Modeling finger development and persistence in initially dry porous media     

John L. Nieber 《Geoderma》1996,70(2-4):207-229

The mechanism for the growth and persistence of gravity-driven fingered flow of water in initially dry porous media is described. A Galerkin finite element solution of the two-dimensional Richards equation with the associated parameter equations for capillary hysteresis in the water retention function is presented. A scheme for upstream weighting of internodal unsaturated hydraulic conductivities is applied to limit smearing of steep wetting fronts. The growth and persistence of a single finger in an initially dry porous media is simulated using this numerical solution scheme. To adequately simulate fingered flow, it was found that the upstream weighting factor had to be negative, meaning that the internodal unsaturated hydraulic conductivities were weighted more by the downstream node. It is shown that the growth and persistence of a finger is sensitive to the character of the porous media water retention functions. For porous media where the water-entry capillary pressure on the main wetting function is less than the air-entry capillary pressure on the main drainage function, a small perturbation will grow into a finger, and during sequential drainage and wetting the finger will persist. In contrast, for porous media where the water-entry capillary pressure on the main wetting function is greater than the air-entry capillary pressure on the main drainage function, the same small perturbation will dissipate by capillary diffusion. The finger widths derived from the numerical simulation are similar to those predicted by analytical theory.  相似文献   

Avoidance of low pH and elevated Al concentrations by Brook Charr (Salvelinus fontinalis) Alevins in laboratory tests     

John M. Gunn  David L. G. Noakes 《Water, air, and soil pollution》1986,30(1-2):497-503

Laboratory studies were conducted to test the ability of brook charr (Salvelinus fontinalis) alevins, the earliest free-swimming life stage of the species, to detect and avoid toxic levels of H⁺ and inorganic Al. Alevins were tested in steep gradient choice tanks using a range of H⁺ (pH 4.0 to 5.5) and Al (0 to 500 μg L^?1) concentrations in low Ca (2.0 mg L^?1) water. The young brook charr actively avoided acidic water with a pH < 5.0. Aluminum additions of 500 μg L^?l increased the avoidance response. The observed behavioral response of alevins to low pH and elevated levels of Al, may be of significant adaptive advantage in systems undergoing acidification.  相似文献   

Positional effect on protein and oil content and composition of soybeans     

Bennett JO  Krishnan AH  Wiebold WJ  Krishnan HB 《Journal of agricultural and food chemistry》2003,51(23):6882-6886

Soybean (Glycine max [L.] Merr.) protein and oil qualities, with respect to monogastric nutrition, have been linked to the relative abundance of specific protein subunits and fatty acids, respectively. An analysis of field-grown soybean seeds by near-infrared spectroscopy revealed significant differences in their protein and oil contents as a function of nodal position. Seed proteins from the plant apex were high in protein and low in oil content, while those from the basal region exhibited an opposite pattern of accumulation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total seed proteins revealed that the beta-subunit of beta-conglycinin content was 4-fold higher in seeds from the apical nodes than in seeds from basal nodes. The glycinin A3 polypeptide content gradually increased in successively lower nodes from the top of the plant. Its accumulation was drastically reduced when nitrogen was applied at specific growth stages. Exogenous nitrogen did not alter the pattern of beta-subunit accumulation, but accrual of the acidic and basic polypeptides of glycinin was diminished. The remaining seed storage protein components were not influenced by nodal position or nitrogen application. Gas chromatographic analysis of fatty acids indicated that only oleic (18:0) and linoleic (18:2) acids showed variability in accumulation at different nodes. Neither the abundance nor the distribution of the fatty acids was altered by nitrogen application.  相似文献   

Investigating tropical deforestation using two-stage spatially misaligned regression models     

Deepak K. Agarwal  Alan E. Gelfand  John A. Silander 《Journal of Agricultural, Biological & Environmental Statistics》2002,7(3):420-439

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Historical Trace Metal Accumulation in the Sediments of an Urbanized Region of the Lake Champlain Watershed, Burlington, Vermont   总被引：3，自引：0，他引：3  

Ellen L. Mecray  John W. King  Peter G. Appleby  Allen S. Hunt 《Water, air, and soil pollution》2001,125(1):201-230

