Natural Lakes

Commensurate with its long eventful geological history and complex geomorphology, Asia has a large diversity of natural lakes that vary in their age, area, depth, hydrology, water quality, and biodiversity. Asia has the world's largest (Caspian Sea), oldest and deepest (Lake Baikal) lakes as well as those lying at the highest (^6000 m) and lowest elevation (Dead Sea, >400 m below sea level), and with highest salinity (>400%). Lakes larger than 1000km2 and those more than 100 m deep are listed in Tables 1 and 2. Some regions such as the central Asian highland and Indonesia have a very high concentration of lakes: Mongolia has >3500 lakes (>10 ha), most of which are brackish or saline and small. Only 12 lakes have an area of more than 100 km2. There are 2800 lakes (>100 ha area) in China and of these more than half are in Tibet. In central Asia, Kyrgyzstan has 1923 lakes covering about 684 km2. Distributed over all major islands of Indonesia, there are about 520 lakes of which three are among the world's 20 deepest lakes. Within Himalaya, some regions have a very high concentration of lakes: there are 227 lakes in Sikkim (about 7000 km2 area) at altitudes rising up to 6000 m; and 90 lakes lie among the glaciers at 4460 m to 5645 m altitude within 650 km2 of Khumbu Himal (East Nepal) region. The Indian subcontinent (excluding Himalaya) has very few natural lakes of which most are of fluvial origin (floodplain lakes). There is no natural lake in the Arabian Peninsula and in Sri Lanka.

Most of the natural lakes originated variously from tectonic activities over the past several million years. Lake Baikal (Russia) originated in a rift valley about 25 million years ago. The rift valley is still seismically active, and reported to have become deeper by 9 m after the 1959 earthquate, which had its epicenter in the middle of the lake. The 636 km long and 80 km wide lake with a surface area of 31494 km2 and a maximum depth of 1671 m, has its floor 1285 m below sea level. It is the largest freshwater lake in Asia that holds 23 600 km3, or about 20% of the world's total freshwater resources. It is fed by 300 streams but the only outflow is the River Angara. The lake is also unique in its water quality (very low ion concentration, well mixed water column despite its depth) and high

