A multi-elemental study of plant surface particles in relation to geochemistry and biogeochemistry

Surface particulate material was collected in dry weather from the foliage of gorse bushes (Ulex europaeus L.) at twenty background and mineralised sites in southwest England, together with soil and herbage samples. The foliar dusts were separated in the laboratory into four size fractions, and all the samples were analysed for sixteen elements by inductively coupled plasma (I.C.P.) emission spectrometry. Regression analysis of the data showed that the analytical values determined for foliar surface particles were correlated (P > 95%) in at least one particulate fraction with soil concentrations for the following elements: Cu, Pb, Mn, Zn, Al, Ca, Cr, Fe, Be, Sr, Ba, P and Cd. The multi-elemental data, supported by electron microprobe analysis and visual and microscopic examination of the particles, showed that plant material, as well as soil dust, contributed substantially to the chemistry of plant surface particles. Factors influencing the trace element chemistry of plant surfaces are discussed and should be appreciated if particle collection methods are to be applied as a routine geochemical/biogeochemical technique.     

Spatial Variability of Turbulent Fluxes in the Roughness Sublayer of an Even-Aged Pine Forest

The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (_u, _w) and temperature (_T) are more planar homogeneous than their vertical flux of momentum (u_* ²) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO₂ and water vapour. While the spatial variability in fluxes was significant (>15 %), this unique data set confirmed that single tower measurements represent the canonical structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the moving-equilibrium hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u_*, especially when u_* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (I_w) and the arrival frequency of organized structures (/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.     

Geometric assessment of the kodak DCS Pro back

This paper reports on an investigation into the suitability of the Kodak DCS Pro Back for use in close range photogrammetric measurement. The camera back, being used in conjunction with a medium-format non-metric camera, has been assessed with a view to using it for low- to medium-order photogrammetric work in architectural recording. Examinations centred upon the stability of the camera back with respect to the camera body and the effects of the removable infrared filter that is present immediately above the camera's focal plane. Ultimately the camera combination was deemed suitable for application in recording of this kind and is now in active use by the Metric Survey Team at English Heritage.     

天然和人为地震活动性的对比研究

为了充分发挥现有的区域性、地方性数字地震台站在防震减灾中的作用，中国地震局地球物理研究所与美国达拉斯南卫理大学地球科学系合作开展“中美合作延庆一怀来盆地和海城地区天然和人为地震活动性的对比研究”。该合作项目以北京西北的延庆一怀来盆地与东北辽宁的海城地区作为流动地震观测试验场，计划在现有台网的基础上，在近震源与区域性的距离上布设15套由STS—2型宽频带数字地震仪组成的流动地震台网加密观测，以改善在区域性距离上台距过长、不利于分析、解释、研究所观测到地震记录的状况。2002年秋，双方在河北怀来一带首先架设了5个宽频带数字地震台并随即投入观测。到2003年3月上旬，中方又在预定地点架设了另5个宽频带数字地震台。目前，已建成的10个宽频带数字地震台仪器运行正常，运用已获得的研究区内天然和人为地震的高质量记录，合作双方按照计划开展了相关的研究工作。     

Snow Avalanche Hazards and Management in Canada: Challenges and Progress

Avalanche impacts in Canada, including fatalities, are summarized for residential and public areas, as well as roads, ski areas, backcountry recreation, and resource industries. Methods for managing avalanche hazard, which include defence structures, zoning, forecasting and explosive control, are outlined. Problems with current avalanche hazard management are identified and progress at solving these problems is identified with an emphasis on residential areas, backcountry recreation and resource industries.     

Regional groundwater focusing of nitrogen and noble gases into the Hugoton-Panhandle giant gas field, USA

