Land Degradation in the Oases on the South Side of the Taklimakan Desert

塔里木盆地绿洲及其周围的年蒸散量是不同的。根据计算，于阗站年降水量约为25 ~ 100 mm，年蒸散量约为100 mm。由于绿洲的潜在蒸散量可达500 mm以上，部分荒漠地区的潜在蒸散量可达1000 mm。塔里木盆地南部绿洲分布在25 ~ 100 mm等雨量线之间。北部大部分绿洲位于25 mm ~ 200 mm等雨量线之间，年蒸散量为100 mm ~ 200 mm等雨量线；因此，较高的温度仍可能导致蒸散量普遍增加。目前，由于流量的波动，沙漠河流的长度每年都有很大的变化。例如，克里亚河（1991年）的年流量为7.0G×10^8 m^3，其中56%的流量（4.0×10^8 m^3）被用作农业灌溉用水，而其余的流量（3.0×10^8 m^3）则流入地下，每年补充地下水。克里雅河流域根据水文条件可划分为以下4个区域：①位于昆仑山的上游，由于支流交汇，河水化学成分的纵向变化较为复杂。②中部为冲积扇，克里雅绿洲位于冲积扇的顶端。该地区河水的下游化学变化十分复杂。3)在下部，蒸发对化学和同位素组成的影响较大。下游的河水在化学上和同位素上更集中。(4)在克里雅河最下游分汊处，克里雅河下游水化学变化复杂，地下水化学表现出较大的区域性差异。民丰绿洲的灌溉农业依赖于从尼雅河引水。少

The annual evapotranspiration varies in and around oases in the Tarim Basin. According to our calculations, the annual precipitation is about 25-100 mm, and annual evapotranspiration is about 100 mm at Khotan station. Since the potential evapotranspiration can reach above 500 mm in the oases, in some desert areas it can reach 1000 mm. The oases in the southern part of the Tarim Basin are located between 25 mm and 100 mm isohyet. Many oases in the northern part are located between 25 mm-200 mm isohyet and experienced 100 mm-200 mm isograms of annual evapotranspiration ; therefore, higher temperatures may still lead to a general increase in evapotranspiration.At present, the length of rivers in the desert changes greatly year by year due to fluctuations in the amount of discharge.For example, the annual discharge of the Keriya River (1991) is 7.0G×10^8 m^3, and 56% of that discharge (4.0×10^8 leaches m^3), is used as irrigation water for agriculture, while the remainder (3.0×10^8 m^3) in … More to the ground, recharging the groundwater annually.The Keriya River basin can be divided into the following four regions by hydrological conditions :1) In the upper part, which is located in the Kunlun Mountains, the longitudinal change in the chemical composition of river water is complicated because of the conjunctions of tributary streams.2) The middle part contains an alluvial fan, on the toe of which the Keriya Oasis is located. In this region, the downstream change in the water chemistry of the river water is very complicated.3) In the lower part, evaporation has a great in fluence on the chemical and isotopic compositions. The river water is more concentrated chemically and isotopically heavier in the lower reach.4) In the lowermost part, where the Keriya River diverges into some channels, the downstream change in the water chemistry of the river is complex and the groundwater chemistry shows a great regional variety.The irrigated agriculture practiced in the Minfeng oasis has relied on water diverted from the Niya river. Less