Dust production and the release of iron oxides resulting from the aeolian abrasion of natural dune sands

Global dust trajectories indicate that significant quantities of aeolian-transported iron oxides originate in contemporary dryland areas. One potential source is the iron-rich clay coatings that characterize many sand-sized particles in desert dunefields. This paper uses laboratory experiments to determine the rate at which these coatings can be removed from dune sands by aeolian abrasion. The coatings impart a red colour to the grains to which previous researchers have assigned variable geomorphological significance. The quantities or iron removed during a 120 hour abrasion experiment are small (99 mg kg(-1)) and difficult to detect by eye; however, high resolution spectroscopy clearly indicates that ferric oxides are released during abrasion and the reflectance of the particles alters. One of the products of aeolian abrasion is fine particles (<10 mum diameter) with the potential for long distance transport. Copyright (C) 2004 John Wiley Sons, Ltd.

Does reactive surface area depend on grain size? Results from pH 3, 25 circle C far-from-equilibrium flow-through dissolution experiments on anorthite and biotite

Laboratory determined mineral weathering rates need to be normalised to allow their extrapolation to natural systems. The principle normalisation terms used in the literature are mass, and geometric- and BET specific surface area (SSA). The purpose of this study was to determine how dissolution rates normalised to these terms vary with grain size. Different size fractions of anorthite and biotite ranging from 180-150 to 20-10 mu m were dissolved in pH 3, HCl at 25 degrees C in flow through reactors under far from equilibrium conditions. Steady state dissolution rates after 5376 h (anorthite) and 4992 h (biotite) were calculated from Si concentrations and were normalised to initial- and final- mass and geometric-, geometric edge- (biotite), and BET SSA. For anorthite, rates normalised to initial- and final-BET SSA ranged from 0.33 to 2.77 X 10(-10) mol(feldspar) m(-2) s(-1), rates normalised to initial- and final-geometric SSA ranged from 5.74 to 8.88 X 10(-10) mol(feldspar) m(-2) s(-1) and rates normalised to initial- and final-mass ranged from 0.11 to 1.65 mol(feldspar) g(-1) s(-1). For biotite, rates normalised to initial- and final-BET SSA ranged from 1.02 to 2.03 X 10(-12) mol(biotite) m(-2) s(-1), rates normalised to initial- and final-geometric SSA ranged from 3.26 to 16.21 X 10(-12) mol(biotite) m(-2) s(-1), rates normalised to initial- and final-geometric edge SSA ranged from 59.46 to 111.32 x 10(-12) mol(biotite) m(-2) s(-1) and rates normalised to initial- and final-mass ranged from 0.81 to 6.93 X 10(-12) mol(biotite) g(-1) s(-1). For all normalising terms rates varied significantly (p <= 0.05) with grain size. The normalising terms which gave least variation in dissolution rate between grain sizes for anorthite were initial BET SSA and initial- and final-geometric SSA. This is consistent with: (1) dissolution being dominated by the slower dissolving but area dominant non-etched surfaces of the grains and, (2) the walls of etch pits and other dissolution features being relatively unreactive. These steady state normalised dissolution rates are likely to be constant with time. Normalisation to final BET SSA did not give constant ratios across grain size due to a non-uniform distribution of dissolution features. After dissolution coarser grains had a greater density of dissolution features with BET-measurable but unreactive wall surface area than the finer grains. The normalising term which gave the least variation in dissolution rates between grain sizes for biotite was initial BET SSA. Initial- and final-geometric edge SSA and final BET SSA gave the next least varied rates. The basal surfaces dissolved sufficiently rapidly to influence bulk dissolution rate and prevent geometric edge SSA normalised dissolution rates showing the least variation. Simple modelling indicated that biotite grain edges dissolved 71-132 times faster than basal surfaces. In this experiment, initial BET SSA best integrated the different areas and reactivities of the edge and basal surfaces of biotite. Steady state dissolution rates are likely to vary with time as dissolution alters the ratio of edge to basal surface area. Therefore they would be more properly termed pseudo-steady state rates, only appearing constant because the time period over which they were measured (1512 h) was less than the time period over wich they would change significantly. (c) 2006 Elsevier Inc. All rights reserved.

