Experimental study and numerical simulation of denitrification in saturated porous media

The effect of denitrification on the behavior of nitrate in saturated sandy soil was studied in the laboratory and the results were compared with the temporal and spatial concentration of nitrate in nonreactive (without denitrification) and reactive (with denitrification) cases. A laboratory model was fabricated to study steady one-dimensional flow and to transport nitrate with or without denitrification. Denitrification at various rates has been simulated with varied C∶N ratios and detention time. Retardation constant, dispersivity, and degradation constants have been computed using existing analytical models supporting adsorption and zero and/or first order production or decay. It was found that such analytical models can be used to fit the concentration of nitrate in saturated porous media for a C∶N ratio between 2 and 5.     

Modeling of throughfall chemistry and indirect measurement of dry deposition

Precipitation over a forested watershed is altered by interaction with plant surfaces which act as a filter for airborne gases and particles. This results in a major transfer to the forest floor of materials captured, washed, and leached from the forest canopy. Sequential samples of wetfall and sequential samples of throughfall under deciduous and coniferous trees were collected and chemically analyzed for major anions and cations. A simple washoff, mixing model based on leaf area index was used to simulate throughfall chemistry and to decouple foliar exudation from dry deposition. Model results gave excellent predictions of the measured sequential throughfall using estimated values of dry deposition. The model can also be used to calculate dry deposition, if the sequential throughfall data and wetfall data are used as input variables.     

Simulation of gravity fingering in porous media using a modified invasion percolation model

We introduce a modified invasion percolation (MIP) model for the immiscible displacement of a nonwetting fluid by a wetting fluid within a porous network. The model includes the influence of gravity and is applicable in the quasi-static limit of infinitesimal flow rate where viscous forces are negligible with respect to gravity and capillary forces. The incorporation of gravity alone creates complicated, pore-scale gravity fingers. To properly model wetting fluid invasion where macroscopic gravity fingers form, we incorporate a pore-scale geometric capillary smoothing function we refer to as facilitation.Facilitation models the physics of wetting fluid invasion of pores by modifying the capillary pressure required to fill a pore based on the number of adjacent necks connecting the pore to the invading wetting fluid. The wetting fluid invasion facilitation process creates compact clusters and macroscopic fronts in horizontal simulations and in combination with gravity, creates macroscopic, gravity fingers that are in qualitative agreement with physical experiments. The MIP model yields much different imbibition front structures than standard invasion percolation. For MIP, capillary fingering, capillary facilitation, and gravity fingering compete to determine the wetted network structure as a function of pore-size distribution.     

Effect of humic acid on the sedimentation and transport of nanoparticles silica in water-saturated porous media

Journal of Soils and Sediments - Nano silicon particles (nSiO2) is one of the most widely used industrial engineered nanomaterials (ENMs). The extensive applications of nSiO2 may pose potential...     

Genotypic variation in partitioning of phosphorus in relation to nitrogen and dry matter during wheat grain development

Phosphorus has many similarities to N for plant nutrition, but little is known regarding P partitioning among genotypes and factors that affect it. Experiments were conducted to measure variation in partitioning of P and its relationship to N, dry matter, and yield components of wheat (Triticum aestivum L.). Sixteen cultivars grown under field conditions were sampled at anthesis for P, N, and dry matter and at maturity for the same constituents and for yield components. Relationships among the traits were determined by Spearman rank correlation coefficients. Accumulation of P and dry matter during grain development and grain HI, NHI, and PHI differed significantly among genotypes. Post‐anthesis P, N, and dry matter accumulation correlated positively as did HI, NHI, and PHI, but accumulation of the constituents was not related to their His. The positive associations were attributed to requirement of P and N for growth and their accumulation as reserve compounds in grain. Genotypic variation in PHI may be as useful as variation in HI and NHI for wheat improvement.     

Ozone effects on dry matter partitioning and chlorophyll fluorescence during plant development of wheat

In closed-chamber fumigation experiments dry matter partitioning and chlorophyll fluorescence of wheat were studied, analysing the effects of ozone during different stages of plant development. Ozone causes enhanced leaf senescence, leading to a loss of green leaf area and, consequently to a decreased supply of assimilates, affecting (in increasing order of severeness) stem, ear and grain productivity because of reduced storage pools for translocation. Leaves of plants before shooting stage were most sensitive but the lack of green leaf area after ear emergence had the most pronounced effects on grain yield.Measurements of photochemical capacity showed that evidence for negative ozone effects could be found in changes of chlorophyll fluorescence parameters in leaf sections not yet showing visible ozone injury. Negative effects on photosynthesis were more distinct with increasing accumulated ozone dose, with increasing age of leaf tissue and with increasing ozone sensitivity of the cultivar. The changes in chlorophyll fluorescence are most likely to be explained by a decreased pool size of plastoquinones caused by ozone.     

