2. THE PHYSICAL SETTING

2.1 Origins

The Qinghai-Xizang Plateau is an immense fault block formed by tectonic movements in the Tertiary, when the Indian Plate converged upon the Eurasian Plate. The uplift of the Himalayan, Karakorum and Kunlun ranges blocked the path of monsoons from the south west, causing the plateau region to become arid. Drainage lines to the Indian Ocean were impounded as lakes, those in terminal basins destined to become progressively more saline. Mass extinctions occurred among the flora and fauna, notably the fish (e.g. Wu 1980).

The Qinghai Lake depression on the north-eastern rim of the plateau originated by downfaulting during the Quaternary, over 2 M years ago (Academia Sinica 1979, Chen 1981, Liu 1987). The ancestral lake in the depression was fed by melting glaciers, and drained to the Huanghe (Yellow River). About 130,000 years ago, further uplift of the eastern rim turned the drainage inward to form an endorheic basin. The former link with the Huanghe was preserved as the Daotang River (Daotanghe), unique in the region because it now flows from east to west (“backwards”), away from the ocean.

With closure of the basin, successive humid phases maintained an abundant water supply to a lake perhaps one third larger than its modern counterpart, with a depth of more than 50 m. The climate became cold and increasingly arid about 25,000 years ago, and a warming trend developed about 10,000 years ago (Chen et al. 1990, Wang & Chen 1990). Cold-warm and prolonged wet-dry periods alternated until about 1500 years ago, when conditions became similar to those of today. With onset of the drying trend the lake level began a slow regression that has continued, with interruptions, to the present day. Extant shoreline terraces suggest that the lake has regressed some 20 km along its east-west axis (presently about 106 km) since its peak in the late Pleistocene (cf. Chen 1991).

2.2 Geography

Qinghai Lake, or Qinghai Hu, is the largest lake in China. It takes its name (variously Chi'nghai, Tsinghai) from the Mongolian qing, meaning ‘sky blue’. The Mongolian and Tibetan names for the lake are Koko Nor and Cuo Wen Bu, respectively. The name Qinghai ('blue lake') dates from the 4th Century AD (Chen 1991), when the region first came under Chinese control, and was adopted by the province on its inauguration in 1926.

The lake is a vast expanse of water with a circumference of about 360 km (Fig. 1.1), lying between 36°32'–37°15'N and 99°36– 101°47'E, on the north-eastern margin of the Qinghai-Xizang Plateau about 135 km from the provincial capital of Xining (population 800,000). The surrounding region has a desert climate, typical of semi-arid grasslands, but is strongly influenced by altitude (Köppen classification BW). Winters are extremely cold and summers are mild, with average monthly temperatures ranging between-12.7°C in January (minimum-30°C) and 12.4°C in July (maximum 28°C). Ice covers the lake from November to March each year. Annual precipitation and evaporation vary in the region, but average about 386 and 1460 mm respectively.

In the course of the lake's historical regression two small lakes (Erhai, Gahai: Fig. 1.1) have become isolated from the main water body, and Haiyan Bay in the north-eastern region appears to be in the process of separation (cf. Chen 1991). The main lake has become progressively shallower (and possibly more saline: see section 3.3). Changes in the water level have been especially marked over the past three decades, due to increasing aridity and, to some extent, diversions of water for irrigation. The shoreline of 30 years ago remains as a conspicuous terrace 2–3 m above the present lake level.

The lake is fed by more than 40 streams, but most are intermittent and few contribute significant discharges. The main rivers are the Buha, which contributes about half of the total inflow, the Shaliu, Haergai, Heima and Qianji (Fig. 1.1). Each has a well-developed alluvial fan 5–15 km wide.

The lake basin is part of a terraced piedmont plain of alluvial and lacustrine sediments flanked by heavily-eroded mountains within 2–10 km of the lake shore. Fine sands predominate along the northern shore, and in southern areas there are extensive beaches of limestone cobbles. The regional soils are highly permeable and calcareous, becoming increasingly alkaline in the subsoil, and include red and grey sandstones and light-gray and clay-like limestones. Analyses of two typical agricultural soils are shown in Table 2.1. There appears to be no information about the use of crop fertilizers, although human and animal manure certainly would be used.

Plant communities around the lake are dominated by hardy species tolerant of climatic extremes. The most conspicuous plants are grasses and low-lying woody shrubs, and trees occur only in copses associated with isolated settlements. Wormwood species (Artemisia spp.) are ubiquitous, and nettles, hollyhocks and asters also are common. Coarse tussock grasses (e.g. Poa spp.) are abundant during the summer months and provide pasture for large herds of grazing animals. Although grasslands predominate, a band of marshland occurs around the lake shore between the mouths of the Shaliu and Haergai rivers. A list of more than 500 plant species from the region has been compiled by Professor Lu Shonglian, Northwest Plateau Institute of Biology, Xining.

Table 2.1
Analyses of two agricultural soils typical of the region of Qinghai Lake, courtesy of Professor Lu Shonglian, Northwest Plateau Institute of Biology, Xining.

Bird Island (Niadao), near the mouth of the Buha River at the western end of the lake, is a sanctuary for large seasonal populations of water birds, mainly bar-headed geese (Anser ichthyaetus), brown-headed gulls (Larus brunnicephalus), black-headed gulls (L. ichthyaetus) and cormorants (Phalacrocorax carbo sinensis), plus many less common species including ducks, snipe and terns. The island supports over 100,000 birds, yet has a breeding area of only 67,000 m² (Chen 1987). The lake nominally has five islands, but Bird Island, Egg Island and Sand Island (Shadao) became peninsulas during the 1970s as a result of the falling lake level and siltation from inflowing rivers (section 3.3). Only Haxingshan and Three Stones islands remain separate.

The lake region supports 90,500 people (1987 census) of whom 75% earn a livelihood from agriculture and animal husbandry. There are communes and many isolated settlements, but the only large population centre is the town of Gangca (population about 50,000), situated on the Shaliu River about 15 km from the lake (Fig. 1.1). The land around the southern shore is populated mainly by itinerant Tibetan herdsmen and devoted to graying, whereas the northern shore is occupied by Mongolians involved in crop production as well as grazing. The grasslands support large herds of domestic animals, including 1.94 M sheep and goats, 490,000 yaks, 43,000 horses and 1200 donkeys and camels. Some 14,908 ha are planted to crops, mainly rape and barley. Agricultural production is valued at US$14.13 M, or nearly 94% of total local production.

Further information about the natural history of the lake may be found in the report (in Chinese) of a survey made in 1961–63 by the Institutes of Geology (Lanzhou), Hydrobiology (Wuhan), Microbiology (Beijing) and Geology & Paleobiology (Nanjing), and published by Academia Sinica (1979). The report is an invaluable source of data and is quoted extensively in the following pages. Other information is provided by a series of semi-popular articles translated into English and published by The Qinghai Science & Technology Weekly (1987). In addition, Appendix I contains a bibliography of published articles about Qinghai Lake, most of them in Chinese. The published Chinese literature is sparse, difficult to access and sometimes contradictory, and whilst efforts have been made to cross-check secondhand data used in this report, the reader should be cautious in taking information out of context.