualandary Crossing, is undertaken to maintain suitablewater depths and water quality for skiing.
Interpretation of the aquatic ecology of theYenyening Lakes and salt river system fromaerial photographyAlthough the nature conservation values of the YenyeningLakes are well recognized (Yenyening Lakes
Management Strategy, 1996; Water and Rivers Commis-sion, 2002), little information exists on the aquatic ecol-ogy of the lakes. Recent work on the ecology ofsecondary saline wetlands in the Wheatbelt region byDavis et al. (2003) and Strehlow et al. (2005) suggestedthat three possible ecological regimes may exist in thesesystems: clear, macrophyte-dominated; turbid, phyto-plankton-dominated; and clear, benthic microbial matdominated.
The concept of two states, clear water dominated byaquatic macrophytes and turbid water dominated by phy-toplankton, has been described in shallow European lakesundergoing eutrophication (Scheffer, 1998; Jeppesenet al., 1990; Blindow et al., 1993; Scheffer et al., 1993;Moss et al., 1996;). Davis et al. (2003) extended thisapproach and identified contrasting aquatic vegetationstates that were closely associated with different salinities.They suggested that salinization results in thedominance of a small number of salt-tolerant submergedaquatics (Ruppia, Lepilaena, Chara, andLamprothamnium). With increasing salinity, these sys-tems may undergo further change to microbial mat-dominated systems comprising mainly cyanobacteria andhalophilic bacteria.
Because of the difficulties in demonstrating stabilityand the alternative nature of these states, Strehlow et al.(2005) suggested that the term “ecological regime” shouldbe used sensu Scheffer and Carpenter (2003).
Sim et al. (2006a) suggested that the upper limit forsubmerged aquatics may be as high as 90 mgL�1 TDS.Additionally, however, the submerged aquatics studiedso far in Wheatbelt wetlands also appear to have arequirement for a seasonal water regime. Benthic micro-bial mats appeared to be dominant in seasonalwaterbodies at salinities >90 mgL�1 or at lower salin-ities if a permanent water regime is present. Positivefeedback loops are likely to exist such that matscan outcompete (and overgrow) germinating seedlingsunder a permanent water regime. Conversely aquaticscan germinate and seedlings quickly develop asa seasonal wetland refills, effectively disrupting theconditions needed for benthic mat development (Simet al., 2006b).
An upper limit of salinity has not been determined forturbid, phytoplankton-dominated systems. Moss et al.(1996) suggested that this state is likely to dominate atconcentrations of total phosphorus > 150 mgL�1.
Aerial photography revealed the presence of bothturbid, phytoplankton-dominated and clear, benthicmicrobial mat–dominated regimes in the YenyeningLakes and Salt River system. The different colors presentin pools in The Channels, under low-flow conditions,were most likely to have been produced by phytoplanktonblooms or dense benthic microbial mats. Althoughthe presence of phytoplankton and microbial matscan be established from aerial photography, accompany-ing field surveys are needed to determine speciescomposition.
PLAYA LAKE CHAINS: THE EXAMPLE OF THE YENYENING LAKES OF THE UPPER AVON RIVER CATCHMENT OF WESTERN AUSTRALIA 615
The presence of clear, macrophyte-dominated regimeswas not easily determined from the aerial photographyavailable; however, the field visit made to Ossig’s Lakein May 2004 revealed the presence of extensive dead matsof Lamprothamnium sp. and some live material. Thissuggested that conditions were suitable for the develop-ment of a clear, macrophyte-dominated regime in at leastsome of the lakes within the system. Stands of macro-phytes provide a direct source of food for herbivores suchas swans and habitat for invertebrates which, in turn,provide food for ducks and waders.
Conceptual model of the interaction betweenhydrology, geomorphology, and ecology in theYenyening Lakes and salt river systemThe complex pattern of lunettes, linear banks, mounds,and shallow channels present within the Yenyening Lakessystem suggests that the retention time of water within thesystem is likely to be high under low to moderate flows.The exception would be the infrequent, episodic, veryhigh flows such as those recorded in January 2000. Thehighly seasonal climatic regime of the region (cool, wetwinters and hot, dry summers) also indicates that mostof the shallow lakes would undergo extensive summerdrying in low and average rainfall years. However, thepresent complex drainage network ensures that lakes dryto differing degrees, as indicated by different waterlevels in different lakes induced by retentiveness.Thus the present drainage network maintains a majordegree of physical and ecological diversity even in itsdegraded state.
