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191.
塔克拉玛干沙漠中发育有众多的古河道,其密集区主要集中在大沙漠中部。不同河流的古河道,含水层岩性有明显差异,地下水的富水性也明显不同。但沿古河道,地下水富水性均较两侧好,水质也相对较好,多为淡水和微咸水,为在沙漠区寻找水资源提供了方向  相似文献   
192.
The determination of the bottom of a subfossil meandering palaeochannel is important for investigations of the palaeohydrology of valley bottoms, and crucial for the quantitative estimation of past river discharges. The authors present a procedure on the basis of which the bottom of a palaeochannel can be precisely determined. It is based on an analysis of the stratigraphic variability of such features of deposits as: mean diameter, standard deviation of the grain-size composition, the percentage of sand, and ignition loss.  相似文献   
193.
A partial balance of mineral N is given for the basins of two coastal rivers in a forest zone in the Ivory Coast. The dry and wet depositions on the basin surfaces is given for particulate matter (NO3 , NH4 +). The quantity of mineral N washed away in the rivers is evaluated. The losses from leaching of the soils by rainwater are about 0.33 to 1.0% of the atmospheric depositions for NH4 +–N and 2.2 to 5.8% for NO3 –N. The yearly atmospheric input of N compounds to the ecosystem, about 1.4 g N m–2 y–1, is at least 14% of mineral N formed in the soils and is therefore quite significant.  相似文献   
194.
陈斯盾 《福建地质》1995,14(2):132-138
本文在1:5万尤溪县等四幅区域调研工作的基础上,就本区广泛分布的梨山组沉积岩的沉积环境。通过沉积地层的基本层序划分、地方性剖面模式层序的建立及采用相分析,划分出辫状河及交织河沉积。辫状河积的河道宽、深化值大、沙滩及坝形成侧向连续的带状砂体。细粒沉积薄而少,多呈不连续状,构成“砂包泥”的宏观特征,交织河流具低梯度、低弯度、快速填积的低能及广阔的洪泛盆地,河道沉积的砂体在侧向上包含于细粒沉积物中,由于  相似文献   
195.
疏勒河断裂带中段为一隐伏基底断裂。由于规模较大,并且充填了低阻的构造角砾岩,因此对VLF有很好的响应。本文分析了该构造的VLF响应特点,指出在本区用VLF方法寻找隐伏构造的有效性和局限性。  相似文献   
196.
Different mathematical models of river planform changes exist or are being developed. They are reviewed here by discussing a two-dimensional depth-averaged model, various meander models and a model for the braided Brahmaputra-Jamuna River in Bangladesh. Much emphasis is placed on topics where further research is needed. It is concluded that the models help in understanding the underlying processes, but cannot yet be considered generally valid and easy-to-use software packages. In the hands of experienced geomorphologists or river engineers, however, some of the models do already form valuable tools which allow better predictions of future river planforms.  相似文献   
197.
A137Cs-balance for the catchment of the River Öre in central northern Sweden which received about 30 kBq m–2 of radiocesium from the Chernobyl accident was calculated for the period 1986–1991. Altogether, slightly less than 10% of the total deposition in the catchment was estimated to be exported from the terrestrial parts during this period of time. More than 90% of this loss is transported with the River Öre to the outer sea of the Gulf of Bothnia. The retention in Lake Örträsket which is the only lake along the river course and the Öre Estuary outside the river mouth was thus slightly less than 10%. Nearly all of the radiocesium deposited in the lake is permanently retained in the sediments and successively covered with less radioactive sediment. A considerable export of radiocesium from the estuary to the outer sea takes place due to resuspension and subsequent transport by wind and wave generated currents.  相似文献   
198.
近百年长江中游旱涝的变化   总被引:1,自引:0,他引:1  
利用史料和器测雨量记录重建的近百年长江中游区域平均逐年旱涝等级指数序列研究了旱涝变化特征,发现:(1)20世纪前涝后旱,(2)22年、5-6年和2-3年的准周期振动,(3)6个交替出现的旱涝阶段。  相似文献   
199.
关于成矿系列的结构   总被引:6,自引:1,他引:6  
成矿系列是一个自然系统,它由若干矿床成因类型组成。各矿床类型间的时空结构关系表现为各类型间的“共生性”、“过渡性”和“重叠性”;其物质结构关系表现为“互补性”.本文按系统论观点,分析了上述结构,提出长江中下游铁铜成矿系列的新模式,并指出研究成矿系列的结构对预测矿产的重要意义.  相似文献   
200.
Dissolved (dialysis in situ) and total concentrations ofCu, Zn, Cd and Al in eight mining polluted rivers in the Røros area, central Norway, were determinedby atomic absorption spectrometry (flame and graphite furnace) and compared to pH, Caconcentration and alkalinity through seasonal variations in river discharge. Totalconcentrations of the metals were highest during early spring flood and during summer andautumn rain episodes. Dissolved concentrations also increased as the spring floodproceeded, but small discharge peaks within this 2 month period as well as a considerableautumn flood episode appeared to lower rather than to raise the dissolved metal concentrations.Consequently the dissolved fractions of Zn, Cd and Al showed a significant negative correlationwith river discharge, and were low at the discharge peaks. Possibly high sediment concentrationsoccurring at high flood conditions more than counteracted desorption induced by pHdecrease, and led to decreased dissolved fractions through adsorption. Cu speciationon the other hand seemed to be more closely linked to pH. Alkalinity and Ca concentration,both assumed to protect aquatic life from metal pollution, were significantly lowerduring episodes with high Cu and Al total concentrations.  相似文献   
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