基于栅格空间信息定量化的湖南西部地区生态环境综合评价

以湖南西部地区为研究区域,采用遥感影像作为主要数据源,针对区域主要生态问题,利用栅格数据结构为主的数字环境模型,建立了生态环境质量综合评价模型. 对区域生态环境质量的空间分异格局进行了研究,通过将评价结果与数字高程模型迭加分析,研究了生态环境质量的垂直地带性分布规律,探索适合以山高坡陡为主要地貌特征的山区生态评价方法,结果显示,湖南西部地区生态环境综合指数呈正态分布,大部分地区环境质量属一般. 总体环境状况东南部好于西北部,河谷盆地优于山地. 研究表明,利用遥感和地理信息系统技术进行区域生态环境评价,具有数据采集快速、客观,评价和制图自动化,评价结果空间定位精度高,直观性与实用性强等优点.     

湘中锑(金)矿床成矿物质来源——Ⅰ.微量元素及其实验地球化学证据

为了查明湘中盆地中-低温梯（金）矿床的成矿物质来源，文章应用高分辨率ICP-MS、ICP-AES等方法对岩石与矿石进行了系统测定，并结合作者以往分析数据和实验地球化学结果，对该区盆地及周边基底地层与矿床中的微量元素分布特征及其水/岩反应效应进行了综合分析和系统研究。结果表明：Sb、Au等成矿元素在元古界基底碎屑岩中具有高的背景含量，在近似成矿条件下的水/岩反应实验中，成矿元素的淋出率达20%～90%，元古界基底碎屑岩中的金（锑、钨）矿床的周围蚀变围岩中出现明显的金负异常区。而盆地内泥盆系统地层中的高锑含量仅局限于锑矿床（化）及其蚀变围岩中；湘中锑（金）矿床中的矿石与基底碎屑岩具有相似的稀土元素球粒陨石标准化配分曲线特征，以上微量元素地球化学特征充分证明该区锑（金）矿床锑、金等成矿物质主要来源于元古界底碎屑岩。     

Impact of Southern Oscillation on the Frequency of Monsoon Depressions in the Bay of Bengal

The impact of Southern Oscillation on thecyclogenesis over the Bay of Bengal duringthe summer monsoon has been investigated.The analysis of correlation coefficients(CCs) between the frequency of monsoondepressions and the Southern OscillationIndex (SOI) reveals that more depressionsform during July and August of El Niñoyears. Due to this, the seasonal frequencyof monsoon depressions remains little higherduring El Niño epochs even though thecorrelations for June and September are notsignificant. The CCs for July and August aresignificant at the 99% level.The El Niño-Southern Oscillation (ENSO)is known to affect Indian MonsoonRainfall (IMR) adversely. The enhancedcyclogenesis over the Bay of Bengal duringJuly and August is an impact of ENSO whichneeds to be examined closely. Increasedcyclogenesis over the Bay of Bengal may bereducing the deficiency in IMR duringEl Niño years by producing more rainfallover the eastern parts of India duringJuly and August. Thus there is a considerablespatial variation in the impact of ENSOon the monsoon rainfall over India and El Niñoneed not necessarily imply a monsoonfailure everywhere in India.The area of formation of monsoon depressionsshifts eastward during El Niño years.Warmer sea surface temperature (SST) anomaliesprevail over northwest and adjoiningwestcentral Bay of Bengal during premonsoon andmonsoon seasons of El Niño years.May minus March SOI can provide useful predictionsof monsoon depression frequencyduring July and August.     

