Modeling radium and radon transport through soil and vegetation

A one-dimensional flow and transport model was developed to describe the movement of two fluid phases, gas and water, within a porous medium and the transport of 226Ra and 222Rn within and between these two phases. Included in this model is the vegetative uptake of water and aqueous 226Ra and 222Rn that can be extracted from the soil via the transpiration stream. The mathematical model is formulated through a set of phase balance equations and a set of species balance equations. Mass exchange, sink terms and the dependence of physical properties upon phase composition couple the two sets of equations. Numerical solution of each set, with iteration between the sets, is carried out leading to a set-iterative compositional model. The Petrov-Galerkin finite element approach is used to allow for upstream weighting if required for a given simulation. Mass lumping improves solution convergence and stability behavior. The resulting numerical model was applied to four problems and was found to produce accurate, mass conservative solutions when compared to published experimental and numerical results and theoretical column experiments. Preliminary results suggest that the model can be used as an investigative tool to determine the feasibility of phytoremediating radium and radon-contaminated soil.     

Bioaccumulation and human health risk assessment of chromium and nickel in paddy rice grown in serpentine soils

The natural abundance of Cr and Ni in serpentine soils is well-known, but the food safety of rice grown in these hazardous paddy soils is poorly understood. The study evaluated the bioaccumulation of chromium (Cr) and nickel (Ni) in rice (Oryza sativa) grown in serpentine-derived paddy soils in the Philippines. Surface soil (0–20 cm) samples were collected and characterized across three (i.e., Masinloc, Candelaria, and Sta. Cruz) paddy areas in Luzon Island, Philippines. At least 3 to 4 whole rice plants at mature stage were uprooted manually in each sampling point where the soil samples were collected. The total Cr and Ni concentrations in rice (i.e., roots, shoots, and grains) and soil, soil physicochemical properties, bioaccumulation factor (BAF), translocation factor (TF), and the hazard quotients (HQ) were determined. Results revealed that Cr and Ni in rice were accumulated mostly in the roots. Although paddy soils had elevated total Cr and Ni concentrations, the BAF and soil-to-root TF values for Cr and Ni were < 1. In terms of human health risks, results further revealed low risk for both male and female Filipino adults as HQ values for Cr and Ni were < 1. While it is safe to consume rice grown in the area in terms of Cr and Ni dietary intake, more studies are necessary to understand the dynamics and bioavailability of these heavy metals in other crops and drinking water from tube wells in these areas in order to provide a more holistic human health-based assessments and to ensure consumer safety in serpentine areas. In addition, a more reliable data on Cr and Ni speciation in serpentine soils and crops is critically important. Further studies are also needed to understand the contribution of bioavailable heavy metals in improving the soil health to achieve food safety.

     

Assessments and decisions in Metellina segmentata (Araneae: Metidae): evidence of a pheromone involved in mate guarding

Assessments and decision-making underlying the initiation of mate guarding in a common web-building spider, Metellina segmentata, are examined in a series of field and laboratory studies. Adult males do not build webs but wander in search of females and mating opportunities. Adult males then wait at the edge of the webs of females and guard them prior to courtship and mating. Guarded females were heavier, larger and carried more mature eggs than solitary females. An active process of information gathering is apparent from introductions of males to the webs of females. Males make accurate assessments about female quality, even in the absence of the resident female. Cues involving web architecture are not used. Males may assess pheromonal cues on the web of the female in deciding whether to guard or abandon a female.     

Parasitism in a social wasp: effect of gregarines on foraging behavior, colony productivity, and adult mortality

Behavior in eusocial insects likely reflects a long history of selection imposed by parasites and pathogens because the conditions of group living often favor the transmission of infection among nestmates. Yet, relatively few studies have quantified the effects of parasites on both the level of individual colony members and of colony success, making it difficult to assess the relative importance of different parasites to the behavioral ecology of their social insect hosts. Colonies of Polybia occidentalis, a Neotropical social wasp, are commonly infected by gregarines (Phylum Apicomplexa; Order Eugregarinida) during the wet season in Guanacaste, Costa Rica. To determine the effect of gregarine infection on individual workers in P. occidentalis, we measured foraging rates of marked wasps from colonies comprising both infected and uninfected individuals. To assess the effect of gregarines on colony success, we measured productivity and adult mortality rates in colonies with different levels of infection prevalence (proportion of adults infected). Foraging rates in marked individuals were negatively correlated with the intensity of gregarine infection. Infected colonies with high gregarine prevalence constructed nests with fewer brood cells per capita, produced less brood biomass per capita, and, surprisingly, experienced lower adult mortality rates than did uninfected or lightly infected colonies. These data strongly suggest that gregarine infection lowers foraging rates, thus reducing risk to foragers and, consequently, reducing adult mortality rates, while at the same time lowering per-capita input of materials and colony productivity. In infected colonies, queen populations were infected with a lower prevalence than were workers. Intra-colony infection prevalence decreased dramatically in the P. occidentalis population during the wet season.An erratum to this article can be found at     

Nature and extent of metal-contaminated soils in urban environments (keynote talk)

