the origin of shallow lakes in the khorezm province
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ORIGINAL PAPER
The origin of shallow lakes in the Khorezm Province,Uzbekistan, and the history of pesticide use around theselakes
Michael R. Rosen . Arica Crootof . Liam Reidy . Laurel Saito . Bakhriddin Nishonov .
Julian A. Scott
Received: 4 March 2016 / Accepted: 22 September 2016
� Springer Science+Business Media Dordrecht (outside the USA) 2016
Abstract The economy of the Khorezm Province in
Uzbekistan relies on the large-scale agricultural pro-
duction of cotton. To sustain their staple crop, water
from the Amu Darya is diverted for irrigation through
canal systems constructed during the early to mid-
twentieth century when this region was part of the
Soviet Union. These diversions severely reduce river
flow to the Aral Sea. The Province has [400 small
shallow (\3 m deep) lakes that may have originated
because of this intensive irrigation. Sediment cores
were collected from 12 lakes to elucidate their origin
because this knowledge is critical to understanding
water use in Khorezm. Core chronological data indicate
that the majority of the lakes investigated are less than
150 years old, which supports a recent origin of the
lakes. The thickness of lacustrine sediments in the cores
analyzed ranged from 20 to 60 cm in all but two of the
lakes, indicating a relatively slow sedimentation rate
and a relatively short-term history for the lakes.
Hydrologic changes in the lakes are evident from loss
on ignition and pollen analyses of a subset of the lake
cores. The data indicate that the lakes have transitioned
from a dry, saline, arid landscape during pre-lake
conditions (low organic carbon content) and low pollen
concentrations (in the basal sediments) to the current
freshwater lakes (high organic content), with abundant
freshwater pollen taxa over the last 50–70 years.
Sediments at the base of the cores contain pollen taxa
M. R. Rosen (&)
Water Science Field Team, U.S. Geological Survey, 2730
North Deer Run Road, Carson City, NV 89701, USA
e-mail: mrosen@usgs.gov
A. Crootof � J. A. ScottGraduate Program of Hydrologic Sciences, University of
Nevada Reno, 1664 N. Virginia Street,
Mail Stop 0175, Reno, NV 89557, USA
L. Reidy
Department of Geography, University of California,
Berkeley, 507 McCone Hall #4740, Berkeley, CA 94720,
USA
L. Saito
Department of Natural Resources and Environmental
Science, University of Nevada Reno, Mail Stop 186, 1664
N. Virginia Street, Reno, NV 89557, USA
B. Nishonov
Laboratory of Surface Water Quality Investigation,
Hydrometeorological Research Institute, 72 K.
Makhsumov Str., Tashkent, Uzbekistan 700052
Present Address:
A. Crootof
School of Geography and Development, University of Arizona,
PO Box 210076, Tucson, AZ 857017, USA
Present Address:
J. A. Scott
U.S. Forest Service, Rocky Mountain Research Station, 2150
Centre Ave, Bldg. A, Suite 368, Fort Collins, CO 80526, USA
Present Address:
L. Saito
The Nature Conservancy, One E. First Street, Suite 1007,
Reno, NV 89501, USA
123
J Paleolimnol
DOI 10.1007/s10933-016-9914-2
dominated by Chenopodiaceae and Tamarix, indicating
that the vegetation growing nearby was tolerant to arid
saline conditions. The near surface sediments of the
cores are dominated by Typha/Sparganium, which
indicate freshwater conditions. Increases in pollen of
weeds and crop plants indicate an intensification of
agricultural activities since the 1950s in the watersheds
of the lakes analyzed. Pesticide profiles of DDT
(dichlorodiphenyltrichloroethane) and its degradates
and c-HCH (gamma-hexachlorocyclohexane), which
were used during the Soviet era, show peak concentra-
tions in the top 10 cm of some of the cores, where
estimated ages of the sediments (1950–1990) are
associated with peak pesticide use during the Soviet
era. These data indicate that the lakes are relatively
young (mostly \150 years old) and that without
irrigation and canal inputs from the Amu Darya, the
lakes would not exist as freshwater lakes.
Keywords Lake formation � DDT � HCH �Limnogeology � Central Asia � Sediment cores
Introduction
In arid regions of the world, perennial freshwater
resources are scarce: high rates of evaporation often
lead to the salinization of fresh water, particularly of
shallow lakes and groundwater. Where these arid
landscapes support agriculture, it is important to
understand the sustainability of freshwater resources.
One such arid landscape where water resource
sustainability is a growing concern is the Khorezm
Province of Uzbekistan. Khorezm is in the Aral Sea
Basin and lies along the Amu Darya (‘‘darya’’ means
‘‘river’’ in Persian) in southwestern Uzbekistan
(Fig. 1). The Amu Darya has a watershed of about
1,385,045 km2 and flows from glacial melt water in
the Pamir Mountains and Tian Shan historically to
the Aral Sea, but no longer reaches the Aral Sea due
to withdrawals for irrigation. Khorezm covers an area
of 6050 km2 and is home to approximately 1.7 mil-
lion residents (The Governmental Portal of the
Republic of Uzbekistan 2016). With annual precip-
itation averaging approximately 92 mm, Khorezm
predominately has an arid continental climate
(Letolle and Chesterikoff 1999; Wehrheim et al.
2008).
Despite the arid climate, Khorezm is one of the
most agriculturally productive regions in Uzbekistan.
An extensive network of canals (Fig. 2) supplies the
Province with irrigation water throughout most of the
year (Wehrheim et al. 2008; Veldwisch 2008). Since
Uzbekistan gained independence in 1991, the country
has remained dependent on the cash flow from their
agricultural exports, which make up approximately
37 % of the country’s gross domestic product (Martius
et al. 2009). With over 16,000 km of irrigation canals
in Khorezm, 3.5–4.0 km3 of water is diverted from the
Amu Darya during the growing season and
1.0–1.5 km3 during the winter season to produce cash
crops such as cotton, wheat and rice. Furrow irrigation
is used for cotton, while flood irrigation is used for
wheat and rice. Irrigation water that is not lost to
evapotranspiration or groundwater is channeled into
9000 km of drainage canals throughout the Province
(Oberkircher et al. 2011).
Over 400 lakes have been identified in the Province
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
the lakes in the south Khorezm is due to their location
in the depressions between dunes in the regional
desert. Local residents believe the lakes have existed
for thousands of years and the lakes currently have
both cultural significance and prestige in the commu-
nity (Oberkircher et al. 2011). Therefore, changes to
agricultural practices that could affect the water
balance of these lakes must take into account the use
of these lakes and their sustainability. Water balance
studies on two lakes in Khorezm showed that without
the addition of surface water from irrigation canals,
the lakes were likely to desiccate after irrigation ends
(Scott et al. 2011). Although irrigation with Amu
Darya water has existed in the region for more than
2000 years (Tolstov 2005; Boroffka 2010), intensive
irrigation likely began in the early to mid-1900s, so it
is possible that the lakes are less than 100 years old.
Twelve lakes (‘‘kul’’ in the Uzbek language) were
chosen for this study (Fig. 1): Ata (ATA), Dovud
(DOV), Eshan Rabat (ESH), Gauk (GAU), Khod-
jababa (KHO), Koshkopyr (KOS), Nayman (NAY),
Sapcha (SAP), Shur (Koshkopyr) (SHK), Shur (Yan-
giaryk) (SHY), Tuyrek (TUY) and Xitoy (XIT). These
study lakes are well distributed across the Province
and are characteristic of the small (0.02–1.6 km2
J Paleolimnol
123
area), shallow (\3 m deep) lakes found in Khorezm.
Table 1 contains details about the size and land use
around each lake.