Modeling of the development of humus horizons in soils of Crimea

Current approaches to the simulation of pedogenesis processes in time are considered. Models for the formation of humus horizon on parent rocks of different genesis in Crimea are presented. Formation rates of humus horizons have been determined, which allows developing the remediation strategies for mining dumps of mineral deposits in Crimea.     

Consequences of variation in male harem size to population persistence: Modeling poaching and extinction risk of Bengal tigers (Panthera tigris)

As a broad scientific consensus in support of anthropogenic global warming emerged in the 1980s, a few biologists were quick to make predictions of the likely impacts in the tropics. Most conservation biologists, however, saw climate change as a much less immediate threat to tropical terrestrial ecosystems than deforestation, logging, and hunting. There has been a rapid shift in opinion in the last few years, with the widespread recognition that the climate is already changing at a rate that is relevant to current conservation actions in the tropics. Unfortunately, more than a decade of relative neglect of climate change research has left tropical biologists with little hard information on which to plan a response. The most widely used climate projections for the tropics do not represent the full range of model possibilities and do not reflect the current rates of greenhouse gas emission. The 2–3 °C rise that is commonly assumed could be 4–6, or even 7 °C, while projections for rainfall and other climate variables have still greater uncertainty. These climatic uncertainties are compounded by our ignorance about the potential biological consequences of these changes. It is very likely, however, that the majority of the tropics will soon be subject to climatic conditions that have not existed anywhere on Earth for millions of years. It’s a new world and all bets are off.     

Production and persistence of urease activity in soils

Addition of urea to Iowa soils did not induce urease activity, but production of urease activity was observed on addition of glucose and other organic materials that promote microbial activity. The persistence of the urease activity produced on addition of these materials varied with the soil, but, with each soil studied, the urease activity after addition of organic materials eventually was identical to that of the unamended soil. No increase or decrease in urease activity was observed when unamended or urea-treated soils were incubated under aerobic conditions for several months. It is concluded that soil constituents protect urease against microbial degradation and other processes leading to inactivation of enzymes and that every soil has a stable level of urease activity determined by the ability of its constituents to provide this protection.     

Flumioxazin soil persistence and mineralization in laboratory experiments

Flumioxazin is an herbicide registered for use in soybean and peanut. However, few published papers concerning the soil persistence of flumioxazin are available. Therefore, laboratory studies were initiated to determine the half-life (t(1/2)) of flumioxazin in Greenville sandy clay loam and Tifton loamy sand soils when incubated at 15 and 25 degrees C. Results indicated that temperature had little effect on flumioxazin persistence. The t(1/2) for the Greenville soil was 17.9 and 16.0 days while the Tifton soil was 13.6 and 12.9 days, at 15 and 25 degrees C, respectively. These data correspond to the greater clay content of the Greenville soil (32%) as compared to the Tifton soil (2%). Therefore, the Greenville soil had greater soil adsorption and less flumioxazin was generally available to be degraded by soil microorganisms. In soils that were heat treated to reduce microbe populations, 99% of initial flumioxazin was accounted for after 16 days. Mineralization of flumioxazin, measured as 14CO2 evolution, was also greater in the Tifton soil (2.2% after 64 days) than in the Greenville soil (2.0% after 64 days). From these data, it was concluded that microbes were the most influential factor concerning the degradation of flumioxazin.     

The abundance of hollow-bearing trees in urban dry sclerophyll forest and the effect of wind on hollow development

Anthropogenic change, particularly in urban landscapes, has resulted in the fragmentation of indigenous vegetation into often small isolated ‘remnants’. The persistence of arboreal fauna in small urban remnants in part depends on the distribution and abundance of habitat resources within the remnant. We surveyed 44 small (<2.5 ha) eucalypt remnants located within the south-eastern suburbs of metropolitan Melbourne to ascertain the abundance of hollow-bearing trees, an important ecological resource. The probability of a live or dead tree containing a hollow was investigated in relation to site variables that influenced exposure to wind, a factor thought to increase the propensity of hollow formation in eucalypt trees. A total of 2678 live and 224 dead eucalypt trees were surveyed, of which 350 live (12%) and 70 dead (31%) trees were hollow-bearing. The probability of a tree being hollow-bearing was strongly positively associated with the diameter of the tree, however, past management practices have lead to a paucity of large (>80 cm DBH) trees in small urban remnants. We found that variables that measured exposure to wind were correlated with the chance that a live tree will be hollow-bearing while reducing the chance that a dead tree will be hollow-bearing. Although highly variable, the number of hollow-bearing trees contained within small urban remnants (mean of 5.8 ha⁻¹) fell well below that contained in areas of un-logged non-urban forest. Our results indicated that large numbers of hollow-bearing tree are unlikely to be recruited into urban remnants for a significant time-span and as such there is an increased importance placed on maintaining the current inventory of hollow-bearing trees for the maintenance of biodiversity in urban areas.     

