【作者】 陈雪梅；

【导师】 黄小忠； 张家武；

【作者基本信息】 兰州大学 ， 自然地理学， 2012， 硕士

【摘要】 目前的全球变化是自然和人类活动长期共同作用的结果,孢粉学的研究必须重视人类活动的影响,才能更好地恢复和重建古植被和古气候。农业活动是人类活动的重要内容,农作物分布的地域性差异及地层中农作物花粉辨识的困难,使得人类农业活动影响下的孢粉组合研究较少且进展缓慢。黑河流域地处西北干旱、半干旱地区,生态环境脆弱,人类农业活动历史悠久,目前人类农业活动已成为其环境变化的主要影响因素。为了很好的认识流域环境变化及农业发展历史,本研究通过对流域不同农田、荒地和荒漠的76个表土样品,东灰山遗址剖面的37个样品和尾闾湖泊剖面的38个样品的孢粉分析,以期根据孢粉组合特征揭示流域晚全新世以来的环境演化及农业活动历史。通过对小麦地、小米地、云杉林,草甸的表土样品及湿地和遗址剖面样品中禾本科花粉粒径测量和分析,发现小麦花粉粒径范围在37.5μm-64μm之间,湿地中芦苇花粉粒径范围为在22μm-28μm,遗址中禾本科花粉粒径的分布范围和云杉林、草甸及小米地样品中禾本科花粉粒径范围一致,主要分布在22μm-37.5μm之间,因此无法通过花粉粒径测量将粟的花粉与野生杂草花粉进行区分。41个农田表土样品花粉分析结果表明,农作物花粉是农田花粉组合的主要成分,平均含量为45.6%；农作物以外的草本花粉平均含量为48.7%,乔木(平均1.6%)和灌木(平均4.2%)花粉含量较低。种植的农作物不同,其花粉组合特征亦有差别：油菜地中油菜花粉占绝对优势,其他草本花粉很少；玉米地、小麦地、大麦地以及混作地花粉组合以农作物以外的草本花粉为主,农作物花粉次之。同样种植禾本科作物,小麦地、玉米地、大麦地孢粉组合也有差异。农田花粉组合随海拔变化有一定的规律：十字花科(油菜)花粉主要出现在2000米以上,峰值出现在2800米；农作物禾本科花粉则出现在海拔2000米以下,这与绿洲农业的分布海拔相符合,因此它是农业活动的重要指示花粉。农田周边荒地的花粉组合中草本花粉占主导,灌木花粉含量上升,农作物花粉含量急剧下降且花粉浓度较高。荒漠戈壁人类活动影响微弱,花粉类型单一,以旱生植被藜科、麻黄、白刺等为主,农作物花粉零星出现。农田、荒地及荒漠中花粉组合对比研究有助于提取指示人类农业活动的孢粉指示物：农作物禾本科花粉在农田、荒地和荒漠中含量逐渐降低,表明农作物禾本科花粉传播能力较弱,地层中出现一定比例的谷物类禾本科花粉可以判断当地或附近有农田；人类农业活动会导致花粉浓度降低,农田中孢粉浓度在所有植被带中最低,与人类的施肥翻耕除草等有关；农田中乔灌木花粉及其他草本花粉的低含量与人类农业生产中有意识去除杂草的举措有关；低海拔地区农田中,湿/中生草本花粉百分含量与旱生草本花粉百分含量的比值(W/D)可能指示人类活动对局地环境的影响。东灰山遗址文化层孢粉类型单一,浓度较低,小麦花粉含量较高,平均23.2%,表明遗址在距今3000多年前已栽培小麦,这与浮选出的12.2%碳化小麦种子结果相吻合。表明农作物禾本科花粉对农业活动有响应,孢粉分析的方法可以被用于追溯东灰山遗址早期小麦等作物的栽培,同时也可将其应用到没有碳化种子等大化石及遗存的湿地、湖泊沉积物中,以分析其早期的农业活动。嘎顺诺尔湖泊剖面孢粉结果表明：公元9世纪70年代至14世纪中期,花粉浓度和A/C比值均较低,白刺、麻黄等旱生植物花粉含量较高,揭示区域气候湿度适中或偏干,植被盖度较低,且以荒漠植被为主。剖面孢粉谱中少量的农作物禾本科花粉与西夏和元朝河西地区及额济纳旗地区的农业活动相符合。公元14世纪中期至18世纪晚期,该阶段对应全球典型的小冰期时期。该时段花粉浓度和A/C值较高,藜科、白刺等荒漠植物花粉含量明显下降,指示区域环境较湿润,植被状况较好。19世纪至今,花粉浓度及A/C比值最低,藜科、白刺、麻黄等花粉含量显著增加,指示区域气候干旱,环境变差,以荒漠植被为主。孢粉谱中出现的农作物禾本科花粉,可能指示明清时期河西地区的农业开发活动。更多还原

