The Origin of Shallow Lakes in the Khorezm Province, Uzbekistan, and the History of Pesticide Use Around These Lakes

J Paleolimnol DOI 10.1007/s10933-016-9914-2

ORIGINAL PAPER

The origin of shallow lakes in the Khorezm Province, Uzbekistan, and the history of pesticide use around these lakes

Michael R. Rosen . Arica Crootof . Liam Reidy . Laurel Saito . Bakhriddin Nishonov . Julian A. Scott

Received: 4 March 2016 / Accepted: 22 September 2016 Ó Springer Science+Business Media Dordrecht (outside the USA) 2016

Abstract The economy of the Khorezm Province in 150 years old, which supports a recent origin of the Uzbekistan relies on the large-scale agricultural pro- lakes. The thickness of lacustrine sediments in the cores duction of cotton. To sustain their staple crop, water analyzed ranged from 20 to 60 cm in all but two of the from the Amu Darya is diverted for irrigation through lakes, indicating a relatively slow sedimentation rate canal systems constructed during the early to mid- and a relatively short-term history for the lakes. twentieth century when this region was part of the Hydrologic changes in the lakes are evident from loss Soviet Union. These diversions severely reduce river on ignition and pollen analyses of a subset of the lake ﬂow to the Aral Sea. The Province has [400 small cores. The data indicate that the lakes have transitioned shallow (\3 m deep) lakes that may have originated from a dry, saline, arid landscape during pre-lake because of this intensive irrigation. Sediment cores conditions (low organic carbon content) and low pollen were collected from 12 lakes to elucidate their origin concentrations (in the basal sediments) to the current because this knowledge is critical to understanding freshwater lakes (high organic content), with abundant water use in Khorezm. Core chronological data indicate freshwater pollen taxa over the last 50–70 years. that the majority of the lakes investigated are less than Sediments at the base of the cores contain pollen taxa

M. R. Rosen (&) B. Nishonov Water Science Field Team, U.S. Geological Survey, 2730 Laboratory of Surface Water Quality Investigation, North Deer Run Road, Carson City, NV 89701, USA Hydrometeorological Research Institute, 72 K. e-mail: [email protected] Makhsumov Str., Tashkent, Uzbekistan 700052

A. Crootof Á J. A. Scott Present Address: Graduate Program of Hydrologic Sciences, University of A. Crootof Nevada Reno, 1664 N. Virginia Street, School of Geography and Development, University of Arizona, Mail Stop 0175, Reno, NV 89557, USA PO Box 210076, Tucson, AZ 857017, USA

L. Reidy Present Address: Department of Geography, University of California, J. A. Scott Berkeley, 507 McCone Hall #4740, Berkeley, CA 94720, U.S. Forest Service, Rocky Mountain Research Station, 2150 USA Centre Ave, Bldg. A, Suite 368, Fort Collins, CO 80526, USA

L. Saito Present Address: Department of Natural Resources and Environmental L. Saito Science, University of Nevada Reno, Mail Stop 186, 1664 The Nature Conservancy, One E. First Street, Suite 1007, N. Virginia Street, Reno, NV 89557, USA Reno, NV 89501, USA 123 J Paleolimnol dominated by Chenopodiaceae and Tamarix, indicating Despite the arid climate, Khorezm is one of the that the vegetation growing nearby was tolerant to arid most agriculturally productive regions in Uzbekistan. saline conditions. The near surface sediments of the An extensive network of canals (Fig. 2) supplies the cores are dominated by Typha/Sparganium,which Province with irrigation water throughout most of the indicate freshwater conditions. Increases in pollen of year (Wehrheim et al. 2008; Veldwisch 2008). Since weeds and crop plants indicate an intensification of Uzbekistan gained independence in 1991, the country agricultural activities since the 1950s in the watersheds has remained dependent on the cash flow from their of the lakes analyzed. Pesticide profiles of DDT agricultural exports, which make up approximately (dichlorodiphenyltrichloroethane) and its degradates 37 % of the country’s gross domestic product (Martius and c-HCH (gamma-hexachlorocyclohexane), which et al. 2009). With over 16,000 km of irrigation canals were used during the Soviet era, show peak concentra- in Khorezm, 3.5–4.0 km3 of water is diverted from the tions in the top 10 cm of some of the cores, where Amu Darya during the growing season and estimated ages of the sediments (1950–1990) are 1.0–1.5 km3 during the winter season to produce cash associated with peak pesticide use during the Soviet crops such as cotton, wheat and rice. Furrow irrigation era. These data indicate that the lakes are relatively is used for cotton, while flood irrigation is used for young (mostly \150 years old) and that without wheat and rice. Irrigation water that is not lost to irrigation and canal inputs from the Amu Darya, the evapotranspiration or groundwater is channeled into lakes would not exist as freshwater lakes. 9000 km of drainage canals throughout the Province (Oberkircher et al. 2011). Keywords Lake formation Á DDT Á HCH Á Over 400 lakes have been identified in the Province Limnogeology Á Central Asia Á Sediment cores of Khorezm (Kaiser 2005). These lakes are located in natural depressions in the landscape and some, but not all, have irrigation canals that supply water to the lakes in the summer. The north–south linear orientation of Introduction the lakes in the south Khorezm is due to their location in the depressions between dunes in the regional In arid regions of the world, perennial freshwater desert. Local residents believe the lakes have existed resources are scarce: high rates of evaporation often for thousands of years and the lakes currently have lead to the salinization of fresh water, particularly of both cultural significance and prestige in the commu- shallow lakes and groundwater. Where these arid nity (Oberkircher et al. 2011). Therefore, changes to landscapes support agriculture, it is important to agricultural practices that could affect the water understand the sustainability of freshwater resources. balance of these lakes must take into account the use One such arid landscape where water resource of these lakes and their sustainability. Water balance sustainability is a growing concern is the Khorezm studies on two lakes in Khorezm showed that without Province of Uzbekistan. Khorezm is in the Aral Sea the addition of surface water from irrigation canals, Basin and lies along the Amu Darya (‘‘darya’’ means the lakes were likely to desiccate after irrigation ends ‘‘river’’inPersian)insouthwesternUzbekistan (Scott et al. 2011). Although irrigation with Amu (Fig. 1). The Amu Darya has a watershed of about Darya water has existed in the region for more than 1,385,045 km2 and flows from glacial melt water in 2000 years (Tolstov 2005; Boroffka 2010), intensive the Pamir Mountains and Tian Shan historically to irrigation likely began in the early to mid-1900s, so it the Aral Sea, but no longer reaches the Aral Sea due is possible that the lakes are less than 100 years old. to withdrawals for irrigation. Khorezm covers an area Twelve lakes (‘‘kul’’ in the Uzbek language) were of 6050 km2 and is home to approximately 1.7 mil- chosen for this study (Fig. 1): Ata (ATA), Dovud lion residents (The Governmental Portal of the (DOV), Eshan Rabat (ESH), Gauk (GAU), Khod- Republic of Uzbekistan 2016). With annual precip- jababa (KHO), Koshkopyr (KOS), Nayman (NAY), itation averaging approximately 92 mm, Khorezm Sapcha (SAP), Shur (Koshkopyr) (SHK), Shur (Yan- predominately has an arid continental climate giaryk) (SHY), Tuyrek (TUY) and Xitoy (XIT). These (Le´tolle and Chesterikoff 1999;Wehrheimetal. study lakes are well distributed across the Province 2008). and are characteristic of the small (0.02–1.6 km2 123 J Paleolimnol