Predicted and observed finger diameters in field soils

Wetting front instability resulting in fingered flow has been found in both wettable and nonwettable soils. Understanding how and when this phenomenon occurs under field conditions is greatly limited. Laboratory research has resulted in a number of expressions for finger diameter. In this paper we test the applicability of one of these equations for three different soils in the Netherlands where detailed soil sampling of moisture content was done earlier. In addition, information needed for finger prediction, such as the main wetting and drying loops of the soil moisture characteristic curves and the unsaturated and saturated soil conductivities, were measured in the laboratory. Results show that predicted finger diameters for the two sandy soils agreed well with the observed moisture patterns, while for the loess soil the wetting front was flat as predicted. The finger diameters in dry soil were based on the main wetting loop and in the wet soils were dependent on the main drying loop.     

Jerusalem artichoke growth,development, and field storage. I. Numerical assessment of plant part development and dry matter acquisition and allocation

Abstract

Expanding commercial interest in the use of inulin as a bulking agent for artificial sweeteners, dietary fiber health supplement, fat replacement for processed foods, feed stock for fructose syrups, and a wide range of potential industrial products, has stimulated research on inulin‐containing crops such as the Jerusalem artichoke. To better understand the developmental physiology of the crop and to identify potential breeding objectives, the temporal pattern of development of individual plant parts (shoots, branches, leaves, flowers, stolons, tubers, and roots) and the allocation of dry matter into the same plant parts were monitored in the cultivar ‘Sunchoke’ over the entire growing season and during in situ field storage during the early winter, 32 weeks after planting. While number of shoots (～9) peaked in week 10, the number of branches (42.8), stolons (49.4), and tubers (85.5) reached a maximum 24–28 weeks after planting. Number of leaves (～525) peaked between weeks 20–24 after planting, as did number of flowers (～55). The Jerusalem artichoke allocated the major portion of its dry matter (dm) into aboveground plant parts during the first half of the growing season. Approximately 16 weeks after planting, the pattern of allocation shifted dramatically with: a) near cessation in the acquisition of dry matter; and b) the reallocation of existing dry matter from the aboveground organs into the tubers. By the 16th week after planting, 85% of the total dm was in the aboveground plant parts, but declined to 28% by the 30th week. Of the total dm, 92% was accrued during the first 16 weeks and only 8% thereafter. The shift in dry matter resources coincided with a dramatic decrease in leaf number and in leaf and branch dry weight. By the end of the season, the harvest index reached 0.70 and the tuber yield 14.61 dm ha^?1. Yield improvement could potentially be facilitated through lengthening the logarithmic period of carbon fixation and by earlier tuber induction and development.     

离体培养下锌对春小麦子粒形成及干物质积累的影响

采用离体穗培养技术研究了锌对春小麦后期生长及产量的影响。结果表明,在Zn2+浓度为6.mmol/L的处理小麦的生长发育状况最好,其旗叶内叶绿素含量、倒一节长度、穗粒数、结实率、千粒重以及穗的干重与对照相比差异均达到显著或极显著水平;倒二节长度和小花数与对照的差异不显著。低锌和锌过量(Zn2+浓度为0.3和300mmol/L)条件下,小麦的生长发育受阻,各项性状指标均低于对照,不利于产量的提高;而且锌过量不但降低产量还造成锌肥的浪费和环境污染。     

Salinity and the persistence of parathion in flooded soils

The persistence of parathion in five coastal saline soils of varying electrical conductivity and in one nonsaline soil sample was studied under flooded conditions. Parathion was decomposed faster in nonsaline soil than in saline soils and its stability increased with increasing electrical conductivity. The addition of salts to the nonsaline soil at 4, 8 and 16 dS^?1 increased the persistence of parathion. Nitro-group reduction, and not hydrolysis, was the major route of parathion degradation in saline and nonsaline soils. The accumulation of aminoparathion was less pronounced in saline soils than in nonsaline soil concomitant with slow degradation of parathion in saline soils. The inhibition of nitro-group reduction in saline soils was related to low microbial activities as reflected in decreased dehydrogenase activity and slow iron reduction.     

