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91.
“Non rainfall” atmospheric water (dew, fog, vapour adsorption) supplies a small amount of water to the soil surface that may be important for arid soil micro-hydrology and ecology. Research into the direct effects of this water on soil is, however, lacking due to instrument and technical constraints. We report on the design, development, construction and findings of an automated microlysimeter instrument to directly measure this soil water cycle in Stellenbosch, South Africa during winter. Performance of the microlysimeter was satisfactory and results obtained were compared to literature and fell within the expected range. “Non rainfall” atmospheric water input into bare soil (river sand) was between 0.88 and 1.10?mm per night while evaporation was between 1.39 and 2.71?mm per day. The study also attempted to differentiate the composition of “non rainfall” atmospheric water and results showed that vapour adsorption contributed the bulk of this input.  相似文献   
92.
Groundwater samples collected at sites where in situ chemical oxidation (ISCO) has been deployed may contain binary mixtures of groundwater contaminants and permanganate (MnO4), an oxidant injected into the subsurface to destroy the contaminant. Commingling of the oxidant and contaminant in aqueous samples may negatively impact the quality of the sample as well as the analytical instruments used to quantify contaminant concentrations. In this study, binary mixtures comprised of (1) a multicomponent standard with permanganate and (2) groundwater samples collected at two ISCO field sites were preserved with ascorbic acid. Ascorbic acid reacts rapidly with the MnO4 and limits the reaction between MnO4 and the organic compounds in the mixture. Consequently, most of the compounds in the multicomponent standard were within the control limit for quality assurance. However, despite timely efforts to preserve the samples, the rapid reaction between permanganate and contaminant caused the concentration of several sensitive compounds to fall significantly below the lower control limit. Concentrations of volatile organic compounds in the field‐preserved binary mixture groundwater samples were greater than in samples refrigerated in the field and preserved upon arrival at the laboratory, indicating the time‐dependency and benefit of field preservation. The molar ratio of ascorbic acid required to neutralize KMnO4 was 1.64 (mol ascorbic acid/mol KMnO4); this provided a baseline to estimate the volume of ascorbic acid stock solution and/or the weight of crystalline ascorbic acid required to neutralize MnO4. Excess ascorbic acid did not negatively impact the quality of the aqueous samples, or analytical instruments, used in the analyses.  相似文献   
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94.
Reports of abruptly declining flows of Canada's Athabasca River have prompted concern because this large, free‐flowing river could be representative for northern North America, provides water for the massive Athabasca oil‐sands projects and flows to the extensive and biodiverse Peace–Athabasca, Slave and Mackenzie River deltas. To investigate historic hydrology along the river and its major tributaries, we expanded the time series with interpolations for short data gaps; calculations of annual discharges from early, summer‐only records; and by splicing records across sequential hydrometric gauges. These produced composite, century‐long records (1913–2011) and trend detection with linear Pearson correlation provided similar outcomes to nonparametric Kendall τ‐b tests. These revealed that the mountain and foothills reaches displayed slight increases in winter discharges versus larger declines in summer discharges and consequently declining annual flows (~0.16% per year at Hinton; p < 0.01). Conversely, with contrasting boreal contributions, the Athabasca River at Athabasca displayed no overall trend in monthly or annual flows, but there was correspondence with the Pacific Decadal Oscillation that contributed to a temporary flow decline from 1970 to 2000. These findings from century‐long records contrast with interpretations from numerous shorter‐term studies and emphasize the need for sufficient time series for hydrologic trend analyses. For Northern Hemisphere rivers, the study interval should be at least 80 years to span two Pacific Decadal Oscillation cycles and dampen the influence from phase transitions. Most prior trend analyses considered only a few decades, and this weakens interpretations of the hydrologic consequences of climate change. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
95.
