GGR Critical Review of Analytical Developments in 2003

The articles that comprise this critical review serve to draw attention to research papers published in specific fields of interest during 2003, provide critical comment on the relevance and importance of individual publications in these fields, and offer an overview of the comparative importance of advances in particular areas. In this way, these articles aim to assist experts in the field by keeping them informed of relevant recent publications, as well as providing an important resource for students or early career researchers who are embarking on studies in an area new to them. This year, five papers provide summaries of developments in bulk sample determinations employing (1) ICP-AES and ICP-MS (trace elements), (2) XRF and atomic absorption spectrometry and INAA, (3) isotope ratio measurements (TIMS, MC-ICP-MS, ICP-MS, ToF), as well as in situ measurements conducted using (4) secondary ion mass spectrometry and (5) laser ablation ICP-MS (trace element and isotope ratio determinations).     

Intraseasonal oscillation of the rainfall variability over Rwanda and evaluation of its subseasonal forecasting skill

非洲中东部地区的经济主要依靠自给农业支撑,该地区农业经济对降水的变化尤为敏感.本文以卢旺达为例,观测分析指出卢旺达的次季节降雨主要集中在10-25天;根据次季节尺度降水变率的单点相关方法,发现卢旺达的次季节降水变率和周围区域变化一致;进一步合成结果显示该地区次季节降水变率与异常西风有关,这可追溯到赤道地区西传的赤道Rossby波.最后,本文评估了当前动力模式ECMWF对 卢旺达地区(即非洲中东部)次季节降水变率的预报能力,发现EC模式在对该区域降水和相关风场指数的预报技巧都在18天左右,且预报技巧表现出一定的年际差异,这可能与热带太平洋的背景海温信号有关.该工作增进了当 前对非洲中东部地区的次季节降水变率和预测水平的认知,并且对该地区国家粮食安全和防灾减灾具有启示性意义.     

A new map of glacigenic features and glacial landsystems in central mainland Nunavut,Canada

A new digital map of glacial geomorphic features and interpreted glacial landsystems was produced for an area covering ~415 000 km² in the Keewatin Sector of the Laurentide Ice Sheet (LIS) in Nunavut. The map integrates information from previous surficial geology maps and >14 000 field stations, and is significantly improved by the detailed inventory of ~152 000 glacigenic features using high-resolution ArcticDEM data and Landsat 8 imagery. From this, we identify and map coherent patterns of landform development (landsystems) between the Manitoba border and the Arctic coast, many of which are entirely new and others that are significantly modified or updated. In particular, we recognize six separate ice streams, including one probable remnant ice stream, and we delineate numerous palimpsest streamlined landscapes with associated ice-flow trends and relative ages. A continuum of relict terrains with varying basal ice thermal conditions is mapped for the first time in the ice divide migration zone between Baker Lake and Wager Bay. In addition, deglacial cold-based retreat terrains and preserved warm-based landscapes unaffected by younger glacial events have been identified. These new georeferenced, multi-scale data sets and interpreted glacial landsystems provide a comprehensive framework to strengthen reconstructions of the glacial history and dynamics of one of the largest ice domes of the LIS, identify distinct glacial sediment transport paths for applications to mineral exploration, and test numerical modelling of the LIS in support of climate change studies and long-term evolution of modern ice sheets.     

崎岖地形动植物栖息地生态环境遥感制图与应用

传统制图方法周期长、成本较高,影响了大面积精细动植物栖息地生态环境制图的生产。鉴此,本文采用IKONOS(VHR)图像对香港郊野公园崎岖地形的动植物栖息地生态环境制图进行了研究。由于香港植被的多样性,而且观察的动植物相互作用出现于结构的层面,所以对动植物栖息地的分类应以结构为基础而非以植物为基础。本文利用图像处理技术,运用决策树之多层次地物导向分割分类(MOOSC)方法绘制九种动植物栖息地类型图。MOOSC方法和其他现有的几种分类方法相比,其分类精度高、成本低。     

A field comparison of two methods for the determination of copper complexation: Bacterial bioassay and fixed-potential amperometry

Complexation of copper added to seawater was determined by bacterial bioassay and fixedpotential amperometry. Consistent results were obtained by these two fundamentally different methods. The results of this study support the validity of both techniques and the field applicability of fixed-potential amperometry.The intercomparison studies were performed on samples collected at the N.Y.C. sewage sludge dumpsite and in relatively unpolluted coastal waters. In this limited study, the calculated free cupric ion concentrations at ambient total copper concentrations were similar at both sites.     