Aral Sea Kazakhstan

Caspian Sea Study Area

Uzbekistan Turkmenistan

Study Lakes Lakes Political Boundaries

Study Lake Abbreviations 1 XIT 2 KOS 3 SHK 4 KHO

Amu Darya 5 DOV 1 2 6 SAP 7 GAU 8 ESH 9 TUY 10 SHY 3 5 11 ATA 12 NAY 6 4 7 10

9 11 8 12

N West Central East

01020

Kilometers

Fig. 1 Map of the Khorezm region of Uzbekistan showing names corresponding to the abbreviations in the ﬁgure are: Ata lakes in the region (grey areas) and the locations of the lakes (ATA), Dovud (DOV), Eshan Rabat (ESH), Gauk (GAU), studied (black areas). Lakes are arbitrarily divided into West, Khodjababa (KHO), Koshkopyr (KOS), Nayman (NAY), Central, East locations for plotting purposes and to illustrate Sapcha (SAP), Shur (Koshkopyr) (SHK), Shur (Yangiaryk) how geographic location affects analysis of these lakes. Lake (SHY), Tuyrek (TUY) and Xitoy (XIT) area), shallow (\3 m deep) lakes found in Khorezm. acceptable standards by as much as 80 % (Severskiy Table 1 contains details about the size and land use et al. 2005; Fayzieva et al. 2004). Pesticide pollution around each lake. was presumed to be prevalent in the region because In addition to water availability, water quality is crops were historically sprayed with organochlorine also a concern in Khorezm because it can deviate from pesticides such as dichlorodiphenyltrichloroethane

123 J Paleolimnol

Lakes

Canals Political Boundaries

Amu Darya

N Kilometers 01020

Fig. 2 Map of the Khorezm region of Uzbekistan showing the the most part they are not visible through the irrigation canals. densely constructed irrigation and drainage canals in the region Location of irrigation canals are from the Zentrum fur (lakes are in grey areas). The map is the same area as shown in Entwicklungforschung (ZEF) Fig. 1. The lakes studied are not plotted on this map because for

(DDT) and gamma-hexachlorocyclohexane (c-HCH, DDT in water is pH and temperature dependent. Wolfe better known as Lindane) (Galiulin and Bashkin et al. (1977) found DDT to have a half-life of 8 years 1996). While DDT and HCH will degrade by micro- with a pH of 7 and a temperature of 27 °C. Degrada- bial and abiotic decomposition, these pesticides are tion of both DDT and HCH occurs primarily by known to be persistent and can still be found in water biological processes; Sharom et al. (1980) found DDT bodies, soils and the atmosphere worldwide long after and HCH to be degraded much more quickly in water application (Smol 2008; Rosen and Van Metre 2010; when microbes were present. Korosi et al. 2015). In soils, DDT has a recorded half- Several studies have investigated the presence of life of 2–20 years depending on local temperature, soil DDT and HCH in humans, water, and surface type, pH, redox potential, moisture and organic carbon sediment samples in the lower Amu Darya region. content. HCH, which is much less persistent, has an Beginning in 1987, the Central Asian Science average half-life in topsoil of 2 months (Manz et al. Research Institute of Irrigation conducted a study to 2001). Because DDT is highly insoluble, it is not assess the ecological and toxicological situation in usually present in high concentrations in the water lakes and reservoirs in the lower Amu Darya region. column, but will accumulate in bed sediments (Zweig Jensen et al. (1997) found high concentrations of et al. 1999; Hill and McCarty 1967). The hydrolysis of metals and pesticides in the blood of children living in

123 J Paleolimnol

Table 1 General information about the lakes studied, including percent agricultural land around each lake determined from satellite imagery from 2002 to 2006 supplied by C. Conrad Lake name and Area of ﬁelds Lake area Buffer Cotton Rice Wheat– Wheat– Wheat– Agriculture abbreviation used within 0.5 km (m2) size (m2) (%) (%) rice (%) other Fallow (total %) in text of lake (m2) crop (%) (%)

Eshan Rabat, ESH 4,318,997 1,584,779 5,903,776 6.60 1.89 0.00 0.00 0.00 8.49 Sapcha, SAP 1,437,084 66,708 1,503,792 22.22 0.00 0.00 0.00 0.00 22.22 Koshkupyr, KOS 1,321,057 71,343 1,392,400 24.00 8.00 0.00 4.00 0.00 36.00 Gauk, GAU 2,925,062 1,196,442 4,121,504 25.68 4.05 2.70 6.76 1.35 40.54 Shur (Koshkupyr), SHK 2,520,212 487,372 3,007,584 16.67 0.00 3.70 16.67 3.70 40.74 Shur (Yangiaryk), SHY 1,286,637 50,067 1,336,704 25.00 12.50 0.00 4.17 0.00 41.67 Tuyrek, TUY 1,756,635 192,725 1,949,360 14.29 11.43 2.86 11.43 2.86 42.86 Xitoy, XIT 2,981,545 304,519 3,286,064 32.20 10.17 1.69 10.17 5.08 59.32 Khodjababa, KHO 1,768,577 236,479 2,005,056 36.11 13.89 5.56 5.56 0.00 61.11 Dovud, DOV 2,412,139 539,749 2,951,888 32.08 7.55 7.55 18.87 1.89 67.92 Nayman, NAY 2,177,317 161,915 2,339,232 23.81 40.48 2.38 16.67 7.14 90.48 Ata, ATA 1,631,098 95,478 1,726,576 48.39 25.81 12.90 6.45 0.00 93.55

