Optimizing the removal of small fish passage barriers

Removing small artificial barriers that hinder upstream migrations of fish is a major problem in riparian habitat restoration. Because of budgetary limitations, it is necessary to prioritize barrier removal and repair decisions. These have usually been based on scoring and ranking procedures, which, although simple to use, can be very inefficient in terms of increasing the amount of accessible instream habitat. We develop a novel decision-making approach, based on integer programming techniques, which optimizes repair and removal decisions. Results show based on real datasets of barrier culverts located in Washington State that scoring and ranking is over 25% below the optimum on average and a full 100% below in the worst case, producing no net habitat gain whatsoever. This is compared to a dynamic programming method that was able to find optimal solutions in less than a second, even for problems with up to several hundred variables, and a heuristic method, which found solutions with less than a 1% average optimality gap in even less time.     

Absorption of Gaseous Air Pollutants By a Standardized Plant Canopy

Concentration profiles for hydrogen fluoride(HF), sulfur dioxide(SO₂), ozone (O₃), nitrogen dioxide(NO₂), and nitric oxide(NO) generated in a standardized alfalfa canopy are presented. Wind, light, temperature, and carbon dioxide(CO₂) profiles, canopy pollutant uptake rates, and canopy structural data are also given. Canopy pollutant concentration profile characteristics were studied to evaluate the relative potentials for major air pollutants to penetrate into canopies. The study was conducted in an environmental growth chamber equipped to control automatically environmental conditions and monitor continuously gas exchange rates. HF, SO₂, and NO₂ profiles suggested that these gases were removed efficiently by the upper portion of the canopy as well as by the immediate subsurface vegetation. The steady state HF profile showed the greatest displacement within the canopy. The NO profile was displaced the least. The uptake rate of NO by plants was apparently too slow in comparison with gas transport and mixing within the canopy to affect the internal profile substantially. O₃ appeared to be readily deposited on the surface tissues, but the deeper tissues in the canopy had less effect on the concentration profile. Data are also presented to show the relationship between NO₂ concentration within the canopy and changes in the air concentration above the vegetation. The results indicated that gas transport between the atmosphere and canopy interior was rapid. The data presented should be of current interest to agriculturists, researchers, administrators, and environmental planners concerned with effects of air pollutants on plants and on the fate of pollutants in the microenvironment.     

Ambient nitrogen oxides exposure and early childhood respiratory illnesses

Acute respiratory infections are common in children below 5 years and recent studies suggest a possible link with air pollution. In this study, we investigated the association between ambient nitrogen oxides (NO_x) and bronchitis or upper airway inflammation.This longitudinal study was conducted in Teplice and Prachatice districts, Czech Republic. Children were followed from birth to 4.5 years of age. Data were compiled from medical records at delivery and at follow up, and from self-administered questionnaires from the same two time points. Air pollution monitoring data were used to estimate exposure over five different averaging periods ranging from three to 45 days prior to an episode. To quantify the association between exposure and outcome, while accounting for repeated measure correlation we conducted logistic regression analysis using generalized estimating equations.During the first 2 years of life, the adjusted rate ratio for bronchitis associated with interquartile increase in the 30-day average NO_x was 1.31 [95% confidence interval (CI): 1.07, 1.61] and for two to 4.5 year olds, it was 1.23 (95% CI: 1.01, 1.49). The 14-day exposure also had stable association across both age groups: below 2 years it was 1.25 (95% CI: 1.06, 1.47) and for two to 4.5 years it was 1.21 (95% CI: 1.06, 1.39). The association between bronchitis and NO_x increased with child's age in the under 2 years group, which is a relatively novel finding.The results demonstrate an association between NO_x and respiratory infections that are sufficiently severe to come to medical attention. The evidence, if causal, can be of public health concern because acute respiratory illnesses are common in preschool children.     

A Model for Gaseous Pollutant Sorption by Leaves

A model simulating pollutant exchange with isolated leaves that integrates factors which have been found to be important in regulating pollutant uptake by leaves is presented. The model is patterned after an electrical analogue simulator and was designed to emphasize the effects of pollutant and leaf properties on the process. The article discusses the relative significance of factors affecting gas transfer, sorption of pollutants by leaf surfaces, and pollutant solubility and fate on the uptake process. Data is presented showing uptake of ozone by exposed mesophyll and several epidermal surfaces chosen for their different surface characteristics. The model was used to derive a mathematical expression for the exchange process which was rearranged to define internal (average) pollutant solute concentration in terms of external concentration, leaf and boundary layer diffusion resistance, surface sorption and pollutant solubility. The importance of estimating internal solute concentration is discussed.     

