黑河下游额济纳绿洲生态需水关键期及需水量

黑河流域中生态最为脆弱、植被退化最为严重而对全流域生态治理目标的实现极为关键的地区在下游额济纳绿洲.黑河分水方案主要控制年总量,由来水过程确定分水时机,采用“全线闭口、集中下泄”的分水方式,这容易导致分水与下游绿洲需水的时间错位.要实现黑河分水对下游天然绿洲的作用和意义,不仅要充分保证分水量,更要选择适宜的分水时间,如果分水错过了下游绿洲生态需水的关键期,将会直接影响绿洲植被的正常生长.要维持黑河下游额济纳绿洲健康、稳定和持续发展,确定生态需水的关键期是首当其冲的问题.本文通过对黑河下游额济纳绿洲地下水位时空动态变化过程、天然植被耗水过程和绿洲生态过程及水文过程的关系研究,确定了黑河下游额济纳绿洲生态需水的关键期.建议在生态关键期保障输送必需的水量,合理调节水库出水量与河道径流量,保障4月和8月关键期的需水量,其中4月至少要保证0.80亿m3的输水量,8月至少要保证1.08亿m3的输水量,确保下游绿洲植被的生理需水,同时考虑到前期缺水和随后的月份水量消耗,尽可能增加关键月的配水量.

Determination of Critical Period and Requirment of Ecological Water Demanded in the Ejina Oasis in Lower Reaches of the Heihe River

Due to its extremely vulnerable ecological condition and its seriously degraded vegetation, the Ejina Oasis, located in lower reaches of the Heihe River, has key importance for realizing the goal of improving the environmental quality of the whole Heihe River Basin. The present plan for allocating the water to areas along the river is characterized by definite yearly quantity and inflow-determined letting-out time. Under this scheme, the water requirement by plant and water supply through allocating are often not simultaneous, the growing of the vegetation in the oasis is consequently affected. So, we should pay as same or more attention on the letting-out time of water as on water quantity allocated. In order to make the time of requirement and supply meet, we must be aware of the critical period of the plant species in the oasis. By monitoring the temporal-spatial variation of groundwater level at lower reaches of the Heihe River as well as analyzing the relationship between water consumption by natural vegetation and eco-hydrological process in the Ejina Oasis, we pointed out the key periods and quantity of ecological water requirement for the local vegetation as follows. At least 0.80×108 m3 and 1.08×108m3 of ecological water should be replenished in April and August, respectively, if rational regulating reservoirs outflow and channel runoff are concerned.