the Aral Sea Basin of Kazakhstan that had signs of early to mid-1900s when the region was part of the disease. The UNESCO Aral Sea Project (1992–1996) Soviet Union. Understanding the origin of these lakes and INTAS 1039 Project (2002–2003) continued this is important to provide guidance for the development research and found that between 1989 and 2002 there of water management strategies in this water-scarce was a sharp decrease in RDDT and RHCH concentra- region, as changes to land and water management tions in water and bottom sediment samples from the could change the hydrology and water balance of the Amu Darya delta (Karimov et al. 2005). These studies lakes (Scott et al. 2011), potentially leading to provide information about water quality in the Amu desiccation and introduction of potentially toxic lake Darya delta region, but do little to quantify pesticide bed material to the air. This study is the first, to our concentrations in Khorezm even though this region knowledge, to assess the origin of these lakes, and the was also subjected to large quantities of agrochemicals historical role they play in the hydrology of the region. when it was part of the Union of Soviet Socialist We hypothesized that the lakes are young (\100 years Republics (USSR or Soviet Union). The rapid old) based on the amount of irrigation that is used in decrease in pesticide concentrations in Amu Darya the region, and that non-polar pesticides such as delta sediments (Karimov et al. 2005) may have also RDDT and RHCH should be present in sediment cores occurred in the lake sediments in Khorezm. Quanti- at concentrations reflecting the Soviet use of these fying pesticide pollution in the lakes, particularly for pesticides in the 1950s to 1980s. The objectives of this RDDT and RHCH, provides valuable information study were to use sediment cores to determine the age about the biological functions and human health of the lakes using 210Pb and 137Cs dating and to concerns associated with the lakes. Throughout this analyze the lake sediment cores for RDDT and RHCH paper RDDT refers to the sum of DDT and its major at small enough intervals to determine the timing of metabolites dichlorodiphenyldichloroethylene (DDE) peak pesticide application. and dichlorodiphenyldichloroethane (DDD). Simi- larly, RHCH is defined as the sum of c-HCH and a- HCH isomers. Materials and methods Although irrigated agriculture has existed in the Khorezm region for at least 2000 years (Tolstov Twelve lakes (Fig. 1) in Khorezm, Uzbekistan were 2005), intensive irrigation in Khorezm began in the cored from 2008 to 2010 using a home-made coring 123 J Paleolimnol platform and a custom engineered percussion corer. accurate results. However, 210Pb could be used to While this technique may have smeared the sediment– check ages calculated using 137Cs in 10 of the 15 cores. water interface, we are confident that the down-core One lake core (XIT) had no 137Cs peak or useable record is representative of the history of each lake due 210Pb profile (there wasn’t logarithmic decay of the to consistent trends seen in the sedimentological and 210Pb data), and the March 2008 KHO core had a small pesticide records discussed below. TUY and KHO 137Cs peak near the surface of the lake sediments, were cored on two occasions, in March and July 2008. indicating that sediment from the top of XIT and one Cores were taken from the edge of the lakes in March of the KHO lake cores was likely eroded. The age of and from the lake centers in July. The lake edge cores XIT and its sedimentation rate could not be deter- were taken to determine whether the lake centers’ core mined because of the lack of useable 137Cs peak and profiles were consistent across the entire lake. All 210Pb data (see Rosen et al. 2016), but the data are other lakes were cored once near the deepest area of included to show patterns with depth. However, 210Pb the lake. Penetration into lakebed sediment was data for GAU gave reasonable sedimentation rates, generally greater than 1 m. Cores were cut to the and these were used for calculating the age of the lake. sediment–water interface in the field and packed with Based on the difference between 210Pb and 226Ra, sorbent material to prevent movement of the sediment background 210Pb activities are around 20 Bq/kg. within the core barrels. Cores were kept cold and Constant rate of supply (CRS) method was used for vertical at all times during storage and transport to simplicity and comparability between 137Cs and 210Pb. Tashkent, Uzbekistan, for analysis. In Tashkent, the Where both 137Cs and 210Pb sedimentation rates could cores were sliced into 2.5 cm sections and visual be calculated for the same lake, the average rate was identification of clay and sand units were made during used to calculate ages. The global 1964 above-ground slicing. As described in detail below, all cores were nuclear testing 137Cs peak was used as the primary analyzed for 210Pb and 137Cs at Eawag, ETH, marker for the 137Cs model, with the time the lake core

Switzerland. Loss on ignition (LOI550), and pesticides was collected as the other marker. In 3 cores (SHY, were analyzed at the Laboratory of Surface Water NAY, and KHO), a small spike in the 137Cs activity Quality Investigation, Hydrometeorological Research above the 1964 peak may be the result of the 1986 Institute, Uzbekistan. Cores from ESH, KOS, and XIT Chernobyl accident (Appleby 2001) that spread 137Cs were analyzed in detail for pollen at the Paleocology over much of Europe and parts of Asia (see Rosen Laboratory, University of California, Berkeley, USA, et al. 2016). These peaks were used as additional with supplemental data from the top and bottom of the controls in these cores. Samples were dried, homog- cores from DOV, SHK, and ATA used to verify enized, and analyzed using a gamma counting spec- interpretations from the detailed examination. All data trometer using methods presented in Appleby (2001). used in this assessment of the lakes are available at Results of 137Cs and 210Pb counting are presented in Rosen et al. (2016). Rosen et al. (2010) and Table 2. Dates are plotted on diagrams as averages of 137Cs and 210Pb calculated 210Pb and 137Cs age dating of the cores ages where both methods allowed calculation of ages.

Individual 2.5 cm thick slices of core sediments from Loss on ignition each core (5.0 cm thick slices were used for the March

2008 TUY core) were analyzed at ETH-Eawag For loss on ignition (LOI550), sediment samples were Aquatic Research labs (Switzerland) from the top dried at 105 °C for 6 h until constant weight was down until no detection or low detection of 210Pb or obtained to remove water. The weight was recorded 137Cs was encountered. Data from 210Pb analyses did and the sample was then placed in a mufﬂe furnace at not always show consistent exponential decay in some 550 °C for 6 h (Heiri et al. 2001). The difference in of the lakes sampled. These results could be due to weights between the sample dried at 105 °C and the (a) physical or biological mixing at the surface; weight after the sample was placed in the mufﬂe 210 (b) changes in the Pb supply due to changes in the furnace determined the LOI550 percentage. Samples patterns of sediment focusing (Appleby 2001)or were not treated with HCl because this could remove (c) core slices that were vertically too thick to get some organic material (Beasy and Ellison 2013) and 123 Paleolimnol J

Table 2 Age determinations for the lakes studied using 137 Cs and 210 Pb constant rate of supply methods Date/location of cores samples 137 Cs Age dating 210 Pb age dating with CRS model Mean of 137 Cs and 210 Pb Date core Lake abbreviation Location of Mud Depth of Sed. rate Number of Date of Sed. rate Number of Date of Mean was (see text for lake core in the depth 137 Cs peak (cm/year) years to lake origin (cm/year) years to lake origin sedimentation collected names) lake (cm) in core bottom of (calendar bottom of (calendar rate (cm/year) (cm) lake sediment years) lake sediment years)