Table 1 Natural lakes in Asia that are more than 100 m deep

Lake

Characteristic

Depth, m

Lake Baikal, Russia

Tectonic

1637

Caspian Sea, Russia

Endorheic saline

1025

Lake Dieng Plateau,

Crater

884

Indonesia

Lake Issyk-Kul, Kazakhstan

Endoheric/

668

monomitic

Lake Matano, Indonesia

Tectonic

590

Lake Toba, Indonesia

Volcanic/tectonic

529

Sarez Lake, Tajikistan

Tectonic

505

Lake Van, Turkey

Saline

451

Lake Poso, Indonesia

Tectonic

450

Lake Tazawa, Japan

Volcanic, caldera

423.4

Heaven lake, China

Crater lake

384

Lake Chonji/Tianchi, China

Crater

384

Lake Shikotsu, Japan

Crater

360.1

Lake Wisdom, New Guinea

Volcanic, caldera

360

Dead Sea, Israel

Endorheic/

330

hypersaline

Lake Towada, Japan

Volcanic, caldera

326.8

Lake Teletskoye, Russia

Tectonic

325

Lake Dibawah, Indonesia

Tectonic

309

Lake Singkarak, Indonesia

Tectonic

268

Lake Khuvsgul, Mongolia

Freshwater

262

Lake Kara Kul, Tajikistan

Glacial/tectonic lake

240

Lake Segara Anak,

Crater

230

Indonesia

Lake Ranau, Indonesia

Tectonic/volcanic

229

Lake Mainit, Philippines

Freshwater

223

Lake Karakul, Tajikistan

Meteoritic impact

220

Lake Mashu, Japan

Endoheric

211.4

Lake Towuti, Indonesia

Tectonic

203

Lake Toya, Japan

Volcanic caldera

179.7

Lake El'gygytgyn, Russia

Meteoritic impact

175

Lake Maninjau, Indonesia

Caldera

169

Lake Chuzenji, Japan

Volcanic

163

Lake Pakis, Indonesia

Crater

158

Lake Okutama, Japan

Reservoir

142

Lake Klindungan, Indonesia

Crater

134

Lake Basum Tso, China

Tectonic

120

Lake Kussharo, Japan

Volcanic, caldera

117.5

Lake Ritsa, Georgia

Tectonic/freshwater

116

Lake Umbozero, Russia

Tectonic/freshwater

115

Lake Buhi, Philippines

Rift lake

112

Lake Lanao, Philippines

Rift lake

112

Lake Burdur, Turkey

Salt

110

Lake Biwa, Japan

Freshwater

103.8

Lake Ashi, Japan

Caldera

103.6

Lake Lindu, Indonesia

Tectonic

100

biodiversity (1085 plants and 1550 animal species) of which 60% is endemic. An interesting feature of Lake Baikal is the endemic fauna adapted to deep water (e.g., the long-finned, translucent, Baikal oil fish (Comephorus baicalensis and C. dybowskii) living at a depth of 700-1600 m) and the large diversity of ostracods and flatworms. Lake Baikal is also known for the only freshwater seal, the Baikal Seal (Phoca sibirica).

Table 2 Natural lakes in Asia that are larger than 1000 km2

Lake

Characteristic

Area, km2

Lake Songkhla, Thailand

Natural/brackish

1040

Lake Toba, Indonesia

Volcanic/tectonic

1130

Sevan, Armenia

Tectonic

1236

Lake Vygozero, Russia

Freshwater lake

1250

Kirov Bays, Azerbaijan

Coastal, brackish

1325

to saline

Lake Tengiz, Kazakhstan

Salt

1382

Lake Hyargas, Mongolia

Saline, deep

1407

Lake Tuz, Turkey

Salt/shallow

1500

Lake Hamun-i-Helmand,

Marshy salt lake

1600

Afghanistan

Lake Zaysan, Kazakhstan

Freshwater

1810

Lake Ogan-Komering,

Floodplain

2000

Indonesia

Lake Taihu, China

Riverine,

2428

floodplain

Lake Hulun, China

Freshwater

2339

Lake Namtso, China

Salt

2470

Lake Alakol, Kazakhstan

Salt

2650

Lake Dongting, China

Shallow, riverine

2820-20 000

Lake Aydar, Uzbekistan

Brackish/salt

3000

Lake Uvs Nuur, Mongolia

Salt

3350

Lake Peipus, Estonia

Freshwater lake

3555

Lake Van, Turkey

Saline

3755

Lake Xingkai Hu (=Lake

Riverine

4380

Khanka)

China/Russia

Lake Taymyr, Russia

Freshwater

4560

Lake Urmia (Iranian

Salt

5200

Azerbaijan)

Lake Qinghai, China

Drainless lake/

5694

saline

Lake Issyk-Kul,

Endoheric/

6236

Kazakhstan

monomitic

Lake Balkhash,

Endorheic/saline

16996

Kazakhstan; China

Aral Sea, Kazakhstan/

Glacial/saline

17158

Uzbekistan

Lake Baikal, Russia

Tectonic

31500

Dead Sea, Israel

Endorheic/

40650

hypersaline

Naujan lake, Philippines

Volcanic

81250

Caspian Sea, Russia

Endorheic saline

371 000

Tonle Sap, Cambodia

Riverine

2500-10 000

Lake Poyang, China

Riverine,

3585

floodplain

Lake Hawr al Hammar,

Seasonal flooding

2500

Iraq

Lake Tharthar, Iraq

Seasonal flooding

2700

Lake Dibbis, Iraq

Seasonal flooding

1985

Lake Issyk-kul (=Ysyk-Kol) in Kyrgyzstan is also ca. 25 Ma old lake, located at 1606 m elevation in an intermontane valley in the north of Tien Shan mountains. The 668 m deep lake is 182 km long and up to 60 km wide, and covers an area of 6236 km2. The endorheic lake basin is surrounded by high glacier-capped mountains and receives more than 100 rivers of which Djyrgalan and Tyup are the largest. The water is slightly saline and never freezes. The lake supports relatively few plant and animal species many of which are endemic. The native fisheries have declined in recent years after the introduction of the Sevan trout from Armenia. The freshwater Lake Biwa (Honshu, Japan) is another very old (2 Ma) lake that occupies an oblong tectonic rift basin (104 m deep).