Quantitative assessment of hydrolase production and persistence in soil

The aim of this work was to calculate indices of hydrolase production (Pr) and persistence (Pe) through simple arithmetical calculations. Changes in acid and alkaline phosphomonoesterase, phosphodiesterase, urease, protease, and β-glucosidase activities were monitored under controlled conditions in seven soils with a wide range of properties, in which microbial growth was stimulated by adding glucose and nitrogen. Glucose mineralization was monitored by CO₂–C evolution, and microbial growth was quantified by determining the soil adenosine triphosphate (ATP) content. Hydrolase Pr and Pe indices were numerically quantified by the following relationships: Pr = H / t _H and Pe = (r / H)Δt, respectively, where H indicates the peak value of each measured hydrolase activity, t _H is the time of the peak value, r indicates the residual activity value, and Δt is the time interval t _r − t _H, where t _r is the time of the residual activity value. Addition of glucose and N-stimulated soil respiration increased ATP content and stimulated the production of the measured hydrolase activities in all soils; the measured variable reached a maximum value and then decreased, returning to the value of the control soil. Apart from β-glucosidase activity, whose activity was not stimulated by glucose and N addition, the other measured hydrolase activities showed a trend that allowed us to calculate the Pr and Pe indices using the above-mentioned equations. Acid phosphomonoesterase and protease Pr values were significantly higher in soils under forest or set aside management; the alkaline phosphomonoesterase and phosphodiesterase Pr values were generally higher in the neutral and alkaline soils, and the urease Pr values showed no obvious relationships with soil pH or management. Concerning the persistence of enzyme activities, Pe values of the acid phosphomonoesterase activity were significantly higher in the acidic soils, and those of urease activity were higher in acidic soils and the Bordeaux neutral soil. No relationships were observed between Pe values of alkaline phosphomonoesterase, phosphodiesterase, or protease activities and soil pH or management. The different responses of hydrolases were discussed in relation to soil properties, microbial growth, and regulation at the enzyme molecular level.     

落实“沃土计划”促进旱区农业可持续发展

为了迎接淡水危机的挑战 ,在“雨养农业”建设中通过油渣、绿肥、秸秆“过腹还田”、发展节粮养殖业、扩大粪肥来源 ,通过改掺土积肥为粪草堆肥、提高粪肥质量 ,节约施肥劳力 ,是增加土壤有机质、建设土壤水库、提高降水生产效率、预防旱灾的有效途径     

Urine enhances the leaching and persistence of estrogens in soils

The release of endocrine disrupting chemicals (EDCs) into the environment is of concern due to their potential deleterious effects on freshwater ecosystems and human health. Estrogen losses from agricultural land to freshwater have been implicated as a diffuse source of EDC pollution, however, uncertainty exists about the magnitude of this flux in comparison to other point sources (e.g. sewage treatment plants). Recent reviews have all highlighted the need for more mechanistic studies on hormone behaviour in soil environments. The aim of this study was to investigate the influence of aqueous matrix on the leaching, sorption and persistence of two naturally occurring hormones, estrone and 17β-estradiol in three agricultural grassland soils. The hormones were applied to the surface of the soil in two solvents, distilled water and natural sheep urine. Rainfall was subsequently applied to the top of the soil columns and the leachate collected. In comparison to distilled water, the presence of sheep urine both enhanced and prolonged the amount of estrogen leaching from soil. We hypothesized that this enhanced rate of estrogen migration in soil was due to changes in either estrogen sorption or microbial activity. While the presence of urine did not greatly affect the rate and amount of estrogen sorption to soil (K_d = 4-16) it did significantly reduce the rate of hormone mineralization. Overall, our study shows that vertical estrogen movement is rapid, soil type dependent and regulated by the aqueous matrix in which the hormones are contained. In terms of risk assessment and environmental fate modelling, we conclude that previous studies performed using hormones contained in artificial matrices (e.g. distilled water) may have underestimated their rate of dissipation in the environment.     

Intensity and persistence profiles of flavor compounds in synthetic solutions. Simple model for explaining the intensity and persistence of their aftersmell

Hydroalcoholic solutions containing a single aroma-active compound were evaluated by a sensory panel to determine the difference between ortho and retronasal odor intensities (DeltaI(ro)), buccal savoring, and aftersmell duration. Eight compounds were used. Buccal perception seems to be just a physiologically restricted form of retronasal perception. DeltaI(ro) values were dependent on the panel, although results from the two panels were significantly correlated. Such differences and the aftersmell persistence were also significantly correlated with different physicochemical parameters related to volatility. A simple model to explain such dependence is proposed. The model considers the mouth-throat system as a perfect mixing tank with a finite amount of odorants being progressively diluted by swallowing and purging (both taken as continuous processes). Retronasal intensity is modeled from the odor properties of the liquid in such a tank calculated from orthonasal odor intensity versus concentration (I/log C) curves. The model explains successfully experimental results and has also been successfully applied to instrumental data from other authors.