Modeling Short Range Air Dispersion from Area Sources of Non-buoyant Toxics

A model based on K-theory has been developed for describing the short range air dispersion from area sources of non-buoyant toxics. Model parameter estimation is via boundary layer theory. Lateral dispersion by plume meander is considered but ail other sources of horizontal dispersion are neglected. The model can be applied on and near area sources and it can be adapted for predictions of downwind concentrations with a wide variety of meteorological Inputs.

The model has been evaluated by simulating the data obtained during atmospheric tracer studies and by comparison to vinyl chloride concentrations near the BKK landfill in southern California. The model appears to represent a useful and accurate tool for regulatory planning and risk assessment close to area sources of toxics.     

Three-dimensional patterns of moisture, water repellency, bromide and pH in a sandy soil

Soil water repellency might lead to preferential flow of water and solutes through the unsaturated zone of soils. To study this process in a water repellent sandy field soil, a bromide tracer had been applied on a 2.2 m long and 0.4 m wide plot. The bromide application rate was 8 g/m², and the plot was sampled using 100 cm³ steel cylinders after 52 mm of rainfall in 12 days. A total of seven layers were sampled to a depth of 74 cm. Each layer was sampled at 240 locations in a 40 by 6 grid. All samples were used for the determination of soil water content, degree of actual and potential water repellency, bromide concentration and pH. The spatial distribution of these properties was visualized three-dimensionally and compared. The degree of water repellency, bromide concentration, and pH distribution bore close resemblance to the fingered flow induced soil water content distribution. The degree of potential water repellency was relatively low in places with such fingers. Actual water repellency occurred between the fingers at the dry spots. Bromide was not found, or only in very low concentrations, in such places. Bromide depth profiles clearly indicated the occurrence of diverging flow in the wetter subsoil. Most likely, manuring activities during the last decades resulted in relatively high pH values in the topsoil, and in the subsoil along the recurring fingered flow pathways.     

Enhanced degradation of carbofuran in pacific northwest soils

Abstract

Persistence of ¹⁴C‐carbonyl carbofuran was measured in Pacific Northwest soils that had received 1–14 applications of the insecticide for root weevil control on perennial crops. Insecticide decay curves were obtained in nonautoclaved soil and several autoclaved soil samples from previously‐treated fields and in nonautoclaved soils from paired control sites not previously treated with carbofuran. The insecticide usually degraded faster in soil from previously‐treated fields than in soil from corresponding control fields. Among 26 previously‐treated fields, the pseudo half‐life (time for 50% loss) of carbofuran was < one wk in 11 soils, 1–3 wks in 8 soils and > 4 wks in the remaining soils. Among the nontreated control fields the pseudo half‐life was > than 2 wks in all cases and > than 15 wks in 5 of the soils. The carbofuran decay curve always possessed an initial lag phase where soil mixing enhanced insecticide decline. Carbofuran degraded very slowly in autoclaved soil samples. The half‐life of carbofuran exceeded 16 wk in all autoclaved soils tested and in most instances 85–90% of the original dosage remained when the tests were terminated 112 days after treatment. These results provided evidence that many of the soils which received applications of carbofuran over the past several years have developed a capacity to degrade carbofuran very rapidly.     

Optimal fishery policy with artificial enhancement through stocking: California's white sturgeon as an example

Although optimal fishery policy has been derived from different kinds of economic and biological models, the interaction of fishing policy with artificial stocking policy has not been explicitly considered. We here determine optimal size limits, fishing effort, and stocking rate for three cases of interest: (1) recruitment-limited population, pre-recruitment stocking; (2) adult biomass-limited population, post-recruitment stocking; and (3) adult biomass-limited and recruitment-limited population, post-recruitment stocking. Results show that lower size limits should be set at the size at which the current market value exceeds the total future value of an individual, both to the fishery and to reproduction. Imposition of upper size limits is rarely optimal. Stocking is advisable when the hatchery cost times the relative contribution of stocking to recruitment is less than the contribution to the value of the catch. Optimal policy ranges from infinite effort at a specific size limit with maximum stocking when the cost of stocking is zero, to lower values of size limit and effort as stocking costs increase, the amount of stocking decreases, and more natural reproduction is optimal. Thus, as hatchery costs decline (or value of captured fish increases), optimal stocking/fishery policy varies from an unstocked fishery to a “put and take” fishery. The results are applied to the sturgeon fishery in the San Francisco Bay Estuary as an example. They imply that a reduced lower size limit and greater fishing mortality together with stocking would be optimal, but that current levels are conservative. The stocking decision depends critically on the values of parameters that are currently poorly known, such as: hatchery costs, survival to the fishery and the mechanisms controlling the sturgeon population.     