The Hugoton-Panhandle giant gas field, located across SW Kansas and the Texas and Oklahoma panhandles in the USA, is the case type example of high nitrogen concentrations in a natural gas being linked with high helium concentrations. We collected 31 samples from producing wells in a north-south traverse of the 350-km-long field. The samples reflect the previously observed north-south change in ⁴He/N₂, with values changing from 0.020 to 0.049 respectively. ³He/⁴He, ²¹Ne/²²Ne, and ⁴⁰Ar/³⁶Ar vary between 0.14-0.25 Ra, 0.0373-0.0508, and 818-1156 respectively, and are caused by quantifiable contributions from mantle, crustal, and atmosphere-derived sources. The atmosphere-derived ²⁰Ne/³⁶Ar ratios are indistinguishable from groundwater values. The crustal ⁴He/²¹Ne* and ⁴He/⁴⁰Ar* ratios show a 60% excess of ⁴He compared to predicted production ratios in the crust and are typical of noble gases released from the shallow crust. The mantle ³He/N₂ and groundwater-recharge ³⁶Ar/N₂ ratios enable us to rule out significant magmatic or atmosphere contributions to the gas field N₂, which is dominantly crustal in origin.Correlated ²⁰Ne/N₂ and ⁴He/N₂ shows mixing between two distinct crustal N₂ components. One N₂ component (N₂*) is associated with the crustal ⁴He and groundwater-derived ²⁰Ne, and the other with no resolvable noble gas contribution. Measured δ¹⁵N_N2 values vary from +2.7‰ to +9.4‰. The N₂* and non-He-associated N₂ endmembers are inferred to have δ¹⁵N_N2 = −3‰ and +13‰ and contribute from between 25-60% and 75-40% of the nitrogen respectively. The non-He-associated nitrogen is probably derived from relatively mature organic matter in the sedimentary column. The δ¹⁵N_N2* value is not compatible with a crystalline or high-grade metamorphic source and, similar to the ⁴He, is inferred to be from a shallow or low metamorphic-grade source rock. ⁴He mass balance requires a regional crustal source, its association with significant magmatic ³He pointing to a tectonically active source to the west of the Hugoton system. The volume of groundwater required to source the ²⁰Ne in the gas field demonstrates the viability of the groundwater system in providing the collection, transport, and focusing mechanism for the ⁴He and N₂*. The N₂*/²⁰Ne ratio shows that the N₂* transport must be in the aqueous phase, and that the degassing mechanism is probably contact between the regional groundwater system and the preexisting reservoir hydrocarbon gas phase.     

Impacts of hydrological changes on phytoplankton succession in the Swan River, Western Australia

The Swan River estuary, Western Australia, has undergone substantial hydrological modifications since pre-European settlement. Land clearing has increased discharge from some major tributaries roughly 5-fold, while weirs and reservoirs for water supply have mitigated this increase and reduced the duration of discharge to the estuary. Nutrient loads have increased disproportionately with flow and are now approximately 20-times higher than pre-European levels. We explore the individual and collective impacts of these hydrological changes on the Swan River estuary using a coupled hydrodynamic-ecological numerical model. The simulation results indicate that despite increased hydraulic flushing and reduced residence times, increases in nutrient loads are the dominant perturbation producing increases in the incidence and peak biomass of blooms of both estuarine and freshwater phytoplankton. Changes in salinity associated with altered seasonal freshwater discharge have a limited impact on phytoplankton dynamics.     

Detection of fluorescent compounds in the environment using granular activated charcoal detectors

Granular activated charcoal (GAC) acts as a general adsorptive medium for organic molecules, and is widely used to capture fluorescent tracer dyes. To investigate the capability of GAC in contaminant screening and tracer adsorption, a number of detectors were deployed for 2-6 days in a range of urban surface waters, and the adsorbed compounds eluted in an alkaline alcohol solution. Simultaneous water samples showed a diverse range of fluorescence environments, ranging from relatively clean, steady groundwater discharge, to highly concentrated and variable treated municipal sewage. A wide variety of organic compounds and dyes were found in the waters, as chronic and acute contaminants. The relationship between charcoal and water spectra depended on exposure time and loading. Short exposure times emphasized short wavelengths, longer exposure times emphasized longer wavelengths at the expense of shorter wavelengths. The magnitude of the effect depended on loading, being greater in enriched waters. In general, charcoal eluent shows a significant gain in fluorescence intensity over water. However, there may be an apparent loss at shorter wavelengths for samples with long exposure times and high loading. A similar bias was also discovered with the elution time of activated charcoal. Short wavelength fluorescence intensity peaked after a few minutes of elution; longer wavelength fluorescence increased over many days. These results show that charcoal is a reasonably effective material for adsorption of longer wavelength compounds. However, the ubiquity of many fluorescent dyes in the environment, and the complex relationship between the waters and the eluent spectrum, suggest that considerable care is required in the interpretation of eluent spectra.