With population growth, industrialization and expansion of irrigated agriculture, in some areas over-exploitation of lake resources, and disruption of the balance of lake ecosystems, have caused problems within lakes such as drying, shrinkage and serious water pollution. This can lead to degradation of the ecological environment around the lake, land desertification, and salinity intensification. Therefore, it is critical to maintain the balance of lake ecosystems. In this paper taking East Juyanhai as the study area we use remote sensing technology and visual interpretation of ETM images of the lake area, and extract data for each month from 2002 to 2012. We determined the lake area using the hydrological guarantee rate method, and used meteorological data on wind speed, relative humidity, air temperature, vapor pressure, and precipitation from the Ejinaqi weather station. We determined the lake leakage coefficient, and constructed a lake ecological water requirement model by applying the water balance principle, conducting preliminary estimates for each month, and determining the annual average ecological water requirement for different guarantee rates in East Juyanhai.
The results were as follows: in January to March each year, the lake area in East Juyanhai remained unchanged. In April, the lake area began to decrease. The lake area reached a minimum in July, and the lake area gradually increased in August. After October, the lake area remained stable. The evaporation water consumption of East Juyanhai was highest from May to August, and maximum evaporation was in June. The average annual evaporation of water consumption under the guarantee rates of 50%, 75%, 95% was 1.7910×10⁸ m³, 1.6072×10⁸ m³, and 1.0373×10⁸ m³, respectively. The leakage of East Juyanhai was reasonably low; the average annual leakage under the guarantee rates of 50%, 75%, 95% was 15.0788×10⁴ m³, 13.5314×10⁴ m³, and 8.7334×10⁴ m³, respectively. Precipitation was mainly concentrated in June to October, and the average annual precipitation recharge under the guarantee rates of 50%, 75%, 95% was 118.1083×10⁴ m³, 105.9882×10⁴ m³, 68.4062×10⁴ m³, respectively. The average annual ecological water requirement of East Juyanhai under the guarantee rates of 50%, 75%, 95% was 1.7807×10⁸ m³, 1.5980×10⁸ m³, and 1.0314×10⁸ m³, respectively; accounted for about 9.66%, 8.66, and 5.59%, respectively, of the average annual runoff of Yingluoxia; about 16.27%, 14.60%, and 9.42%, respectively, of the average annual runoff of Zhengyixia; and about 30.81%, 27.65%, 17.84%, respectively, of the average annual runoff of Langxinshan.
The results showed that: under the minimum guaranteed rate, to maintain the East Juyanhai lake area (23.94 km²), prevent the lake from shrinking, and ensure the surrounding environment is not severely degraded, the minimum ecological water requirement is 1.03×10⁸ m³; under the appropriate guaranteed rate, to maintain the East Juyanhai lake area (37.09 km²) and initially improve the surrounding ecological environment, the minimum ecological water requirement is 1.60×10⁸ m³; under the ideal guaranteed rate, to maintain the East Juyanhai lake area (41.33 km²) and ensure that the surrounding ecological environment is greatly improved, the minimum ecological water requirement is 1.78×10⁸ m³.
This research can provide the basis for rational allocation of Heihe River Basin's water resources. According to the results on ecological water requirements at different guarantee rates, management schedules for East Juyanhai's water resources must account for the relative proportions of upper, middle and lower runoff to ensure the rational allocation of water resources in the Heihe River Basin. The results of the study are also a valuable reference for the restoration and reconstruction of East Juyanhai's surrounding vegetation.