The origin of some old lakes is traced back to the geological events that gave birth to the Asian continent. The Caspian Sea, the world's largest lake (surface area about 394 000 km2 and total volume 78 000 km3), which lies east of the Caucasus and north of the Elburz Mountains, and 28 m below the sea level, evolved over the past >7M years, passing through phases of constriction and expansion and large water level changes. The collision of the Arabian Peninsula with west Asia pushed up the Elburz-Kopet Dag and Caucasus Mountains and formed the Sarmatian Lake, composed of the present Black Sea and south Caspian. Further orogenic events separated the Black Sea from South Caspian which started sagging. A mountain arch rose across the south basin dividing it into the Khachmas and Lenkoran Lakes. Subsidence of this land bridge due to continued sagging reunited the two basins (Balakhan Lake). About 3-2 million years BP the lake expanded to more than three times its present area - reconnecting with Black Sea and Aral Sea. The lake surface was at +50 m. During the Pleistocene (2-0.7 Ma BP) the lake level rose and fell in a series of events but the lake level sank deeper each time, reaching its lowest level of —120 m from sea level. These changes were evidently linked to glaciation cycles, and the retreat of glaciers in Russia. In recent years, the water level has fluctuated by a few meters in response to the periodic changes in the course of the Amu-Darya River. The lake level dropped by 3 m between 1930 and 1977 but rose rapidly after 1978 to —26 m mark.

The lake comprises of three basins: a large shallow northern basin (max. 20 m deep), a small middle basin (max. 788 m deep) and a large deep (maximum 1006 m) south basin. The salinity varies from 0.1% to 1.2% along a north-south gradient. The lake is fed by River Volga, which forms a delta on the lake's northern shore, discharging annually an average 237 km3 fresh water (range: 200-450 km3) into the lake. River Kura (16.8km3) and the Ural River (8.1km3) provide other major inflows. During the past few years, water level has again started declining because of the exploitation of R. Volga waters.

Lake Baskunchak, north of the Caspian Sea, is another saline (>30% salinity) lake that lies 21 m below sea level. It also originated by getting isolated from the sea during the Pleistocene.

Two interesting lakes in Israel: Lake Kinneret in the north and Dead Sea in the south, lie in the Jordan rift valley which is a part of the Great Rift Valley system extending from Turkey to Zambezi in Africa. About 3 Ma BP, the valley was flooded from the Meditrerra-nean Sea that deposited thick layers of salts. The orogenic processes raised the land between the rift and the Mediterranean, separating the lakes from the Sea. Further tectonic processes, linked with the northward shift of the Arabian peninsula, resulted in sinking of the southern part deeper than in the north, and the deposition of sediments pushed up the salts as the Mt Sedom on the southwest side. Today, the Dead Sea has its surface 418 m below sea level whereas Lake Kinneret (also known as L. Tiberias or the Sea of Galilee) is 211 m below sea level. Dead Sea is the deepest (max. depth 330 m) hypersaline lake with average 310% salinity. Interestingly, the salts are mostly magnesium and potassium chloride (52% and 37%) and sodium concentration is low. During the past 70 k years, water level of the Dead Sea has fluctuated greatly by several hundred meters, and started dropping in the past few thousand years. High ariditry (<25 mm rain) is also responsible because the inflow from L. Kinneret has declined. L. Kinneret is nearly freshwater though the ionic composition varies at different depths. It is fed by R. Jordan which used to flow through Hula marshes before entering the lake but the river has now been regulated and a part of its flow used for irrigation.

Another large lake, Aral Sea, lies between Kazakhstan and Uzbekistan, in the Aral-Sarykamysh Depression which was formed by tectonic processes and wind erosion, ca. 3 Ma BP. The saline lake is fed by Amu Darya and Syr Darya rivers, which originate in the Pamir ranges and discharge together about 110 km3 of water. However, the diversion of river flow for irrigation has resulted in rapid shrinking of the lake from 68 000 km2 in 1960 to 17160 km2 in 2004 (Figure 2), and consequently a sharp increase in salinity.

Lake Balkhash in eastern Kazakhstan, lies about 1600 km east of Aral Sea, in another tectonic depression surrounded by mountain ranges. The 600-km long and 5-70-km wide lake covers an area of about 16 000 km2. It is an endorheic lake, with its western half being shallow (6 m deep) fresh to brackish water and eastern half being deep (26 m) and saline (up to 7%). The lake receives about 80% of its water from R. Ili flowing from Tien Shan mountain ranges in China. Excessive water diversion for cotton cultivation has lowered the lake area and increased its salinity.