Orographic precipitation in the tropics: experiments in Dominica

The “natural laboratory” of mountainous Dominica (15°N) in the trade wind belt is used to study the physics of tropical orographic precipitation in its purest form, unforced by weather disturbances or by the diurnal cycle of solar heating. A cross-island line of rain gauges and 5-min radar scans from Guadeloupe reveal a large annual precipitation at high elevation (7 m yr^{−1}) and a large orographic enhancement factor (2 to 8) caused primarily by repetitive convective triggering over the windward slope. The triggering is caused by terrain-forced lifting of the conditionally unstable trade wind cloud layer. Ambient humidity fluctuations associated with open-ocean convection may play a key role. The convection transports moisture upward and causes frequent brief showers on the hilltops. The drying ratio of the full air column from precipitation is less than 1% whereas the surface air dries by about 17% from the east coast to the mountain top. On the lee side, a plunging trade wind inversion and reduced instability destroys convective clouds and creates an oceanic rain shadow.

Intra-specific variation affects the structure of the natural enemy assemblage attacking pea aphid colonies

1. Intra-specific variation in plant defence traits has been shown to profoundly affect herbivore community structure. Here we describe two experiments designed to test whether similar effects occur at higher trophic levels, by studying pea aphid–natural enemy interactions in a disused pasture in southern England. 2. In the first experiment, the numbers and identity of natural enemies attacking different monoclonal pea aphid colonies were recorded in a series of assays throughout the period of pea aphid activity. 3. In the summer assay, there was a significant effect of clone on the numbers of aphidophagous hoverfly larvae and the total number of non-hoverfly natural enemies recruited. Clone also appeared to influence the attack rate suffered by the primary predator in the system, the hoverfly Episyrphus balteatus, by Diplazon laetatorius, an ichneumonid parasitoid. Colonies were generally driven to extinction by hoverfly attack, resulting in the recording of low numbers of parasitoids and entomopathogens, suggesting intense intra-guild predation. 4. To further examine the influence of clonal variation on the recruitment of natural enemies, a second experiment was performed to monitor the temporal dynamics of community development. Colonies were destructively sampled every other day and the numbers of natural enemies attacking aphid colonies were recorded. These data demonstrated that clonal variation influenced the timing, abundance, and identity of natural enemies attacking aphid colonies. 5. Taken together, these data suggest that clonal variation may have a significant influence on the patterns of interactions between aphids and their natural enemies, and that such effects are likely to affect our understanding of the ecology and biological control of these insect herbivores.

Design and analysis of climate model experiments for the efficient estimation of anthropogenic signals

Presented herein is an experimental design that allows the effects of several radiative forcing factors on climate to be estimated as precisely as possible from a limited suite of atmosphere-only general circulation model (GCM) integrations. The forcings include the combined effect of observed changes in sea surface temperatures, sea ice extent, stratospheric (volcanic) aerosols, and solar output, plus the individual effects of several anthropogenic forcings. A single linear statistical model is used to estimate the forcing effects, each of which is represented by its global mean radiative forcing. The strong colinearity in time between the various anthropogenic forcings provides a technical problem that is overcome through the design of the experiment. This design uses every combination of anthropogenic forcing rather than having a few highly replicated ensembles, which is more commonly used in climate studies. Not only is this design highly efficient for a given number of integrations, but it also allows the estimation of (nonadditive) interactions between pairs of anthropogenic forcings. The simulated land surface air temperature changes since 1871 have been analyzed. The changes in natural and oceanic forcing, which itself contains some forcing from anthropogenic and natural influences, have the most influence. For the global mean, increasing greenhouse gases and the indirect aerosol effect had the largest anthropogenic effects. It was also found that an interaction between these two anthropogenic effects in the atmosphere-only GCM exists. This interaction is similar in magnitude to the individual effects of changing tropospheric and stratospheric ozone concentrations or to the direct (sulfate) aerosol effect. Various diagnostics are used to evaluate the fit of the statistical model. For the global mean, this shows that the land temperature response is proportional to the global mean radiative forcing, reinforcing the use of radiative forcing as a measure of climate change. The diagnostic tests also show that the linear model was suitable for analyses of land surface air temperature at each GCM grid point. Therefore, the linear model provides precise estimates of the space time signals for all forcing factors under consideration. For simulated 50-hPa temperatures, results show that tropospheric ozone increases have contributed to stratospheric cooling over the twentieth century almost as much as changes in well-mixed greenhouse gases.

