lowerreachestheseseasonal variations areless pro-
nounced because so much water isremoved byirri-
gation channels and reservoirs. Inthisarea the sa-
linity ofwater isvery high because of a low water
flow.Thus, in1989 and 1990 mineralizationduring
the full-waterperiod in thelowerreaches was437–
679 and 336–598 mg1–1respectively. Itincreased
significantly in the dryseason to922–3999 mg1–1in
1989 and t o 973–1868 mg1–1in 1990.
Increases in mineralization wereaccompanied by
the generalcontamination ofwater in theriver. Pol-
lutantsincluded almost alldangerouschemical sub-
stances: oil products, phenols, heavy metals,orga-
nic substances, etc.(Table 1). In1989–1990, atend-
encytowards a decrease inpesticidecontent in the
Amu-Daryawater wasnoticed. In1990 and1991,
the concentration of D D T and itsmetabolites in the
TuyamuyunReservoir was0.1–20.0 mg1–1, and the
concentration ofotherorganochlorine pesticides,
0.015–0.616 mg1–1. Pollution causeddeath ofsilver
carp,Hypophthalmichthysmolitrix,on a massive
scale in thisreservoir.ers and lakes wasextremelycontaminated by chem-
icals due todisposal ofdrainagewastefrom thearea
of irrigatedlandcultivation (Chembarisov1989).
The increased mineralization (from1000 t o1420 mg
1 –1) and contamination of thedrainage waterswith
pesticides,mineralfertilizers, andsalts changed the
hydrochemical regime of the rivers and lakes. In the
1950s, themeancontent ofions in theAmu-Darya
water was 540 mg1–1(Rogov1957), whileduring the
lastdecade itvariedbetween 600 and1500 mg1–1
The highest level ofpollution is in the lower
reaches of the AmuDaryaRiver. In 19892 , the mean
annualmineralization of water was1525.5 mg1–1
near thetowm ofNukus(215 kmfrom themouth),
and in 1990,936.8 mg1–1.
Changes in the hydrochemical regime of the
Amu DaryaRiverwereaugmented bydecreases in
the annualdischarge. The mineralcontent of water
in the Amu DaryaRiverdepends to agreat extent
on fluctuations in thevolume ofwater discharge.
Until thetime whenriver flowbecameregulated
(the1960s), thefluctuationswerecausedmostly by
variations in the melting ofglacier-snow in the up-
per reaches. Aspring-summerpeak ofwater and a
dry fallwerequitedistinct.Even nowthese season-
al fluctuations in thewaterlevel areexpressed in
the upper andmiddle reaches of the river. In the
Changes in the Aral SeaThe Aral Seaecosystem hasundergoneconsiderable
changeduring thelast 30years. It was thefourth big-
gestlake on theplanet. Itchangedfrom abrackish-
waterlakewith anaveragewatersalinity10.3 in 1961
to a salt-water onewith asalinity of37–38.Water lev-(^2) Yearbook on SurfaceWaterQuality andEfficiency ofWater
protectionMeasures in Uzbekistan in 1989.1991.Goskomgidro-
met USSR.Tashkent, Pt. I.Vol. 4.Book 1–5 (in Russian).
Table 1. Water pollution in two areas of the Amu Darya River, near towns of Termez (middle reaches) and Nukus (lower reaches).
Chemicals Termez Nukus
1989 1990 I989 1990
Concentration MAC Concentration MAC Concentration M A C Concentration MAC
fact or factor factor factor
Phenols 0.004 mg I^143 0.008 mg1–1 83 0.004 mg1–1 43 0.0 I0 mg1–1 103
Oil products 0.18 mg1–1 3.63 0.04 mg 1^1 0.83 0.15 mg1^133 – –
Copper 8.8μg1–1 8.83 10.0 μg I^1103 10 .0μ g 1-1 103 10.7 μg I^1 10.63
α -benzenehexachloride 0.028 mg1–1 2.83 0.019 mg1–1 1.93 ND – N D –
γ-benzenehexachloride 0.013 mg1–1 1.33 0.015 mg1–1 1.53 ND – N D –
Nitrate nitrogen 0.037 mg1–1 1.93 0.027 mg1–1 1.43 0.042 mg1–1 0.23 1.42 2.13
*Number oftimes of MAC(MaximumAllowableConcentrations. PDK inRussian), aregivenaccording to the Sovietstandards (see
Feshbach & Friendly 1992); N D = notdetermined.