Several other tectonic lakes in central Asia are large and deep; e.g., Lake Hovsgol (Khuvsgul) in Mongolia is a 262 m deep, 2 Ma old lake with freshwater of pristine quality whereas Lake Alakol at 347 m altitude in Kazakhstan is 54 m deep saline lake with an area of 2 650 km2. Lake Zaysan in eastern Kazakhstan, however, is a large 106-km long (1,810 km2) freshwater lake at 420 m elevation, and is the source of Irtysh River. Khar-us lake (1157 m altitude) is another large (1852 km2) but shallow (only 4 m) freshwater lake. Lake Teletskoye, the largest lake (233 km2) at 434 m altitude in the Altai Mountains is 325 m deep tectonic lake.

In Qinghai-Xizang plateau, lakes have developed under the influence of the vertical, transversal, and oblique tectonic movements resulting in a lattice-like network of lakes. Most lakes are therefore long and narrow. Many fault valleys were later dammed by material deposited by landslide or moraine carried by retreating glaciers or by floods. Other lakes were created by glacial activity. Such lakes are distributed mainly at the periphery of the plateau; they are numerous but small. Most of these lakes are saline and lie at elevations of more than 3000 m. In most cases, the depth has not been determined yet. L. Qinghai (5 694 km2) lying at 3205 m between Hainan and Haibei provinces, is the largest of them. During the past few decades, following the drying up of most of the tributary streams, the water level has gone down and several smaller lakes have separated from it near its periphery. The second largest lake in the region is Nam Co (2 470 km2) lying close to Lhasa, at 4718 m altitude. Lake Pangong Tso (4250 m altitude), a transboundary lake with about two-thirds of its 134 km length in China and the rest in India, also lies in a dammed fault valley. Lake Mansarovar (=Mapham Yutso) is a freshwater lake (320 km2) at 4556 m altitude near Mt Kailash. Together with the adjacent Rakshastal lake (=La'nga Co), it is not only of great religious importance but four major rivers Sutlej, Brahmaputra (=Tsangpo), Indus and Karnali, have their source in its vicinity. Other important lakes in Tibet region are: Puma Yumco (5030 m elvation), Yamdrok (620 km2) and Dagze Co (260 km2).

In Yunnan province (China) there are numerous rift-valley lakes that are deep and developed during the late Tertiary or early Quaternary, along tectonic fracture belts. For example, Lakes Chehu, Yang Zong Hai, Fu Xian Hu (155 m deep), Xing Yun Hu, and Tong Hai lie along the Xiao Jiang fracture zone and Lakes Lugu Hu (93 m deep), Jian Chuan Hu, Er Hai, etc lie along the Hong He (Red River) fracture zone. Most of the important lakes in Inner Mongolia (Lake Hu Lun Hu and Lake Dai Hai), Xinjiang (Lakes Bosi iugun' .

KAZAKHSTAN

KAZAKHSTAN

Figure 2 (Continued)

ZBEKISTAN \

Karakalpakstan

Figure 2 (Continued)

Figure 2 Changes in the area of Aral Sea between 1973 (a) and 2004 (b) following the diversion of river flows for cotton cultivation in arid Central Asia. (From URL: na.unep.net/digital_atlas2/webatlas.php?id=11.)

Teng Hu, Saili Mu Hu, Bulun Tuo Hu, Aibi Hu) and northern Hebei province are also relatively large and of tectonic origin. Tectonic lakes in Indonesia include Lakes Diatas, Dibawah, Lindu, Mahalona, Poso, Ranau Rawa Danau, Singkarak, Tawar Laut, Towuti and Yamur, and in Japan the better known are L. Akoi, L. Kizaki, and L. Nakatsuna. Major lakes in Nepal lie in deep gorges (e.g., Lake Rara; 167 m deep) or in blocked valleys (e.g., Lake Phewa).

Numerous lakes developed under the influence of glaciers either solely or in combination with the tectonic processes, throughout the Himalayan ranges from Kashmir in the west to Arunachal Pradesh in the east, particularly at elevations beyond approx. 2000 m. These lakes are generally small and relatively shallow. Many of them occupy fault depressions with blockages created by moraine or landslides. The outflows from most of the high altitude glacial lakes gradually turn into major rivers. Noteworthy among these lakes are Gangabal, Nilnag, Kounsarnag, Kishensar and Alipather in Kashmir, Tso Moriri (a large, 75 m deep brackishwater lake), Tso Kar and Statsapuk Tso, Yaye Tso, Khagyar Tso, Pangur Tso in Ladakh, Chandratal, Nainital and Bhimtal in Himachal and Uttarakhand, and Lake Tsomgo in Sikkim. In Nepal and Sikkim Himalaya, the lakes occur also at elevations beyond 5000 m; for example, Lake Sonlaphyo Tso at 6230 m in Sikkim.