Maximum rates of nitrate removal in a denitrification wall

Denitrification walls are constructed by mixing a carbon source such as sawdust into soils through which ground water passes. These systems can reduce nitrate inputs to receiving waters by enhancing denitrification. Maximum rates of nitrate removal by denitrification need to be determined for design purposes. To determine maximum rates of nitrate removal we added excess nitrate (50 mg N L(-1)) to a trench up-gradient of a denitrification wall during a 9-d trial. Bromide (100 g L(-1)) was also added as a conservative tracer. Movement of nitrate and bromide was measured from shallow wells and soil samples were removed for measurements of denitrification, carbon availability, nitrate, and other microbial parameters. Rates of nitrate removal, determined from the ratio of NO3-N to Br and ground water flow, averaged 1.4 g N m(-3) of wall d(-1) and were markedly greater than denitrification rates determined using the acetylene block technique (average: 0.11 g N m(-3) of wall d(-1)). These nitrate removal rates were generally lower than reported in other denitrification walls. Denitrification rates increased when nitrate was added to the laboratory incubations, indicating that despite large nitrate inputs in the field, denitrification remained limited by nitrate. This limitation was partially attributed to nitrate predominantly moving through zones of greater hydraulic conductivity or in the mobile fraction of the ground water and slow diffusion to the immobile fraction where denitrifiers were active.     

The prospect of alien life in exotic forms on other worlds

The nature of life on Earth provides a singular example of carbon-based, water-borne, photosynthesis-driven biology. Within our understanding of chemistry and the physical laws governing the universe, however, lies the possibility that alien life could be based on different chemistries, solvents, and energy sources from the one example provided by Terran biology. In this paper, we review some of these possibilities. Silanes may be used as functional analogs to carbon molecules in environments very different from Earth; solvents other than water may be compatible for life-supporting processes, especially in cold environments, and a variety of energy sources may be utilized, some of which have no Terran analog. We provide a detailed discussion of two possible habitats for alien life which are generally not considered as such: the lower cloud level of the Venusian atmosphere and Titan’s surface environment.     

Effect of monosodium methanarsonate application on cuticle wax content of cocklebur and cotton plants

Leaf cuticle waxes were extracted from monosodium methanearsonate (MSMA)-resistant (R) and -susceptible (S) common cocklebur (Xanthium strumarium L.) and cotton (Gossypium hirsutum L.) plants at 0, 3, 5, and 7 days after treatment (DAT) following 1x and 2x MSMA applications. Wax constituents were analyzed by gas chromatography (GC) with flame ionization detection and compared to alkane and alcohol standards of carbon lengths varying from C21 to C30. Differences in waxes were calculated and reported as change per ng mm2-1. Tricosane (C23) was found to increase following MSMA applications. All other alkanes decreased by 7 DAT, with some showing a linear effect over time in the R-cocklebur. Alcohol constituents were also observed to decrease by 7 DAT. Total arsenic in the extracted wax fraction was determined, with greatest quantities detected in the R-cocklebur. Wax changes are not believed to play a role in cotton tolerance, since changes in cuticle concentrations were minimal. Cocklebur resistance to MSMA is not due to cuticle constituents; the wax changes are a secondary effect in response to herbicide application.     

Incorporating putatively neutral and adaptive genomic data into marine conservation planning

The availability of genomic data for an increasing number of species makes it possible to incorporate evolutionary processes into conservation plans. Recent studies show how genetic data can inform spatial conservation prioritization (SCP), but they focus on metrics of diversity and distinctness derived primarily from neutral genetic data sets. Identifying adaptive genetic markers can provide important information regarding the capacity for populations to adapt to environmental change. Yet, the effect of including metrics based on adaptive genomic data into SCP in comparison to more widely used neutral genetic metrics has not been explored. We used existing genomic data on a commercially exploited species, the giant California sea cucumber (Parastichopus californicus), to perform SCP for the coastal region of British Columbia (BC), Canada. Using a RAD-seq data set for 717 P. californicus individuals across 24 sampling locations, we identified putatively adaptive (i.e., candidate) single nucleotide polymorphisms (SNPs) based on genotype–environment associations with seafloor temperature. We calculated various metrics for both neutral and candidate SNPs and compared SCP outcomes with independent metrics and combinations of metrics. Priority areas varied depending on whether neutral or candidate SNPs were used and on the specific metric used. For example, targeting sites with a high frequency of warm-temperature-associated alleles to support persistence under future warming prioritized areas in the southern coastal region. In contrast, targeting sites with high expected heterozygosity at candidate loci to support persistence under future environmental uncertainty prioritized areas in the north. When combining metrics, all scenarios generated intermediate solutions, protecting sites that span latitudinal and thermal gradients. Our results demonstrate that distinguishing between neutral and adaptive markers can affect conservation solutions and emphasize the importance of defining objectives when choosing among various genomic metrics for SCP.