Challenges in elevated CO2 experiments on forests

Current forest Free Air CO2 Enrichment (FACE) experiments are reaching completion. Therefore, it is time to define the scientific goals and priorities of future experimental facilities. In this opinion article, we discuss the following three overarching issues (i) What are the most urgent scientific questions and how can they be addressed? (ii) What forest ecosystems should be investigated? (iii) Which other climate change factors should be coupled with elevated CO2 concentrations in future experiments to better predict the effects of climate change? Plantations and natural forests can have conflicting purposes for high productivity and environmental protection. However, in both cases the assessment of carbon balance and how this will be affected by elevated CO2 concentrations and the interacting climate change factors is the most pressing priority for future experiments.

Rheology of magmas with bimodal crystal size and shape distributions: insights from analog experiments

Magmas in volcanic conduits commonly contain microlites in association with preexisting phenocrysts, as often indicated by volcanic rock textures. In this study, we present two different experiments that inves- tigate the flow behavior of these bidisperse systems. In the first experiments, rotational rheometric methods are used to determine the rheology of monodisperse and polydisperse suspensions consisting of smaller, prolate particles (microlites) and larger, equant particles (phenocrysts) in a bubble‐free Newtonian liquid (silicate melt). Our data show that increasing the relative proportion of prolate microlites to equant pheno- crysts in a magma at constant total particle content can increase the relative viscosity by up to three orders of magnitude. Consequently, the rheological effect of particles in magmas cannot be modeled by assuming a monodisperse population of particles. We propose a new model that uses interpolated parameters based on the relative proportions of small and large particles and produces a considerably improved fit to the data than earlier models. In a second series of experiments we investigate the textures produced by shearing bimodal suspensions in gradually solidifying epoxy resin in a concentric cylinder setup. The resulting textures show the prolate particles are aligned with the flow lines and spherical particles are found in well‐organized strings, with sphere‐depleted shear bands in high‐shear regions. These observations may explain the measured variation in the shear thinning and yield stress behavior with increasing solid fraction and particle aspect ratio. The implications for magma flow are discussed, and rheological results and tex- tural observations are compared with observations on natural samples.

The effect of farming system and fertilisers on pests and natural enemies: A synthesis of current research

Organic agriculture is becoming widespread due to increased consumer demand and regulatory and political support. Organic agriculture can increase arthropod diversity but the response of pests and their natural enemies is variable. Fertiliser is an important component of agricultural systems and its effects on pests and natural enemies will influence agroecosystems. In this study, meta-analysis and vote-counting techniques were used to compare farming system (organic and conventional) and fertiliser effects on arthropod pests and their natural enemies. The meta-analyses indicated that pests generally benefitted from organic techniques, this is particularly evident when experiments were carried out on a smaller scale. Pest responses to organic and conventional fertiliser types were divergent, plant composts benefitted pest arthropods while the opposite was true for manures, this has implications for pest management. Most natural enemy groups responded positively to organic farming although this was not true for Coleopterans. Experimental scale had a prominent impact on natural enemy responses with farm scale studies showing particularly positive effects of organic agriculture on natural enemies. This suggests that it is large scale features of organic agriculture such as landscape heterogeneity that are beneficial to natural enemies. Natural enemy responses to organic fertilisers were positive indicating that field scale management practices including fertiliser can also be important in pest management.

Developing a reliable strategy to infer the effective soil hydraulic properties from field evaporation experiments for agro-hydrological models

The Richards equation has been widely used for simulating soil water movement. However, the take-up of agro-hydrological models using the basic theory of soil water flow for optimizing irrigation, fertilizer and pesticide practices is still low. This is partly due to the difficulties in obtaining accurate values for soil hydraulic properties at a field scale. Here, we use an inverse technique to deduce the effective soil hydraulic properties, based on measuring the changes in the distribution of soil water with depth in a fallow field over a long period, subject to natural rainfall and evaporation using a robust micro Genetic Algorithm. A new optimized function was constructed from the soil water contents at different depths, and the soil water at field capacity. The deduced soil water retention curve was approximately parallel but higher than that derived from published pedo-tranfer functions for a given soil pressure head. The water contents calculated from the deduced soil hydraulic properties were in good agreement with the measured values. The reliability of the deduced soil hydraulic properties was tested in reproducing data measured from an independent experiment on the same soil cropped with leek. The calculation of root water uptake took account for both soil water potential and root density distribution. Results show that the predictions of soil water contents at various depths agree fairly well with the measurements, indicating that the inverse analysis is an effective and reliable approach to estimate soil hydraulic properties, and thus permits the simulation of soil water dynamics in both cropped and fallow soils in the field accurately. (C) 2009 Elsevier B.V. All rights reserved.

