天山北麓晚全新世环境演变及其人类活动的影响

在天山北麓(坡)不同海拔、不同植被带、不同沉积相选取剖面, 进行14C测年和沉积相、孢粉、粒度、磁化率及烧失量分析, 探讨晚全新世的环境演变. 通过对比艾比湖、大西沟、东道海子、桦树窝子和四厂湖等剖面反映的环境信息, 结果表明: 晚全新世以来, 气候有冷暖干湿波动, 但干旱的总面貌未发生根本变化. 反映在植被上, 山区森林、低山丘陵区草原-荒漠草原、平原区荒漠-荒漠草原的植被景观无根本变化, 但是在森林的上下界限、平原河谷林的发育程度、平原低地草甸的面积上, 随气候的变化而发生波动.平原湖泊受环境变化的影响十分明显. 晚全新世以来, 平原湖泊水面变化频繁, 3.1～2.4 ka BP, 1.7～1.3 ka BP和1.27～0.3 ka BP时期是高湖面阶段.1.7～0.6 ka BP的中世纪, 气候比较湿润, 温暖, 平原湖泊处于高水位期, 1.7～1.3 ka BP期间天山的云杉林带下限下移, 林带加宽, 自然环境处于最好阶段.人为活动只是在近代对环境产生较大影响, 主要表现在对平原地区水系和自然绿洲的影响上, 河流流量减少、流程缩短、尾闾湖消亡、扇缘溢出带北移、地下水位降低, 泉水流量减少等成为普遍现象.人工绿洲取代自然绿洲, 自然绿洲大面积减少, 尾闾湖滨绿洲大面积消亡, 平原河谷绿洲面积减少, 扇缘溢出带绿洲和大河三角洲绿洲为人工绿洲取代.

Environmental Evolvement and Human Activity Impact in the Late Holocene on the North Slopes of the Tianshan Mountains, China

Several cross-sections were selected at different elevations, different vegetation zones and different sedimentary faces on the north slopes of the Tianshan Mountains. Substitutive indexes for environmental study (including sedimentary phase, pollen, grain size, magnetic susceptibility, cautery lost, and {~{14}C} dating) show that there has been the climatic oscillation of cold/warm and dry/wet since the beginning of the late Holocene, but the arid features did not basically change. There is no significant change in vegetation pattern, including alpine forest, grassland-steppe on low mountain and hill, steppe-desert on the plain. But both of the upper and lower timberlines, developing level of the valley forest, and marshland area on the lowland distinctly change with climatic oscillation. The lakes on plains have significantly varied with environmental change, especially the lake surface area. The periods from 3.1 to 2.4, 1.7 to 1.3, and 1.27 to 0.3 ka BP were high lake level stages. The climate was relatively moist and warm, with high lake level, during the Middle Ages from 1.7 to 0.6 ka BP. The lower timberline of the Tianshan conifer forest moved downward, the forest zone was widened, and the natural environment appeared the optimum time from 1.7 to 1.3 ka BP. Human activity has significantly impacted the environment in latter history period only, and mainly influenced the plain runoff system and the oases. On the plain regions appear river discharge decreasing, shortening of the of the river courses, drying-up of the tail-lakes, northward migrating of the fan-margin, lowering-down of the ground water and spring discharge decreasing. Artificial oases replaced the natural oases. The area of natural oases tremendously decreases, including the lakeshore oases, valley-plain oases, fan-margin oases and delta oases.