In addition to water availability, water quality is
also a concern in Khorezm because it can deviate from
acceptable standards by as much as 80 % (Severskiy
et al. 2005; Fayzieva et al. 2004). Pesticide pollution
was presumed to be prevalent in the region because
crops were historically sprayed with organochlorine
pesticides such as dichlorodiphenyltrichloroethane
8
7
53
4
12
1
9 11
2
6
10
Aral Sea
Caspian Sea
Study Lakes
LakesPolitical Boundaries
0 10 20
Kilometers
Uzbekistan
Kazakhstan
Turkmenistan
Amu Darya
West Central East
1 XIT2 KOS3 SHK4 KHO5 DOV6 SAP7 GAU8 ESH9 TUY10 SHY11 ATA12 NAY
Study Lake Abbreviations
Study Area
N
Fig. 1 Map of the Khorezm region of Uzbekistan showing
lakes in the region (grey areas) and the locations of the lakes
studied (black areas). Lakes are arbitrarily divided into West,
Central, East locations for plotting purposes and to illustrate
how geographic location affects analysis of these lakes. Lake
names corresponding to the abbreviations in the figure are: Ata
(ATA), Dovud (DOV), Eshan Rabat (ESH), Gauk (GAU),
Khodjababa (KHO), Koshkopyr (KOS), Nayman (NAY),
Sapcha (SAP), Shur (Koshkopyr) (SHK), Shur (Yangiaryk)
(SHY), Tuyrek (TUY) and Xitoy (XIT)
J Paleolimnol
123
(DDT) and gamma-hexachlorocyclohexane (c-HCH,better known as Lindane) (Galiulin and Bashkin
1996). While DDT and HCH will degrade by micro-
bial and abiotic decomposition, these pesticides are
known to be persistent and can still be found in water
bodies, soils and the atmosphere worldwide long after
application (Smol 2008; Rosen and Van Metre 2010;
Korosi et al. 2015). In soils, DDT has a recorded half-
life of 2–20 years depending on local temperature, soil
type, pH, redox potential, moisture and organic carbon
content. HCH, which is much less persistent, has an
average half-life in topsoil of 2 months (Manz et al.
2001). Because DDT is highly insoluble, it is not
usually present in high concentrations in the water
column, but will accumulate in bed sediments (Zweig
et al. 1999; Hill and McCarty 1967). The hydrolysis of
DDT in water is pH and temperature dependent.Wolfe
et al. (1977) found DDT to have a half-life of 8 years
with a pH of 7 and a temperature of 27 �C. Degrada-tion of both DDT and HCH occurs primarily by
biological processes; Sharom et al. (1980) found DDT
and HCH to be degraded much more quickly in water
when microbes were present.
Several studies have investigated the presence of
DDT and HCH in humans, water, and surface
sediment samples in the lower Amu Darya region.
Beginning in 1987, the Central Asian Science
Research Institute of Irrigation conducted a study to
assess the ecological and toxicological situation in
lakes and reservoirs in the lower Amu Darya region.
Jensen et al. (1997) found high concentrations of
metals and pesticides in the blood of children living in
Lakes
Canals
Political Boundaries
0 10 20Kilometers
Amu Darya
N
Fig. 2 Map of the Khorezm region of Uzbekistan showing the
densely constructed irrigation and drainage canals in the region
(lakes are in grey areas). The map is the same area as shown in
Fig. 1. The lakes studied are not plotted on this map because for
the most part they are not visible through the irrigation canals.
Location of irrigation canals are from the Zentrum fur
Entwicklungforschung (ZEF)
J Paleolimnol
123
the Aral Sea Basin of Kazakhstan that had signs of
disease. The UNESCO Aral Sea Project (1992–1996)
and INTAS 1039 Project (2002–2003) continued this
research and found that between 1989 and 2002 there
was a sharp decrease in RDDT and RHCH concentra-
tions in water and bottom sediment samples from the
Amu Darya delta (Karimov et al. 2005). These studies
provide information about water quality in the Amu
Darya delta region, but do little to quantify pesticide
concentrations in Khorezm even though this region
was also subjected to large quantities of agrochemicals
when it was part of the Union of Soviet Socialist
Republics (USSR or Soviet Union). The rapid
decrease in pesticide concentrations in Amu Darya
delta sediments (Karimov et al. 2005) may have also
occurred in the lake sediments in Khorezm. Quanti-
fying pesticide pollution in the lakes, particularly for
RDDT and RHCH, provides valuable information
about the biological functions and human health
concerns associated with the lakes. Throughout this
paper RDDT refers to the sum of DDT and its major
metabolites dichlorodiphenyldichloroethylene (DDE)
and dichlorodiphenyldichloroethane (DDD). Simi-
larly, RHCH is defined as the sum of c-HCH and a-HCH isomers.
Although irrigated agriculture has existed in the
Khorezm region for at least 2000 years (Tolstov
2005), intensive irrigation in Khorezm began in the
early to mid-1900s when the region was part of the
Soviet Union. Understanding the origin of these lakes
is important to provide guidance for the development
of water management strategies in this water-scarce
region, as changes to land and water management
could change the hydrology and water balance of the
lakes (Scott et al. 2011), potentially leading to
desiccation and introduction of potentially toxic lake
bed material to the air. This study is the first, to our
knowledge, to assess the origin of these lakes, and the
historical role they play in the hydrology of the region.
We hypothesized that the lakes are young (\100 years
old) based on the amount of irrigation that is used in
the region, and that non-polar pesticides such as
RDDT and RHCH should be present in sediment cores
at concentrations reflecting the Soviet use of these
pesticides in the 1950s to 1980s. The objectives of this
study were to use sediment cores to determine the age
of the lakes using 210Pb and 137Cs dating and to
analyze the lake sediment cores for RDDT and RHCHat small enough intervals to determine the timing of
peak pesticide application.
Materials and methods
Twelve lakes (Fig. 1) in Khorezm, Uzbekistan were
cored from 2008 to 2010 using a home-made coring
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
abbreviation used
in text
Area of fields
within 0.5 km
of lake (m2)
Lake area
(m2)
Buffer
size (m2)
Cotton
(%)
Rice
(%)
Wheat–
rice (%)
Wheat–
other
crop (%)
Wheat–
Fallow
(%)
Agriculture
(total %)
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
J Paleolimnol
123
platform and a custom engineered percussion corer.
While this technique may have smeared the sediment–
water interface, we are confident that the down-core
record is representative of the history of each lake due
to consistent trends seen in the sedimentological and
pesticide records discussed below. TUY and KHO
were cored on two occasions, in March and July 2008.
Cores were taken from the edge of the lakes in March
and from the lake centers in July. The lake edge cores
were taken to determine whether the lake centers’ core
profiles were consistent across the entire lake. All
other lakes were cored once near the deepest area of
the lake. Penetration into lakebed sediment was
generally greater than 1 m. Cores were cut to the
sediment–water interface in the field and packed with
sorbent material to prevent movement of the sediment
within the core barrels. Cores were kept cold and
vertical at all times during storage and transport to
Tashkent, Uzbekistan, for analysis. In Tashkent, the
cores were sliced into 2.5 cm sections and visual
identification of clay and sand units were made during
slicing. As described in detail below, all cores were
analyzed for 210Pb and 137Cs at Eawag, ETH,
Switzerland. Loss on ignition (LOI550), and pesticides
were analyzed at the Laboratory of Surface Water
Quality Investigation, Hydrometeorological Research
Institute, Uzbekistan. Cores from ESH, KOS, and XIT
were analyzed in detail for pollen at the Paleocology
Laboratory, University of California, Berkeley, USA,
with supplemental data from the top and bottom of the
cores from DOV, SHK, and ATA used to verify
interpretations from the detailed examination. All data
used in this assessment of the lakes are available at
Rosen et al. (2016).
210Pb and 137Cs age dating of the cores
Individual 2.5 cm thick slices of core sediments from
each core (5.0 cm thick slices were used for the March
2008 TUY core) were analyzed at ETH-Eawag
Aquatic Research labs (Switzerland) from the top
down until no detection or low detection of 210Pb or137Cs was encountered. Data from 210Pb analyses did
not always show consistent exponential decay in some
of the lakes sampled. These results could be due to
(a) physical or biological mixing at the surface;
(b) changes in the 210Pb supply due to changes in the
patterns of sediment focusing (Appleby 2001) or
(c) core slices that were vertically too thick to get
accurate results. However, 210Pb could be used to
check ages calculated using 137Cs in 10 of the 15 cores.