Satellite and Ground Based Monitoring of Aerosol Plumes

Plumes of atmospheric aerosol have been studied using a rangeof satellite and ground-based techniques. The Sea-viewing WideField-of-view Sensor (SeaWiFS) has been used to observe plumesof sulphate aerosol and Saharan dust around the coast of theUnited Kingdom. Aerosol Optical Thickness (AOT) was retrievedfrom SeaWiFS for two events; a plume of Saharan dusttransported over the United Kingdom from Western Africa and aperiod of elevated sulphate experienced over the Easternregion of the UK. Patterns of AOT are discussed and related tothe synoptic and mesoscale weather conditions. Furtherobservation of the sulphate aerosol event was undertaken usingthe Advanced Very High Resolution Radiometer instrument(AVHRR). Atmospheric back trajectories and weather conditionswere studied in order to identify the meteorologicalconditions which led to this event. Co-located ground-basedmeasurements of PM₁₀ and PM_2.5 were obtained for 4sites within the UK and PM_2.5/10 ratios were calculatedin order to identify any unusually high or low ratios(indicating the dominant size fraction within the plume)during either of these events. Calculated percentiles ofPM_2.5/10 ratios during the 2 events examined show thatthese events were notable within the record, but were in noway unique or unusual in the context of a 3 yr monitoringrecord. Visibility measurements for both episodes have beenexamined and show that visibility degradation occurred duringboth the sulphate aerosol and Saharan dust episodes.     

The role of stand history in assessing forest impacts

Air pollution, harvesting practices, and natural disturbances can affect the growth of trees and forest development. To make predictions about anthropogenic impacts on forests, we need to understand how these factors affect tree growth. In this study the effect of disturbance history on tree growth and stand structure was examined by using a computer model of forest development. The model was run under the climatic conditions of east Tennessee, USA, and the results compared to stand structure and tree growth data from a yellow poplar-white oak forest. Basal area growth and forest biomass were more accurately projected when rough approximations of the thinning and fire history typical of the measured plots were included in the simulation model. Stand history can influence tree growth rates and forest structure and should be included in any attempt to assess forest impacts.     

Bacterial community structure in soils contaminated by polycyclic aromatic hydrocarbons

Bacterial community structure was examined in polycyclic aromatic hydrocarbon (PAH) contaminated soil taken from a timber treatment facility in southern Ireland. Profiles of soil bacterial communities were generated using a molecular fingerprinting technique, terminal restriction fragment length polymorphism (TRFLP), and results were interpreted using sophisticated multivariate statistical analysis. Findings suggested that there was a correlation between PAH structure and bacterial community composition. Initial characterisation of soil from the timber treatment facility indicated that PAH contamination was unevenly distributed across the site. Bacterial community composition was correlated with the type of PAH present, with microbial community structure associated with soil contaminated with two-ringed PAHs only being distinctly different to communities in soils contaminated with multi-component PAH mixtures. Typically the number of bacterial ribotypes detected in samples did not appear to be adversely affected by the level of contamination.     

Efficiency of perchlorate consumption in road flares, propellants and explosives

When an explosive detonates or a propellant or flare burns, consumption of the energetic filler should be complete but rarely is, especially in the presence of large amounts of non-combustible materials. Herein we examine three types of perchlorate-containing devices to estimate their potential as sources of contamination in their normal mode of functioning. Road flares, rocket propellants and ammonium nitrate (AN) emulsion explosives are potentially significant anthropogenic sources of perchlorate contamination. This laboratory evaluated perchlorate residue from burning of flares and propellants as well as detonations of ammonium nitrate emulsion explosives. Residual perchlorate in commercial products ranged from 0.094 mg perchlorate per gram material (flares) to 0.012 mg perchlorate per gram material (AN emulsion explosives). The rocket propellant formulations, prepared in this laboratory, generated 0.014 mg of perchlorate residue per gram of material.     

How identity of the homopteran trophobiont affects sex allocation in a symbiotic plant-ant: the proximate role of food

We provide evidence for the proximate role of food in sex allocation by an ant species, and demonstrate how identity of the homopteran partner affects benefits to colonies of a plant-symbiotic ant. The system studied includes a plant-ant that nests in swollen hollowed internodes of a myrmecophyte, and two species of homopteran trophobionts (a coccid and a pseudococcid) tended inside domatia by these ants, for which they are an essential source of food. Total investment in pupae was greater for ant colonies that tended solely or primarily coccids than for those that tended pseudococcids. In particular, biomass invested in sexuals increased more rapidly with size of the colony in trees where ants tended coccids. This greater investment in sexuals was not made at the expense of investment in workers, but reflected increased resources available to coccid-tending colonies. Higher reproductive output indicates that ant fitness may be greater when they tend coccids. These additional resources led to a greater increase in production of alate females than in that of males. Consequently, the sex investment ratio of coccid-tending colonies was more female biased than in those that tended pseudococcids. Differences in resource supply affected numbers of individuals produced but not per-individual investment, with one partial exception: in very small colonies, pseudococcid-tending colonies produced small workers while coccid-tending colonies did not, further underlining the higher resource supply to coccid-tending colonies. This study provides evidence for the proximate role played by food in sex allocation at the colony level. We discuss our results in the context of hypotheses aimed at explaining sex ratio at the colony and population levels.