The high retention times produced by the complexwithin-lake and channel geomorphologies combined withshallow, seasonal water regimes indicate that conditionsare likely to be suitable for high rates of benthic and watercolumn primary production in these systems. Prior to theland clearing associated with European settlement, thissystem would have supported a rich freshwater ecosystemprobably dominated by submerged aquatics. This systemwould have supported the prolific birdlife of ducks andswans described by the early explorers (Cross, 1833).The increase in salinity, water depths, and nutrientsthat accompanied clearing and subsequent croppingwould have moved the aquatic system in the directionof dominance by phytoplankton or benthic mats.However, the presence of submerged aquatics at Ossig’sLake indicates that the salinity levels and waterregimes are not so disrupted that an irreversible shift inecological regime has occurred. Although it is unlikelythat these waterbodies will ever be restored to a fresherstate, their current diversity needs to be recognized andprotected.
and Hazard 2000 to 2050, Commonwealth of Australia. http://www.audit.ea.gov.au/anra/land/sal_risk/AUS.cfm?region_code=AUS&
Bari, M. A., 2002. The salt and water balance modelling of theYenyening Lakes system and its catchment, pp. 38–4.9. InWaterand Rivers Commission, 2002, Yenyening Lakes ManagementStrategy 2002–2012. Report No. WRM 32. Perth, WesternAustralia, 72 pp.
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Beard, J. S., 1999. Evolution of the river systems of the south-westdrainage division, Western Australia. Journal of the RoyalSociety of Western Australia, 82, 147–164.
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Bettenay, E., 1962. The salt lake systems and their associatedaeolian features in the semi-arid regions of Western Australia.J Soil Science, 13(1), 10–17.
Blindow, I., Andersson, G., Hargeby, A., and Johansson, S., 1993.Long-term pattern of alternative stable states in two shalloweutrophic lakes. Freshwater Biology, 30, 159–167.
Boggs, D. A., Boggs, G. S., Eliot, I., and Knott, B., 2006. Regionalpatterns of salt lake morphology in the lower Yarra Yarra drain-age system of Western Australia. Journal of Arid Environments,64, 97–115.
Bowler, J. M., 1973. Clay dunes: their occurrence, formationand environmental significance. Earth-Science Reviews, 9,315–333.
Chivas, A. R., Andrews, A. S., Lyons, W. B., Bird, M. I., andDonnelly, T. H., 1991. Isotopic constraints on the origin of saltsin Australian playas 1 sulphur. Palaeography, Palaeocli-matology, Palaeoecology, 84, 309–332.
Chin, R. J., 1986a. Explanatory notes on the Corrigin geologicalsheet. Western Australian Geological Survey, 1:250,000 series.
Chin, R. J., 1986b. Explanatory notes on the Kellerberrin geologi-cal sheet. Western Australian Geological Survey, 1:250,000series.
Cross, J., 1833. Journals of several expeditions made in WesternAustralia during the years 1829, 1830, 1831 and 1832 underthe sanction of the Governor, Sir James Stirling. London,Facsimile edition. 1980. Nedlands: University of WesternAustralia Press.
Davis, J., McGuire, M., Halse, S., Hamilton, D., Horwitz, P.,McComb, A., Froend, R., Lyons, M., and Sim, L., 2003. Whathappens when you add salt: predicting impacts of secondarysalinisation on shallow aquatic ecosystems using an alternativestates model. Australian Journal of Botany, 51, 715–724.
Gentilli, J. (ed.), 1971. Climates of Australia and New Zealand.In World Survey of Climatology. Amsterdam: Elsevier, Vol. 13.
Gentilli, J., 1993. Floods in the desert – heavy rain in the dry regionsof Western Australia. Western Australian Naturalist, 19,201–218.
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Cross-referencesAral SeaClassification of Lakes from Hydrological FunctionDead SeaMyponga Reservoir, South Australia: The Influence of Nutrients,Phytoplankton, Pathogens, and Organic Carbon on Water QualityPoopó Lake, BoliviaWater Balance of Lakes
POOPO LAKE, BOLIVIA
Lars BengtssonDepartment of Water Resources Engineering, LundUniversity, Lund, Sweden
DescriptionLake Poopó is located on the Bolivian high plains at3,700 m above the sea level. The lake is part of the TDPSsystem (Lake Titicaca, the Desaguadero River, LakePoopó, and the Salares (Salt Flats), Figure 1) forming anextensive endorheic basin. Lake Titicaca is the highest sit-uated of the world’s large lakes. The Desaguadero Riverlinks Lake Titicaca with the downstream Lake Poopó.Lake Poopó is an extremely shallow lake with a meandepth of less than 2 m below the outlet sill level. At spill-over level the lake surface is very large and exceeds3,000 km2. However, since it is so shallow, the lake mayin very dry periods dry out. In the present-day climate,there is very seldom any outflow from the lake, whichmeans that the water level and thus the surface area arehighly variable. The lake is in principle a terminal lake.The water is salty. The character of the lake is illustratedin Figure 2, which shows the flat shores.
