艾比湖的湖岸地貌及其反映的湖面变化

LAKE SURFACE CHANGES INDICATED BY THE SHORE LANDFORM OF AIBY LAKE, WESTERN JUNGAR BASIN, CHINA

艾比湖为一典型的内陆干旱区封闭型湖泊。干旱区的湖泊对气候和环境变化的响应非常敏感。该湖自形成以来的变化在湖岸地貌中留下了很好的记录。对湖积堤和湖成阶地的系统研究以及对湖积平原的分析结果展现了艾比湖的湖面变化过程。

Aiby Lake is a typical closed lake in inland of arid area, is mainly recharged by surface runoff and flank groundwater, and maintains the lake surface equilibrium by evaporation from the lake surface. The total area of the watershed is about 50, 000 km^2, and there are 47 stream systems in big or small size in the watershed, which are mainly recharged by precipitation. Currently, only can Bortala River and Jinghe River recharge the lake, a few of them can recharge it by a little floodwater, among which the stream of Kuitun River cutout in 1970s and a little returned water can flow into the lake only occasionally. There are mainly three types of shore land form: lacustrine embankments, terraces and plains. The measured lacustrine embankments are 11, they are sequenced as B_0.B_1, …, B_(10). There are big differences in developed degree and remained degree from different regions. The remains of the main lacustrine embankments, B_1, B_2, B_8, B_9 and B_(10), can be found in all the regions around the lake, their elevations are 205, 212, 227, 230 and 238m respectively. e dating data show that Bio and B_9 formed 4, 550±72 aBP and 2, 860 ±a BP respectively, and it is estimated that B_2 formed 400 - 300 years ago after comparing. The lacustrine embankments in- dicate that the lake is in a shrinking stage since 5, 000 years. Many researches on the terraces have been carried out, the divisions, however, are not u- unified. Through elevation control, 8 main terraces can be divided, and they are sequenced as T_1, T_2, …, T_8. The elevation of the highest terrace is 280m. Although there are no dating data about the terraces, the terraces have a good corresponding relation faith the lacustrine em- bankments: B_(10) is located at the front edge of T_6; B_9 and B_8 are located at the back edge and front edge of T_5 respectively; B_7 and B_6 at the back edge and front edge of T_4 respectively; B_2 at front edge of T_3; B_1 at the front edge of T_2; and B_0 at the back edge of T_1. The lacustrine plains formed in the different periods mainly distribute on the nothwest- ern, western and eastern sides of the lake, and the change direction of the lake surface shifted in a small amplitude along with the change of the lake shape and lake bed shape. The change of the lake surface reflects the big change of the regional environment. The preliminary area of the lake was much larger than 3, 000 km^2, it maintained about 3, 000 km^2 5, 000 a BP, then it shrinked gradually. The water area of the lake was still about 1, 300 km^2 at the beginning of this century, but it shriked to about 500 km^2 from 1950s to 1970s. It is considered that shrinkage of the lake is a natural process and reflects the change of the regional environment. In a yardstick of 500 - 1, 000 years, it was mainly influenced by regional cli- mate, but mainly influenced by human activities in recent 5 decades.