华北平原下垫面荒漠化和绿化对气候的影响

从大气热力学能量方程,水汽守恒方程以及降水与大气水汽含量和相对湿度的经验关系出发,本文假定大尺度环流不受地表下垫面变化的影响,不考虑大气辐射吸收与水汽和温度的反馈作用,对大气和地表能量过程作参数化处理,建立了一个反映区域年平均温度和降水的变化与地表反射率和波恩比变化之间的关系。计算分析表明,对于线性尺度为550km的华北平原来说,如果地表下垫面从目前状态变成沙漠的话,年平均温度将增加2.14°C,年降水量将减少536.1mm。如果华北平原全部绿化、年平均温度变化不大,年降水量可增加21.2mm。     

江汉平原农田渍害机理研究*

本文提出了江汉平原的渍害标准,并从地表水动态,地下水动态、微地貌及垦殖与耕作等主导因子分析入手,探讨了江汉平原渍害的形成原因和形成过程,为渍害的诊断改造和利用提供了理论依据。     

平原地区活断层研究

本文归纳、总结了近几年来山东省地震局在工程地震工作中采用的平原地区活断层研究的方法。几个典型实例证明,这一方法在平原地区活断层研究中是行之有效的,获得了良好的、具有科学价值的结果,同时讨论了与这一方法有关的几个问题。     

The abnormal mantle and deep tectonic process in the southern region of North China Plain

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海河平原地下水资源可持续利用前景评价

本文通过综合分析海河平原地下水资源盈余量以及建立典型三级区平原开采系数与地下水水位下降速率、地面沉降速率的关系,分析了各三级区平原依靠环境容量可扩大开采量,根据疏干时限性评价指标对海河平原地下水的开采潜力进行了评价,客观展现了维持现状开采条件下研究区地下水资源可持续利用的暗淡前景。     

Factors affecting arsenic concentration in groundwaters from Northwestern Chaco-Pampean Plain,Argentina

The concentration of arsenic measured in groundwater from three aquifers in the study area located in the Eastern Tucuman province, Argentina, mostly depends on the lithology, but the spatial and temporal variations of concentrations seem to be also controlled by pH changes, climatic factors, and human perturbations. The highest concentrations of As (more than 1,000 μg L⁻¹) were found in the shallow aquifer, made of As-rich loess, while the lowest concentrations were measured in the deep confined aquifer, consisting of alternating layers of alluvial sands/gravels and clays. Intermediate values were measured in the semiconfined aquifer made of the fluvial sediments deposited in the Salí River valley, that alternate in the upper part of the sedimentary sequence with layers of loess. Because most of As in the loess is considered to be adsorbed onto Fe-oxyhydroxide coatings, the increase of pH in the flow direction (west-east) leads to increasing arsenic concentrations towards the eastern border of the study area. The decomposition of organic wastes poured into the Salí River or associated with local and diffuse sources of contamination in the eastern part of the study area depletes dissolved oxygen, which leads to the reductive dissolution of Fe and Mn oxyhydroxides, and to the subsequent release of the adsorbed and co-precipitated As. This process mainly affects shallow groundwater and the upper part of the semiconfined aquifer. Geochemical and hydrological data also suggest that rising water table levels at the end of the wet season may also lead to reductive dissolution of As-rich Fe oxyhydroxides in the shallow aquifer.     

Origin and stratigraphy of phreatomagmatic deposits at the Pleistocene Sinker Butte Volcano, Western Snake River Plain, Idaho