Next to Lake Poopó is also Lake Uru-Uru. TheDesaguadero River divides into two river arms, onebranch into Lake Poopó and another into Lake Uru-Uru.Lake Uru-Uru spills over into Lake Poopó. LakeUru-Uru dries out every year. Its maximum depth is 1 m,when the surface area is 300–400 km2. Prior to 1985 theDesaguadero River ran through Lake Uru-Uru beforeentering into Lake Poopó itself. At high water levels thetwo lakes constitute one single lake.
The Salinas, two huge salt accumulations from oldlakes, Salar de Coipasa and Salar de Uyuni, are south ofand downstream Lake Poopó. Enormous changes havetaken place of the hydrology of the Bolivian Altiplano.Several lacustrine layers have been found in the sedimentsfrom the Salares. During the Tauca period (26,000–15,000 BP), the lower part of the Altiplano constituteda large single lake basin, Lake Tauca. In a drier climate thislake developed into three lake basins, Lake Poopó and thetwo Salinas, of which today the Salinas are saltaccumulations.
Today Lake Poopó can be considered to be a closedlake rarely having any outflow. Last time there was out-flow from the lake was in the mid 1980s. In early 2001the lake almost reached its sill level. The lake seems tohave been dry between 1939 and 1944 and almost dryin the early 1970s and again in 1994–1996. In a normalyear the lake area varies between about 2,000 km2
in March at the end of the wet period and 1,000 km2 inNovember at the end of the dry period. The variation ofthe lake surface area over 50 years is shown in Figure 3.As can be seen, there is a close relation to the water levelof Lake Titicaca.
Poopo Lake, Bolivia, Figure 1 The Titicaca-Desaguadero-Poopo-Salares (TDPS) system on the Bolivian High Plateau(From Pillco Zola, 2007).
Poopo Lake, Bolivia, Figure 2 The shores of Lake Poopo(Photo Lars Bengtsson).
POOPO LAKE, BOLIVIA 617
Also since the lake is a terminal lake, it means that notonly salt but all sorts of pollutants are trapped in the lake.On the mountain slopes at the eastern side of Lake Poopó,mine activities have been going on for centuries. There areleakage of water very high in heavy metals from miningponds and even more leakage from abandoned old mines.The high content of metals is visible from the color of thewater and the sediments in some of the small riversflowing into Lake Poopó. In spite of poor environmentalconditions, indigenous poor people living on the lakeshores still get their income from fishing.
The water balance of Lake Poopó is much determinedby the Desaguadero River flow. The flow from thisriver constitutes almost 70% of the water input to thelake, while the contribution from regional rivers is only
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Poopo Lake, Bolivia, Figure 3 Computed and observed (from satellite images and water stage) lake area of Lake Poopo(Drawn from data presented by Pillco and Bengtsson, 2006a).
618 POOPO LAKE, BOLIVIA
10–15%. Precipitation on the lakes, 370 mm per yearnonuniformly distributed, is about 20% of the water input.The water loss from evaporation is about 1,800 mm.
BibliographyArgollo, J., and Mourguiart, P., 2000. Late Quaternary climate
history of the Bolivian Altiplano. Quaternary International,72, 37–51.
Beveridge, M., Stanford, E., and Coutts, R., 1985. Metal concentra-tions in the exploited fishes of an endorheic saline lake in the tinsilver province of Bolivia. Aquaculture and Fisheries Manage-ment, 16, 41–53.
Boulange, B., Rodrigo, L. A., and Vargas C., 1978. Morphologieformation et aspects sedimentologiques du lac Poopó (Bolivie).Cahiers ORSTOM., Series Geologie X(1), 69–78.
Marin, R. P., and Quintanilla, J. A., 2002. Efectos Ambientalessobre las Pesquerias de los Ecosistemas de los Lagos Poopóy Uru-Uru. Report. University of San Andrés, Institute of Ecol-ogy, La Paz.
Minchin, J., 1882. Notes on a journey through part of the Andeantableland of Bolivia. Proceedings of the Royal GeographicalSociety of London, 4, 67.
Pillco Zolá, R., 2007. Response of Bolivian Altiplano lakes toseasonal and annual climate variations, PhD-thesis Rep. 1040Water Resources Engineering, Sweden, Lund University.
Pillco Zolá, R., and Bengtsson, L., 2006a. Long-term and extremewater level variations of the shallow Lake Poopó, Bolivia.Hydrological Sciences Journal, 51, 98–114.
Pillco Zolá, R., and Bengtsson, L., 2006b. Three methods for deter-mining the area-depth relationship of Lake Poopó, a large shal-low lake in Bolivia. Lakes & Reservoirs: Research andManagement, 12, 275–284.
Cross-referencesAral SeaHydrodynamics of Very Shallow LakesPlaya Lake Chains: The Example of the Yenyening Lakes of theUpper Avon River Catchment of Western AustraliaTiticaca LakeSouth America, Lakes ReviewWater Balance of Lakes