Volcanological and petrological evolution of Marsili Seamount (southern Tyrrhenian Sea)

A swath bathymetric survey was conducted on Marsili Volcano, the biggest seamount in the Tyrrhenian Sea. It stands 3000 m above the surrounding oceanic crust of the 3500 m-deep Marsili back-arc basin and is axially located within the basin. The seamount has an elongated shape and presents distinctive morphology, with narrow (<1000 m) ridges, made up of several elongated cones, on the summit zone and extensive cone fields on its lower flanks. A dredging campaign carried out at water depths varying between 3400 and 600 m indicates that most of Marsili Seamount is composed of medium-K calc-alkaline basalts. Evolved high-K andesites were only recovered from the small cones on the summit axis zone. Petrological and geochemical characteristics of the least differentiated basalts reveal that at least two varieties of magmas have been erupted on the Marsili Volcano. Group 1 basalts have plagioclase and olivine as dominant phases and show lower Al, Ca, K, Ba, Rb and Sr, and higher Fe, Na, Ti and Zr with respect to a second type of basaltic magma. Group 2 basalts reveal the presence of clinopyroxene as an additional phenocryst phase. In addition, the two basaltic magmas have different original pre-eruptive H₂O content (group 1, H₂O-poor and group 2, H₂O-rich). Moreover, comparison of the compositional trends and mineralogical compositions obtained from MELTS [Ghiorso, M.S., Sack, R.O., Contrib. Mineral. Petrol. 119 (1995) 197–212] fractional crystallization calculations reveal that the evolved andesites can only exclusively be derived from a low-pressure (0.3 kbar) fractionation of magmas compositionally similar to the least evolved group 2 basalts. Finally, we suggest that the high vesicularity of the basalts sampled at relatively great depths (>2400 m) on the edifice is governed by H₂O and, probably, CO₂ exsolution and is not a feature indicative of shallow water depth eruption.     

Predicting average annual groundwater levels from climatic variables: an empirical model

On the basis of one-dimensional theoretical water flow model, we demonstrate that the groundwater level variation follows a pattern similar to recharge fluctuation, with a time delay that depends on the characteristics of aquifer, recharge pattern as well as the distance between the recharge and observation locations. On the basis of a water budget model and the groundwater flow model, we propose an empirical model that links climatic variables to groundwater level. The empirical model is tested using a partial data set from historical records of water levels from more than 80 wells in a monitoring network for the carbonate rock aquifer, southern Manitoba, Canada. The testing results show that the predicted groundwater levels are very close to the observed ones in most cases. The overall average correlation coefficient between the predicted and observed water levels is 0.92. This proposed empirical statistical model could be used to predict variations in groundwater level in response to different climate scenarios in a climate change impact assessment.     

Evaluating Earthquake-Triggered Landslide Hazard at the Basin Scale Through Gis in the Upper Sele River Valley

To evaluate techniques for assessing earthquake-triggeredlandslide hazard in the Southern Apennines (Italy), a GIS-based analysis was used to modelseismically induced slope deformations. Geological, geotechnical, geomorphological and seismologicaldata were integrated into a standard earthquake slope stability model. The model assessed thelandslide potential that existed during the 1980 Irpinian earthquake in the Upper Sele river Valley.The standard Newmark displacement analysis, widely used for predicting the location of shallowunstable slopes, does not take into account errors and/or uncertainties in the input parameters.Therefore, a probabilistic Newmark displacement analysis technique has been used. Probabilistictechniques allow, e.g., an estimation of the probability that a slope will exceed a certain criticalvalue of Newmark displacement. In our probabilistic method, a Monte-Carlo based simulation modelis used in conjunction with a GIS. The random variability of geotechnical data is modelled by probabilitydensity functions (pdfs), while for the seismic input three different regression laws wereconsidered. Input probability distributions are sampled and the resulting values input into empiricalrelations for estimating Newmark displacement. The outcome is a map in which to each siteis related a spatial probability distribution for the expected displacement in response to seismic loading.Results of the experiments show a high grade of uncertainty in the application of the Newmarkanalysis both for the deterministic and probabilistic approach in a complex geological setting suchas the high Sele valley, quite common in the Southern Apennines. They show a strong dependence onthe reliability of the spatial data used in input, so that, when the model is used at basin scale,results are strongly influenced by local environmental condition (e.g., topography, lithology, groundwatercondition) and decrease the model performance.     

