Coastal geoindicators of environmental change in the humid tropics

The primary geoindicators appropriate for monitoring environmental changes in the humid tropics are transitory surface water levels, shoreline position, wetlands distribution, coral reefs, landforms, and sediment sequence and composition. Lateral zonations and temporal successions of vegetation also can be used as geoindicators of riverine and shoreline changes. All of these coastal geoindicators are sensitive to regional tectonic processes and anthropogenic alterations and they typically reflect significant changes in coastal conditions such as fluvial processes, coastal energy, water quality, relative sea level, and sediment supply. Where humid tropical coasts coincide with active tectonic margins, indicators of seismic activity are critical to understanding coastal changes associated with co-seismic subsidence or uplift, tsunamis, and liquefaction of coastal sediments. Coastal landforms and sedimentary deposits that record late Quaternary environmental changes include perched fluvial and marine terraces, delta-plain morphologies, crevasse-splay deposits, peats and other paleosols, beach ridges, mud capes, and mud volcanoes. Although these features and deposits typically reflect environmental changes spanning more than 100 years, they are relevant to modern processes, management of coastal lands and resources, and prediction of future conditions. In some regions of the humid tropics, large coastal areas are unaffected by hurricanes or typhoons. Nevertheless, these tropical coasts are vulnerable to other non-storm processes, such as El Niño events, tsunamis, and monsoons that increase water levels, and cause widespread flooding and beach erosion. The environmental and political significance of coastal geoindicators increases when they are integrated and applied to issues of human safety and health such as hazards mapping, risk assessment, and dispersion of contaminated sediments. However, to be relevant, those socio-environmental applications demand accurate predictions of future trends and rates of change.     

湿地扇扇中辫状水道沉积微相-岩石相划分方法

综合应用岩心、测井、分析化验等资料,对湿地扇扇中辫状水道粗碎屑沉积特征进行了详细研究,提出了沉积微相-岩石相的划分方法。根据不同岩石相的物性、电性及含油性特征,将扇中辫状水道微相细分为辫状水道砂砾岩相、辫状水道粗砂岩相和辫状水道细砂岩相。研究结果表明,沉积微相-岩石相对油水分布具有明显的控制作用,其中以辫状水道砂砾岩相单井日产油能力最高,辫状水道粗砂岩相次之,辫状水道细砂岩相最低,比较符合油田的开发实际。辫状水道粗砂岩相因物性最好,剩余油丰度高,可作为下一步挖潜的主要目标。     

Potential use of freshwater molluscs for monitoring river pollution

To control the increasing pollution of streams in urban and industrial areas, ecological criteria such as indicator properties of organisms and biocoenoses are required. Hereby, the distribution and abundance of populations is determined by their genetic structure, that react in different ways to the intensity of burdening parameters. The Saar River is excessively polluted by industrial sewage, thermal wastes and chemicals. Therefore monitoring programs were established to analysze the structure of benthic populations in order to control the influence of the present pollution of the river. Genetic and population-ecological analyses of the freshwater gastropodPhysa acuta Drap. indicate gradually significant differences in the allele frequencies and their heterozygoties. The results demonstrate correlated strategies in different populations, whereby balanced allele frequency distribution patterns indicate the influence of the toxic substances. These analyses serve for a better understanding of evolutionary processes in urban environments as well as for an objective consideration of the indicator systems by detecting changes before the extinction of a taxon.     

River sinuosity in a humid tropical river basin,south west coast of India

The variability in ground water potential at different regions of the Meenachil River basin and the remarkable distribution of palaeodeposit of sand at its middle to lower reaches have led to interpret the sinuosity indexes of the main channel as well as the tributaries of the River for elucidating the relationship between mathematical expressions and filed observations. The measurement of digital elevation model-derived river sinuosity was carried out for 846 km² of the basin area of Meenachil River. The drainage networks of 10 major sub-watersheds and four mini-watersheds were delineated using remote sensing data—geocoded false colour composite of Indian Remote Sensing satellite (IRS)-1D (LISS III) data with a spatial resolution of 23.5 m—coupled with the Survey of India toposheets (1:50,000). The calculation of the sinuosity indexes were carried out using Arc GIS (8.3 version) software. Hydraulic sinuosity indexes, topographic sinuosity index and standard sinuosity index were calculated. The study depicts the remarkable correlation between theoretical data sets with field observations and the influence of tectonic control on river planforms. Three structurally controlled regions of Meenachil River basin were established using Remote Sensing and Geographical Information System.     