Mar-08 KHO1 Edge 37.5 20 0.45 82 1926 ?? ? Jul-08 KHO2a Center 25 Cesium peak at top of core 0.22 114 1894 Jul-08 SHK Center 50.0 22.5 0.51 98 1910 0.73 70 1938 0.61 Mar-08 TUY1 Edge 30.0 15 0.34 88 1920 0.35 86 1922 0.35 Jul-08 TUY2 Center 30.0 7.5 0.17 176 1832 0.35 86 1922 0.26 Jul-08 TUY3 Center 35.0 7.5 0.17 205 1803 0.27 130 1878 0.22 2009 ATA Center 27.5 12.5 0.28 99 1909 0.34 80 1929 0.31 2009 GAUb,c Center [70 Cesium peak at top of core 0.27 259 1750 0.14 2010 NAY Center 45.0 32.50 0.71 64 1945 0.64 70 1940 0.67 2010 SAPb Center [62.5 12.5 0.27 230 1780 ?? ? 2010 SHY Center 20.0 10.00 0.22 92 1918 ?? ? 2010 XITa Center 47.5 Cesium peak at top of core ?? ? 2010 ESH Center 45.0 12.5 0.27 166 1844 0.36 125 1885 0.32 2010 DOV Center 50.0 12.50 0.27 184 1826 ?? ? 2010 KOS Center 45.0 7.50 0.16 276 1734 0.10 450 1560 0.13 ‘‘?’’ indicates inconsistent 210 Pb activities obtained down core, so no sedimentation rate could be generated a May be eroded at the top b Age to bottom of core–clay all the way to bottom c May be eroded at the top of the core or the cesium peak is below 70 cm depth 123 J Paleolimnol all lakes except ESH, which had calcium carbonate slices were homogenized as wet sediment and then air- precipitated around macrophyte stems in the near dried at 20 °C. Double extraction of pesticides from surface sediments, were undersaturated with respect to the sediment was done using n-hexane ? acetone. carbonate minerals. LOI550 is used here as a qualita- Sample cleanup was conducted using concentrated tive assessment of organic carbon content of the sulfuric acid for elimination of organic substances. sediments because LOI550 percentages can be affected Extracts were dried with Na2SO4, reconcentrated, and by lithology (Santisteban et al. 2004). However, trends injected into an Agilent 6890 chromatograph with a down core can be useful and comparable using the capillary column. In addition, the absolute dried bulk same LOI550 method for lakes from the same geologic density of the sediment was determined by weighing setting with a similar lithology, as is the case for the homogenized and air-dried samples after they were sediments from the lakes studied. Replicates were heated in a muffle furnace at 105 °C for 6 h. Samples analyzed on 10–20 % of samples analyzed. Agree- were checked to ensure that the recorded weights were ment was generally within 10 %. In figures included constant. Replicates were analyzed on 1–3 samples in here, replicate data are plotted as the average of the most cores and results are generally within 25 % of replicates. each other. A blank, using bottled water, was run on one occasion and no RHCH or RDDT was detected, Pollen analysis but because some RHCH and RDDT were detected in many samples of prelacustrine sands, where detections Standard pollen extraction and preparation procedures would not be expected, low concentrations of RHCH were followed (Faegri and Iversen 1989). One tablet and RDDT (below 5 lg/kg for RDDT and below containing approximately 20,848 Lycopodium spores 2.5 lg/kg for RHCH) were considered as background was added to each sample for control purposes and not environmentally relevant. In figures, replicate (Stockmarr 1971). Samples were sieved with a data are plotted as the average of the replicates. 125 lm mesh filter to remove large debris and processed with the following treatments: hydrochloric acid, potassium hydroxide, hydrofluoric acid, iso- Results propanol wash, nitric acid, glacial acetic acid, and acetolysis. The residues were stained with safranin, Age dating dehydrated with tertiary butyl alcohol, suspended in silicone oil, and mounted on microscope slides. Pollen The lacustrine sediment in all of the lakes except GAU was counted at the 4009 magnification with 10009 to and SAP is B50 cm. Below 50 cm depth, all cores determine fine detail. Pollen grains and fern spores penetrated relatively clean sand that formed from were identified to the lowest possible taxonomic level either riverine or eolian processes. Cesium-137 pro- using the UC Berkeley Museum of Paleontology’s files for all the lakes show that all of the 1964 above- collection of over 10,000 modern pollen samples and ground testing 137Cs peak activities are shallower than published pollen keys (McAndrews et al. 1973; Kapp 22.5 cm from the sediment–water interface (Table 2), et al. 2000). Unknown grains were noted and drawn. except for NAY core, which is at 32.5 cm depth. Lakes Damaged, torn or crumpled grains that were uniden- SHY, NAY, and KHO (lake center core), show a small tifiable were counted as ‘‘Indeterminate’’. A minimum 137Cs peak between 2.5 and 5.0 cm depth, 17.5 and of 400 grains were counted for at least 9 samples on 20 cm depth, and 7.5 and 10 cm depth, respectively, cores from KOS, XIT, and ESH. Pollen counts were which are interpreted to be the spike from the 1986 compiled and plotted using the CALPALYN program Chernobyl accident. The small Chernobyl peak is (Bauer et al. 1991). almost exactly half-way between the surface (2008 or 2010) and the 1964 137Cs peak in all three cores. The Pesticide analyses maximum age of the lakes calculated using the 137Cs sedimentation rates is 276 years before collection of The methodology used to analyze pesticide residues in the cores, and the minimum age is 64 years. sediments followed the standard techniques used by Lead-210 CRS models were constructed for 10 of Uzhydromet (RD 52.24.71-88 1988). Core sample the cores, but only eight have 137Cs profiles that can be 123 J Paleolimnol

