Quantifying the temporal dynamics of wood in large rivers: field trials of wood surveying,dating, tracking,and monitoring techniques

Wood plays an important role in stream ecology and geomorphology. Previous studies of wood in rivers have quantified spatial distributions but temporal dynamics remain poorly documented. The lack of such data is related to limitations of existing methods, especially when applied to large rivers. Five techniques are field‐tested to assess their utility for quantifying the temporal dynamics in rivers: repeated high‐resolution aerial surveys, the measurement of wood physical characteristics as proxies for ¹⁴C dating, passive and active radio frequency identification (RFID) tags, radio transmitters, and video. The spatial distribution of wood is surveyed using aerial imagery with a resolution finer than 0·10 m. The estimation of temporal trends by repeated aerial‐based surveys needs to consider vegetation growth and hiding. Wood residence times can be calculated using ¹⁴C analysis, but the assessment of wood physical characteristics including decay status and wood density offers a cheaper, if less accurate, alternative. Wood resistance to penetration is tested but results are not significant. Radio transmitters are reliable for multi‐year (～5 year) surveys and can be detected at 800 m. Passive RFID tags are limited by a read range of 0·30 m but are reliable for longer term (>5 year) studies. Active RFID tags combine a moderate read range (10–300 m) and low cost with in‐flood detection but require more testing. Video monitoring of wood passing on the surface of a river is successfully implemented. For a single flood on the Ain River (France), wood transport rates are an order of magnitude higher on the rising limb of the hydrograph than on the falling limb. Overall, the techniques improve the ability to gather the data needed to understand wood transfer processes and calibrate budgets of wood in rivers. Copyright © 2009 John Wiley & Sons, Ltd.     

Probabilistic Simulation of Remediation at a Site Contaminated by Trichloroethylene

A new probabilistic remediation simulation package, PREMChlor, was used to simulate the effect of contaminant source and plume remediation at a site contaminated by trichloroethylene (TCE). First, the PREMChlor model was calibrated to the plume using a deterministic approach to represent the site conditions prior to remediation activities, which occurred in 1999. The calibrated model was then used in a probabilistic mode to conduct a simulation of the effects of field source and plume remediation activities during the period after 1999. This probabilistic simulation considers uncertainties in seven key parameters: the initial source mass and concentration, the relationship between source mass removal and source concentration, the effectiveness of the source remediation, the groundwater velocity, the background plume degradation rate, and the plume treatment effectiveness. The simulation results compare favorably with the observed data collected after 1999, and show the influence of the remediation efforts on the plume.     

River loads of suspended solids, nitrogen, phosphorus and herbicides delivered to the Great Barrier Reef lagoon

Degradation of coastal ecosystems in the Great Barrier Reef (GBR) lagoon, Australia, has been linked with increased land-based runoff of suspended solids, nutrients and pesticides since European settlement. This study estimated the increase in river loads for all 35 GBR basins, using the best available estimates of pre-European and current loads derived from catchment modelling and monitoring. The mean-annual load to the GBR lagoon for (i) total suspended solids has increased by 5.5 times to 17,000ktonnes/year, (ii) total nitrogen by 5.7 times to 80,000tonnes/year, (iii) total phosphorus by 8.9 times to 16,000tonnes/year, and (iv) PSII herbicides is 30,000kg/year. The increases in river loads differ across the 10 pollutants and 35 basins examined, reflecting differences in surface runoff, urbanisation, deforestation, agricultural practices, mining and retention by reservoirs. These estimates will facilitate target setting for water quality and desired ecosystem states, and enable prioritisation of critical sources for management.     

An interferometric investigation of emission lines from the solar corona

The profiles of the Fe xiv, 5303, and Fe x, 6374, emission lines of the solar corona have been observed at different positions using a photoelectric scanning Fabry-Perot interferometer. These profiles were obtained during the eclipse of 7th March 1970, in Mexico and at the Pic-du-Midi coronagraph in October, 1970. The half-widths of these profiles were determined for both the coronal lines and temperatures were derived from these widths. No systematic temperature variation was discovered, however there was some suggestion of the existence of a fluctuation with time in the width of the emission lines.     

P波随时间衰减:以两条加利福尼亚地震破裂带为例

地震预测是地震学研究一个基本目标,而理解地震周期是地震预测的重要环节.遗憾的是,由于地震断层带不但结构复杂,大地震前后短时间内的震源过程更是随时间迅速变化,这些复杂因素使得常规研究方法不再适用.一类特殊的微震成群地发生在主震断层几乎同一地点上,震源系数几乎相同,近年来地震学界通称其为震群(earthquakemultiplet).本文论证如何将这类特殊的微震作为一组人工震源来阐述美国西部两次大地震(LomaPrieta和MorganHill)的震后弛豫过程.在加利福尼亚LomaPrieta(1989年9月18日,M7.0)及MorganHill(1984年4月24日,M6.2)附近的主震破裂带中就发生了此类震群.其中有两组各包含11个重复地震的震群,分别位于这两个破裂带中,其波形资料质量高,波形及震级变化极小,因而可与实验室条件下的人工震源相比.这些震群地震资料可直接用于计算P波沿波程衰减(即t)的时间性变化,其方法的简单性及结果的精确性都与实验室水平相当.我们的结果显示,每个震群周围分别存在一个异常体,在其各自主震之后的10个月中,该异常体中的P波衰减迅速上升并降落.衰减峰值发生在LomaPrieta地震后2～3周,其震群深度为10.2km.此峰值在MorganHill地震后5～6个月发生,其震群中心深度为2.6km.这两个事例中,t波动峰值都超过此前获得的加利福尼亚大致同一地区t绝对值的100%[1].此结果显示了因同震裂隙张开和震后弛豫过程(如流体移动、裂隙复原及岩石压缩),以及孔隙度和流体饱和度在主震源体部分区域发生的变化.衰减达峰值的时间之显著差异则提示我们,裂隙闭合及伴随的流体移动是负载敏感的,深度越大达峰值越快,反之亦然.如将此方法应用于主震前多重地震的资料,将有望更好地理解最终导致主震断层带大破裂的震前微破裂的物理过程.     