流域水资源实时监控管理系统研究

根据我国流域水文水资源特点和供用水特征,基于目前流域所面临的水资源短缺和污染问题,需要研究和开发流域水资源实时监控管理系统.其重点应放在现有监测站点的调整与完善,水库运行规则、技术参数的校核与调整,洪水资源调控与地下水人工回灌,污水处理回用与生态环境需水量,防洪与兴利统一调度,地表水与地下水资源联合运用管理等技术研究,以及水资源实时调度管理方案付诸实施后效益与风险分析、系统的标准化等方面.     

Past glaciation in the tropics

Tropical glaciers are considered along three meridional profiles, for the Australasian sector, Africa and the Americas. Evaluated are the annual mean freezing level 0 °C, modern equilibrium line altitude MEL, and past equilibrium line altitude PEL. The calculation of 0 °C is based on a 1958–1997 global data set; MEL refers to estimates concerning the first half of the 20th century; and the timing of the PEL is not generally known. 0 °C stands around 4000–5000 m, with lower levels in the outer tropics. MEL is reached in the Australasian sector on four mountains, and in Africa on three mountains, near the Equator, near or above 0 °C. In the American cordilleras many peaks are still glaciated, above 0 °C, but in the arid southern tropical Andes even summits above 6000 m do not reach MEL. The PEL stands between 3000 m and 5000 m, high in the equatorial zone, but highest in the arid southern tropical Andes. The height difference between MEL and PEL is of order 1000 m, with regional differences. Deglaciation dates range between 15,000 and 8000 years BP, with later timing towards the higher elevations. This synopsis suggests priority targets for further research: morphological mapping and age determination in the High Atlas of Morocco; timing of deglaciation in the High Semyen of Ethiopia and the Altos de Cuchumatanes of Guatemala; exploration in the highlands of Lesotho and of the Dominican Republic; and glaciation in the arid southern tropical Andes.     

Troposphere-to-stratosphere transport in the tropics

The analysis of the data collected over Brazil, Northern Australia and Africa from balloons, high altitude aircraft and satellites during the recent HIBISCUS, TROCCINOX, SCOUT-O3 and AMMA European campaigns, has led to significant revision in the understanding of troposphere-to-stratosphere transport. Repeated observations of strong updrafts of adiabatically cooled and washed-out tropospheric air rich in chemical and greenhouse gases by convective overshooting over the three continents, demonstrate the high frequency of occurrence of such events in contrast to their generally assumed scarcity. Moreover, global scale information provided by ODIN and CALIPSO satellite observations suggests that the mechanism could play a major, if not dominant, role in troposphere-to-stratosphere transport in contrast to the generally evoked slow ascent by radiative heating. Ignored by global scale models because of their limited extension and duration, convective overshootings might have a significant impact on the chemistry and climate of the stratosphere.     

山底河流域煤矿酸性矿井水野外监测

酸性矿井水在我国鲁西南、山西、内蒙、云南和贵州等煤矿区普遍存在,酸性矿井水其pH往往在2~5之间,高SO₄²⁻、HB、TDS、Fe、Mn。这些物质进入地下水、地表水或土壤后,会对其造成严重危害。文章选择山西阳泉市典型废弃煤矿区山底河流域为研究区,通过水文地质调查,水文地质钻探,水文地质剖面等方法阐述山底流域地层岩性,水文地质条件概况,得出受煤矿开采影响,与天然条件下相比山底河流域的地表水和地下水的补给、径流、排泄条件均发生了根本变化。补给通过破坏产生的导水裂隙带运移,以垂向运动为主;径流通过坑道,导水裂隙带运移,以横向运动为主;排泄以矿坑排水和泉水溢出方式为主。并简述山底河流域煤矿酸性矿井水试验站观测站分布情况与水化学特征。     

桂林毛村岩溶地下河流域水土流失遥感动态监测研究

为了给西南岩溶地区石漠化发展演变的研究工作提供一定的科学依据和决策支持,选择桂林毛村岩溶地下河流域作为研究区,利用两期遥感影像对该区影响水土流失的三个主要自然要素,即地形坡度、植被覆盖度和土地利用方式进行信息提取,并以地理信息系统为分析平台,参考水土流失强度分级标准,对该区两个时期的水土流失状况进行对比分析。调查监测结果显示,研究区随着坡度的增大,水土越容易流失,而且水土流失强度级别增大;植被覆盖度对水土流失强度起着控制性作用,为抑制并缩减水土流失面积,应保护植被,退耕还林;研究区土地利用变化比较缓慢,导致水土流失面积变化幅度不大。上述结果表明,利用遥感技术手段,可为当地的经济发展和水土流失的监测、评价、预测及治理提供参考。      