210 210 compared to the Pb profiles. All of the Pb- also had LOI550 decreasing to 3.7 % (from [17 % at calculated sedimentation rates are similar to those the top of the core), indicating that the transition to calculated using 137Cs peaks. Sedimentation rates non-lacustrine sediments was not far below the bottom range from 0.10 to 0.73 cm/yr and those sedimenta- of the core. Several cores show a slowdown of tion rates that can be compared by using duplicate increasing LOI550 around 1970–1990, with a final cores from the same lake are B0.22 cm/yr different increase in LOI550 in the last 20 years or so. (Table 2). Given this potential error in sedimentation rate, each centimeter of core could be in error by Pollen 5 years in each direction, so dates are a minimum of ±10 years per centimeter of core, and more likely Selected major pollen and spore profiles were devel- ±20 years, if other errors such as mixing are incor- oped for three of the lakes (KOS, ESH and XIT) and porated. The maximum age of the lakes calculated are displayed in Fig. 4a–c and used to discuss the using the 210Pb models is 450 years prior to core results of the record. Pollen concentration is measured recovery and the minimum age is 70 years. Some as grains/cm3 (see Rosen et al. 2010). Preliminary lakes have younger ages with sedimentation rates pollen data from the bottom, middle and top sections calculated from 137Cs peaks compared to ages derived of two additional lakes (ATA, DOV and SHK) are from 210Pb others have younger ages calculated with presented in Rosen et al. (2010). 210Pb models compared to 137Cs derived ages (see Table 2). Koshkopyr There appear to be three groups of lake ages for the onset of lacustrine sedimentation. Older lakes (SAP, Two pollen zones were defined for the KOS record KOS and possibly GAU) appear to have formed before (Fig. 4a) based on changes in the abundance of certain 1800. Other lakes appear to have begun forming aquatic and riparian pollen types and the first appear- between 1880 and 1920 (ESH, SHK, KHO, and TUY), ance of several agricultural and weedy pollen types. and still others appear to have formed between 1930 Changes and reversals in the aquatic and riparian and 1960 (NAY, DOV, ATA, and SHY). One lake record reflect local environmental change and natural (XIT) could not be assigned to any groups because age plant succession in the lake. The overall pollen record models could not be constructed for this lake because shows variation through time, especially for the last there was no real 137Cs peak and 210Pb did not decay one hundred years. exponentially (see Rosen et al. 2016). It is possible that sediment at the top of XIT was eroded during past low Zone 2: ca. 1840–1900 (22–15 cm) The high lake levels. However, XIT transitioned from sand to percentages of Chenopodiaceae (Goosefoot family) lake muds by 50 cm depth, indicating a time of ([40 %) and Tamarix (salt-cedar) (*20 %) at the formation that is similar to the other lakes that were bottom of this zone (Fig. 4a) indicate that plants dated, assuming erosion did not remove more than adapted to dry saline conditions were locally common. 20 cm of sediment from the lake. Low percentages (\1 %) of tree pollen Juglans (walnut), Pinus (pine) and Populus (aspen) suggests Loss on ignition an open environment with few trees. The presence of large Poaceae (grass family) pollen with a size range Loss on ignition data show dramatic increases in the of 42–51 lm (Chaturvedi et al. 1998) reflects the organic matter component of the sediment once cultivation of Oryza sativa (Asian rice) locally. Pollen lacustrine sedimentation begins in all lakes (Fig. 3a– concentrations in this zone average 30,000 grains/ 3 d). LOI550 values range from 5 to 23 % at the tops of cm . the cores, and between 3.7 and 0.6 % in the sand at the bottom of the cores. The GAU core consisted of mud Zone 1 ca. 1901–2010 (15–0 cm) The pollen record down to 70 cm depth, however, the LOI550 decreased changes dramatically in zone 1. It is characterized by from 7 % at the top of the core to 1.7 % at the bottom sharp decreases in both Chenopodiaceae and Tamarix of the core, indicating that the transition to sand was and the first appearance of weedy and additional crop likely not far below this depth. Similarly, the SAP core pollen types. Rumex acetosella and Plantago 123 J Paleolimnol lanceolata both appear at 15 cm. Solanum spp. record. Chenopodiaceae is the dominant pollen type (potato) pollen appears at the 12.5 cm level while throughout the core and averages between *30 and Malvaceae (cotton) first appears at the 10 cm interval. 40 % between 30 and 0 cm. Pollen concentrations are Typha/Sparganium (cattails) steadily increase from variable and range between 10,000 and 70,000 grains/ *10 % at the base of this zone to over 40 % in the cm3. near surface sediments. There is a slight increase in Populus between 12 and 5 cm to 3 % of the pollen Xitoykul The XIT core is undated but there are some sum but it drops again towards the top of the zone to similarities with the KOS record (Fig. 4c). \1 %. Pollen concentrations average close to Chenopodiaceae, Tamarix, and Poaceae are the 64,000 grains/cm3 in this upper section. dominant pollen types in the lower part of the record but all decrease towards the top. Typha/Sparganium is Eshan Rabat The general ESH pollen record low (7 %) in the basal sediments but increases to (Fig. 4b) does not change significantly during the almost 60 % of the pollen sum above the 7.5 cm level. past 100 years. Weed (Rumex spp., Plantago The pollen of Myriophyllum (water mil-foil) averages lanceolata) and crop pollen (Solanum spp., 8 % in the basal sediments and then declines all the Malvaceae, and Oryza sativa) types are present way to the surface. Myriophyllum is an emergent throughout the record from the basal sediments aquatic that does well in shallow water environments. (30 cm) to the top of the core. There is a sharp Weedy pollen (Rumex acetosella; Plantago increase in Poceae pollen in the upper 2.5 cm of the lanceolata) first appear at or above 20 cm. Monolete

Fig. 3 Loss on ignition (LOI550) percentages for all lakes Khorezm. Dashed lines show where sand is located in the studied plotted by calendar years, except XIT, which is plotted bottom of the cores. Lacustrine sedimentation begins where the by depth. a Lakes located in the western, b central, and c eastern line becomes solid. Due to uncertainties in the age models, part of Khorezm. d The 3 cores taken in TUY from the edge and errors in age dates may be as high as ± 20 years (see text for center part of the lake. TUY is located in the eastern part of explanation) 123 J Paleolimnol

A Koshkopyr TREES RIPARIAN & AQUATICS HERBS & SHRUBS AGRICULTURAL

3 lanceolata spp. acetosella grains/cm CHRONOLOGYYears A.D. Populus Juglans Pinus Salix Tamarix Typha/ Sparganium CYPERACEAE Myriophyllum CHENOPODIACEAE POACEAE ASTERACEAE Monolete SporesOrzya sativa MALVACEAEPlantago Solanum Rumex Pollen Concentration 0

2000 2

1981 5

1961 8

1942 10 Zone 1 1923 12 Depth in cm. 1904 15

1885 18 1865

20 Zone 2

1846 22 02 01 010105101520015304503040 10203040 010 0101 024 010101010 50,000 % Total Pollen and Spores B Eshan Rabat TREES RIPARIAN & AQUATICS HERBS & SHRUBS AGRICULTURAL

spp. grains/cm Pollen Concentration Solanum Rumex acetosella CHRONOLOGYYears A.D.Populus Juglans Pinus Salix Tamarix Typha/ CYPERACEAEMyriophyllum CHENOPODIACEAE POACEAE ASTERACEAE Monolete SporesOrzya sativa MALVACEAEPlantago lanceolata Sparganium 0 2006 2 1998 5 1990 8 1982 10 1974 12 1967 15 1959

Depth in cm. 18 1951 20 1944 22 1936 25 1928 28 1920 30 02 0203 0240 5 10 15 20 25 30 0 5 10 15 20 024 040 1020304001020 010240120102 01201 0 50,000 C % Total Pollen and Spores Xitoykul TREES RIPARIAN & AQUATICS HERBS & SHRUBS AGRICULTURAL

3 spp. lanceolata acetosella

grains/cm PopulusJuglans Pinus Salix Tamarix Typha/Sparganium CYPERACEAEMyriophyllum CHENOPODIACEAE POACEAE ASTERACEAEMonolete SporesOrzya sativa MALVACEAESolanum Plantago Rumex Pollen Concentration 0