Enrichissement en uranium authigène dans les sédiments glaciaires de l'océan AustralEnrichments in authigenic uranium in glacial sediments of the Southern Ocean

Four sediment cores from the Polar frontal zone and the Antarctic zone in the Indian sector of the Southern Ocean present an increase of authigenic uranium during glacial periods. We show that this increase in uranium is due to a combination of (i) an increase in the lateral transport of organic matter, (ii) a decrease in the oxygen in deep waters, and (iii) a process of diagenesis. It appears that uranium concentration cannot be used as a proxy of palaeoproductivity in the Southern Ocean, as previously suggested by Kumar et al. in 1995. To cite this article: L. Dezileau et al., C. R. Geoscience 334 (2002) 1039–1046.     

The geography of water conflict and cooperation: internal pressures and international manifestations

Studies on transboundary water conflict and cooperation generally consider interstate relations over shared water resources as distinct from intrastate relations. While connections have been made between international water relations and regional relationships in general, it is conceivable that international water conflict and cooperation may also be influenced by domestic water events and vice versa. This paper seeks to investigate the dynamics of water interactions across geographic scale and their relationship to broader international affairs. The research approach involves the creation of an analytical framework for assessing possible linkages between external and internal interactions over freshwater resources. The framework is applied to three case studies – the Middle East, South Asia and Southern Africa – utilizing 'event data'. To validate the findings from the quantitative analyses, the results are compared with conventional qualitative understandings of water and overall relations in the three regions. The comparison demonstrates not only the efficacy of the analytical framework in general, but also highlights, at least in terms of the specific case studies selected, the disparate water dynamics across geographic regions and the importance of considering water events, both national and international, within larger political and historical contexts.     

两湖平原农业洪害特征与减灾技术措施

两湖平原是我国农业水资源最丰富的地区之一，河湖水系四通八达，农业生产条件优越。由于人类不适当的经济活动，大规模围湖垦殖破坏了两湖平原自然生态环境，洪涝频繁发生，农业损失严重。两湖平原必须实施综合性的农业减灾技术措施：长江上中游地区实施退耕还林、全面启动天然林保护工程，保持水土；两湖地区实行退田还湖，提高湖泊分蓄洪能力；应用GPS、GIS技术预警，有效调度洪水；调整湖区农业结构，发展避洪农业。     

Infiltration on mountain slopes: a comparison of three environments

Water is well established as a major driver of the geomorphic change that eventually reduces mountains to lower relief landscapes. Nonetheless, within the altitudinal limits of continuous vegetation in humid climates, water is also an essential factor in slope stability. In this paper, we present results from field experiments to determine infiltration rates at forested sites in the Andes Mountains (Ecuador), the southern Appalachian Mountains (USA), and the Luquillo Mountains (Puerto Rico). Using a portable rainfall simulator–infiltrometer (all three areas), and a single ring infiltrometer (Andes), we determined infiltration rates, even on steep slopes. Based on these results, we examine the spatial variability of infiltration, the relationship of rainfall runoff and infiltration to landscape position, the influence of vegetation on infiltration rates on slopes, and the implications of this research for better understanding erosional processes and landscape change.Infiltration rates ranged from 6 to 206 mm/h on lower slopes of the Andes, 16 to 117 mm/h in the southern Appalachians, and 0 to 106 mm/h in the Luquillo Mountains. These rates exceed those of most natural rain events, confirming that surface runoff is rare in montane forests with deep soil/regolith mantles. On well-drained forested slopes and ridges, apparent steady-state infiltration may be controlled by the near-surface downslope movement of infiltrated water rather than by characteristics of the full vertical soil profile. With only two exceptions, the local variability of infiltration rates at the scale of 10° m overpowered other expected spatial relationships between infiltration, vegetation type, slope position, and soil factors. One exception was the significant difference between infiltration rates on alluvial versus upland soils in the Andean study area. The other exception was the significant difference between infiltration rates in topographic coves compared to other slope positions in the tabonuco forest of one watershed in the Luquillo Mountains. Our research provides additional evidence of the ability of forests and forest soils to preserve geomorphic features from denudation by surface erosion, documents the importance of subsurface flow in mountain forests, and supports the need for caution in extrapolating infiltration rates.