Sinker Butte is the erosional remnant of a very large basaltic tuff cone of middle Pleistocene age located at the southern edge of the western Snake River Plain. Phreatomagmatic tephras are exposed in complete sections up to 100 m thick in the walls of the Snake River Canyon, creating an unusual opportunity to study the deposits produced by this volcano through its entire sequence of explosive eruptions. The main objectives of the study were to determine the overall evolution of the Sinker Butte volcano while focusing particularly on the tephras produced by its phreatomagmatic eruptions. Toward this end, twenty-three detailed stratigraphic sections ranging from 20 to 100 m thick were examined and measured in canyon walls exposing tephras deposited around 180° of the circumference of the volcano.Three main rock units are recognized in canyon walls at Sinker Butte: a lower sequence composed of numerous thin basaltic lava flows, an intermediate sequence of phreatomagmatic tephras, and a capping sequence of welded basaltic spatter and more lava flows. We subdivide the phreatomagmatic deposits into two main parts, a series of reworked, mostly subaqueously deposited tephras and a more voluminous sequence of overlying subaerial surge and fall deposits. Most of the reworked deposits are gray in color and exhibit features such as channel scour and fill, planar-stratification, high and low angle cross-stratification, trough cross-stratification, and Bouma-turbidite sequences consistent with their being deposited in shallow standing water or in braided streams. The overlying subaerial deposits are commonly brown or orange in color due to palagonitization. They display a wide variety of bedding types and sedimentary structures consistent with deposition by base surges, wet to dry pyroclastic fall events, and water saturated debris flows.Proximal sections through the subaerial tephras exhibit large regressive cross-strata, planar bedding, and bomb sags suggesting deposition by wet base surges and tephra fallout. Medial and distal deposits consist of a thick sequence of well-bedded tephras; however, the cross-stratified base-surge deposits are thinner and interbedded within the fallout deposits. The average wavelength and amplitude of the cross strata continue to decrease with distance from the vent. These bedded surge and fall deposits grade upward into dominantly fall deposits containing 75–95% juvenile vesiculated clasts and localized layers of welded spatter, indicating a greatly reduced water-melt ratio. Overlying these “dryer” deposits are massive tuff breccias that were probably deposited as water saturated debris flows (lahars). The first appearance of rounded river gravels in these massive tuff breccias indicates downward coring of the diatreme and entrainment of country rock from lower in the stratigraphic section. The “wetter” nature of these deposits suggests a renewed source of external water. The massive deposits grade upward into wet fallout tephras and the phreatomagmatic sequence ends with a dry scoria fall deposit overlain by welded spatter and lava flows.Field observations and two new ⁴⁰Ar–³⁹Ar incremental heating dates suggest the succession of lavas and tephra deposits exposed in this part of the Snake River canyon may all have been erupted from a closely related complex of vents at Sinker Butte. We propose that initial eruptions of lava flows built a small shield edifice that dammed or disrupted the flow of the ancestral Snake River. The shift from effusive to explosive eruptions occurred when the surface water or rising ground water gained access to the vent. As the river cut a new channel around the lava dam, water levels dropped and the volcano returned to an effusive style of eruption.     

东北平原西部沙地近10年的沙质荒漠化

东北平原西部沙地位于欧亚大陆中纬度巨型沙带的东部边缘，为我国沙质荒漠化土地的东缘，是我国自然环境最好的沙区，随着经济的发展，生态环境遭到严重破坏，沙质荒漠化景观日益明显，尤其是南部的科尔沁沙地，沙质荒漠化已十分严重，已经超过与其相邻的西部环境条件更差的沙区，利用RS和GIS，根据NOAA/AVHRR数据建立的沙质荒漠化监测指标，对东北平原西部沙地沙质荒膜化现代过程进行了动态监测，在此基础上利用TM数据对沙质荒漠化的发展方式与成因进行了深入的探讨，并有针对性地提出了区域沙质荒漠化的防治对策。     

Sandy desertification trend in western Northeast China Plain in the past 10 years

The west sandy land of the Northeast China Plain is located in the eastern huge sandy belt of mid-latitude in Eurasia and the eastern fringe of desertified land with best bio-climatic conditions in China. Over-extensive regional development has made the desertified landscape very obvious, especially in Horqin Sandy Land where desertification is more serious than that in Hushandake Sandy Land with worse bio-climatic conditions. There were some researches on the desertification in western No…     

Delivery of upper-basin sediment to the lower neuse river,North Carolina,U.S.A.

Extensive storage of upper-basin Piedmont sediment and apparent low sediment supply to streams in lower-basin Coastal Plain areas generates questions as to the source of alluvium in lower reaches of rivers of the U.S. Atlantic drainage. This was investigated on the Neuse River, North Carolina, using a mineralogical indicator of sediment source areas. The utility of mica flakes for discriminating between Piedmont and non-Piedmont sources of sediment in the lower Coastal Plain reaches of the Neuse was established on the basis of an examination of the U.S. National Soils Database and of 26 soil surveys of the North Carolina Coastal Plain. From the Neuse River estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments. Mica flakes become more common upstream. This suggests that a very small proportion of the sediment eroded in the Piedmont portion of the watershed is delivered to the river mouth. The small amounts which presumably do reach the lower Coastal Plain are so diluted by Coastal Plain-derived alluvium that no Piedmont origin can be discerned. This demonstrates a dominantly Coastal Plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems. More importantly, results suggest that upper- and lower-basin sediment dynamics are not only non-linearly related, but may be virtually decoupled.