Depth in cm. 20

35 02010101 0 5 10 15 0 15304560 03 0480 10203001020 010102 010101010 35,000 70,000 % Total Pollen and Spores Fig. 4 Selected pollen and spore taxa for a KOS, b ESH, and c XIT. Due to uncertainties in the age models, errors in age dates may be as high as ± 20 years (see text for explanation) 123 J Paleolimnol spores (ferns) are found throughout the length of the two of the lakes, and extrapolation of even these record along with the pollen of Orzya sativa. poorly constrained ages does not make the lake Malvaceae only appears at the 25 cm level, while sediments older than a few hundred years. In addition,

Solanum appears above the 20 cm level. Pollen the LOI550 data for both SAP and GAU are\5 % and concentrations average 20,000 grains/cm3 below decline near the base of the cores, possibly indicating 30 cm while concentrations increase towards the top that pre-lacustrine conditions are not far from the base of the record to an average of about 60,000 grains/ of these cores. cm3. The reason for the variable ages of the lakes is difficult to determine as there is no clear pattern. The Pesticides variability may reflect either poor age control in some of the lakes caused by variable smearing of 210Pb or Pesticide concentrations in all cores are relatively low 137Cs peaks, or other mechanical or chemical diffusion compared to lakes worldwide (for example see Elpiner or mixing within the lake. Klaminder et al. (2012) 1995; Rosen and Van Metre 2010), \10 lg/kg for found that cesium deposited during the Chernobyl both RDDT and RHCH, except for a few samples from accident migrated down core, obscuring the 1964 TUY, ESH, and DOV (Figs. 5a–d, 6a–d). Concentra- global peak in a lake located near Chernobyl that tions were generally highest in the upper part of the received high amounts of fallout from the accident. cores, generally from 1960 to 1990 for RDDT. Spikes While the lakes in Uzbekistan were not in the path of of higher than background concentrations are partic- high fallout from Chernobyl (Po¨lla¨nen et al. 1997), ularly noticeable in ESH, TUY, and SHK for RDDT, some of the lakes may show possible Chernobyl peaks and in DOV, TUY, SHY and SHK for RHCH. In 5 of (e.g., NAY and SAP). This may indicate some the lakes, the highest RHCH concentrations are at the downward migration of cesium in these lakes. In top of the cores (DOV, SAP, KOS, SHY, and SHK). some lakes, the first deposited muds may represent There is no apparent correlation between pesticide natural depressions that may have been playas or concentrations in the lakes and percentage of recent ephemeral saline lakes. Salt was visually identified in agricultural lands around the lakes (Table 1). ESH, KOS sediments, which is an indication of a saline past which has the lowest agricultural land use around the for this lake, and the calculated age for the start of lake, has the highest RDDT concentration of any of the lacustrine sedimentation is older in KOS than the other lakes (Table 1). However, the only surface water lakes. Other possible causes of the variability is inflow to the lake is a drainage canal, which contains mixing of sediment due to human and/or animal the runoff and groundwater from upstream agricultural disturbance, or eroded sediment being washed into the fields. lakes in the suspended load via irrigation water and being deposited on or mixed with younger aged sediments. However, except for a few cases (i.e., TUY Discussion cores), calculated 137Cs and 210Pb ages are consistent (within 20–40 years) Alternatively, irrigation may Age dating have a much longer history in the region. There is limited knowledge of pre-Soviet irrigation canals that The age models constructed from 137Cs and 210Pb could go back more than 2000 years (Tolstov 2005; dating are relatively consistent, but are somewhat Boroffka 2010). However, the distribution of lakes simplistic (CRS model only). This is because the formed prior to 1900 appears random and does not decay curves of unsupported 210Pb are not always suggest any regional trend. In contrast, three of the exponential and so may have some error associated younger lakes, which formed post-1900 (NAY, ATA, with the dates. In some cases, 137Cs peaks are not sharp and SHY) cluster in the eastern area of Khorezm and so may not provide an exact date for the 1964 (Fig. 1). Historical data on where and how much global atmospheric testing peak. However, even with irrigation was used in the region was not collected in these uncertainties, it is clear that the lakes have not most parts of Khorezm because water meters were not existed for thousands of years because the thickness of in place, and in some areas still are not used. Without lacustrine sediment in the lakes is \60 cm in all but information on the historical use of irrigation in 123 J Paleolimnol

Fig. 5 Concentrations of RHCH for all lakes studied plotted by line becomes solid. Dashed vertical line at 2 lg/kg is the calendar years, except XIT, which is plotted by depth. a Lakes concentration above which the concentrations are above located in the western, b central, and c eastern part of Khorezm. analytical background concentrations and may be environmen- d Concentrations of RHCH for the 3 cores taken in TUY from tally relevant. Due to uncertainties in the age models, errors in the edge and center part of the lake. TUY is located in the eastern age dates may be as high as ± 20 years (see text for part of Khorezm. Dashed lines show where sand is located in the explanation) bottom of the cores. Lacustrine sedimentation begins where the

Khorezm, it is impossible to determine precisely the likely began forming around 1920 as indicated by the date of origin of the lakes. However, as discussed 210Pb, rather than at the earlier dates calculated from below, the 12 study lakes appear to have started out as the 137Cs of the lake center cores. natural depressions, possibly with saline water con- The 2 cores from KHO show different issues as tributing to the depressions before irrigation began. compared to the TUY cores. For the KHO cores, the Two lakes (TUY and KHO) had multiple cores core taken near the center of the lake has no 137Cs dated and analyzed (Table 2). For lake TUY, one was peak, indicating either erosion or dredging of the lake taken on the edge of the lake (TUY-1) and 2 cores were because the lake muds are thin in this core (25 cm) taken in the center of the lake (TUY-2 and TUY-3). compared to the lake edge core that is 37.5 cm thick. The core from the edge of the lake has a younger age Although an age of the lake for the basin center core calculated for the bottom of the core using a 137Cs can be determined from the 210Pb data, the age is likely peak at 7.5 cm depth for both lake center cores. overestimated due to missing sediment and possible However, TUY-2 core has a 210Pb age that is similar to mixing, although this age is used for plotting purposes. the age of the lake edge core using the 137Cs peak, and The ages calculated for both cores differ by 35 years., TUY-3 has a 210Pb age that is about 40 years older. It Due to the missing top of the lake center core, the 1926 may be that the ages indicated by the 137Cs data of both age for the lake edge core is more consistent with the lake center cores are too old and that the lake more age of lacustrine deposition of muds in the majority of

123 J Paleolimnol

Fig. 6 Concentrations of RDDT for all lakes studied plotted by line becomes solid. Dashed vertical line at 5 lg/kg is the calendar years, except XIT, which is plotted by depth. a Lakes concentration above which the concentrations are above located in the western, b central, and c eastern part of Khorezm. analytical background concentrations and may be environmen- d Concentrations of RDDT for the 3 cores taken in TUY from tally relevant. Due to uncertainties in the age models, errors in the edge and center part of the lake. TUY is located in the eastern age dates may be as great as ± 20 years (see text for part of Khorezm. Dashed lines show where sand is located in the explanation) bottom of the cores. Lacustrine sedimentation begins where the other lakes studied and with the timing of increased within 30 years. The steady increase in LOI550 in the irrigation during the period of the Soviet Union. last 30–50 years indicates that the lakes are becoming more productive and that perennial relatively fresh

Lacustrine sediments and LOI550 water is present in the lakes. The increasing productivity means that more water and nutrients are The short length (\60 cm) of the lacustrine sediments available to the lakes. Stratigraphic increases in in most of the cores except for GAU and SAP suggests organic carbon content (related to higher lake produc- a short depositional history for the lakes. Sharp tivity) coincided with the peak of Soviet expansion of increases in LOI550 occur in all lakes above basal irrigation between 1951 and 1991, and it is likely that quartz sands, and the percentage of organic matter this expansion of irrigation and fertilizer use has present in the muds increase to the surface, except in allowed for the increased productivity in these lakes.

