Second-order modeling of arsenite transport in soils

Rate limited processes including kinetic adsorption-desorption can greatly impact the fate and behavior of toxic arsenic compounds in heterogeneous soils. In this study, miscible displacement column experiments were carried out to investigate the extent of reactivity during transport of arsenite in soils. Arsenite breakthrough curves (BTCs) of Olivier and Windsor soils exhibited strong retardation with diffusive effluent fronts followed by slow release or tailing during leaching. Such behavior is indicative of the dominance of kinetic retention reactions for arsenite transport in the soil columns. Sharp decrease or increase in arsenite concentration in response to flow interruptions (stop-flow) further verified that non-equilibrium conditions are dominant. After some 40-60 pore volumes of continued leaching, 30-70% of the applied arsenite was retained by the soil in the columns. Furthermore, continued arsenite slow release for months was evident by the high levels of residual arsenite concentrations observed during leaching. In contrast, arsenite transport in a reference sand material exhibited no retention where complete mass recovery in the effluent solution was attained. A second-order model (SOM) which accounts for equilibrium, reversible, and irreversible retention mechanisms was utilized to describe arsenite transport results from the soil columns. Based on inverse and predictive modeling results, the SOM model successfully depicted arsenite BTCs from several soil columns. Based on inverse and predictive modeling results, a second-order model which accounts for kinetic reversible and irreversible reactions is recommended for describing arsenite transport in soils.     

Yield and leaf area index estimations for sunflower plants using unmanned aerial vehicle images

Vegetation is commonly monitored to improve efficiency of various agricultural practices. Spatial and temporal changes in plant growth and development can be monitored with the aid of remote sensing techniques employing ground, aerial, and satellite platforms. Unmanned aerial vehicles (UAV) and multi-spectral cameras developed for UAVs have an important potential for agricultural management activities with high-resolution spatial and temporal images. However, UAV images should be assessed based on ground measurements for using these images as a decision-support tool in agriculture. This study was conducted to estimate sunflower leaf area index (LAI) and yield with the aid of Normalized Difference Vegetation Index (NDVI) images generated from raw UAV images. Furthermore, UAV-based NDVI values were compared with NDVI values calculated by using hyper-spectral measurements carried out with a ground-based spectroradiometer. Between July and August of 2017, six flight missions were conducted and spectral measurements were made simultaneously. A significant correlation (R²?=?0.77) was determined between NDVI values that belong to UAV platform and spectroradiometer. Also, regression models developed for sunflower LAI and yield estimation depending UAV-based NDVI have R² values of 0.88 and 0.91, respectively.     

Direct and indirect effects of climate and fishing on changes in coastal ecosystem services: a historical perspective from the North Sea

Humanity depends on the marine environment for a range of vital ecosystem services, at global (e.g. climate regulation), regional (e.g. commercial fisheries) and local scales (e.g. coastal defence and recreation). At the same time, marine ecosystems have been exploited for centuries, and many systems today are under stress from multiple sources. Recent studies have shown how both climate change and fishing have caused long-term changes in the marine environment. However, there is still poor understanding of how these changes influence change in coastal ecosystem services. In this paper, an integrated modelling approach is used to assess how the final delivery of marine ecosystem services to coastal communities is influenced by the direct and indirect effects of changes in ecosystem processes brought about by climate and human impacts, using fisheries of the North Sea region as a case study. Partial least squares path analysis is used to explore the relationships between drivers of change, marine ecosystem processes and services (landings). A simple conceptual model with four variables—climate, fishing effort, ecosystem process and ecosystem services—is applied to the English North Sea using historic ecological, climatic and fisheries time series spanning 1924–2010 to identify the multiple pathways that might exist. As expected, direct and indirect links between fishing effort, ecosystem processes and service provision were significant. However, links between climate and ecosystem processes were weak. This paper highlights how path analysis can be used for analysing long-term temporal links between ecosystem processes and services following a simplified pathway.     

Colloid mobilization and arsenite transport in soil columns: effect of ionic strength

Colloid generation and transport in soils is of significance because of suspected colloid-facilitated transport of contaminants to the groundwater. In this study, colloid mobilization and its effect on the transport of arsenite [As(III)] were investigated in Olivier (fine-silty, mixed, active, thermic Aquic Fraglossudalfs) and Windsor (mixed, mesic typic Udipsamments) soil columns. Input solution of 10 mg L(-1) As(III) in 0.01 M NaCl was applied to water-saturated columns, and followed by leaching with deionized water (DIW). Flow interruptions were performed during the As(III) input and DIW leaching phases. Turbidity, electrical conductivity (EC), and pH of column effluents were monitored with time. Total and dissolved concentrations of As, Fe, and Al were analyzed. Effluent results demonstrated that colloid-facilitated transport contributed little to arsenic movement when the solution ionic strength was maintained constant. Mobilization of colloidal amorphous material and enhanced transport of As(III) were observed as a result of changes in ionic strength of the input solution. The peak of colloid generation coincided with peak concentrations of Fe, suggesting mobilization of Fe oxides and facilitated transport of As(III) adsorbed on oxide surfaces. Colloid mobilization was enhanced due to flow interruption in the Olivier column, which suggests slow dissociation of aggregated colloidal particles. Moreover, effluent results indicate significant effect of organic matter in stabilizing aggregates of colloidal particles.     