Both caldera and crater lakes are common in southeast Asia, particularly Indonesia. The caldera lakes are formed by volcanic eruptions followed by the collapse of the dome causing large and deep depressions, the caldera. Crater lakes develop by filling in of the extinct craters. Lake Toba, in the middle of north Sumatra (Indonesia) is the world's largest caldera lake (100 km long and 30 km wide) at an elevation of 900 m. It lies near a fault line running along the Sumatra Fracture Zone, and was formed about 71 500 ± 4000 years ago, by a huge eruption, the largest within the last two million years. The volcano spewed out about 2000 km3 of lava flow and 800 km3 of ash which was carried by the winds westwards up to the Indian subcontinent and deposited there as a 15-cm thick layer (up to 6 m thick at one site in central India). The volcanic dome in the middle of the lake formed a large island in the lake. The area is seismically active with frequent earthquakes and smaller eruptions near the margin of the caldera and lava domes. Some parts of the caldera have been uplifted (for example, Samosir Island by 450 m). Within Sumatra, Lake Maninjau is another caldera lake formed by a volcanic eruption ca. 52 000 years BP. The caldera measuring 20 x 8 km is occupied by the 99.5 km2 lake with a maximum depth of 165 m. The lake outflows on its west into the Antokan river which has been used for hydropower generation. Lake Wisdom (360 m deep) and Lake Dakataua (120 m deep) are two major caldera lakes in Papua-New Guinea. Lake Yak Loum in Ratanakiri province of Vietnam is another large caldera (about 75 km in diameter and 48 m deep). The deepest lake (373 m) in China, Lake Tian Chi is also a caldera lake, in the Bai Tou Shan (=Changhai) mountain at 2194m altitude (area 10 km2). Volcanic eruptions have recurred here quite frequently (in 1597, 1668, and 1702). Lake Kurile is a large caldera (formed 6440 BC) in the southern Kamchatka Peninsula. It has an area of 77 km2 and an average depth of 176 m (maximum 306 m). Lake Taal of Philippines (234 km2, 172 m deep) is a large caldera lake in a volcanically active region and its basin has been modified several times. An eruption in 1754 created an outflow (R. Pansipit) on its southwest corner and another eruption in 1911 in the middle of the lake created a 45 km2 island with a small crater lake on it. In Japan, the 327-m deep Lake Towada, 233-m deep Lake Ikeda and the 179-m deep Lake Toya are major caldera lakes.

The largest freshwater lake in the Philippines, Laguna de Bay (949 km2) was formed by a combination of volcanic and tectonic activities which separated it from the Manila Bay. Lake Lanao (340 km2, 112 m deep) in Philippines was formed by the collapse of a volcano and tectonic-volcanic damming of the basin between two mountain ranges and similarly Lake Buhi (18 km2) was formed following the collapse of Mt Iriga caused by an earthquake in 1641 ad. Lava flows often create large dams blocking the tectonic valleys or even rivers. Lake Sevan (Armenia) located at 1950 m elevation is one such large lake. The lake is nearly triangular and divided into two basins, a small, 95 m deep northwestern part and a large shallower southeastern part. The freshwater lake is nearly endorheic because only <10% of total inflow is released through the only stream Razdan. In an effort to reduce evaporation losses and increase the flow in the river for irrigation, the lake area has been reduced from 1416 km2 to 1241 km2 and water level lowered by about 20 m. Lake Van (=Van Golu) in Turkey near its border with Iran is another large endorheic brackishwater lake that was formed by lava flow from the Nemrut volcano blocking the natural drainage to the Murat River. The basin of Lake Urmia, another large shallow (maximum 16 m) saline lake in Iran is also encircled by lava. Lake Jing Po Hu (area 95 km2, maximum depth 62 m) of Heilongjiang province in China was formed by Quaternary basalt lava dam blocking the outlet of River Mu Dan Jiang. Similarly, Lake Wu Da Lian Chi (18.47km2) of Dedu county (China) was formed when River Bai

He was blocked by lava from a volcanic eruption in 1719-1721.