Innovative monitoring tools for the complex spatial dynamics of river chemistry: case study for the Alpine region

Chemical reactions in aqueous geochemical systems are driven by nonequilibrium conditions, and their dynamics can be deduced through the distributional analysis (identification of probability laws) of complex compositional indices. In this perspective, compositional data analysis offers the possibility to investigate the behavior of the composition as a whole instead of isolated chemical species, with the awareness that multispecies systems are characterized by the simultaneous interactions among all their parts. We addressed this problem using D???1 isometric log-ratio coordinates describing the D compositional dataset of the river chemistry of the Alpine region (D number of variables), thus working in the \({{\mathbb{R}}^{D - 1}}\) statistical sample space. The D???1 coordinates were chosen using the decreasing variance criterion so that each one could provide information about different space–time properties for the investigated geochemical system. Coordinates dominated by heterogeneity appear to be able to capture regime shifts only on a long-time period and monitor processes on a very wide scale. On the other hand, coordinates characterized by lower variability present multimodality, thus capturing the presence of alternative states in the analyzed spatial domain also for the current time. Further developments are needed to determine the ranges of conditions for which variability and other statistics can be useful indicators of regime shifts on different time–space scales in geochemical systems.     

地下河系统水动态监测网络优化对比分析:以桂林海洋-寨底地下河系统为例

基于我国南方地区岩溶发育极不均匀、水位水质动态变化快的特点,通过对信息熵法和防污性能法所得结果的对比,分析在缺少系列监测资料条件下,利用岩溶水系统防污性能评价结果快速布设地下河系统水动态监测网的可行性及其布设原则。根据防污性能评价结果,结合水循环特征,桂林海洋-寨底地下河系统水动态监测网需由17个监测站组成;采用信息熵法对现有35个监测站进行优化后,认为只需要12个监测站就可组成最优监测网,但这12个监测站点与采用防污性能评价法得到的点位完全重合,且均位于防污性能差的地区。对比分析认为,以地下水系统防污性能评价结果布设地下水动态监测网是可行性的,因为岩溶发育区既是防污性能差的地区,也是地下水动态变化快的地区,能充分反映地下河系统水质水量变化。采用防污性能评价法布设地下水动态监测网时,需要充分认识和了解地下河系统水文地质条件和地下河管道结构特征,且需要遵循以下原则:(1)在岩溶发育相对较弱的系统中部(基本上不存在防污性能差的地区)不设置监测站点;(2)在距离地下河出口较近的岩溶发育区内(即防污性能差的地区)监测站点可由地下河出口替代;(3)对于多支管道系统,岩溶发育相对较弱且距离较短的小型支管道上可以不布设监测站,由支管道与主管道交汇处的监测站代替。     

VEBEX: Vegetation and surface energy balance experiment for the tropics

Surface features such as soil moisture and vegetation have a profound impact on the surface energy balance and the atmospheric boundary layer. To quantify this effect for a tropical location, a detailed field experiment, VEBEX, was designed and successfully executed in a tropical site at Bangalore, India. VEBEX was a joint experiment between the North Carolina State University, Indian Institute of Science (IISc), and the University of Agricultural Science (UAS) at Bangalore, India. Continuous surface meteorological measurements were taken over an entire crop period (pre-sowing to post-harvest). During different stages of the plant growth, intensive observations of surface turbulence, and measurements of physiological and soil moisture measurements were also conducted. The results obtained provide an insight into the unusually strong variability for the tropics. Interpretation of the observations and an overview of the analysis procedure and future research initiatives are also presented.     

The development of regolith exploration geochemistry in the tropics and sub-tropics

This essay traces the development of geochemical exploration from its early beginnings in the modern era during the 1930s, concentrating especially in its application to deeply weathered terrain in the tropics and sub-tropics. Following promising results obtained in temperate regions in North America and Europe, test orientation surveys were conducted to see whether similar procedures were applicable in the tropics, where conventional geological prospecting was largely precluded due to the extensive cover of a deep lateritic regolith and consequent lack of outcrop. After initial work in Sierra Leone and Nigeria, the emphasis transferred to East Africa in the 1950s and 1960s, aimed principally at Cu exploration. Many of the basic principles for exploration in dominantly residual, free-draining terrain were quickly established in this period. Exploration in terrains with more complex weathering histories, however, raised a number of difficulties due to leaching and secondary concentrations of elements, problems in selecting and identifying appropriate sample media, and extensive transported overburden. These were encountered especially in more arid regions in Australia and Africa during exploration for Ni and Au during the 1970s and 1980s. This led to a change in approach, placing weathering and geochemical dispersion in the context of regolith and landscape evolution –a return to the early concept of landscape geochemistry. The 3D expression of mineralization in the landscape is depicted as empirical conceptual models, that account for both relict features and active processes, and portray element associations, dispersion mechanisms and host materials. They also indicate suitable sample media, sampling intervals and procedures for analysis and interpretation.     

