MODELING THE IMPACT OF MULTICOMPONENT VOCs ON GROUND WATER USING THE STEFAN‐MAXWELL EQUATION1

ABSTRACT: Computer programs that model the fate and transport of organic contaminants through porous media typically use Fick's first law to calculate vapor phase diffusion. Fick's first law, however, is limited to the case of a single, dilute species diffusing into a stagnant, high concentration, bulk vapor phase. When dealing with more than one diffusing species and at higher concentrations, the multicomponent coupling effects on vapor phase diffusion and advection of the various constituents become significant. VLEACH, a one‐dimensional finite difference model developed for the U.S. Environmental Protection Agency (USEPA), is typical of the models using Fick's first law to model vapor‐phase diffusion. The VLEACH model was modified to accommodate up to 10 components and to calculate the binary diffusion coefficients for each of the components based on molecular weight, molecular volume, temperature and pressure, and to address the coupling effects on multiple component vapor phase diffusion and its impact on ground water. The resulting model was renamed MC‐CHEMSOIL. At low vapor phase concentrations, MC‐CHEMSOIL predicts identical ground water impacts (dissolved phase loading) to those from VLEACH 2.2a. At higher vapor phase concentrations, however, the relative difference between the models exceeded 20 percent.     

Energetics of mixing for the filling box and the emptying-filling box

The mixing efficiency of a plume in a filling box and an emptying-filling box is calculated for both transient and steady states. The mixing efficiency of a plume in a filling box in an asymptotic state is 1/2, independent of the details of this state or how the plume is modelled. The mixing efficiency of a plume in an emptying-filling box in steady state is \(1 - \xi \), where \(\xi = h/H\), the depth of the ambient layer h normalised by the height of the box H. A deeper mixed layer therefore corresponds to a higher mixing efficiency. These results shed light on the interpretation of mixing efficiencies of open and closed systems.

     

A methodology for estimating health benefits of electricity generation using renewable technologies

At Copenhagen, the developed countries agreed to provide up to $100 bn per year to finance climate change mitigation and adaptation by developing countries. Projects aimed at cutting greenhouse gas (GHG) emissions will need to be evaluated against dual criteria: from the viewpoint of the developed countries they must cut emissions of GHGs at reasonable cost, while host countries will assess their contribution to development, or simply their overall economic benefits. Co-benefits of some types of project will also be of interest to host countries: for example some projects will contribute to reducing air pollution, thus improving the health of the local population.This paper uses a simple damage function methodology to quantify some of the health co-benefits of replacing coal-fired generation with wind or small hydro in China. We estimate the monetary value of these co-benefits and find that it is probably small compared to the added costs. We have not made a full cost-benefit analysis of renewable energy in China as some likely co-benefits are omitted from our calculations. Our results are subject to considerable uncertainty however, after careful consideration of their likely accuracy and comparisons with other studies, we believe that they provide a good first cut estimate of co-benefits and are sufficiently robust to stand as a guide for policy makers.In addition to these empirical results, a key contribution made by the paper is to demonstrate a simple and reasonably accurate methodology for health benefits estimation that applies the most recent academic research in the field to the solution of an increasingly important problem.     

Toxicity of sediment pore water in Puget Sound (Washington, USA): a review of spatial status and temporal trends

Data from toxicity tests of the pore water extracted from Puget Sound sediments were compiled from surveys conducted from 1997 to 2009. Tests were performed on 664 samples collected throughout all of the eight monitoring regions in the Sound, an area encompassing 2,294.1 km². Tests were performed with the gametes of the Pacific purple sea urchin, Strongylocentrotus purpuratus, to measure percent fertilization success as an indicator of relative sediment quality. Data were evaluated to determine the incidence, degree of response, geographic patterns, spatial extent, and temporal changes in toxicity. This is the first survey of this kind and magnitude in Puget Sound. In the initial round of surveys of the eight regions, 40 of 381 samples were toxic for an incidence of 10.5 %. Stations classified as toxic represented an estimated total of 107.1 km², equivalent to 4.7 % of the total area. Percent sea urchin fertilization ranged from >100 % of the nontoxic, negative controls to 0 %. Toxicity was most prevalent and pervasive in the industrialized harbors and lowest in the deep basins. Conditions were intermediate in deep-water passages, urban bays, and rural bays. A second round of testing in four regions and three selected urban bays was completed 5–10 years following the first round. The incidence and spatial extent of toxicity decreased in two of the regions and two of the bays and increased in the other two regions and the third bay; however, only the latter change was statistically significant. Both the incidence and spatial extent of toxicity were lower in the Sound than in most other US estuaries and marine bays.     

