Heterogeneous structure around the Jemez volcanic field, New Mexico, USA, as inferred from the envelope inversion of active-experiment seismic data

We analyse active-experiment seismic data obtained by the 1993 Jemez Tomography Experiment (JTEX) programme to elucidate the heterogeneous structure of the Jemez volcanic field, which is located at the boundary between the Colorado Plateau and the Rio Grande Rift. Using a single isotropic scattering assumption, we first calculate the envelope Green's functions for the upper and lower crust and the uppermost mantle. By fitting the theoretical envelopes with the observed three-component data, we estimate depth-dependent features of the scattering coefficients around Valles Caldera. We estimate the ratios of scattering coefficients, rather than scattering coefficients themselves, because of the uncertainty of the seismic efficiency of the explosive sources and knowledge of absolute site-amplification factors. The strongest scattering coefficients are observed at a shallow depth beneath the Valles Caldera. This is considered to be related to the complex structure caused by two episodes of caldera formation and the ensuing resurgent uplift in the caldera, etc. The depth-dependent characters of the scattering coefficients for the Colorado Plateau and the Rio Grande Rift are similar to each other: a transparent upper crust and a heterogeneous lower crust (small and large scattering coefficients, respectively). However, the scattering coefficients beneath the Rio Grande Rift are several times larger than those beneath the Colorado Plateau. Depths of the lower crust and the Moho boundary beneath the Rio Grande Rift are shallower than those of the Colorado Plateau. From their geological settings and other geophysical results around the region, we infer that the larger scattering coefficients of the rift are associated with rift formation and volcanic activity, such as magma ascent from the upper mantle to the crust.     

Diatoms from gut contents of museum specimens of an endangered minnow suggest long-term ecological changes in the Rio Grande (USA)

Diatoms consumed by Rio Grande silvery minnows (Hybognathus amarus) collected 104 years apart were used to deduce ecological requirements of this endangered species and to infer a possible cause of its decline based on environmental conditions in the Rio Grande. In 1874, foraged diatoms were largely motile, silt tolerant generalist and epipelic species (e.g. Navicula capitatoradiata, Navicula cryptotenella, Nitzschia palea, Sellaphora pupula) somewhat tolerant to pollution and indicative of eutrophic conditions, low dissolved oxygen, and high biological oxygen demand (BOD). In contrast, diatoms foraged in 1978 were mainly nonmotile epipsammic species (Fragilariaceae) sensitive to pollution and characteristic of low nutrient, oligotrophic conditions with high dissolved oxygen and low BOD. The large-scale difference in composition of the foraged diatom assemblages is consistent with a decline in nutrients and a shift in trophic state commonly associated with river regulation by dams. The results suggest that facilitating allochthonous input of detritus and nutrients into the Rio Grande ecosystem to meet foraging requirements for algivorous and detritivorous fish species such as H. amarus would be a good river restoration strategy.     

Population mobility and the survival of small farming in the Rio Grande Valley, Jamaica

The relationship between population mobility and farming is complex and has been the focus of numerous studies. Despite differing perspectives on the subject, there is an increasing realization that migration sustains farming in many rural communities, but with contradictory effects. Notwithstanding this conclusion, there is a paucity of village level studies that explain the precise ways in which migration in its various forms affects the survival of small farms. This paper reports on the results of a village level study of migration and small farming in the Rio Grande Valley of Jamaica. Apart from highlighting the various ways in which migration affects small farming at the local level, the study confirms the contradictory impact of migration on small farming in this remote agricultural community. It is noted, however, that the net effect is positive and the capital and labour resources, which are made available as a result of migration, play pivotal roles in the survival of small-scale farming as an economic activity in the area.     

作物生物学特性对耗水量的影响

本文根据农田蒸发实验资料,分析了作物生物学特性对耗水量的影响。结果表明,C₃植物(小麦、大豆)和C₄植物(玉米、谷子)在耗水量、耗水日变化过程和耗水特性系数等方面有明显的差异。     

Water use efficiency in an arid watershed: a case study

Integrated Water Resource Management (IWRM) becomes increasingly important in arid watersheds, where water resources are scarce and demands are rising under increased population pressure. In this case study, we present the results from the Elqui Valley in Chile, where water resources are shared between agriculture, mining operations, hydropower generation and drinking water for nearby cities. An IWRM model was applied to visualize water resources distribution in the catchment and determine irrigation and water use efficiencies. After calibration with observed surface and groundwater measurements, the model showed large differences in efficiencies between different irrigation sectors. Most notably, irrigation sectors with the highest irrigation security, i.e., higher water rights per hectare, were characterized with lower water use efficiencies. Frequent water deficits were present in sectors downstream of the main reservoir, which was related to limited water rights per hectare, lower irrigation efficiencies and higher water demands due to larger agricultural areas. In subsequent scenario analyses, the model was used to evaluate the impact of improved irrigation and water use efficiencies in these downstream sectors, to confirm an important reduction in water deficits, except for drought years when surface water resources are insufficient. In a third scenario, groundwater resources were allowed to compensate for water deficits, effectively reducing these in most irrigation sectors, especially during droughts. Expansion of the current agricultural area by 37% was evaluated, as a future scenario, and was found to be unsustainable, as aquifer levels are lowered to such levels that make annual recharge insufficient.     