Indonesia has many lakes formed in the craters of extinct volcanoes. For example, Klindungan (134 m), Pakis (158 m), Segara Anak (230 m), Telaga Ngebel (46 m) and Telaga Pasir (35 m), Tigawarna (60 m) and Tondano (20 m). Several lakes in Japan are deep crater lakes; e.g., Shikotsu (360 m), Mashu (211.5 m).

Maar lakes are extensively distributed in volcanic areas of North-East China, South-East China and especially in Leizhou Peninsula of Guangdong and in Huinan district of Jilin, and in Indonesia.

There are several interesting lakes formed by mete-oritic impacts. Lake Kara-Kul (25-km diameter, >220 m deep) in Tajikistan at 3,900 m elevation in the Pamir ranges was formed by a meteorite impact about 5 Ma BP. Lake El'gygytgyn (about 15 km diameter and 175 m deep) in northeast Siberia sits in a meteoritic impact crater created 3.6 million years ago. Lake Lonar in western India is a rather small crater lake (1.5 km diameter) whereas Lake Khajjiar (about 3 ha) in Himachal Pradesh (India) is also believed to have been formed by a meteoritic impact.

The next most common lakes are riverine lakes or of fluvial origin. The Asian continent has some of the world's major river systems draining its landscape. Most of these originate from the central highland and meander through the vast floodplains before discharging into the oceans. There are thousands of fluvial lakes in the floodplains of Indus, Ganga and Brahmaputra in south Asia, Yangtse and Huanghe in eastern, northwestern and Jianghan plains in China, Tigris and Euphrates in Iraq, Irrawady in Myanmar, and the Mekong in southeast Asia. The most notable example is the Tonle Sap in Cambodia which shrinks and expands dramatically from 2500 km2 to 10 000 km2 as it drains into the Mekong and gets flooded from the latter during the period of high precipitation (Figure 3). Lake Loktak in Manipur (NE India) was a similar smaller lake that alternately got flooded from or drained into the Imphal river until its water level was regulated by a barrage. In the Yangtse river basin, tectonic activities and fluvial processes have interacted to create a large number of lakes. Lake Dongting spreads from 2820 to 20 000 km2 during annual floods from Yangtse and four other rivers. It has been shrinking rapidly because of high sediment load received from the R. Yangtse. Lake Poyang connects with R. Yangtse through Han and Xiu rivers. Another large shallow lake Taihu (max. depth 2.6 m) lies in the delta of Yangtse with which it is connected by many streams but the water flux is heavily regulated. The Amur (Heilongjiang), Sungari and Ussuri rivers, poor drainage has resulted in many large and shallow lakes such as the Lake Xing Kai Hu (Lake Khanka) on the borders of China and Russia (maximum depth 10.0 m). The only natural lakes in Vietnam, Be Be (4.5 km2) and Ho-Tay (or West Lake, 4.13 km2) have a maximum depth of 3.5 m.

The floodplain lakes (=ox bow lakes) which have either become isolated from the rivers or are periodically connected with them during flood period are known variously in different countries. These are Tals in northern India, beels in eastern India: for example, Kabar Tal, Suraha Tal, Deepor beel and Sareshwar beel. In Bangladesh, these are haors (generally formed in tectonic depressions) or baors (cut off meander loops) such as Hakaluki haor (344.4 km2), Tangua haor (255 km2), Baluhar baor (2.8 km2), Marjat baor (2.5 km2) and Gobindapur baor (2.2 km2). In Iraq, these are called Hawr or Hor. Tasek Bera, Tasek Cini and Ulu Lepar in Pahang (Malaysia) are also shallow foodplain lakes.

In Iraq, the seasonally flooded shallow lakes such as Tharthar, Habbaniya, Hawr al Hammar, Dibbis, Hawr Dalmaj, Hawr Ibn Najim, Hawr al Suway-qiyah, Hawr as Saniyah, and Hawr Hawizeh are spread over hundreds of square km areas.

