内蒙古鄂托克旗天然草地植被生态需水量研究

开展天然草地植被生态需水量研究,对维持草地系统生态健康和可持续发展意义重大。该研究以干旱风沙草原区鄂托克旗为研究对象,基于联合国粮农组织推荐的Penman-Monteith公式及美国农业部土壤保持局推荐的有效降水量计算方法,对各草地类型的生态需水量和生态缺水量进行计算,并对不同类型天然草地生态需水和降雨资源之间的平衡关系进行分析。结果表明:全旗全年生态需水量在丰水年为2.94×10~9m~3、平水年为3.07×10~9 m~3、枯水年为3.10×10~9m~3;全旗生态缺水量在丰水年为2.72×10~8m~3、平水年为5.00×10~8m~3、枯水年为1.15×10~9m~3。草地中生态需水量由大到小依次为温性荒漠草原类、温性草原化荒漠类、低地草甸类、温性荒漠类、温性草原类。在整个生长季中,鄂托克旗各草地类型生态需水在3、6、10月为盈余状态,其余月份均为严重亏缺状态。鄂托克旗草地生态系统整体处于水分亏缺状态,尤其是惠农站代表区,在枯水年水分亏缺指数超过50%。低地草甸类草地缺水程度较严重,建议在该类型草地分布范围内发展人工草地,温性草原化荒漠类草地缺水程度较轻,建议在鄂托克旗适当发展。研究结果可为区域草地水资源高效利用和退化草原系统恢复重建提供理论依据。

Ecological water requirement of natural grassland vegetation in the Otog Banner of Inner Monglia

Natural grasslands have become essential to the development of pastoral areas, due mainly to the area of natural grassland accounts for more than 90% of the available grasslands in China. Furthermore, pastoral areas have great potential for ecological barriers and national food security. However, the grassland resources are rapidly decreasing in a seriously damaged ecosystem, particularly with the climate of global warming and regional drying. Vegetation restoration can be an important measure for ecosystem restoration on the natural grasslands. Therefore,water is the dominant factor to control the growth of vegetation in the regional drying grasslands. The ecological water requirement (EWR) of natural grassland can be defined as the amount of water required to maintain normal growth of vegetation in the special ecosystems. It is necessary to coordinate the water use relationship between economic development and ecological environment in pastoral areas, thereby achieving the rational allocation of water resources. In this study, a Penman-Monteith formula was utilized to calculate the evapotranspiration of reference crops in the Otog Banner of northern China from 1960 to 2016. A Mann-Kendall test was conducted to evaluate changing trend of evapotranspiration with time. A remote sensing inversion of soil moisture content was also used to calculate the limiting coefficient of soil moisture. An investigation was made to count the coverage rate of vegetation in the natural grassland and the growth period of dominant plants in different grassland types. A piecewise single average crop coefficient method (FAO-56) was used to calculate the crop coefficient in the grasslands. The reference evapotranspiration contributed to obtaining the limiting coefficient of soil water, the crop coefficient, the requirement and shortage of ecological water for various grassland types in different regions. A tradeoff was gained to clarifythe relationship between ecological water demand and rainfall resources for the different types of natural grassland. The results are as follows: 1) The grassland ecosystem in the OtogBanner was in a state of water deficit as a whole, especially in the representative area of Huinong station, where the water deficit was more than 50% in a dry year. 2) The annual EWR of the whole banner was 2.94×109 m3 in wet years, 3.07×109 m3 in normal water years, and 3.10×109 m3 in dry years. The annual ecological water shortage was 2.72×108m3 in wet years, 5.00×108 m3 in normal years, and 1.15×109 m3 in dry years. The EWRs of grasslands were ranked from large to small: the temperate desert steppe, temperate steppe desert, lowland meadow, temperate desert, and temperate steppe. 3) There was an unbalanced state of EWR for all kinds of grassland vegetation in the Otog Banner. Specifically, the serious water shortage occurred in May, followed by August, April, July, and September, whereas, there was a surplus state of EWR in March, June, and October, where the largest surplus EWR occurred in June. A suggestion was made to store the rainwater in surplus months, thereby solving the spatiotemporal unbalance of rainwater resources in different seasons. These recommendations can greatly contribute to maintaining the healthy and sustainable development of grassland ecology.