Travel time controls the magnitude of nitrate discharge in groundwater bypassing the riparian zone to a stream on Virginia's coastal plain

Groundwater that bypasses the riparian zone by travelling along deep flow paths may deliver high concentrations of fertilizer‐derived NO₃^? to streams, or it may be impacted by the NO₃^? removal process of denitrification in streambed sediments. In a study of a small agricultural catchment on the Atlantic coastal plain of Virginia's eastern shore, we used seepage meters deployed in the streambed to measure specific discharge of groundwater and its solute concentrations for various locations and dates. We used values of Cl^? concentration to discriminate between bypass water recharged distal to the stream and that contained high NO₃^? but low Cl^? concentrations and riparian‐influenced water recharged proximal to the stream that contained low NO₃^? and high Cl^? concentrations. The travel time required for bypass water to transit the 30‐cm‐thick, microbially active denitrifying zone in the streambed determined the extent of NO₃^? removal, and hydraulic conductivity determined travel time through the streambed sediments. At all travel times greater than 2 days, NO₃^? removal was virtually complete. Comparison of the timescales for reaction and transport through the streambed sediments in this system confirmed that the predominant control on nitrate flux was travel time rather than denitrification rate coefficients. We conclude that extensive denitrification can occur in groundwater that bypasses the riparian zone, but a residence time in biologically active streambed sediments sufficient to remove a large fraction of the NO₃^? is only achieved in relatively low‐conductivity porous media. Instead of viewing them as separate, the streambed and riparian zone should be considered an integrated NO₃^? removal unit. Copyright © 2011 John Wiley & Sons, Ltd.     

Observations of mine seismicity in the eastern Wasatch Plateau,Utah, U.S.A.: A possible case of implosional failure

In the summer of 1984, a three-dimensional, high-resolution microearthquake network was operated in the vicinity of two coal mines beneath Gentry Mountain in the eastern Wasatch Plateau, Utah. During a six-week period, approximately 3,000 seismic events were observed of which the majority were impulsive, higher frequency (>10 Hz), short duration (<2–3 sec) events probably associated with the caving of the roof from a longwall operation. In contrast, 234 of the largest located events appeared to occur predominantlybeneath the mines to a depth of 2 to 3 km consistent with previous studies. The magnitudes of these events ranged from less thanM _c 0 to 1.6. In addition to the unusual depths of these latter events, an anomalous aspect displayed by the events was an apparent dilatational focal mechanism suggesting a non-double-couple, possibly implosional source. Implosional events have been observed in other studies of mine seismicity; however, the generally inadequate instrumental coverage of the focal sphere has cast some doubt on the validity of such mechanisms. Previously suggested source mechanisms for such implosional events have included tensional failure through strata collapse, and a shear-implosional displacement mechanism. Shear failure must be involved in the failure process of the Gentry Mountain implosional events as evidenced by well-defined shear waves in the observed seismograms. Simultaneous monitoring in the East Mountain coal mining area to the south by the University of Utah revealed typical shear failure events mixed with implosional events. The observed double-couple, reverse focal mechanisms at East Mountain were similar to mechanisms determined in previous studies and a composite focal mechanism determined in this study for a sequence outside the mining areas. This suggested that the shear events within the mining areas are being influenced by the regional tectonic stress field. Thus in addition to the seismic events associated with caving of the roof from the longwall operation, there appear to be at least two other types of mining-induced seismic events occurring in the eastern Wasatch Plateau, both submine in origin: (1) events characterized by apparent non-double-couple possibly implosional focal mechanisms and well-defined shear waves; and (2) shear events, which are indistinguishable from tectonic earthquakes and may be considered mining triggered earthquakes. The small mining-induced stress changes that occur beyond a few hundred meters from the mine workings suggest both types of seismic events are occurring on critically stressed, pre-existing zones of weakness. Topography, overburden, method of mining, and mine configuration also appear to be significant factors influencing the occurrence of the implosional submine events.     

The use of7LiOH-impregnated filters for the collection of acidic gases and analysis by instrumental neutron activation analysis

A simple system was designed using⁷LiOH-impregnated filters to collect acidic gases from ambient air and from highly concentrated volcanic plumes or gas streams. These filters were developed for analysis using instrumental neutron activation analysis, but other analytical techniques could be used as well. The sampling system was designed to use a series of 1–3 M⁷LiOH-impregnated filters to collect high concentrations of acidic gases found in gas plumes of active volcanoes. The filters are quantitative for SO₂ and the halide acids when sufficient base is present to neutralize the acidic species. Extremely high concentrations of SO₂ may not be collected quantitatively since SO₂ is a relatively weak Lewis acid compared to the halide acids. The acidic oxides of Sb, As, and Se were also collected quantitatively. A particle filter preceded the impregnated filters in order to remove particles from the fumes. This system has proven effective under difficult sampling conditions and, since it is portable and light weight, it could be used for many volcanological applications where high levels of acidic gaseous phase species need to be collected.