The majority of the lakes in the arid regions are saline to brackish. In the cold-arid regions of central Asia, they are usually endorheic and depend largely upon snowmelt from surrounding glacier-covered mountain peaks. High rates of evaporation result in increasing salinity. Innumerable lakes in the Qinghai Tibet Plateau region were formed by the epeirogenic processes followed by glacial activity. In Mongolia, some of the very large, though shallow, saline lakes include Uvs Nuur (3350 km2), Urureg (238 km2), Achit (290 km2), Khar Nuur (575 km2), Durgun (305 km2), Hyargas (1407km2), Telmen (194km2), Sangiyn Dalay (165 km2), Oygon (61.3 km2), Khyargas Lake (140 km2), Boon-tsagaan (252 km2) and Orog (140 km2). In Kazakhstan, Lake Tengiz is a large shallow (max. 6.5 m) saline lake. Kazakhstan shares with Uzbekistan a group of shallow brackish water lakes (Aydar Kul, Arnasay and Tuzkan), which cover together about 4000 km2.

In hot deserts, lakes have developed due to poor drainage that is caused by impervious subsurface layers formed by the precipitation of calcium salts. In Syria, the only shallow salt lake is Sabkat al Jabboul. Azraq oasis in eastern Jordan is a large (about 100 km2) complex of marshes fed largely by springs. Iran has a large network of lakes and lagoons south of the Caspian Sea. Anjali wetlands (Anjali Murdab) are among the most significant. In northern Azarbayjan province lies a large (4830 km2) hypersaline lake Orumiyeh (=Urmia). Numerous saline, brackish (Perishan, Maharloo, Bakhtegan, Tashk) and freshwater lakes (Dasht-e-Arjan and Haft Barm lakes) occur in the central Fars province.

The Neiriz (=Niriz or Neyriz) lake alone, when flooded during periods of heavy rainfall, covers some 1800 km2 but gets fragmented into many smaller shallow water bodies/marshes during the dry period. Another complex of freshwater lakes (Hamoun-i-Puzak, Hamoun-i-Sabari, and Hamoun-i-Helmand) lies in the Seistan basin on the east. Important lakes in Afghanistan include Jamoun-i-puzak, Lake Hashmat (near Kabul), Dasht-e-Nawar, and Abi-Estada.

Eolian lakes are also formed in deserts where huge volumes of sand transported by wind are deposited to block the flow of natural channels. These generally

April 13, 2003

small, shallow, and saline lakes are common in desert areas of India (e.g., Sambhar, Deedwana, and Pachpadra lakes in Rajasthan), Afghanistan (e.g., Hamun-e-Helmand), Iran, Middle East and China. Several lakes in region east to River Heihe for example, Lake Yihezagede Haizi of Inner Mongolia is between the sand dunes.

Karst lakes, which are formed by the dissolution of carbonate rocks or salt deposits, are relatively few. Major karst lakes of importance occur in southwest China. The Phong Nha-Ke Bang National Park (Vietnam) is the oldest major karst area in Asia, and has been subjected to massive tectonic changes. It includes

0 50 100

Hamun Lake

April 13, 2003

0 50 100

Figure 3 (Continued)

ADEOS-II/GLI 250m October 10, 2003

ADEOS-II/GLI 250m October 10, 2003

0 50 100

Figure 3 Seasonal changes in the areal extent of lake Tonle Sap during the dry and rainy season. Portions shown in green represent vegetation areas, portions shown in red or brown, nonvegetation areas; and portions shown in black or blue are water areas. April 2003: Fig. 3b and Oct. 2003: Fig. 3b. (from http://www.eorc.jaxa.jp/en/imgdata/topics/2004/img/tp040419_03.jpg and http://www.eorc.jaxa.jp/en/imgdata/topics/2004/img/tp040419_02.jpg).

65 km of caves and underground rivers. In Papua-New Guinea, Wongabi and Louise are karst lakes. Also in Turkey, there are several karst lakes in western Taurus.

The coastline of the Asian continent is studded with numerous lagoons which exchange water with the sea through a narrow mouth. Some of these lagoons have in recent years turned into completely closed freshwater bodies. Depending upon their size and orientation, most of the lakes exhibit zonation along a salinity gradient, a part of the lake distant from the sea remains freshwater. Important examples are Dongqian lake in Ninpo city and West lake in Hangzhou city in China, Lakes Chilika, Pulicat and Vembnad in India, and Lake Songhkla in Thailand. Lake Kolleru on the east coast of India was a lagoon that gradually turned into a freshwater lake though it maintained a sea connection until the last century. There are numerous small lagoons along the coastline of Sri Lanka and along the Mediterranean coast in Turkey. Interestingly, most of these lagoons have a very high biodiversity and secondary productivity.

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