Isolation, characterization and diuron transformation capacities of a bacterial strain Arthrobacter sp. N2

A bacterial strain able to transform diuron was isolated from a soil by enrichment procedures. Strain isolation was realized by plating on minimal-agarose medium spread with this herbicide and selecting the colonies surrounded by a clear thin halo. One strain was characterized and identified as an Arthrobacter sp. It metabolized diuron and the final transformation product, 3,4-dichloroaniline, was produced in stoichiometric amounts. The transformation of diuron at different concentrations was more efficient in the presence of alternative sources of carbon and nitrogen. The bacterial activity was also evaluated in soil microcosms with a consequent disappearance of diuron and concomitant appearance of 3,4-dichloroaniline, of which the concentration decreased thereafter. Bacterial cells inoculated in the microcosms survived as viable but eventually nonculturable cells.     

Net energetic advantage drives honey bees (Apis mellifera L) to nectar larceny in Vaccinium ashei Reade

Carpenter bees (Xylocopa spp.) act as primary nectar thieves in rabbiteye blueberry (Vaccinium ashei Reade), piercing corollas laterally to imbibe nectar at basal nectaries. Honey bees (Apis mellifera L) learn to visit these perforations and thus become secondary nectar thieves. We tested the hypothesis that honey bees make this behavioral switch in response to an energetic advantage realized by nectar-robbing flower visits. Nectar volume and sugar quantity were higher in intact than perforated flowers, but bees (robbers) visiting perforated flowers were able to extract a higher percentage of available nectar and sugar so that absolute amount of sugar (mg) removed by one bee visit is the same for each flower type. However, because perforated flowers facilitate higher rates of bee flower visitation and the same or higher rates of nectar ingestion, they are rendered more profitable than intact flowers in temporal terms. Accordingly, net energy (J) gain per second flower handling time was higher for robbers on most days sampled. We conclude that the majority evidence indicates an energetic advantage for honey bees that engage in secondary nectar thievery in V. ashei.Communicated by R. Page     

Retention and runoff losses of atrazine and metribuzin in soil

Minimizing herbicide runoff and mobility in the soil and thus potential contamination of water resources is a national concern. Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] and atrazine [2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine] dynamics in surface soils and in runoff waters were studied on six 0.2-ha sugarcane (Saccharum spp.) plots of a Commerce silt loam (fine-silty, mixed, superactive, nonacid, thermic Fluvaquentic Endoaquept) during three growing seasons under different best management practices. Metribuzin was applied in the spring as a postemergence herbicide and atrazine was applied following winter harvest. Both herbicides were applied on top of the sugarcane rows as 0.6- or 0.9-m band width application, or broadcast application, where the entire area was treated. Maximum effluent concentrations were measured from the broadcast treatment and ranged from 600 to 1100 microg L(-1) for atrazine and 250 to 450 microg L(-1) for metribuzin. Atrazine runoff losses were highest for the broadcast treatment (2.8-11% of that applied) and lowest for the 0.6-m band treatment (1.9-7.6%), with a similar trend for metribuzin losses. Measured extractable herbicides from the surface soil exhibited a sharp decrease with time and were well described with a simple first-order decay model. For atrazine, estimates for the decay rate (lambda) were higher than for metribuzin. Results based on laboratory adsorption-desorption (kinetic-batch) measurements were consistent with field observations. The distribution coefficients (Kd) for atrazine exhibited stronger retention over time in comparison with metribuzin on the Commerce soil. Moreover, discrepancies between adsorption isotherm and desorption indicated slower release and that hysteresis was more pronounced for atrazine compared with metribuzin.     

Nexus between indigenous ecological knowledge and ecosystem services: a socio-ecological analysis for sustainable ecosystem management

Environmental Science and Pollution Research - The well-being of the human society cannot be ensured and sustainable unless the flow of Ecosystem Services (ESs) would be matching with their...     

Novel Composite Films Based on Acrylic Fibers Waste/Nano-chitosan for Congo Red Adsorption

Journal of Polymers and the Environment - The current research aimed to use waste to treat waste; to recycling of acrylic fibers waste combined with nano-chitosan for use as an adsorbent to remove...