Felsic mineral crystallization trends in differentiating alkaline basic magmas

Contributions to Mineralogy and Petrology - Mineral compositional relationships have been studied in a variety of alkaline basic rocks from small, highlevel intrusions. These small intrusions must...     

Structural analysis of sheath folds with horizontal X-axes,northeast Canada

Early Proterozoic supracrustal rocks occur below a thick nappe of Archaean basement gneiss in the Melville Peninsula where sheath folds are exposed in a wide zone of middle Proterozoic dynamothermal metamorphism. Outcrop patterns of truncated isoclinal sheath folds resemble cylindrical folds except in relatively small areas around the paraboloidal caps. Bulk extension axes are parallel to strike in the belt as shown by isoclinal sheath folds with horizontal central axes (X-axes), as well as similarly aligned mullion structure and rotated scapolite prisms. Extension axes converge from northeast to southwest in the apparent flow direction.     

Arctic sea ice and the Madden–Julian Oscillation (MJO)

Arctic sea ice responds to atmospheric forcing in primarily a top-down manner, whereby near-surface air circulation and temperature govern motion, formation, melting, and accretion. As a result, concentrations of sea ice vary with phases of many of the major modes of atmospheric variability, including the North Atlantic Oscillation, the Arctic Oscillation, and the El Niño-Southern Oscillation. However, until this present study, variability of sea ice by phase of the leading mode of atmospheric intraseasonal variability, the Madden–Julian Oscillation (MJO), which has been found to modify Arctic circulation and temperature, remained largely unstudied. Anomalies in daily change in sea ice concentration were isolated for all phases of the real-time multivariate MJO index during both summer (May–July) and winter (November–January) months. The three principal findings of the current study were as follows. (1) The MJO projects onto the Arctic atmosphere, as evidenced by statistically significant wavy patterns and consistent anomaly sign changes in composites of surface and mid-tropospheric atmospheric fields. (2) The MJO modulates Arctic sea ice in both summer and winter seasons, with the region of greatest variability shifting with the migration of the ice margin poleward (equatorward) during the summer (winter) period. Active regions of coherent ice concentration variability were identified in the Atlantic sector on days when the MJO was in phases 4 and 7 and the Pacific sector on days when the MJO was in phases 2 and 6, all supported by corresponding anomalies in surface wind and temperature. During July, similar variability in sea ice concentration was found in the North Atlantic sector during MJO phases 2 and 6 and Siberian sector during MJO phases 1 and 5, also supported by corresponding anomalies in surface wind. (3) The MJO modulates Arctic sea ice regionally, often resulting in dipole-shaped patterns of variability between anomaly centers. These results provide an important first look at intraseasonal variability of sea ice in the Arctic.     

Abrupt deglaciation on the northeastern Tibetan Plateau: evidence from Lake Qinghai

We inferred the climate history for Central Asia over the past 20,000 years, using sediments from core QH07, taken in the southeastern basin of Lake Qinghai, which lies at the northeastern margin of the Tibetan Plateau. Results from multiple environmental indicators are internally consistent and yield a clear late Pleistocene and Holocene climate record. Carbonate content and total organic carbon (TOC) in Lake Qinghai sediments are interpreted as indicators of the strength of the Asian summer monsoon. Warm and wet intervals, associated with increased monsoon strength, are indicated by increased carbonate and TOC content. During the glacial period (~20,000 to ~14,600 cal year BP), summer monsoon intensity remained low and relatively constant at Lake Qinghai, suggesting cool, dry, and relatively stable climate conditions. The inferred stable, cold, arid environment of the glacial maximum seems to persist through the Younger Dryas time period, and little or no evidence of a warm interval correlative with the Bølling–Allerød is found in the QH07 record. The transition between the late Pleistocene and the Holocene, about 11,500 cal year BP, was abrupt, more so than indicated by speleothems in eastern China. The Holocene (~11,500 cal year BP to present) was a time of enhanced summer monsoon strength and greater variability, indicating relatively wetter but more unstable climatic conditions than those of the late Pleistocene. The warmest, wettest part of the Holocene, marked by increased organic matter and carbonate contents, occurred from ~11,500 to ~9,000 cal year BP, consistent with maximum summer insolation contrast between 30°N and 15°N. A gradual reduction in precipitation (weakened summer monsoon) is inferred from decreased carbonate content through the course of the Holocene. We propose that changes in the contrast of summer insolation between 30°N and 15°N are the primary control on the Asian monsoon system over glacial/interglacial time scales. Secondary influences may include regional and global albedo changes attributable to ice-cover and vegetation shifts and sea level changes (distance from moisture source in Pacific Ocean). The abruptness of the change at the beginning of the Holocene, combined with an increase in variability, suggest a threshold for the arrival of monsoonal rainfall at the northeastern edge of the Tibetan Plateau.