GAU (Fig. 3a–d). In most lakes, LOI550 percentages The three cores from TUY show similar patterns to are highest since 1950 when most irrigation was the other cores, with much higher LOI550 percentages occurring. LOI550 percentages in all lakes are below at the top of the cores. However, increases in LOI550 10 % before 1950 (except for a few samples just above are not steady in these cores (Fig. 3d) and there is a

10 % in GAU), and after 1950 many lakes show steady period between 1930 and 1970 where LOI550 does not increases in LOI550, with some lakes reaching 20 % increase, particularly in the cores taken near the center 123 J Paleolimnol

of the lake. LOI550 then increases sharply in the last contain lower pollen concentrations possibly due to 30 years or so. The cause for the constant LOI550 the high sand content in these sections of the cores. period in TUY is not known, but some of the other While rice pollen is encountered at all levels, the lakes (e.g., SAP, NAY, and ESH) also have this period first appearance of weedy pollen and other plant crops of constant LOI550 at about the same time. It may be (cotton and potatoes) occur near the top of the cores related to water availability or longer-term climate and become more abundant, likely reflecting intensi- changes, but given how heavily water is manipulated fication of agricultural activities after freshwater in this region, it is more likely caused by changes in inputs from irrigation to the area. The transition to water availability to these lakes. pollen types dominated by freshwater plants in the sediment is concomitant with the greater carbon Pollen content of the upper sediments, and higher pollen concentrations overall at both sites. The combination For the purposes of the discussion we examine the of these factors demonstrates that the lakes are KOS and the undated XIT record together as both have becoming fresher and more productive over time. similar recent paleoecological histories. The pollen The lack of pollen variation in ESH may be content of the basal sediments in both KOS and XIT explained by its position on the border of the irrigated records the composition of the vegetation growing in area in Khorezm (Fig. 1). There is little irrigated land the area prior to the establishment of the lakes, and around the lake, and the lake receives only irrigation initial plant succession once the water bodies became drainage water and has no outlet (Crootof et al. 2015). permanent. Low percentages of tree pollen (Pinus, The lake water is currently hyposaline to hypersaline Juglans, Populus, and Salix) in both records suggest (8 g/L up to 50 g/L) depending on the season and trees were not locally common at the time of lake water supply to the lake. During drought conditions, formation. The abundance of Chenopodiaceae and evapotranspiration is high and salinity increases Tamarix in the lower sections of both records suggest substantially compared to the other lakes studied here that these lakes initially had arid environments as both (Crootof et al. 2015). Increased aridity is detrimental are characteristic of saline soils. The Chenopodiaceae to the preservation of pollen, which may be another is relatively floristic rich (4.2 %) in the arid and semi- factor in the lack of pollen variation observed in ESH. arid zones across Uzbekistan while Tamarix, a salt Thus, variations in pollen types are more variable and tolerant species, is common in high saline water less definitive than the other lakes. table sites (Gintzburger 2003). The desert soils of Preliminary data from DOV and ATA both show Uzbekistan have evolved under semi-arid and arid that they have similar paleoecological histories to conditions and have been intensively studied for their KOS and XIT, as they are initially dominated by plants agricultural development due to the availability of adapted to arid environments and eventually replaced irrigation water (Le´tolle and Mainguet 1993). by plants adapted to more freshwater conditions. SHK Following freshwater inputs from irrigation there is is similar to the ESH site as there is little variation in a dramatic increase in Typha/Sparganium and corre- the down-core pollen record. sponding decreases in Chenopodiaceae and Tamarix. This change in vegetation provides evidence for the Pesticide occurrence transition to freshwater environments reflected by natural plant succession in and around the lake. The pesticides DDT and HCH were used extensively in Myriophyllum is present at both sites but at different Uzbekistan in general and in Khorezm specifically abundances in the early part of both lake histories. The from the 1950s through 1991 (when Uzbekistan gained low levels of Myriophyllum at KOS suggest that the its independence). In the late 1970s, the total amount of lake filled in quickly when irrigation water became pesticides used in Central Asia generally was between available. At XIT Myriophyllum persists for longer in 30 and 35 kg/ha, almost 30 times higher than in the rest the basal sediments suggesting the lake existed as a of the former Soviet Union during this time (UNESCO shallow pond initially before the lake became deeper 2000). Therefore, high concentrations of these pesti- and more permanent. In general, the basal sediments cides might be expected in soil and lake sediments.