Modeling the Reduction of Vapor Phase Emissions from Surface Soils Due to Soil Matrix Effects: Porosity/Tortuosity Concepts

ABSTRACT

A major route for transport of volatile organic compounds within porous media is vapor phase diffusion. The diffusion rate through a porous medium is less than that through free-air due to the decreased cross-sectional area available for gas movement and the increased path length due to pore tortuosity. Numerous empirical expressions have been published that relate the diffusion coefficient in porous media to the diffusion coefficient in free-air (unobstructed gas phase). Published measurements of relative diffusivity and air-filled porosity were combined into a database. Empirical expressions available in the literature, including the popular Millington-Quirk equation, were evaluated along with a fourth-degree polynomial expression developed by the authors to determine the best type of equation to predict relative diffusivity as a function of air-filled porosity over the domain of values for porosity ranging from 0.071 to 1 for different types of materials. Mean square deviations were used as the statistical test to compare equations. The polynomial expression developed in this project produced a significantly different effective diffusion coefficient (1.3 x 10^-6 m²/sec) compared to values of 9.2 x 10^-6 m²/sec and 3.1 x 10^-6 m²/ sec predicted by forms of the Millington-Quirk equation for a specific case.     

The effect of maternal body size on embryo survivorship in the broods of pregnant male pipefish

The occurrence of male pregnancy in the family Syngnathidae (seahorses, pipefishes, and sea dragons) provides an exceptionally fertile system in which to investigate issues related to the evolution of parental care. Here, we take advantage of this unique reproductive system to study the influence of maternal body size on embryo survivorship in the brood pouches of pregnant males of the broad-nosed pipefish, Syngnathus typhle. Males were mated with either two large females, two small females, a large then a small female, or a small then a large female. Our results show that offspring survivorship depends on an interaction between female body size and the number of eggs transferred by the female. Eggs of larger females deposited in large numbers are more likely to result in viable offspring than eggs of smaller females laid in large numbers. However, when females deposited smaller numbers of eggs, the eggs from smaller females were more likely to produce viable offspring compared to those from larger females. We found no evidence that this result was based on mating order, the relative sizes of competing females, or egg characteristics such as dry weight of eggs. Additionally, male body size did not significantly influence the survivorship of offspring during brooding. Our results suggest that the factors underlying offspring survivorship in pipefish may be more complex than previously believed, with multiple factors interacting to determine the fitness of individual offspring within the broods of pregnant males.     

Deep sea benthic bioluminescence at artificial food falls, 1,000–4,800 m depth,in the Porcupine Seabight and Abyssal Plain,North East Atlantic Ocean

Natural bioluminescence (that not mechanically stimulated by human intervention) produced by organisms on the seafloor of the northeast Atlantic ocean between 970 and 4,800 m depth was examined using an image intensifying (ISIT) camera mounted on an autonomous lander system. In the absence of bait little or no luminescence was observed but with bait present there was a significant inverse relationship with depth, Log₁₀ (1 + number of events h⁻¹) = 1.7627–0.3235 depth (km) (r ² = 0.8158, P < 0.001) indicating an average of 2.6 events h⁻¹ at 4 km and 28 h⁻¹ at 1 km. But in an area at ca. 1 km depth near carbonate and coral mounds the mean was 133 events h⁻¹, much higher than predicted. In this bioluminescent hot spot 52–483 events h⁻¹ were observed including moving luminescent targets and release of patches of luminescent material into the water around the bait so that on occasions the whole area around the bait was illuminated persisting on a time scale of minutes. At abyssal depths, luminescence was much less than reported at similar depths in the tropical NE Atlantic off Cape Verde. The sources of luminescence could not be determined but in the most active areas were associated with presence of eels Synaphobranchus kaupii which although themselves not luminescent may have stimulated luminescence from prey organisms such as ostracods (Vargula norvegica).     

Light environment and mating behavior in Trinidadian guppies (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>)

Male guppies, Poecilia reticulata, have color patterns that result from a balance between natural selection for crypsis to avoid predators and sexual selection for bright, complex patterns that attract females. Males use displays to show off these patterns to potential mates, but their conspicuousness also depends on the light environment in which they are viewed. We investigated variation in natural underwater guppy light environments in Trinidad, West Indies, and found that mating behavior is correlated with both the ‘quantity’ (total irradiance) and ‘quality’ (spectral composition) of light: light intensity and the proportion of ultraviolet light were negatively related to display rates. Experimental manipulation of light environment to mimic natural daily changes demonstrated that these relationships are causal and are independent of time of day effects. At lower light levels, when guppies are less detectable by visually hunting predators, females had more opportunity for active mate choice, because males displayed more. However, these light conditions may reduce the ability of females to accurately discriminate between males. Guppy mating behavior is therefore strongly affected by light environment, and this may have important effects on sexual selection.