One lake core (XIT) had no 137Cs peak or useable210Pb profile (there wasn’t logarithmic decay of the210Pb data), and theMarch 2008 KHO core had a small137Cs peak near the surface of the lake sediments,
indicating that sediment from the top of XIT and one
of the KHO lake cores was likely eroded. The age of
XIT and its sedimentation rate could not be deter-
mined because of the lack of useable 137Cs peak and210Pb data (see Rosen et al. 2016), but the data are
included to show patterns with depth. However, 210Pb
data for GAU gave reasonable sedimentation rates,
and these were used for calculating the age of the lake.
Based on the difference between 210Pb and 226Ra,
background 210Pb activities are around 20 Bq/kg.
Constant rate of supply (CRS) method was used for
simplicity and comparability between 137Cs and 210Pb.
Where both 137Cs and 210Pb sedimentation rates could
be calculated for the same lake, the average rate was
used to calculate ages. The global 1964 above-ground
nuclear testing 137Cs peak was used as the primary
marker for the 137Cs model, with the time the lake core
was collected as the other marker. In 3 cores (SHY,
NAY, and KHO), a small spike in the 137Cs activity
above the 1964 peak may be the result of the 1986
Chernobyl accident (Appleby 2001) that spread 137Cs
over much of Europe and parts of Asia (see Rosen
et al. 2016). These peaks were used as additional
controls in these cores. Samples were dried, homog-
enized, and analyzed using a gamma counting spec-
trometer using methods presented in Appleby (2001).
Results of 137Cs and 210Pb counting are presented in
Rosen et al. (2010) and Table 2. Dates are plotted on
diagrams as averages of 137Cs and 210Pb calculated
ages where both methods allowed calculation of ages.
Loss on ignition
For loss on ignition (LOI550), sediment samples were
dried at 105 �C for 6 h until constant weight was
obtained to remove water. The weight was recorded
and the sample was then placed in a muffle furnace at
550 �C for 6 h (Heiri et al. 2001). The difference in
weights between the sample dried at 105 �C and the
weight after the sample was placed in the muffle
furnace determined the LOI550 percentage. Samples
were not treated with HCl because this could remove
some organic material (Beasy and Ellison 2013) and
J Paleolimnol
123
Table
2Agedeterminationsforthelakes
studiedusing
137Csand
210Pbconstantrate
ofsupply
methods
Date/locationofcoressamples
137CsAgedating
210PbagedatingwithCRSmodel
Meanof137Cs
and
210Pb
Datecore
was
collected
Lakeabbreviation
(see
textforlake
nam
es)
Locationof
core
inthe
lake
Mud
depth
(cm)
Depth
of
137Cspeak
incore
(cm)
Sed.rate
(cm/year)
Number
of
years
to
bottom
of
lakesedim
ent
Dateof
lakeorigin
(calendar
years)
Sed.rate
(cm/year)
Number
of
years
to
bottom
of
lakesedim
ent
Dateof
lakeorigin
(calendar
years)
Mean
sedim
entation
rate
(cm/year)
Mar-08
KHO1
Edge
37.5
20
0.45
82
1926
??
?
Jul-08
KHO2a
Center
25
Cesium
peakat
topofcore
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
peakat
topofcore
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
XIT
aCenter
47.5
Cesium
peakat
topofcore
??
?
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
inconsistent210Pbactivitiesobtained
downcore,so
nosedim
entationrate
could
begenerated
aMay
beeroded
atthetop
bAgeto
bottom
ofcore–clay
alltheway
tobottom
cMay
beeroded
atthetopofthecore
orthecesium
peakisbelow
70cm
depth
J Paleolimnol
123
all lakes except ESH, which had calcium carbonate
precipitated around macrophyte stems in the near
surface sediments, were undersaturated with respect to
carbonate minerals. LOI550 is used here as a qualita-
tive assessment of organic carbon content of the
sediments because LOI550 percentages can be affected
by lithology (Santisteban et al. 2004). However, trends
down core can be useful and comparable using the
same LOI550 method for lakes from the same geologic
setting with a similar lithology, as is the case for the
sediments from the lakes studied. Replicates were
analyzed on 10–20 % of samples analyzed. Agree-
ment was generally within 10 %. In figures included
here, replicate data are plotted as the average of the
replicates.
Pollen analysis
Standard pollen extraction and preparation procedures
were followed (Faegri and Iversen 1989). One tablet
containing approximately 20,848 Lycopodium spores
was added to each sample for control purposes
(Stockmarr 1971). Samples were sieved with a
125 lm mesh filter to remove large debris and
processed with the following treatments: hydrochloric
acid, potassium hydroxide, hydrofluoric acid, iso-
propanol wash, nitric acid, glacial acetic acid, and
acetolysis. The residues were stained with safranin,
dehydrated with tertiary butyl alcohol, suspended in
silicone oil, and mounted on microscope slides. Pollen
was counted at the 4009magnification with 10009 to
determine fine detail. Pollen grains and fern spores
were identified to the lowest possible taxonomic level
using the UC Berkeley Museum of Paleontology’s
collection of over 10,000 modern pollen samples and
published pollen keys (McAndrews et al. 1973; Kapp
et al. 2000). Unknown grains were noted and drawn.
Damaged, torn or crumpled grains that were uniden-
tifiable were counted as ‘‘Indeterminate’’. A minimum
of 400 grains were counted for at least 9 samples on
cores from KOS, XIT, and ESH. Pollen counts were
compiled and plotted using the CALPALYN program
(Bauer et al. 1991).
Pesticide analyses
The methodology used to analyze pesticide residues in
sediments followed the standard techniques used by
Uzhydromet (RD 52.24.71-88 1988). Core sample
slices were homogenized as wet sediment and then air-
dried at 20 �C. Double extraction of pesticides from
the sediment was done using n-hexane ? acetone.
Sample cleanup was conducted using concentrated
sulfuric acid for elimination of organic substances.
Extracts were dried with Na2SO4, reconcentrated, and
injected into an Agilent 6890 chromatograph with a
capillary column. In addition, the absolute dried bulk
density of the sediment was determined by weighing
homogenized and air-dried samples after they were
heated in a muffle furnace at 105 �C for 6 h. Samples
were checked to ensure that the recorded weights were
constant. Replicates were analyzed on 1–3 samples in
most cores and results are generally within 25 % of
each other. A blank, using bottled water, was run on
one occasion and no RHCH or RDDT was detected,
but because some RHCH and RDDT were detected in
many samples of prelacustrine sands, where detections
would not be expected, low concentrations of RHCHand RDDT (below 5 lg/kg for RDDT and below
2.5 lg/kg for RHCH) were considered as background
and not environmentally relevant. In figures, replicate
data are plotted as the average of the replicates.
Results
Age dating
The lacustrine sediment in all of the lakes except GAU
and SAP is B50 cm. Below 50 cm depth, all cores
penetrated relatively clean sand that formed from
either riverine or eolian processes. Cesium-137 pro-
files for all the lakes show that all of the 1964 above-
ground testing 137Cs peak activities are shallower than
22.5 cm from the sediment–water interface (Table 2),
except for NAY core, which is at 32.5 cm depth. Lakes
SHY, NAY, and KHO (lake center core), show a small137Cs peak between 2.5 and 5.0 cm depth, 17.5 and
20 cm depth, and 7.5 and 10 cm depth, respectively,
which are interpreted to be the spike from the 1986
Chernobyl accident. The small Chernobyl peak is
almost exactly half-way between the surface (2008 or
2010) and the 1964 137Cs peak in all three cores. The
maximum age of the lakes calculated using the 137Cs
sedimentation rates is 276 years before collection of
the cores, and the minimum age is 64 years.