【Abstract】 The current global change is the result of concerted action of both long-term natural and human activities, therefore, more attentions have to be paid to the human influences in palynological studies in order to better recover and reconstruct the paleo-vegetation and paleo-climate. Human agricultural activity is one of the most important parts of human activities. Pollen assemblage characteristics influenced by the human activities is very complicated due to the regional differences of crops distribution. Thus, studying modern pollen assemblages is necessary, and this kind of research is rare in this area. Heihe River Basin, which is famous for agricultural development, is located in arid and semi-arid regions of northwestern China with a fragile ecological environment, and human agricultural activities are the main factors impacted on its vegetation and environmental changes. To better understand the vegetation and environmental changes as well as the history of agricultural development of the Heihe River Drainage, a total of76modern soil samples were collected from different cultivated fields, wastelands together with desert in the upper and middle reaches of Heihe River Basin, meanwhile,37profile samples were taken in Donghuishan Site, as well as38strata samples selected in Ganxu Nur. The purpose of the research is to investigate the ancient agricultural history of this area, as well as the environmental evolution.Poaceae pollen from a series of surface samples collected from several cultivated fields (wheat fields and millet fields), as well as a few non-cultivated lands (spruce land, meadow land and wetland) and archaeological site, were measured to establish the standard size to distinguish two types of Poaceae pollen:cereal type and natural one. Result of Poaceae pollen grain size measurements discovered that the grain length of wheat pollen is between37.5μm and64μm, while the pollen diameters range of Phragmites australis in wetland varied from22μm-28μm. Samples collected from archaeological site of this study, meadow land as well as spruce land of Heihe River Drainage Basin, show the same distribution character as those from millet fields, in which the pollen sizes vary from22to55μm, and its highest size frequency falls between24and 40μm, thus there are no means to distinguish the millet pollen from those wild species through diameter measuring method.The pollen assemblages of41surface soil samples collected from farmlands suggest that the crop pollen is one of the main components in the pollen assemblages with an average of45.6%and the average percentage of other grass pollen is about48.7%, as well as low frequencies of arboreal pollen and shrub pollen whose contents are1.6%and4.3%separately. When different crops are planted, the abundances of the crop type pollen are different. The average percentage of Brassica campestris pollen is85.8%in the rape fields, while the other herbs except crop pollen types are dominant in those farmlands planted with corn, wheat and mixed crops. The relationship between farmland pollen assemblages and altitude indicates that the Cruciferae pollen mainly appears in a height which is higher than2000m and its percentage peaks at2800m. The Cereal-type of Poaceae (>37.5μm) pollen mainly appears below the height of2000m, which is in accordance with the distribution altitude of the oasis agriculture. Therefore, it could be considered as an important indicator of human agricultural activities.The pollen assemblages of the wastelands, compared with those from cultivated fields, are dominated with herbs pollen, and the shrubs pollen content increase but the percentages of the agricultural Poaceae pollen decrease sharply, meanwhile, the pollen concentration is relatively high. In the desert, with rare human activities impacted, the pollen types is monotonous, mainly consist of Chenopodiaceae, Ephedra and Nitraria pollen. The abundance of cereal pollen in the desert is extremely rare.Comparing the pollen characteristics of the farmlands, wasteland and desert can make contribution to the identification of meaningful and rewarding information on human activities indicated by pollen. The percentages of cereal-type Poaceae in cultivated fields, wasteland and desert decreased gradually which indicate that the cereal-type Poaceae pollen have a relatively lower transmission capacity and it can be identified as an important indicator of agricultural activities when there are a certain amount of those kinds of pollen in the strata. Besides, the pollen concentrations have some relationship with the human activities, and the agricultural activities could make the pollen concentration lower. The lower pollen concentration of the cultivated fields is the results of the agricultural policies such as fertilizer and weeding, which also caused lower frequencies of arboreal and shrubs pollen as well as herbs pollen except the crops in the farmlands. The variations of the W/D ratio (ratio between pollen percentage of wet herbs and dry herbs) in the low plain (corridor region) could indicate the influences of human activities on the local environment.The pollen records of two cultural strata from Donghuishan site have23.2%of wheat pollen on average suggest that the wheat were cultivated in the site during the past3000years, which coincide with the results of flotation that the wheat grains content are12.2%on average. Besides, the pollen assemblages of Donghuishan site are similar with those of modern wheat fields, but different from the natural desert and wastelands in this area, indicate that the crop pollen responds to the agricultural activities and the pollen analysis method could be used to trace early agricultural activity in those areas without evidence of grains’remains, especially for wheat cultivation during Neolithic period in northwestern China.The pollen assemblages of lake sediments in Gaxun Nur show that, between870-1350AD, the pollen concentration and A/C ratio are relatively low, and the percentages of xerophytic plant pollen like Nitraria and Ephedra are higher, all of these suggest that the environment of this region is moderate wet and dry, as well as the vegetation cover is lower and dominate with desert vegetation types. The appearance of cereal Poaceae pollen indicated agricultural activities during this period, which is consistent with the agricultural activities of Hexi Corridor and Ejina Banner in Western Xia and Yuan Dynasty documented in history materials. From1350AD to1770AD, which is the Ming and Qing Dynasties of China, this phase corresponds to the global meaningful Little Ice Age. During this period, the pollen concentration and A/C ratio increase and have higher value, which indicate a more humid environment as well as a well developed vegetation condition. From1770AD to present, the pollen concentration and A/C ratio decreased to a relative low value, together with the increase of Chenopodiaceae, Ephedra and many those kinds of dry pollen. These results suggest that the environment became extremely dry and the desert vegetation predominate in this area. The appearance of less amount of crops pollen might indicate the agricultural activities of Hexi Corridor in Ming and Qing Dynasty.更多还原