123 J Paleolimnol

The low concentrations of pesticides found in the likely due to its non-use after 1983, or to the possibility lakes studied is surprising given the history of that other less-expensive pesticides have been used pesticide use in the Aral Sea Basin during the Soviet instead since 1983. era (see for example Galiulin and Bashkin 1996; Concentrations of both RDDT and RHCH are To¨rnqvist et al. 2010). However, pesticides in greater than background concentrations in pre-lacus- Khorezm may not travel far. The region is arid with trine sands in the core taken from the center of TUY little rainfall and runoff into the lakes. The landscape (TUY-2), and concentrations of RDDT are higher in surrounding the lakes has low relief so what runoff core TUY-1 taken on the edge of TUY (Figs. 5d, 6d). does occur does not likely mobilize the agricultural It is not clear why concentrations in the sand would be soils that are far from the lakes. Furthermore, the water as high, or higher than, the lacustrine sediments, but that fills the lakes is predominately Amu Darya water movement through anoxic groundwater is possible (Shanafield et al. 2010; Scott et al. 2011). This water is over a long period of time. Scott et al. (2011) showed stored in a large upstream reservoir above the that although groundwater contributions to this lake agricultural fields and is likely low in pesticides. are small, there is some movement of groundwater to Low concentrations (maximum of 0.14 lg/L for the lake. RDDT and maximum of 0.05 lg/L for RHCH) were Only SHK shows peaks in concentrations of both detected in water samples collected during 2006–2008 RDDT and RHCH (Figs. 5a, 6a). The highest con- (Crootof et al. 2015), indicating that the recent centrations are between 1950 and 1990, which is pesticide concentrations in the lake sediments are during peak use of these pesticides (Li et al. 2004; likely to be low compared to lakes worldwide. While Elpiner 1995). Although the concentrations of RDDT pesticide concentrations in all lakes are low at the lake are low overall, the peak concentration of 45 lg/kg is sediment surface (maximum concentration of 20 lg/ similar to other areas of the world (Rosen and Van kg for both RDDT and RHCH), we observe increasing Metre 2010). In addition, 20 years of degradation concentrations of RHCH at the surface of DOV, KOS, since peak pesticide use in 1990 may be a significant SAP, SHK, and SHY (Fig. 5a–c). The reason for this is way to reduce pesticide contamination because these not known, but pesticide storage areas that contain lakes are relatively carbon-rich, which may cause soils with high concentrations of pesticides still exist higher than usual degradation rates. in the region and could be mobilized (Crootof 2011). It is also possible that the source can be agricultural Origin of the lakes lands with high concentrations of these persistent pesticides in some areas of Khorezm. The need for large amounts of Amu Darya river water The highest concentrations of RDDT are not seen at in an arid environment led to salinization of the soil the surface of the lake sediments. Only four lakes and the need for flushing salts from the soil every (SHK, ESH, NAY, and TUY) have RDDT concentra- spring (Ibrakhimov et al. 2011). The construction of tions in the lake sediments greater than the background irrigation and drainage canals to distribute Amu Darya value of 5 lg/kg (Fig. 5a–d). The three cores from river water likely has led to the formation or TUY all have the RDDT peak at approximately the enhancement of most of the lakes in the region, which same time period, between about 1950 and 1970 supports our results that indicate most of the lakes are (Fig. 5d). The two cores from the center of the lake less than 100 years before present. Evidence for this both peak around 1970. The older age of the RDDT comes from the short length of the lacustrine sedi- peak for the core at the edge of the lake, may be due to ments and age models for the lakes studied. In uncertainty in the age model for this core, or because addition, comparing water level measurements from pesticide applications reached the edge of the lake the 1950s (before the most intensive irrigation began) before it made it to the center of the lake. DDT use in to the mid-2000s from six wells in Khorezm shows Uzbekistan was prohibited in 1983, so the peak in that groundwater levels have risen by more than 10 m concentrations in RDDT concentrations in TUY (Scott et al. 2011). The water table is now near the during the 1970s was likely due to its increased use surface (\2 m) (Ibrakhimov et al. 2011). Given that before the ban. The low concentrations of RDDT in the groundwater table was more than 10 m lower in the shallowest core depths in TUY and all the cores is the 1950s than it is now, it is unlikely that many natural 123 J Paleolimnol lakes would have been able to exist in the arid climate RDDT concentrations between 1960 and 1991 when without a connection to the groundwater or a perma- the region was part of the Soviet Union, remaining nent surface water source. There are no natural surface concentrations of these pesticides are low compared to water connections to the lakes, only constructed published literature, and some lakes continue to have irrigation and drainage canals, so natural lakes would increasing concentrations of RHCH. It is uncertain have had to rely on groundwater to exist year round. why RHCH should still be increasing in some of the Scott et al. (2011) showed that groundwater discharge lakes, as its use has been greatly curtailed since 1991. to TUY and KHO is not sufficient to keep the lakes Although some small natural lakes may exist in perennial, and this is likely the case for most of the Khorezm, they are not the dominant lake type in this other lakes due to the very flat land surface and lack of region. The young ages of the lakes indicate that they vertical head to supply sufficient groundwater to the were formed mostly from imported irrigation water lakes to outstrip evaporation. Although the age of from the Amu Darya. As has been shown by water some of the lakes may predate the large-scale irriga- budget calculations (Scott et al. 2011), without annual tion development by the Soviet Union that led to input of irrigation water, it is unlikely that the lakes declining Aral Sea water levels beginning in 1960 will remain perennial or fresh. Therefore, changes in (Micklin 1988), these lakes may have still formed irrigation practices and water management in the from human-induced water diversions, just at an region will play an important role in the future role of earlier date than is hypothesized here. The Amu Darya these lakes in the Khorezm landscape. flooded seasonally before dams regulated its flows, which may have also provided seasonal water to these Acknowledgments The authors would like to thank Benjamin lakes in earlier times (Tanton and Heaven 1999). Trustman and Scott Mensing for preliminary pollen separations, and Flavio Anselmetti for his help in getting cesium and lead dating done at ETH, Switzerland. Marie Champagne helped to plot the pollen diagrams. This work would not have been possible Conclusions without support and contributions from John Lamers and Zentrum fur Entwicklungforschung (ZEF), Dilorom Fayzieva, Marhabo Bekchonova, Diana Shermetova, Nodirbek Our analysis of the first sediment cores taken from Mullaboev, Margaret Shanafield, and Hayot Ibrakhimov. The lakes in Khorezm indicates thin accumulation of project was funded by a NATO Science for Peace Grant No. lacustrine sediments, and relatively consistent 137Cs 982159 and a grant from the National Science Foundation EAR and 210Pb age dating, which indicate that lakes are 0838239. The US Geological Survey has approved this manuscript for publication. All interpretations reflect the generally less than 150 years old and some are less scientific judgment of the authors and do not necessarily reflect than 100 years old. A few lakes may be older, but the views of their organizations. The use of product names if for limitations in the age dating techniques makes identification and does not imply endorsement of the US assigning older constrained ages uncertain. Government or any of the authors respective organizations. Loss on ignition and pollen data indicate that when perennial lakes began accumulating sediment, they were low in carbon and sediments were composed References mostly of sand. As more water became available through irrigation, lakes became fresher, deposited Appleby PG (2001) Chronostratigraphic techniques in recent sediments. In: Last WM, Smol JP (eds) Tracking envi- fine-grained sediments, and became permanent. The ronmental change using lake sediments, vol 1., Basin highest organic content of the cores is always at or near Analysis, coring, and chronological techniquesKluwer the top of the cores, within sediment that was Academic Publishers, Dordrecht, pp 171–203 deposited since 1950 when water use was greatest. Bauer RE, Edlund E, Orvis K (1991) CALPALYN 2.0. U.C. Based on detailed pollen data from at least two sites Berkeley. Department of Geography Palynology Labora- tory, Berkeley (KOS and XIT) the lakes most likely started out as Beasy KM, Ellison JC (2013) Comparison of three methods for ephemeral saline lakes that became fresh as Amu the quantification of sediment organic carbon in salt mar- Darya irrigation water was transported to the lakes shes of the Rubicon Estuary, Tasmania, Australia. Int J Biol 5:1–13 through irrigation canals, groundwater, and occasional Boroffka NGO (2010) Archaeology and its relevance to climate runoff. Analysis of RHCH and RDDT data indicate and water level changes: a review. In: Kostianoy AG, that while some lakes show peaks in either RHCH or Kosarev AN (eds) The Aral Sea Environment. The 123 J Paleolimnol

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