Lead-210 CRS models were constructed for 10 of
the cores, but only eight have 137Cs profiles that can be
J Paleolimnol
123
compared to the 210Pb profiles. All of the 210Pb-
calculated sedimentation rates are similar to those
calculated using 137Cs peaks. Sedimentation rates
range from 0.10 to 0.73 cm/yr and those sedimenta-
tion rates that can be compared by using duplicate
cores from the same lake are B0.22 cm/yr different
(Table 2). Given this potential error in sedimentation
rate, each centimeter of core could be in error by
5 years in each direction, so dates are a minimum of
±10 years per centimeter of core, and more likely
±20 years, if other errors such as mixing are incor-
porated. The maximum age of the lakes calculated
using the 210Pb models is 450 years prior to core
recovery and the minimum age is 70 years. Some
lakes have younger ages with sedimentation rates
calculated from 137Cs peaks compared to ages derived
from 210Pb others have younger ages calculated with210Pb models compared to 137Cs derived ages (see
Table 2).
There appear to be three groups of lake ages for the
onset of lacustrine sedimentation. Older lakes (SAP,
KOS and possibly GAU) appear to have formed before
1800. Other lakes appear to have begun forming
between 1880 and 1920 (ESH, SHK, KHO, and TUY),
and still others appear to have formed between 1930
and 1960 (NAY, DOV, ATA, and SHY). One lake
(XIT) could not be assigned to any groups because age
models could not be constructed for this lake because
there was no real 137Cs peak and 210Pb did not decay
exponentially (see Rosen et al. 2016). It is possible that
sediment at the top of XIT was eroded during past low
lake levels. However, XIT transitioned from sand to
lake muds by 50 cm depth, indicating a time of
formation that is similar to the other lakes that were
dated, assuming erosion did not remove more than
20 cm of sediment from the lake.
Loss on ignition
Loss on ignition data show dramatic increases in the
organic matter component of the sediment once
lacustrine sedimentation begins in all lakes (Fig. 3a–
d). LOI550 values range from 5 to 23 % at the tops of
the cores, and between 3.7 and 0.6 % in the sand at the
bottom of the cores. The GAU core consisted of mud
down to 70 cm depth, however, the LOI550 decreased
from 7 % at the top of the core to 1.7 % at the bottom
of the core, indicating that the transition to sand was
likely not far below this depth. Similarly, the SAP core
also had LOI550 decreasing to 3.7 % (from[17 % at
the top of the core), indicating that the transition to
non-lacustrine sediments was not far below the bottom
of the core. Several cores show a slowdown of
increasing LOI550 around 1970–1990, with a final
increase in LOI550 in the last 20 years or so.
Pollen
Selected major pollen and spore profiles were devel-
oped for three of the lakes (KOS, ESH and XIT) and
are displayed in Fig. 4a–c and used to discuss the
results of the record. Pollen concentration is measured
as grains/cm3 (see Rosen et al. 2010). Preliminary
pollen data from the bottom, middle and top sections
of two additional lakes (ATA, DOV and SHK) are
presented in Rosen et al. (2010).
Koshkopyr
Two pollen zones were defined for the KOS record
(Fig. 4a) based on changes in the abundance of certain
aquatic and riparian pollen types and the first appear-
ance of several agricultural and weedy pollen types.
Changes and reversals in the aquatic and riparian
record reflect local environmental change and natural
plant succession in the lake. The overall pollen record
shows variation through time, especially for the last
one hundred years.
Zone 2: ca. 1840–1900 (22–15 cm) The high
percentages of Chenopodiaceae (Goosefoot family)
([40 %) and Tamarix (salt-cedar) (*20 %) at the
bottom of this zone (Fig. 4a) indicate that plants
adapted to dry saline conditions were locally common.
Low percentages (\1 %) of tree pollen Juglans
(walnut), Pinus (pine) and Populus (aspen) suggests
an open environment with few trees. The presence of
large Poaceae (grass family) pollen with a size range
of 42–51 lm (Chaturvedi et al. 1998) reflects the
cultivation of Oryza sativa (Asian rice) locally. Pollen
concentrations in this zone average 30,000 grains/
cm3.
Zone 1 ca. 1901–2010 (15–0 cm) The pollen record
changes dramatically in zone 1. It is characterized by
sharp decreases in both Chenopodiaceae and Tamarix
and the first appearance of weedy and additional crop
pollen types. Rumex acetosella and Plantago
J Paleolimnol
123
lanceolata both appear at 15 cm. Solanum spp.
(potato) pollen appears at the 12.5 cm level while
Malvaceae (cotton) first appears at the 10 cm interval.
Typha/Sparganium (cattails) steadily increase from
*10 % at the base of this zone to over 40 % in the
near surface sediments. There is a slight increase in
Populus between 12 and 5 cm to 3 % of the pollen
sum but it drops again towards the top of the zone to
\1 %. Pollen concentrations average close to
64,000 grains/cm3 in this upper section.
Eshan Rabat The general ESH pollen record
(Fig. 4b) does not change significantly during the
past 100 years. Weed (Rumex spp., Plantago
lanceolata) and crop pollen (Solanum spp.,
Malvaceae, and Oryza sativa) types are present
throughout the record from the basal sediments
(30 cm) to the top of the core. There is a sharp
increase in Poceae pollen in the upper 2.5 cm of the
record. Chenopodiaceae is the dominant pollen type
throughout the core and averages between *30 and
40 % between 30 and 0 cm. Pollen concentrations are
variable and range between 10,000 and 70,000 grains/
cm3.
Xitoykul The XIT core is undated but there are some
similarities with the KOS record (Fig. 4c).
Chenopodiaceae, Tamarix, and Poaceae are the
dominant pollen types in the lower part of the record
but all decrease towards the top. Typha/Sparganium is
low (7 %) in the basal sediments but increases to
almost 60 % of the pollen sum above the 7.5 cm level.
The pollen of Myriophyllum (water mil-foil) averages
8 % in the basal sediments and then declines all the
way to the surface. Myriophyllum is an emergent
aquatic that does well in shallow water environments.
Weedy pollen (Rumex acetosella; Plantago
lanceolata) first appear at or above 20 cm. Monolete
A B
C D
Fig. 3 Loss on ignition (LOI550) percentages for all lakes
studied plotted by calendar years, except XIT, which is plotted
by depth. a Lakes located in the western, b central, and c easternpart of Khorezm. d The 3 cores taken in TUY from the edge and
center part of the lake. TUY is located in the eastern part of
Khorezm. Dashed lines show where sand is located in the
bottom of the cores. Lacustrine sedimentation begins where the
line becomes solid. Due to uncertainties in the age models,
errors in age dates may be as high as ± 20 years (see text for
explanation)
J Paleolimnol
123
Koshkopyr
CHRONOLOGY
Years
A.D.
2000
1981
1961
1942
1923
1904
1885
1865
1846
Dep
th in
cm
.
0
2
5
8
10
12
15
18
20
22
Popul
us
0 2 % Total Pollen and Spores
Jugl
ans
0 1
Pinus
0 1
Salix
0 1
Tamar
ix
0 5 10 15 20
Typha
/
Spa
rgan
ium
0 15 30 45
CYPERACEAE
0 3
Myr
ioph
yllum
0 4
CHENOPODIACEAE
0 10 20 30 40
POACEAE
0 10
ASTERACEAE
0 1
Mon
olete
Spores
0 1
Orzya
sativ
a
0 2 4
MALVACEAE
0 1
Plant
ago
lanc
eola
ta
0 1
Sola
num
spp.
0 1
Rumex
aceto
sella
0 1
Pollen
Con
centr
ation
0 50,000
TREES RIPARIAN & AQUATICS HERBS & SHRUBS
3
AGRICULTURAL
Zone 1
Zone 2
grain
s/cm
Eshan Rabat
CHRONOLOGY
Years
A.D.
2006
1998
1990
1982
1974
1967
1959
1951
1944
1936
1928
1920
Dep
th in
cm
.
0
2
5
8
10
12
15
18
20
22
25
28
30
Popul
us
0 2 % Total Pollen and Spores
Jugl
ans
0 2
Pinus
0 3
Salix
0 2 4
Tamar
ix
0 5 10 15 20 25 30
Typha
/
Sp
arga
nium
0 5 10 15 20
CYPERACEAE
0 2 4
Myr
ioph
yllum
0 4
CHENOPODIACEAE
0 10 20 30 40
POACEAE
0 10 20
ASTERACEAE
0 1
Mon
olete
Spores
0 2 4
Orzya
sativ
a
0 1 2
MALVACEAE
0 1
Plant
ago l
ance
olat
a
0 2
Sola
num sp
p.