湖南省农业水问题浅析

湖南省雨水丰沛，农业水资源总量完全可满足农业生产需要和支持其持续发展。但时空分布不均带来了一系列水问题：山丘区的季节性干旱和洪灾，平原区的涝灾；水资源开发利用效率、农田水分生产率低以及工业和城市用水压力等。解决湖南农业可持续发展的水问题，首先是强化雨水资源化过程，加强原有农业水利工程设施的修缮和配套建设，努力建设新的农田灌溉设施；改革农业水管理体制和制度，逐步实现农业水管理的“用水有偿化、投资多元化、经营企业化、管理法制化”；另外要立足省情，推进农业科学用水研究，提高水分生产力。     

应用水资源管理模拟模型研究2000年乌鲁木齐河流域供水方案

乌鲁木齐河流域包括乌鲁木齐市区及其南、北郊区,是全国着名的缺水流域。据分析1990年已经超采地下水资源1.2×10⁸m³,到2000年,流域及城市缺水将十分严重。乌鲁木齐河流域属于内陆河流域,在水资源开发利用过程中,地表水与地下水多次转换,目前该流域水资源的重复利用率已达167%.建立有效的地表水和地下水联合利用模拟模型,可了解地下水资源的动态变化及分析地表水和地下水的相互转换对可利用水资源总量的影响。通过分析得出,节流措施大大地提高了地表水的可利用量,而减少的地下水的可利用量却不多。在开源措施方面,对规划工程进行了方案组合,分析了其实施的必要性。通过大量运算提出该流域2000年六种供水方案,为解决乌鲁木齐市城市发展缺水问题及供水措施规划提供决策参考。     

华北平原农业节水与水量调控

本文从系统观点出发,提出节水农业的系统框架,并针对华北平原农业用水情况,就各种节水措施的应用与潜力进行了分析。最后,结合节水管理,讨论了水量调控的若干原理问题。     

CLIMATOLOGY OF PRECIPITATION DROUGHTS IN ILLINOIS BASED ON WATER SUPPLY PROBLEMS

Drought begins with a reduction in precipitation, but different kinds of precipitation deficiency episodes (duration, intensity, and areal extent) create varying problems for drought-sensitive activities; an agricultural droughttypically is not a water supply drought. Shared characteristics of precipitation deficiency events and related surface water supply problems in Illinois were used to define climatological characteristics of precipitation deficiency droughts that cause problems for water supply systems. The temporal and spatial characteristics of these water supply precipitation droughts were assessed revealing that droughts typically: (a) begin in warm season months; (b) become more widespread when more severe and/or of shorter duration (although all droughts could be expected to cover at least 75%-85% of the state); (c) are more severe and frequent in central Illinois; and (d) end with much above normal precipitation in the initial post-drought months, but tend to recess to slightly drier than normal conditions (but not drought levels).     

WATER RESOURCES OF THE CHUNCHUCMIL MAYA*

ABSTRACT. Chunchucmil, on the Yucatán Peninsula, was densely populated in the Maya Late Classic period (ca. a.d. 550–830), even though it depends principally on groundwater. In the 1990s, hydrologic investigations were conducted to determine whether groundwater could have met domestic and agricultural needs. The region's groundwater is near the surface and is influenced by sea‐level fluctuations; however, geochemical analysis revealed that groundwater quality is not affected by mixing with seawater. The potential exists for high and spatially extensive nitrate contamination in this karstic area, yet water‐quality analyses revealed only moderate levels of nitrate in the groundwater. Agricultural limitations are imposed by chloride, total dissolved solids, and salinity, as indicated by electrical conductivity; domestic water use is limited by the presence of nitrate, sulfate, and chloride. Throughflow in the ring of cenotes (sinkholes) around the Chicxulub impact crater may explain the movement and spatial distribution of water‐quality constituents in Chunchucmil's groundwater.     

博斯腾湖水质矿化度与水资源利用

本文在回顾博斯腾湖环境基本情况及水质评价结果的基础上，提出水资源利用的设想与措施。     

京津渤地区的水资源及开发利用中的环境问題

作者初步估算了京津渤地区的水资源,全区水资源总量多年平均为129.67亿立方米,可供水资源为87.13亿立方米.进而讨论水资源开发利用中的几个环境问题:供需矛盾突出、旱涝频繁、地面沉降和水源污染.并就如何合理利用水资源和保护水资源问题提出了建议.     