This study documents the history ofpollution inputs in the Burlington region of LakeChamplain, Vermont using measurements of anthropogenicmetals (Cu, Zn, Cr, Pb, Cd, and Ag) in four age-datedsediment cores. Sediments record a history ofcontamination in a region and can be used to assessthe changing threat to biota over time and to evaluatethe effectiveness of discharge regulations onanthropogenic inputs.Grain size, magnetic susceptibility, radiometricdating and pollen stratigraphy were combined withtrace metal data to provide an assessment of thehistory of contamination over the last 350 yr inthe Burlington region of Lake Champlain. Magneticsusceptibility was initially used to identify land-usehistory for each site because it is a proxy indicatorof soil erosion. Historical trends in metal inputs inthe Burlington region from the seventeenth through thetwentieth centuries are reflected in downcorevariations in metal concentrations and accumulationrates. Metal concentrations increase above backgroundvalues in the early to mid nineteenth century. Themetal input rate to the sediments increases around1920 and maximum concentrations and accumulation ratesare observed in the late 1960s. Decreases inconcentration and accumulation rate between 1970 andthe present are observed for most metals. Theobserved trends are primarily a function of variationsin anthropogenic inputs and not variations in sedimentgrain size. Grain size data were used to removetexture variations from the metal profiles and resultsshow trends in the anthropogenic metal signals remain. Radiometric dating and pollen stratigraphy providewell-constrained dates for the sediments therebyallowing the metal profiles to be interpreted in termsof land-use history.  相似文献   

A comparison of the properties of manufactured soils produced from composting municipal green waste alone or with poultry manure or grease trap/septage waste     

Oxana N. Belyaeva  Richard John Haynes 《Biology and Fertility of Soils》2010,46(3):271-281

Manufactured soil for landscaping purposes was produced by composting for 6 weeks (1) municipal green waste alone, (2) green waste amended with 25% v/v poultry manure, or (3) green waste immersed in, and then removed from, a mixture of liquid grease trap waste/septage. Composting temperatures increased most rapidly and reached highest values (78oC) in the grease trap/septage-amended green waste. In comparison with green waste alone, addition of poultry manure prolonged the period of elevated temperatures and increased the maximum temperature attained from 52oC to 61oC. Following composting, each of the materials was split into (1) 100% compost, (2) 80% compost plus 20% v/v soil, and (3) 70% compost plus 20% soil plus 10% coal fly ash. Addition of poultry manure or grease trap/septage to green waste prior to composting increased bulk density and reduced total porosity of the composted product. Addition of soil, or soil and ash, to composts increased bulk density, reduced total porosity, decreased percentage macropores, and increased percentage mesopores and available water-holding capacity. Bicarbonate-extractable P, exchangeable NH₄⁺ and NO₃⁻, electrical conductivity (EC), soluble C, soluble C as a percentage of organic C, basal respiration, and metabolic quotient were all markedly greater in the grease trap/septage-amended than poultry manure-amended or green waste alone treatments. Values for extractable P and EC were considered large enough to be damaging to plant growth and germination index (GI) of watercress was less than 60% for all grease trap/septage composts. Extractable P and EC were also high, and GI was <100%, in the green waste alone and poultry manure-amended green waste alone treatments. Addition of soil or soil and ash to these composts resulted in GI values >100%.  相似文献   

Triggering the interferon antiviral response through an IKK-related pathway     

Sharma S  tenOever BR  Grandvaux N  Zhou GP  Lin R  Hiscott J 《Science (New York, N.Y.)》2003,300(5622):1148-1151

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Control of insect pests using trunk injection in a newly established apple orchard     

Charles C. Coslor  Christine Vandervoort  John C. Wise 《International Journal of Fruit Science》2019,19(2):151-164

We evaluated the potential for using preplant trunk injections of emamectin benzoate in nonbearing apple trees. Trees were evaluated for pest injury and emamectin residues throughout the planting season and into the following year. Injections into the trunk best delivered emamectin benzoate to the canopy compared with injections into the taproot, and the higher rate reduced insect pests more than the lower rate. In the following year, differences in insect control between trunk and root injections were less pronounced, but the higher rate of emamectin benzoate persisted longer and better reduced pests relative to the other treatments.  相似文献   

Identifying climate refugia for 30 Australian rainforest plant species,from the last glacial maximum to 2070     

Das  Sourav  Baumgartner  John B.  Esperon-Rodriguez  Manuel  Wilson  Peter D.  Yap  Jia-Yee S.  Rossetto  Maurizio  Beaumont  Linda J. 《Landscape Ecology》2019,34(12):2883-2896

Landscape Ecology - Climate refugia—areas that remain suitable for species during periods of climate disruption—have played an important role in species persistence over time....  相似文献   

Correction to: Individual based modelling of fish migration in a 2-D river system: model description and case study     

Snyder  Marcía N.  Schumaker  Nathan H.  Ebersole  Joseph L.  Dunham  Jason B.  Comeleo  Randy L.  Keefer  Matthew L.  Leinenbach  Peter  Brookes  Allen  Cope  Ben  Wu  Jennifer  Palmer  John  Keenan  Druscilla 《Landscape Ecology》2019,34(5):1197-1197

Landscape Ecology - In the original publication of the article, the third author name has been misspelt. The correct name is given in this Correction. The original version of this article was revised.  相似文献