0 1 2
Rumex
aceto
sella
0 1 0 50,000
TREES HERBS & SHRUBSRIPARIAN & AQUATICS AGRICULTURAL
Pollen
Con
centr
ation
grain
s/cm
3
Xitoykul
Dep
th in
cm
.
0
2
5
8
10
12
15
18
20
22
25
28
30
32
35
Popul
us
0 2 % Total Pollen and Spores
Jugl
ans
0 1
Pinus
0 1
Salix
0 1
Tamar
ix
0 5 10 15
Typha
/Spa
rgan
ium
0 15 30 45 60
CYPERACEAE
0 3
Myr
ioph
yllum
0 4 8
CHENOPODIACEAE
0 10 20 30
POACEAE
0 10 20
ASTERACEAE
0 1
Mon
olete
Spores
0 1
Orzya
sativ
a
0 2
MALVACEAE
0 1
Plant
ago
lanc
eola
ta
0 1
Sola
num
spp.
0 1
Rumex
aceto
sella
0 1
Pollen
Con
centr
ation
grain
s/cm
0 35,000 70,000
TREES HERBS & SHRUBSRIPARIAN & AQUATICS
3
AGRICULTURAL
A
B
C
Fig. 4 Selected pollen and spore taxa for aKOS, b ESH, and cXIT. Due to uncertainties in the age models, errors in age dates may be
as high as ± 20 years (see text for explanation)
J Paleolimnol
123
spores (ferns) are found throughout the length of the
record along with the pollen of Orzya sativa.
Malvaceae only appears at the 25 cm level, while
Solanum appears above the 20 cm level. Pollen
concentrations average 20,000 grains/cm3 below
30 cm while concentrations increase towards the top
of the record to an average of about 60,000 grains/
cm3.
Pesticides
Pesticide concentrations in all cores are relatively low
compared to lakes worldwide (for example see Elpiner
1995; Rosen and Van Metre 2010), \10 lg/kg for
bothRDDT andRHCH, except for a few samples from
TUY, ESH, and DOV (Figs. 5a–d, 6a–d). Concentra-
tions were generally highest in the upper part of the
cores, generally from 1960 to 1990 for RDDT. Spikesof higher than background concentrations are partic-
ularly noticeable in ESH, TUY, and SHK for RDDT,and in DOV, TUY, SHY and SHK for RHCH. In 5 of
the lakes, the highest RHCH concentrations are at the
top of the cores (DOV, SAP, KOS, SHY, and SHK).
There is no apparent correlation between pesticide
concentrations in the lakes and percentage of recent
agricultural lands around the lakes (Table 1). ESH,
which has the lowest agricultural land use around the
lake, has the highestRDDT concentration of any of the
lakes (Table 1). However, the only surface water
inflow to the lake is a drainage canal, which contains
the runoff and groundwater from upstream agricultural
fields.
Discussion
Age dating
The age models constructed from 137Cs and 210Pb
dating are relatively consistent, but are somewhat
simplistic (CRS model only). This is because the
decay curves of unsupported 210Pb are not always
exponential and so may have some error associated
with the dates. In some cases, 137Cs peaks are not sharp
and so may not provide an exact date for the 1964
global atmospheric testing peak. However, even with
these uncertainties, it is clear that the lakes have not
existed for thousands of years because the thickness of
lacustrine sediment in the lakes is\60 cm in all but
two of the lakes, and extrapolation of even these
poorly constrained ages does not make the lake
sediments older than a few hundred years. In addition,
the LOI550 data for both SAP and GAU are\5 % and
decline near the base of the cores, possibly indicating
that pre-lacustrine conditions are not far from the base
of these cores.
The reason for the variable ages of the lakes is
difficult to determine as there is no clear pattern. The
variability may reflect either poor age control in some
of the lakes caused by variable smearing of 210Pb or137Cs peaks, or other mechanical or chemical diffusion
or mixing within the lake. Klaminder et al. (2012)
found that cesium deposited during the Chernobyl
accident migrated down core, obscuring the 1964
global peak in a lake located near Chernobyl that
received high amounts of fallout from the accident.
While the lakes in Uzbekistan were not in the path of
high fallout from Chernobyl (Pollanen et al. 1997),
some of the lakes may show possible Chernobyl peaks
(e.g., NAY and SAP). This may indicate some
downward migration of cesium in these lakes. In
some lakes, the first deposited muds may represent
natural depressions that may have been playas or
ephemeral saline lakes. Salt was visually identified in
KOS sediments, which is an indication of a saline past
for this lake, and the calculated age for the start of
lacustrine sedimentation is older in KOS than the other
lakes. Other possible causes of the variability is
mixing of sediment due to human and/or animal
disturbance, or eroded sediment being washed into the
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
cores), calculated 137Cs and 210Pb ages are consistent
(within 20–40 years) Alternatively, irrigation may
have a much longer history in the region. There is
limited knowledge of pre-Soviet irrigation canals that
could go back more than 2000 years (Tolstov 2005;
Boroffka 2010). However, the distribution of lakes
formed prior to 1900 appears random and does not
suggest any regional trend. In contrast, three of the
younger lakes, which formed post-1900 (NAY, ATA,
and SHY) cluster in the eastern area of Khorezm
(Fig. 1). Historical data on where and how much
irrigation was used in the region was not collected in
most parts of Khorezm because water meters were not
in place, and in some areas still are not used. Without
information on the historical use of irrigation in
J Paleolimnol
123
Khorezm, it is impossible to determine precisely the
date of origin of the lakes. However, as discussed
below, the 12 study lakes appear to have started out as
natural depressions, possibly with saline water con-
tributing to the depressions before irrigation began.
Two lakes (TUY and KHO) had multiple cores
dated and analyzed (Table 2). For lake TUY, one was
taken on the edge of the lake (TUY-1) and 2 cores were
taken in the center of the lake (TUY-2 and TUY-3).
The core from the edge of the lake has a younger age
calculated for the bottom of the core using a 137Cs
peak at 7.5 cm depth for both lake center cores.
However, TUY-2 core has a 210Pb age that is similar to
the age of the lake edge core using the 137Cs peak, and
TUY-3 has a 210Pb age that is about 40 years older. It
may be that the ages indicated by the 137Cs data of both
lake center cores are too old and that the lake more
likely began forming around 1920 as indicated by the210Pb, rather than at the earlier dates calculated from
the 137Cs of the lake center cores.
The 2 cores from KHO show different issues as
compared to the TUY cores. For the KHO cores, the
core taken near the center of the lake has no 137Cs
peak, indicating either erosion or dredging of the lake
because the lake muds are thin in this core (25 cm)
compared to the lake edge core that is 37.5 cm thick.
Although an age of the lake for the basin center core
can be determined from the 210Pb data, the age is likely
overestimated due to missing sediment and possible
mixing, although this age is used for plotting purposes.
The ages calculated for both cores differ by 35 years.,
Due to the missing top of the lake center core, the 1926
age for the lake edge core is more consistent with the
age of lacustrine deposition of muds in the majority of
A B
C D
Fig. 5 Concentrations of RHCH for all lakes studied plotted by
calendar years, except XIT, which is plotted by depth. a Lakes
located in the western, b central, and c eastern part of Khorezm.
d Concentrations of RHCH for the 3 cores taken in TUY from
the edge and center part of the lake. TUY is located in the eastern
part of Khorezm.Dashed lines show where sand is located in the
bottom of the cores. Lacustrine sedimentation begins where the
line becomes solid. Dashed vertical line at 2 lg/kg is the
concentration above which the concentrations are above
analytical background concentrations and may be environmen-
tally relevant. Due to uncertainties in the age models, errors in
age dates may be as high as ± 20 years (see text for
explanation)
J Paleolimnol
123
other lakes studied and with the timing of increased
irrigation during the period of the Soviet Union.