Climate and vegetation: Simulating the African humid period

The outputs of the climate simulated by two General Circulation Models (GCMs), (IPSL and UGAMP) have been used to force a vegetation model (LPJ-GUESS) to analyze the Holocene African humid period (AHP) and related vegetation changes over the 18°W-35°E, 5°S-25°N region. At the continental scale, simulations with the two models confirm the intensified African monsoon during the Holocene as compared to now, and the early but gradual termination of the AHP in eastern regions as compared to western regions. At the regional scale, the two GCMs results present important differences in the timing of the AHP, its spatial extent and the summer rainfall amplitude. Consequently, the vegetation model simulates changes that are globally in agreement with pollen data, but with large differences according to the region and the model considered. During the AHP, the IPSL climate induced proper vegetation changes in the eastern Sahara and in the Sahel, whereas the UGAMP climate induced correct changes in the western Sahara and in the equatorial zone.     

Patterns of mixed siliciclastic‐carbonate sedimentation adjacent to a large dry‐tropics river on the central Great Barrier Reef shelf,Australia

The Great Barrier Reef represents the largest modern example of a mixed siliciclastic‐carbonate system. The Burdekin River is the largest source of terrigenous sediment to the lagoon and is therefore an ideal location to investigate regional patterns of mixed sedimentation. Sediments become coarser grained and more poorly sorted away from the protection of eastern headlands, with mud accumulation focused in localised ‘hot spots‘ in the eastern portion of embayments protected from southeast trade winds. The middle shelf has a variable facies distribution but is dominated by coarse carbonate sand. North of Bowling Green Bay, modern coarse carbonate sand and relict quartzose sand occur. Shore‐normal compositional changes show Ca‐enrichment and Al‐dilution seawards towards the reef, and shore‐parallel trends show Al‐dilution westwards (across bays) along a Ca‐depleted mixing line. Intermediate siliciclastic‐carbonate sediment compositions occur on the middle shelf due to the abundance of relict terrigenous sand, a pattern that is less developed on the narrow northern Great Barrier Reef shelf. Rates of sediment deposition from seismic evidence and radiochemical tracers suggest that despite the magnitude of riverine input, 80–90% of the Burdekin‐derived sediment is effectively captured in Bowling Green Bay. Over millennial time‐scales, stratigraphic controls suggest that sediment is being preferentially accreted back to the coast.     

Carbon river fluxes and weathering CO2 consumption in the Congo and Amazon river basins

Data on carbon river fluxes recently obtained by the authors for the Congo basin within the framework of the PIRAT Program (INSU-CNRS/ORSTOM) are compared with results previously obtained for the Amazon basin. A special interest is devoted to the bicarbonate river fluxes and to their relationships with river discharges. The flux of atmospheric and soil CO₂ consumed by rock weathering is estimated to be 3.1 × 10⁵ and 0.5 × 10⁵ moles/a/km² respectively for the Amazon and the Congo basin. These CO₂ fluxes represent, respectively, 67.4% and 74.7% of the total bicarbonate river fluxes. A comparison to other large river basins shows that this contribution is directly related to the proportion of carbonate rock areas. A transfer function between the weathering CO₂ flux and the river discharge is calculated for each basin and allows the reconstitution of the variations of this flux using the river discharge fluctuations during the last century. These interannual CO₂ fluctuations present average increasing trends of 10% for Amazon basin and only 0.7% for the Congo basin during the last century.     

Urban steeplands in the tropics: an environment of accelerated erosion

The developing countries at present have a high urban growth rate that is likely to continue for at least another quarter-century. In addition, many of these urban centres are located in the Neogene plate boundary zones and are subject to multiple earthquake and volcanic hazards. Slope failures and accelerated surface and channel erosion are particularly severe in cities near active plate margins, and in areas affected also by tropical cyclones. We discuss two extreme cases: Singapore and Kingston (Jamaica). Singapore is located in a stable environment and the urbanization related problems of flood and slope instability have been reduced by proper building and drainage practices at a considerable cost. In Kingston, the external disturbances are repetitive, large-scale, and very difficult to control. The fast-growing cities in the tropics need to be carefully monitored, especially when located in an unstable physical environment. This revised version was published online in July 2006 with corrections to the Cover Date.