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981.
982.
RS和GIS支持下的三江平原沼泽湿地动态变化研究 总被引:81,自引:19,他引:81
以景观生态学理论为基础,采用遥感(RS)和地理信息系统(GIS)相结合的方法,探讨了三江平原沼泽湿地的动态变化特征。结果表明,三江平原沼泽湿地主要分布在富锦、同江和抚远三个县(市),其总面积占全区总面积的51.42%;1980-2000年间三江平原沼泽湿地的分布面积显著下降,1980-1996年间沼泽湿地面积减少了51.33%,1996年之后减少速度明显下降。同时沼泽湿地景观的破碎化显著,斑块数量增加了46%,斑块密度净增加两倍。1980年、1996年、2000年景观的分维湿地面积变化较之全区变化不显著外,其它地区均发生较为显著的变化。 相似文献
983.
984.
三江平原和横断山区的泥炭资源及其合理开发利用 总被引:1,自引:0,他引:1
三江平原和横断山区是我国泥炭资源两大丰富区,作者详细论述了三江平原和横断山区的泥炭资源分布、泥炭资源评价和开发利用与保护问题。泥炭的形成和积累是各种自然因素综合作用的结果。不同地区由于地貌、地质、气候以及各种成矿作用组合的差异,不仅造成泥炭分布的时空不平衡性,而且也影响着泥炭性质、质量,左右着泥炭开发利用的方向。泥炭质量评价以泥炭的性质为依据,是泥炭合理开发利用的基础,决定着泥炭利用的方向和效益。 相似文献
985.
云南三江地区富碱侵入岩与煌斑岩的同源性 总被引:8,自引:1,他引:8
云南三江地区富碱侵入岩与煌斑岩的同源性金志升黄智龙朱成明(中国科学院地球化学研究所,贵阳550002)关键词三江地区富碱侵入岩煌斑岩同源性三江地区富碱侵入岩带(亦称哀牢山-金沙江富碱侵入岩带)是世界上著名的富碱侵入岩带之一,前人对该区富碱侵入岩进行过... 相似文献
986.
The series of climatic events affecting landscapes on the southeastern Atlantic Coastal Plain over the past several thousand years is poorly understood. This is due, in part, to the paucity of depositional basins in this region containing adequately preserved microfossils for paleoecological analyses. This research reconstructs past hydrologic environments from the microfossil record of Peat Bay, a small, peat-filled pond in south-central South Carolina. We cored the deepest location in the pond and retrieved 120 cm of sediment representing 5200 yr of deposition. Fine clays at the base of the core resembled sediments deposited in abandoned channels of the nearby Savannah River, suggesting the basin may have functioned as an oxbow wetland prone to periodic flooding and drying. Overlying peats containing planktonic diatom assemblages mark the onset of persistent open-water conditions ca. 4600 B.P. These data, in conjunction with a small body of paleoecological evidence from other southeastern wetlands, suggest that a hydrologic 'threshold' was surpassed during the mid-Holocene that resulted in flooding and expansion of low-lying depressions that characterize the regional landscape. This is likely the culmination of long-term hydrologic trends related to glacial retreat, including increased precipitation and a rise in ground water levels corresponding to a global rise in sea level. In Peat Bay, lake-like conditions persisted until about 3800 B.P., after which time aerophilic diatoms and remains of other temporary pond organisms dominated the fossil record. Episodic drying of pond sediments during the late-Holocene may have been a response to decreased precipitation, stabilization of the water table and infilling of the pond by decaying vegetation and terrigenous clastics. The microfossil record indicates that temporary pond conditions persisted until recent years (ca. 1985) when the basin returned to a permanently flooded state due to groundwater connection to a large reservoir constructed nearby. 相似文献
987.
Edit Tham-Bozs Andrew S. Murray Annamria Ndor rpd Magyari Edit Babinszki 《Quaternary Geochronology》2007,2(1-4):168-173
To reconstruct the evolution of Late-Quaternary river network in the southeastern part of the Great Hungarian Plain, we have used optically stimulated luminescence (OSL) and heavy mineral analysis of 25 sand samples from the upper 2–8 m of the fluvial units, complemented by four radiocarbon ages. The estimated OSL depositional ages vary between 10 and 47 ka. The heavy mineral composition of the OSL samples was compared to the compositional data of recent river sediments using cluster analysis. The new OSL and heavy mineral data show that from 47 to 10 ka ago the sediments were transported mainly from the northeast direction into the southeastern part of the Great Hungarian Plain by the ancestor of the Tisza river and its northern tributaries, and probably by another large river which also flowed northeast–southwest, parallel to the modern Tisza. Between 23 and 14 ka sediments periodically came from the east and reached the eastern part of our study area. Between 15 and 12 ka ago, sands transported from the southeast also occur in the southeastern and central part of the study area. These data suggest that the modern rivers occupied their present courses only in the last 10 ka. 相似文献
988.
989.
Giovanni Muttoni Cesare Ravazzi Marzia Breda Carlo Laj Alain Mazaud 《Quaternary Research》2007,67(1):161-173
We applied magnetostratigraphy and mammal biostratigraphy to date climate-sensitive pollen cycles and lithostratigraphic units of the Pliocene-Pleistocene Leffe sedimentary succession from the Southern Alps, Italy. The Leffe section was correlated to additional sections (Casnigo, Fornaci di Ranica, and Pianengo) to construct a stratigraphic network along a common fluviatile system (the Serio River) sourced in the Southern Alps and flowing southward into the Po River Basin. We obtained a coherent scenario of climate variability for the last ∼ 2 Myr. At Leffe, lacustrine deposition commenced during the Olduvai Normal Subchron (1.94-1.78 Ma) and lasted up to a chronologic level compatible with Marine Isotope Stage (MIS) 22 (0.87 Ma). Pollen analysis revealed that climate varied cyclically from warm-temperate to cool during this time interval, but never as cold as during glacial intervals. At around MIS 22, climate cooled globally. Gravels, attributed to high-energy braided river systems fed locally by alluvial fans, prograded from the Serio River catchment area over the Leffe Basin and toward the Po Plain in response to a generalized event of vegetation withdrawal and enhanced physical erosion. At this time, Alpine valley glaciers reached their first maximum southward expansion with glacier fronts located at only ∼ 5 km upstream from Leffe. 相似文献
990.
平原区的水文计算在当前生态重建环境中具有重要意义.利用仿雨试验,研究地面坡度小于 3‰的平原区降雨产流的特征,稳定降雨条件下径流系数的变化规律,提出了"最大径流系数法"对平原降雨产流的计算原理,对非稳定及天然条件下的暴雨过程进行了径流计算.结果表明:(1)对仿雨实验变雨强径流计算,计算值与实测值比较相对误差平均为 6.43%;(2)对天然降雨过程的径流计算,计算实例结果误差为 5.9%和 10.9%. 相似文献