Lacustrine sediments and LOI550
The short length (\60 cm) of the lacustrine sediments
in most of the cores except for GAU and SAP suggests
a short depositional history for the lakes. Sharp
increases in LOI550 occur in all lakes above basal
quartz sands, and the percentage of organic matter
present in the muds increase to the surface, except in
GAU (Fig. 3a–d). In most lakes, LOI550 percentages
are highest since 1950 when most irrigation was
occurring. LOI550 percentages in all lakes are below
10 % before 1950 (except for a few samples just above
10 % in GAU), and after 1950many lakes show steady
increases in LOI550, with some lakes reaching 20 %
within 30 years. The steady increase in LOI550 in the
last 30–50 years indicates that the lakes are becoming
more productive and that perennial relatively fresh
water is present in the lakes. The increasing produc-
tivity means that more water and nutrients are
available to the lakes. Stratigraphic increases in
organic carbon content (related to higher lake produc-
tivity) coincided with the peak of Soviet expansion of
irrigation between 1951 and 1991, and it is likely that
this expansion of irrigation and fertilizer use has
allowed for the increased productivity in these lakes.
The three cores from TUY show similar patterns to
the other cores, with much higher LOI550 percentages
at the top of the cores. However, increases in LOI550are not steady in these cores (Fig. 3d) and there is a
period between 1930 and 1970 where LOI550 does not
increase, particularly in the cores taken near the center
A B
C D
Fig. 6 Concentrations of RDDT for all lakes studied plotted by
calendar years, except XIT, which is plotted by depth. a Lakes
located in the western, b central, and c eastern part of Khorezm.
d Concentrations of RDDT for the 3 cores taken in TUY from
the edge and center part of the lake. TUY is located in the eastern
part of Khorezm.Dashed lines show where sand is located in the
bottom of the cores. Lacustrine sedimentation begins where the
line becomes solid. Dashed vertical line at 5 lg/kg is the
concentration above which the concentrations are above
analytical background concentrations and may be environmen-
tally relevant. Due to uncertainties in the age models, errors in
age dates may be as great as ± 20 years (see text for
explanation)
J Paleolimnol
123
of the lake. LOI550 then increases sharply in the last
30 years or so. The cause for the constant LOI550period in TUY is not known, but some of the other
lakes (e.g., SAP, NAY, and ESH) also have this period
of constant LOI550 at about the same time. It may be
related to water availability or longer-term climate
changes, but given how heavily water is manipulated
in this region, it is more likely caused by changes in
water availability to these lakes.
Pollen
For the purposes of the discussion we examine the
KOS and the undated XIT record together as both have
similar recent paleoecological histories. The pollen
content of the basal sediments in both KOS and XIT
records the composition of the vegetation growing in
the area prior to the establishment of the lakes, and
initial plant succession once the water bodies became
permanent. Low percentages of tree pollen (Pinus,
Juglans, Populus, and Salix) in both records suggest
trees were not locally common at the time of lake
formation. The abundance of Chenopodiaceae and
Tamarix in the lower sections of both records suggest
that these lakes initially had arid environments as both
are characteristic of saline soils. The Chenopodiaceae
is relatively floristic rich (4.2 %) in the arid and semi-
arid zones across Uzbekistan while Tamarix, a salt
tolerant species, is common in high saline water
table sites (Gintzburger 2003). The desert soils of
Uzbekistan have evolved under semi-arid and arid
conditions and have been intensively studied for their
agricultural development due to the availability of
irrigation water (Letolle and Mainguet 1993).
Following freshwater inputs from irrigation there is
a dramatic increase in Typha/Sparganium and corre-
sponding decreases in Chenopodiaceae and Tamarix.
This change in vegetation provides evidence for the
transition to freshwater environments reflected by
natural plant succession in and around the lake.
Myriophyllum is present at both sites but at different
abundances in the early part of both lake histories. The
low levels of Myriophyllum at KOS suggest that the
lake filled in quickly when irrigation water became
available. At XIT Myriophyllum persists for longer in
the basal sediments suggesting the lake existed as a
shallow pond initially before the lake became deeper
and more permanent. In general, the basal sediments
contain lower pollen concentrations possibly due to
the high sand content in these sections of the cores.
While rice pollen is encountered at all levels, the
first appearance of weedy pollen and other plant crops
(cotton and potatoes) occur near the top of the cores
and become more abundant, likely reflecting intensi-
fication of agricultural activities after freshwater
inputs from irrigation to the area. The transition to
pollen types dominated by freshwater plants in the
sediment is concomitant with the greater carbon
content of the upper sediments, and higher pollen
concentrations overall at both sites. The combination
of these factors demonstrates that the lakes are
becoming fresher and more productive over time.
The lack of pollen variation in ESH may be
explained by its position on the border of the irrigated
area in Khorezm (Fig. 1). There is little irrigated land
around the lake, and the lake receives only irrigation
drainage water and has no outlet (Crootof et al. 2015).
The lake water is currently hyposaline to hypersaline
(8 g/L up to 50 g/L) depending on the season and
water supply to the lake. During drought conditions,
evapotranspiration is high and salinity increases
substantially compared to the other lakes studied here
(Crootof et al. 2015). Increased aridity is detrimental
to the preservation of pollen, which may be another
factor in the lack of pollen variation observed in ESH.
Thus, variations in pollen types are more variable and
less definitive than the other lakes.
Preliminary data from DOV and ATA both show
that they have similar paleoecological histories to
KOS and XIT, as they are initially dominated by plants
adapted to arid environments and eventually replaced
by plants adapted to more freshwater conditions. SHK
is similar to the ESH site as there is little variation in
the down-core pollen record.
Pesticide occurrence
The pesticidesDDT andHCHwere used extensively in
Uzbekistan in general and in Khorezm specifically
from the 1950s through 1991 (when Uzbekistan gained
its independence). In the late 1970s, the total amount of
pesticides used in Central Asia generally was between
30 and 35 kg/ha, almost 30 times higher than in the rest
of the former Soviet Union during this time (UNESCO
2000). Therefore, high concentrations of these pesti-
cides might be expected in soil and lake sediments.
J Paleolimnol
123
The low concentrations of pesticides found in the
lakes studied is surprising given the history of
pesticide use in the Aral Sea Basin during the Soviet
era (see for example Galiulin and Bashkin 1996;
Tornqvist et al. 2010). However, pesticides in
Khorezm may not travel far. The region is arid with
little rainfall and runoff into the lakes. The landscape
surrounding the lakes has low relief so what runoff
does occur does not likely mobilize the agricultural
soils that are far from the lakes. Furthermore, the water
that fills the lakes is predominately Amu Darya water
(Shanafield et al. 2010; Scott et al. 2011). This water is
stored in a large upstream reservoir above the
agricultural fields and is likely low in pesticides.
Low concentrations (maximum of 0.14 lg/L for
RDDT and maximum of 0.05 lg/L for RHCH) weredetected in water samples collected during 2006–2008
(Crootof et al. 2015), indicating that the recent
pesticide concentrations in the lake sediments are
likely to be low compared to lakes worldwide. While
pesticide concentrations in all lakes are low at the lake
sediment surface (maximum concentration of 20 lg/kg for both RDDT and RHCH), we observe increasingconcentrations of RHCH at the surface of DOV, KOS,
SAP, SHK, and SHY (Fig. 5a–c). The reason for this is
not known, but pesticide storage areas that contain
soils with high concentrations of pesticides still exist
in the region and could be mobilized (Crootof 2011). It
is also possible that the source can be agricultural
lands with high concentrations of these persistent
pesticides in some areas of Khorezm.
The highest concentrations ofRDDT are not seen at
the surface of the lake sediments. Only four lakes
(SHK, ESH, NAY, and TUY) have RDDT concentra-
tions in the lake sediments greater than the background
value of 5 lg/kg (Fig. 5a–d). The three cores from
TUY all have the RDDT peak at approximately the
same time period, between about 1950 and 1970
(Fig. 5d). The two cores from the center of the lake
both peak around 1970. The older age of the RDDTpeak for the core at the edge of the lake, may be due to
uncertainty in the age model for this core, or because
pesticide applications reached the edge of the lake
before it made it to the center of the lake. DDT use in
Uzbekistan was prohibited in 1983, so the peak in
concentrations in RDDT concentrations in TUY
during the 1970s was likely due to its increased use
before the ban. The low concentrations of RDDT in
the shallowest core depths in TUY and all the cores is
likely due to its non-use after 1983, or to the possibility
that other less-expensive pesticides have been used
instead since 1983.