南水北调东线沿线土壤盐渍化初步分析

本文简要分析了南水北调东线输水工程实施后可能引起黄淮海平原土壤次生盐渍化的原因,并提出了相应的防止措施。     

水资源市场化的经济分析及实现途径——东阳、义乌的水权交易引发的思考

义乌出资两亿元买下了东阳 4999.9× 1 0 4 m3水资源的永久使用权。中国首宗水权交易 ,引发了人们对水资源利用市场化的思考。用经济学模型对水资源指令配置模式和市场配置模式进行比较 ,认为市场配置水资源更有效率。水资源市场建立及运行 ,关键在于明确的水资源产权与合理的水价体系。分析了水权、水价问题后 ,提出了水资源市场化的基本思路与政策建议     

冬小麦水分耗散特性与农业节水

本文根据中国科学院禹城综合试验站１９８６年－１９９６年蒸渗仪农田水分模拟试验资料统计；冬小麦全生育期耗水量可达４８２．５ｍｍ，缺水率可达６９．３％；冬小麦全生育不分耗散过程有两个明显的需水峰区和３个关键需水期，为实施节水灌溉提供了实验依据；冬小麦耗水量与环境因子有明显的相关关系，其统计规律可供地下水浅埋区区域灌溉预测参照应用。     

Axial–transverse fluvial interactions in half-graben: Plio-Pleistocene Palomas Basin, southern Rio Grande Rift, New Mexico, USA

Accurate magnetostratigraphic dating of Plio-Pleistocene alluvium in the Palomas half-graben permits correlation of transverse and axial deposits, thus enabling analysis of the movement of alluvial facies belts in time and space for the first time. Northern areas show evidence for basinward progradation of footwall-sourced Matuyama-age alluvial fan deposits over axial channel belt deposits of the ancestral Rio Grande, despite both deposits having similar deposition rates. This gradual ‘forced’ westward migration of the axial belt was in opposition to ongoing eastward growth of hangingwall-sourced fans and tectonic tilt imposed by the bounding Caballo normal fault. Fan growth was coincident with a recently proposed gradual climatic shift that may have increased sediment flux out of transverse catchments. It is also possible that continuing tectonic footwall uplift and divided retreat caused catchment areas to increase, contributing to these trends. Southern areas of the Palomas half-graben feature late Gilbert/early Gauss deposits indicative of rapid westwards progradation of large low-gradient, footwall-sourced fans over axial deposits. This ‘forced’ migration of the ancestral Rio Grande may have occurred due to footwall catchment and fan growth consequent upon initiation and growth of the Red Hills Fault. Subsequent eastward movement of the axial channel belt in late Gauss and Matuyama times overwhelmed these large fans. We attribute this to continued tilting on the Red Hills Fault and to development of the Jornada Fault to the south-east, the axial river belt avulsing north and eastwards through a developing Red Hills/Jornada crossover transfer zone. We conclude generally that facies architecture of axial and transverse elements in half-graben must reflect both climatic influences and the effects of fault development. Careful field mapping, accurate dating and palaeoclimatic studies are all necessary to determine the relative importance of these controls. Although adequate as broad guides, previous purely ‘fixist’ tectonosedimentary models allow for no fault growth, decay or climatic modulation of facies trends and are thus generally inadequate to explain important aspects rift basin stratigraphy.     

中国干旱区水量转化特征及其对环境的影响分析--以新疆阿拉尔灌区为例

新疆的水平循环是,径流形成于山区,流到平原区后不断蒸发和渗漏,最终消耗在沙漠中,或者流入尾闾湖。由于人类活动的影响,水的分布和转化都发生了改变,绿洲中的水量增加,但绿洲以外与河流下游的水量减少,同时有些湖泊缩小甚至干涸,沙漠化发展,自然植被衰退,自然环境退化。     

城镇库区水资源面源污染机制及保护对策研究

城镇水库农业面源污染是中国许多地区水库富营养化的主要源头。针对水库面源污染,采用SWAT模型进行了昆明松华坝水库的污染模拟分析,根据松华坝水库区内的地形、土地利用、土壤、气象、耕种施肥方式运用SWAT模型对松华坝水库的其农业面源污染N、P富营养化问题进行了模拟。模拟结果能够很好与观测实测值吻合,说明模拟具有较好的精度。结果表明,N、P的空间分布主要集中在松华坝水库的支流冷水河与牧羊河河岸沿线的农业区。根据此分布以及区内的农业特点提出了相应的水资源保护措施。     

沙坡头地区风沙土的水热状况

对多年监测资料的研究表明:流动风沙土稳定含水量为2%~3%,凋萎湿度为0.54%,相对有效水分多,对植物生长有利。天然植被下的固定风沙土,在35~40cm以下土层水量减少至1%~2%;人工植被下的固定风沙土水分条件更差,在3m深土层,除降雨后的短时间内,0~60cm土层含水量稍高外,无雨时段,3m深土层的含水量是1%~2%,甚至小于1%。这种水分状况导致多年生深根植物逐渐衰退,适应性一年生草本植物侵入。