An examination of climate sensitivity for idealised climate change experiments in an intermediate general circulation model

Radiative forcing and climate sensitivity have been widely used as concepts to understand climate change. This work performs climate change experiments with an intermediate general circulation model (IGCM) to examine the robustness of the radiative forcing concept for carbon dioxide and solar constant changes. This IGCM has been specifically developed as a computationally fast model, but one that allows an interaction between physical processes and large-scale dynamics; the model allows many long integrations to be performed relatively quickly. It employs a fast and accurate radiative transfer scheme, as well as simple convection and surface schemes, and a slab ocean, to model the effects of climate change mechanisms on the atmospheric temperatures and dynamics with a reasonable degree of complexity. The climatology of the IGCM run at T-21 resolution with 22 levels is compared to European Centre for Medium Range Weather Forecasting Reanalysis data. The response of the model to changes in carbon dioxide and solar output are examined when these changes are applied globally and when constrained geographically (e.g. over land only). The CO2 experiments have a roughly 17% higher climate sensitivity than the solar experiments. It is also found that a forcing at high latitudes causes a 40% higher climate sensitivity than a forcing only applied at low latitudes. It is found that, despite differences in the model feedbacks, climate sensitivity is roughly constant over a range of distributions of CO2 and solar forcings. Hence, in the IGCM at least, the radiative forcing concept is capable of predicting global surface temperature changes to within 30%, for the perturbations described here. It is concluded that radiative forcing remains a useful tool for assessing the natural and anthropogenic impact of climate change mechanisms on surface temperature.

Use of pelleted sericea lespedeza (Lespedeza cuneata) for natural control of coccidia and gastrointestinal nematodes in weaned goats

Infection with Eimeria spp. (coccidia) can be devastating in goats, particularly for young, recently-weaned kids, resulting in diarrhea, dehydration, and even death. Feeding dried sericea lespedeza [SL; Lespedeza cuneata (Dum.-Cours.) G. Don.] to young goats has been reported to reduce the effects of internal parasites, including gastrointestinal nematodes (GIN) but there have been no reports of the effects of feeding this forage on Eimeria spp. in goats. Two confinement feeding experiments were completed on recently-weaned intact bucks (24 Kiko-cross, Exp. 1; 20 Spanish, Exp. 2) to determine effects of SL pellets on an established infection of GIN and coccidia. The bucks were assigned to 1 of 2 (Exp. 1) or 3 (Exp. 2) treatment groups based upon the number of Eimeria spp. oocysts per gram (OPG) of feces. In Exp. 1, the kids were fed 1 of 2 pelleted rations ad libitum; 90% SL leaf meal + 10% of a liquid molasses/lignin binder mix and a commercial pellet with 12% crude protein (CP) and 24% acid detergent fiber (n = 12/treatment group, 2 animals/pen). For Exp. 2, treatment groups were fed 1) 90% SL leaf meal pellets from leaves stored 3 years (n = 7), 2) 90% SL pellets from leaf meal stored less than 6 months, (n = 7), and the commercial pellets (n = 6) ad libitum. For both trials, fecal and blood samples were taken from individual animals every 7 days for 28 days to determine OPG and GIN eggs per gram (EPG) and packed cell volume (PCV), respectively. In Exp. 2, feces were scored for consistency (1 = solid pellets, 5 = slurry) as an indicator of coccidiosis. In Exp. 1, EPG (P < 0.001) and OPG (P < 0.01) were reduced by 78.7 and 96.9%, respectively, 7 days after initiation of feeding in goats on the SL pellet diet compared with animals fed the control pellets. The OPG and EPG remained lower in treatment than control animals until the end of the trial. In Exp. 2, goats fed new and old SL leaf meal pellets had 66.2 and 79.2% lower (P < 0.05) EPG and 92.2 and 91.2% lower (P < 0.05) OPG, respectively, than control animals within 7 days, and these differences were maintained or increased throughout the trial. After 4 weeks of pellet feeding in Exp. 2, fecal scores were lower (P < 0.01) in both SL-fed groups compared with control animals, indicating fewer signs of coccidiosis. There was no effect of diet on PCV values throughout either experiment. Dried, pelleted SL has excellent potential as a natural anti-coccidial feed for weaned goats.