Concentrations of both RDDT and RHCH are
greater than background concentrations in pre-lacus-
trine sands in the core taken from the center of TUY
(TUY-2), and concentrations of RDDT are higher in
core TUY-1 taken on the edge of TUY (Figs. 5d, 6d).
It is not clear why concentrations in the sand would be
as high, or higher than, the lacustrine sediments, but
movement through anoxic groundwater is possible
over a long period of time. Scott et al. (2011) showed
that although groundwater contributions to this lake
are small, there is some movement of groundwater to
the lake.
Only SHK shows peaks in concentrations of both
RDDT and RHCH (Figs. 5a, 6a). The highest con-
centrations are between 1950 and 1990, which is
during peak use of these pesticides (Li et al. 2004;
Elpiner 1995). Although the concentrations of RDDTare low overall, the peak concentration of 45 lg/kg is
similar to other areas of the world (Rosen and Van
Metre 2010). In addition, 20 years of degradation
since peak pesticide use in 1990 may be a significant
way to reduce pesticide contamination because these
lakes are relatively carbon-rich, which may cause
higher than usual degradation rates.
Origin of the lakes
The need for large amounts of Amu Darya river water
in an arid environment led to salinization of the soil
and the need for flushing salts from the soil every
spring (Ibrakhimov et al. 2011). The construction of
irrigation and drainage canals to distribute Amu Darya
river water likely has led to the formation or
enhancement of most of the lakes in the region, which
supports our results that indicate most of the lakes are
less than 100 years before present. Evidence for this
comes from the short length of the lacustrine sedi-
ments and age models for the lakes studied. In
addition, comparing water level measurements from
the 1950s (before the most intensive irrigation began)
to the mid-2000s from six wells in Khorezm shows
that groundwater levels have risen by more than 10 m
(Scott et al. 2011). The water table is now near the
surface (\2 m) (Ibrakhimov et al. 2011). Given that
the groundwater table was more than 10 m lower in
the 1950s than it is now, it is unlikely that many natural
J Paleolimnol
123
lakes would have been able to exist in the arid climate
without a connection to the groundwater or a perma-
nent surface water source. There are no natural surface
water connections to the lakes, only constructed
irrigation and drainage canals, so natural lakes would
have had to rely on groundwater to exist year round.
Scott et al. (2011) showed that groundwater discharge
to TUY and KHO is not sufficient to keep the lakes
perennial, and this is likely the case for most of the
other lakes due to the very flat land surface and lack of
vertical head to supply sufficient groundwater to the
lakes to outstrip evaporation. Although the age of
some of the lakes may predate the large-scale irriga-
tion development by the Soviet Union that led to
declining Aral Sea water levels beginning in 1960
(Micklin 1988), these lakes may have still formed
from human-induced water diversions, just at an
earlier date than is hypothesized here. The Amu Darya
flooded seasonally before dams regulated its flows,
which may have also provided seasonal water to these
lakes in earlier times (Tanton and Heaven 1999).
Conclusions
Our analysis of the first sediment cores taken from
lakes in Khorezm indicates thin accumulation of
lacustrine sediments, and relatively consistent 137Cs
and 210Pb age dating, which indicate that lakes are
generally less than 150 years old and some are less
than 100 years old. A few lakes may be older, but
limitations in the age dating techniques makes
assigning older constrained ages uncertain.
Loss on ignition and pollen data indicate that when
perennial lakes began accumulating sediment, they
were low in carbon and sediments were composed
mostly of sand. As more water became available
through irrigation, lakes became fresher, deposited
fine-grained sediments, and became permanent. The
highest organic content of the cores is always at or near
the top of the cores, within sediment that was
deposited since 1950 when water use was greatest.
Based on detailed pollen data from at least two sites
(KOS and XIT) the lakes most likely started out as
ephemeral saline lakes that became fresh as Amu
Darya irrigation water was transported to the lakes
through irrigation canals, groundwater, and occasional
runoff. Analysis of RHCH and RDDT data indicate
that while some lakes show peaks in either RHCH or
RDDT concentrations between 1960 and 1991 when
the region was part of the Soviet Union, remaining
concentrations of these pesticides are low compared to
published literature, and some lakes continue to have
increasing concentrations of RHCH. It is uncertain
why RHCH should still be increasing in some of the
lakes, as its use has been greatly curtailed since 1991.
Although some small natural lakes may exist in
Khorezm, they are not the dominant lake type in this
region. The young ages of the lakes indicate that they
were formed mostly from imported irrigation water
from the Amu Darya. As has been shown by water
budget calculations (Scott et al. 2011), without annual
input of irrigation water, it is unlikely that the lakes
will remain perennial or fresh. Therefore, changes in
irrigation practices and water management in the
region will play an important role in the future role of
these lakes in the Khorezm landscape.
Acknowledgments The authors would like to thank Benjamin
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. Thisworkwould not have been possible
without support and contributions from John Lamers and
Zentrum fur Entwicklungforschung (ZEF), Dilorom Fayzieva,
Marhabo Bekchonova, Diana Shermetova, Nodirbek
Mullaboev, Margaret Shanafield, and Hayot Ibrakhimov. The
project was funded by a NATO Science for Peace Grant No.
982159 and a grant from the National Science Foundation EAR
0838239. The US Geological Survey has approved this
manuscript for publication. All interpretations reflect the
scientific judgment of the authors and do not necessarily reflect
the views of their organizations. The use of product names if for
identification and does not imply endorsement of the US
Government or any of the authors respective organizations.
References
Appleby PG (2001) Chronostratigraphic techniques in recent
sediments. In: Last WM, Smol JP (eds) Tracking envi-
ronmental change using lake sediments, vol 1., Basin
Analysis, coring, and chronological techniquesKluwer
Academic Publishers, Dordrecht, pp 171–203
Bauer RE, Edlund E, Orvis K (1991) CALPALYN 2.0. U.C.
Berkeley. Department of Geography Palynology Labora-
tory, Berkeley
Beasy KM, Ellison JC (2013) Comparison of three methods for
the quantification of sediment organic carbon in salt mar-
shes of the Rubicon Estuary, Tasmania, Australia. Int J Biol
5:1–13
Boroffka NGO (2010) Archaeology and its relevance to climate
and water level changes: a review. In: Kostianoy AG,
Kosarev AN (eds) The Aral Sea Environment. The
J Paleolimnol
123
Handbook of Environmental Chemistry. Springer. doi:10.
1007/698_2009_1
Chaturvedi M, Datta K, Nair PKK (1998) Pollen morphology of
Oryza (Poaceae). Grana 37:79–86
Crootof A (2011) Assessing water resources in Khorezm,
Uzbekistan for the development of aquaculture. M.S.
Thesis, University of Nevada, Reno, p 106
Crootof A, Mullabaev N, Saito L, Atwell L, Rosen MR, Bek-
chonovaM, Ginatullina E, Scott J, Chandra S, Nishonov B,
Lamers JPA, Fayzieva D (2015) Hydroecological condi-
tion and potential for aquaculture in lakes of the arid region
of Khorezm, Uzbekistan. J Arid Environ 117:37–46.
doi:10.1016/j.jaridenv.2015.02.012
Elpiner LI (1995) Medical–ecological problems of the eastern
Aral-land. GeoJournal 35:43–46
Faegri J, Iversen K (1989) Textbook of pollen analysis, 4th edn.
Hafner Press, New York
Fayzieva DKh, Atabekov NS, Usmanov IA, Azizov AA, Ste-
blyanko SN, Aslov S, Khamzina AS (2004) Hydrosphere
and health of population in the Aral Sea Basin. In: Fayzieva
D (ed) Environmental health in central Asia: The present
and the future. WIT Press, Southampton, pp 51–100
Galiulin RV, Bashkin VN (1996) Organochlorinated com-
pounds (PCBs and insecticides) in irrigated agrolandscapes
of Russia and Uzbekistan. Water Air Soil Pollut
89:247–266
Gintzburger G (2003) Rangelands of the arid and semi-arid
zones in Uzbekistan. ICARDA, Montpellier, p 426
Heiri O, Lotter AF, Lemcke G (2001) Loss-on-ignition as a
method for estimating organic and carbonate content in
sediments: reproducibility and comparability of results.