Plastic production pellets sampled from four beaches along a stretch of coastline (south Devon, SW England) and accompanying, loosely adhered and entrapped material removed ultrasonically have been analysed for major metals (Al, Fe, Mn) and trace metals (Cu, Zn, Pb, Ag, Cd, Co, Cr, Mo, Sb, Sn, U) following acid digestion. In most cases, metal concentrations in composite pellet samples from each site were less than but within an order of magnitude of corresponding concentrations in the pooled extraneous materials. However, normalisation of data with respect to Al revealed enrichment of Cd and Pb in plastic pellets at two sites. These observations are not wholly due to the association of pellets with fine material that is resistant to ultrasonication since new polyethylene pellets suspended in a harbour for 8 weeks accumulated metals from sea water through adsorption and precipitation. The environmental implications and potential applications of these findings are discussed.  相似文献   
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97.
Although Main Streets line small towns from Florida to Alaska, Main Street is more than just a street name; it is a place imbued with local pride, regional identity, and national virtues. This symbolic connection derives from the Midwestern Main Streets of the first half of the twentieth century, a time that coincides with the golden age of the picture postcard. This article explores how the connotative and denotative symbols from this golden age overlap. A sample of 140 postcards from small towns in Kansas and Nebraska with a viable Main Street from 1900 to 1945 was selected from books, personal collections, and Internet auction sites. Our discovery of a disconnect between picture postcard and reality was not surprising, but there was a shift from the significance of basic denotative signs and the particularities of individual Main Streets in the early part of the twentieth century to an increased importance of connotative signs unifying a homogeneous Main Street ideal. Three distinct eras of postcard manipulation emerged from the data: A slightly manipulated 1900–1911 era, a 1912–1930 era emphasizing a corridor of progress, and a 1931–1945 era that displayed a growing detachment from reality and moved from the unique characteristics of a particular town toward a homogenized and idealized “Main Street view.” This article offers empirical evidence for the theoretical propositions of humanist and critical geographers that the representations of the American landscape are becoming increasingly homogenized, contrived, and placeless.  相似文献   
98.
The Northern current is the main circulation feature of the North-Western Mediterranean Sea. While the large-scale to mesoscale variability of the northern current (NC) is well known and widely documented for the Ligurian region, off Nice or along the Gulf of Lions shelf, few is known about the current instabilities and its associated mesoscale dynamics in the intermediate area, off Toulon. Here, we took advantage of an oceanographic cruise of opportunity, the start of a HF radar monitoring programme in the Toulon area and the availability of regular satellite sea surface temperature and chlorophyll a data, to evaluate the realism of a NEMO-based regional high-resolution model and the added value brought by HF radar. The combined analysis of a 1/64° configuration, named GLAZUR64, and of all data sets revealed the occurrence of an anticyclonic coastal trapped eddy, generated inside a NC meander and passing the Toulon area during the field campaign. We show that this anticyclonic eddy is advected downstream along the French Riviera up to the study region and disturbs the Northern current flow. This study aims to show the importance of combining observations and modelling when dealing with mesoscale processes, as well as the importance of high-resolution modelling.  相似文献   
99.
100.
Excavations at Bonneville Estates Rockshelter, Nevada recovered rodent remains from stratified deposits spanning the past ca. 12,500 14C yr BP (14,800 cal yr BP). Specimens from horizons dating to the late Pleistocene and early Holocene include species adapted to montane and moist and cool habitats, including yellow-bellied marmot (Marmota flaviventris) and bushy-tailed woodrat (Neotoma cinerea). Shortly after 9000 14C BP (10,200 cal yr BP) these mammals became locally extinct, or nearly so, taxonomic diversity declined, and the region became dominated by desert woodrats (Neotoma lepida) and other species well-adapted to xeric, low-elevation settings. The timing and nature of changes in the Bonneville Estates rodent fauna are similar to records reported from nearby Homestead and Camels Back caves and provide corroborative data on terminal Pleistocene–early Holocene environments and mammalian responses to middle Holocene desertification. Moreover, the presence of northern pocket gopher (Thomomys talpoides) at Bonneville Estates adds to a sparse regional record for that species and, similar to Homestead Cave, it appears that the ca. 9500 14C yr BP (10,800 cal yr BP) replacement of the northern pocket gopher by Botta's pocket gopher in the Great Salt Lake Desert vicinity was also in response to climate change.  相似文献   
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