Foraging strategies of natural enemies of the peach-potato aphid Myzus persicae

The foraging strategies of two natural enemies of the peach-potato aphid Myzus persicae: the seven-spot ladybird Coccinella septempunctata and the parasitoid wasp Diaeretiella rapae, were investigated. Specifically the roles of plant semiochemicals in the location of plants infested with M. persicae by these natural enemies were examined. I investigated the olfactory responses of female C. septempunctata to volatiles collected from M. persicae and four Brassica cultivars; Brassica rapa, B. juncea, B. napus cultivar ‘Apex’ and B. napus cultivar ‘Courage’ and wild-type Arabidopsis thaliana that were: undamaged, previously infested by M. persicae and infested with M. persicae. C. septempunctata showed no attraction to volatiles from M. persicae alone. C. septempunctata significantly changed its searching behaviour in response to plant volatiles from B. rapa, B. napus cv. ‘Apex’ and Arabidopsis infested with M. persicae. C. septempunctata was also found to display a significant turning bias when foraging on a branching horizontal wire stem. A model was developed to investigate how turning biases affect the foraging efficiency of C. septempunctata in dichotomous branched environments. Simulations using this model indicated that turning biases could potentially increase searching efficiency. D. rapae showed a significant preference for volatiles from M. persicae infested wild-type Arabidopsis but no preference to volatiles from M. persicae alone or M. persicae honeydew. Volatile emissions by Arabidopsis were shown to be localised to the area of aphid-infestation rather than systemic. Using gas chromatography plants infested with M. persicae were shown to emit a quantitatively different volatile blend than undamaged plants. In experiments with jasmonate mutants of Arabidopsis the jasmonate (octadecanoid) wound response pathway was implicated as being important for the production of M. persicae induced volatiles, attractive to D. rapae. Other wound response pathways were also found to be involved in the production of the full blend of M. persicae induced volatiles.

Separation of natural colorants from the fermented broth of filamentous fungi using colloidal gas aphrons

There is a worldwide interest in the development of processes for producing colorants from natural sources. Microorganisms provide an alternative source of natural colorants produced by cultivation technology and extracted from the fermented broth. The aim of the present work was to study the recovery of red colorants from the fermented broth of Talaromyces amestolkiae using the technique of colloidal gas aphrons (CGA) comprising surfactant-stabilized microbubbles. Preliminary experiments were performed to evaluate the red colorants’ solubility in different organic solvents, octanol/water partitioning, and their stability in surfactant solutions, namely hexadecyl trimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyoxyethylenesorbitan monolaurate (Tween 20), which are cationic, anionic and nonionic surfactants, respectively. The first recovery experiments were carried out using CGA generated by these surfactants at different volumetric ratios (VR, 3–18). Subsequently, two different approaches to generate CGA were investigated at VR values of 6 and 12: the first involved the use of CTAB at pH 6.9–10.0, and the second involved the use of Tween 20 using red colorants partially dissolved in ethanol and Tween 20. The characterization results showed that red colorants have a hydrophilic nature. The highest recoveries were obtained with Tween 20 (78%) and CTAB (70%). These results demonstrated that the recovery of the colorants was driven by both electrostatic and hydrophobic interactions. The VR was found to be an important operating parameter and at VR 12 with CTAB (at pH 9) maximum recovery, partitioning coefficient (K = 5.39) and selectivity in relation to protein and sugar (SP = 3.75 and SS = 7.20 respectively) were achieved. Furthermore, with Tween 20, the separation was driven mainly by hydrophobic interactions. Overall CGA show promise for the recovery of red colorants from a fermented broth. Although better results were obtained with CTAB than with Tween 20 the latter may be more suitable for some application due to its lower toxicity.