J Paleolimnol 25:101–110
Hill DW,McCarty PL (1967) Anaerobic degradation of selected
chlorinated hydrocarbon pesticides. J Water Pollut Control
Fed 39:1259–1277
IbrakhimovM,Martius C, Lamers JPA, Tischbein B (2011) The
dynamics of groundwater table and salinity over 17 years
in Khorezm. Agric Water Manag 101:52–61
Jensen S, Mazhitova Z, Zetterstrom R (1997) Environmental
pollution and child health in the Aral Sea region in Kaza-
khstan. Sci Total Environ 206:187–193
Kaiser B (2005) The volume of water reservoirs in Khorezm,
Uzbekistan. Internal report. ZEF/UNESCO Khorezm
Project, Urgench, Uzbekistan and University of Applied
Sciences, Nordostniedersachsen, Germany
Kapp RO, Davis OK, King JE (2000) Ronald O. Kapp’s pollen
and spores, 2nd edn. American Association of Stratigraphic
Palynologists, College Station
Karimov B, Lieth H, Kurambaeva M, Matsapeva I (2005) The
problems of fishermen in the southern Aral Sea region.
Mitig Adapt Strateg Glob Chang 10(1):87–103
Klaminder J, Appleby P, Crook P, Renberg I (2012) Post-de-
position diffusion of 137Cs in lake sediment: implications
for radiocaesium dating. Sedimentology 59:2259–2267
Korosi JB, Cheng W, Blais JM (2015) Organic pollutants in
sediment core archives. In: Blais JM, Rosen MR, Smol JP
(eds) Environmental contaminants: using natural archives
to track sources and long-term trends of pollution.
Springer, Dordrecht, pp 161–185
Letolle R, Chesterikoff A (1999) Salinity of surface waters in
the Aral Sea region. Int J Salt Lake Res 8:293–306
Letolle R, Mainguet M (1993) Aral. Springer, Paris, p 357
Li YF, Zhulidov AV, Robarts RD, Korotova LG (2004) Hex-
achlorocyclohexane use in the former Soviet Union. Arch
Environ Contam Toxicol 48:10–15
Manz M, Wenzel KD, Dietze U, Schuurmann G (2001) Per-
sistent organic pollutants in agricultural soils of central
Germany. Sci Total Environ 277:187–198
Martius C, Froebrich J, Nuppenau EA (2009) Water resource
management for improving environmental security and
rural livelihoods in the irrigated Amu Darya lowlands. In:
Brauch HG (ed) Facing global environmental change:
environmental, human, energy, food, health and water
security concepts. Springer, Berlin, Heidelberg, pp 749–761
McAndrews JH, Berti AA, Norris G (1973) Key to the quater-
nary pollen and spores of the Great Lakes Region. Royal
Ontario Museum Life Sciences Miscellaneous Publication,
Royal Ontario Museum, Toronto, p 61
Micklin PP (1988) Dessication of the Aral Sea: a water manage-
ment disaster in the Soviet Union. Science 241:1170–1176
Oberkircher L, Shanafield M, Ismailova B, Saito L (2011)
Ecosystem and social construction—an interdisciplinary
case study of the Shurkul Lake landscape in Khorezm,
Uzbekistan. Ecol Soc 16(4):20. doi:10.5751/ES-04511-
160420
Pollanen R, Valkama I, Toivonen H (1997) Transport of
radioactive particles from the Chernobyl accident. Atmos
Environ 31:3575–3590
RD 52.24.71-88 (1988) Manual on organochlorine pesticides
and their metabolites determination in bottom sediments.
Rostov-on-Don. p 38 (in Russian)Rosen MR, Crootof A, Reidy, L, Saito L, Nishonov B, Scott JA
(2016) Datasets for determining the origin of shallow lakes
in the Khorezm Province, Uzbekistan, and the history of
pesticide use around these lakes. US Geological Survey
Data Release. https://dx.doi.org/10.5066/F7319T07
Rosen MR, Van Metre PC (2010) Assessment of multiple
sources of anthropogenic and natural chemical inputs to a
morphologically complex basin, Lake Mead, USA.
Palaeogeogr Palaeoclimatol Palaeoecol 294:30–43
Santisteban JI, Mediavilla R, Lopez-Pamo E, Dabrio CJ, Ruiz
Zapata MB, Jose Gil-Garcıa M, Castano S, Martınez-Al-
faro PE (2004) Loss on ignition: A qualitative or quanti-
tative method for organic matter and carbonate mineral
content in sediments? J Paleolimnol 32:287–299
Scott J, Rosen MR, Saito L, Decker D (2011) The influence of
irrigation water on the hydrology and lake water balance of
two small arid-climate lakes in Khorezm, Uzbekistan.
J Hydrol 410:114–125
Severskiy I, Chervanov I, Ponomarenko Y, Novikova NM,
Miagkov SV, Rautalahti E, Daler D (2005) Aral Sea—
GIWA regional assessment 24. University of Kalmar on
behalf of United Nations Environment Programme, Kalmar
Shanafield M, Rosen MR, Saito L, Chandra S, Lamers J, Nis-
honov B (2010) Identification of nitrogen sources to four
small lakes in the agricultural region of Khorezm,
Uzbekistan. Biogeochem J 101:357–368
Sharom MS, Miles JRW, Harris RC, McEwen FL (1980) Persis-
tence of 12 insecticides in water. Water Res 14:1089–1093
Smol JP (2008) Pollution of lakes and rivers: a paleoenviron-
mental perspective, 2nd edn. Blackwell Publishing,
Oxford, p 383
J Paleolimnol
123
Stockmarr J (1971) Tablets with spores used in absolute pollen
analysis. Pollen Spores 13:615–621
Tanton TW, Heaven S (1999) Worsening of the Aral Basin
crisis: Can there be a solution? J Water Resour Plan Manag
125:363–368
The Governmental Portal of the Republic of Uzbekistan (2016)
Uzbekistan Territory. https://www.gov.uz/en/pages/territory
Tolstov SP (2005) Following the tracks of ancient Khorezmian
civilization. United Nations Educational, Scientific and
Cultural Organization. Originally published in Russian in
1948 by the Publishing House of the Academy of Sciences
of the USSR, Moscow-Leningrad, p 313
Tornqvist R, Jarsjo J, Karimov B (2010) Health risks from large-
scale water pollution: trends in Central Asia. Environ
Internat 37:435–442
[UNESCO] United Nations Educational, Scientific, and Cultural
Organization—Division of Water Resources (2000) Water
related vision for the Aral Sea basin for the year 2025. http://
unesdoc.unesco.org/images/0012/001262/126259mo.pdf
Veldwisch GJA (2008) Cotton, rice and water. The transfor-
mation of agrarian relations, irrigation technology and
water distribution in Khorezm, Uzbekistan. Ph.D. Disser-
tation, University of Bonn, Bonn, p 220
Wehrheim P, Schoeller-Schletter A, Martius C (eds) (2008)
Continuity and change: land and water use reforms in rural
Uzbekistan: Socio-economic and legal analyses from the
region Khorezm. Halle/Saale, Germany: Leibniz-Institut
fur Agrarentwicklung in Mittel- und Osteuropa (IAMO).
http://www.iamo.de/dok/sr_vol43.pdf
Wolfe LN, Zepp RG, Paris DR, Baughman GL, Hollis RC
(1977) Methoxychlor and DDT degradation in water: rates
and products. Environ Sci Technol 11:1077–1081
Zweig RD, Morton JD, Stewart M (1999) Source water quality
for aquaculture: a guide for assessment. The World Bank,
Washington, D.C. https://www.extension.org/mediawiki/
files/e/ed/Source_Water_Quality_for_Aquaculture_A_
Guide_for_Assessment.pdf
J Paleolimnol
123
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