Research on the nature and extent of metal-contaminated soil began with an urban garden study in Baltimore, MD (USA). Largest quantities of soil metals were clustered in the inner city with lesser amounts scattered throughout metropolitan Baltimore. The probability values of metal clustering varied from P value 10^?15–10^?23 depending on element. The inner-city clustering of lead (Pb) could not be explained by Pb-based paint alone. A major Pb source was tetraethyl lead (TEL), developed as an anti-knock agent for use in vehicle fuel, thereby making highway traffic flow a toxic substance delivery system in cities. Further study in Minneapolis and St. Paul confirmed the clustering of inner-city soil metals, especially Pb. Based on the evidence, the Minnesota State Legislature petitioned Congress to curtail Pb additives resulting in the rapid phasedown of TEL on January 1, 1986, 10 years ahead of the EPA scheduled ban. Further research in New Orleans, Louisiana (NOLA), verified the link between soil Pb, blood Pb, morbidity, and societal health. Although Pb is a known cause of clinical impairment, there is no known effective medical intervention for reducing children’s blood Pb exposure. Ingestion and inhalation are routes of exposure requiring prevention, and soil is a reservoir of Pb. Children’s blood Pb exposure observed in pre-Hurricane Katrina (August 29, 2005) NOLA underwent substantial decreases 10 years post-Katrina due to many factors including input of low Pb sediment residues by the storm surge and the introduction of low Pb landscaping materials from outside of the city. Investigation on the topic is ongoing.     

Using revealed preferences to estimate the Value of Travel Time to recreation sites

The opportunity Value of Travel Time (VTT) is one of the most important elements of the total cost of recreation day-trips and arguably the most difficult to estimate. Most studies build upon the theoretical framework proposed by Becker (1965) by using a combination of revealed and stated preference data to estimate a value of time which is uniform in all activities and under all circumstances. This restriction is relaxed by DeSerpa's (1971) model which allows the value of saving time to be activity-specific. We present the first analysis which uses actual driving choices between open access and toll roads to estimate a VTT specific for recreation trips, thereby providing a value which conforms to both Becker's and DeSerpa's theoretical models. Using these findings we conduct a Monte Carlo simulation to identify generalizable results for subsequent valuation studies. Our results indicate that 3/4 of the wage rate provides a reasonable approximation of the average VTT for recreation trips, while the commonly implemented assumption of 1/3 of the wage rate generates downward biased results.     

Agrobacterium-mediated transformation of Nicotiana attenuata, a model ecological expression system

Summary. Research into the genetic basis of the ecological sophistication of plants is hampered by the availability of transformable systems with a wealth of well-described ecological interactions. We present an Agrobacterium-mediated transformation system for the model ecological expression system, Nicotiana attenuata, a native tobacco that occupies the post-fire niche in the Great Basin Desert of North America. We describe a transformation vector and a transformation procedure that differs from the standard cultivated tobacco transformation protocols in its use of selectable markers, explants, media and cultivation conditions. We illustrate its utility in the transformations with genes coding for key enzymes in the oxylipin cascade (lipoxygenase, allene oxide synthase, hydroperoxide lyase) in antisense orientations and present high-throughput screens useful for the detection of altered phenotypes for the oxylipin cascade (green leaf volatiles and jasmonic acid after wounding). Received 14 March 2002; accepted 10 May 2002     

Consequences of resource competition for sex allocation and discriminative behaviors in a hyperparasitoid wasp

Population-wide mating patterns can select for equal parental investment in both sexes, but limiting resources, such as mates or developmental substrates, can increase competition leading to biased sex ratios in favor of either sex. Such competition for resources typically occurs in spatially structured populations, where dispersal is limited. In this laboratory study, we investigate if and how resource competition affects sex allocation, discriminative behaviors and competitive interactions of the wingless hyperparasitoid Gelis acororum, which exploits patchily distributed hosts. We show that G. acororum sex ratios are male-biased and that this is not a consequence of constrained reproduction by virgin females. Our results suggest that this pattern of reproductive investment, which is only rarely observed in parasitoids, is a consequence of resource limitation, in terms of hosts rather than mates. Further, G. acororum appears not to respond to intrinsic host quality or to prior oviposition in its host. When competing inter-specifically for host resources, G. acororum outcompetes its congener Gelis agilis, but does so mainly when ovipositing on the host first. Overall, our results suggest that host resource limitation could be an important environmental factor shaping sex allocation in G. acororum, with competition taking place both intra- and inter-specifically.     

Off-road vehicle recreation management policy for public lands in the United States: A case history

Three annual motorcycle races on the Johnson Valley-Parker course in California's Mojave Desert have resulted in conspicuous modifications of soil and vegetation in a Wilderness Study Area (WSA) and in other lands of high resource values. The extent of damage caused by the races, which have involved fewer than 400 participants, exceeded the expectations of the managing agency by 360%–640% and the allowable limits imposed by the agency by 40%–76%. After three races, no resource monitoring results have been obtained by which compliance with the regulations for interim management of the Wilderness Study Area may be judged. Designation of the remaining parts of the course on lands of high resource value was based on criteria subsequently determined by a federal court to be in violation of regulations derived from two Executive Orders.