Contributions of advective and diffusive oxygen transport through multilayer composite caps over mine waste

The relative contributions of four mechanisms of oxygen transport in multilayer composite (MLC) caps placed over oxygen-consuming mine waste were evaluated using numerical and analytical methods. MLC caps are defined here as caps consisting of earthen and geosynthetic (polymeric) components where a composite barrier layer consisting of a geomembrane (1-2 mm thick polymeric sheet) overlying a clay layer is the primary barrier to transport. The transport mechanisms that were considered are gas-phase advective transport, gas-phase diffusive transport, liquid-phase advective transport via infiltrating precipitation and liquid-phase diffusive transport. A numerical model was developed to simulate gas-phase advective-diffusive transport of oxygen through a multilayer cap containing seven layers. This model was also used to simulate oxygen diffusion in the liquid phase. An approximate analytical method was used to compute the advective flux of oxygen in the liquid phase. The numerical model was verified for limiting cases using an analytical solution. Comparisons were also made between model predictions and field data for earthen caps reported by others. Results of the analysis show that the dominant mechanism for oxygen transport through MLC caps is gas-phase diffusion. For the cases that were considered, the gas-phase diffusive flux typically comprises at least 99% of the total oxygen flux. Thus, designers of MLC caps should focus on design elements and features that will limit diffusion of gas-phase oxygen.     

Cotton defoliant runoff as a function of active ingredient and tillage

Cotton (Gossypium hirsutum L.) defoliant runoff was recently identified as an ecological risk. However, assessments are not supported by field studies. Runoff potential of three defoliant active ingredients, dimethipin (2,3-dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4-tetraoxide), thidiazuron (N-phenyl-N-1,2,3-thidiazol-5-yl-urea), and tribufos (S,S,S-tributyl phosphorotrithioate) was investigated by rainfall simulation on strip (ST) and conventionally tilled (CT) cotton in south central Georgia. Simulated rainfall timing relative to defoliant application (1 h after) represented an extreme worst-case scenario; however, weather records indicate that it was not unrealistic for the region. Thidiazuron and tribufos losses were 12 to 15% of applied. Only 2 to 5% of the more water soluble dimethipin was lost. Although ST erosion rates were less, loss of tribufos, a strongly sorbing compound, was not affected. Higher sediment-water partition coefficients (kd) were measured in ST samples. This likely explains why no tillage related differences in loss rates were observed, but it is unknown whether this result can be generalized. The study was conducted in the first year following establishment of tillage treatments at the study site. As soil conditions stabilize, ST impacts may change. Data provide an estimate of the maximum amount of the defoliants that will run off during a single postapplication storm event. Use of these values in place of the default value in runoff simulation models used in pesticide risk assessments will likely improve risk estimate accuracy and enhance evaluation of comparative risk among these active ingredients.     

Effects of mechanical fracturing and experimental trampling on Hawaiian corals

In situ trampling occurred under experimental conditions to quantify the differences in the responses to anthropogenic trampling in four dominant species of Hawaiian corals, Porites compressa, Porites lobata, Montipora capitata, and Pocillopora meandrina. Trampling was simulated daily for a period of nine days at which time further breakage was minimal. Forty treatment colonies produced 559 fragments. Trampling was followed by an 11-month recovery period. Coral colony and fragment mortality was low. All four species were highly tolerant of inflicted damage, suggesting that some species of corals can withstand limited pulse events that allow time for recovery. Growth rates following trampling were significantly lower in the treatment groups for three of the four species. This study demonstrated that very few trampling events can produce significant changes in growth even after a long recovery period. Survivorship of fragments is clearly size- and species-dependent in M. capitata and P. compressa. Smaller fragments (<5 cm) had higher mortality than larger fragments (>5 cm). High breakage rates for M. capitata and P. compressa are consistent with the nearshore, low-energy regions they inhabit—the same environment frequented by skin divers and waders. Mechanical tests were conducted to determine tensile and compressive strengths. Pocillopora meandrina exhibited the strongest skeletal strength, followed in decreasing order by Porites lobata, Porites compressa, and Montipora capitata. The skeletal strength obtained from the experiments correlate with the wave energy present in the environments in the regions they inhabit, suggesting that structural strength of corals is an adaptive response to hydraulic stress.     

Book reviews

Our Stolen Future. How man-made chemicals are threatening our fertility, intelligence and survival. T. Colborn, J. P. Myers & D. Dumanoski, 1996, Boston, Little, Brown, 306 pp. ISBN 0 316 87546, £18.99

Environmental Sociology: a social constructionist perspective. John Hannigan, 1995, London, Routledge, ISBN 0 415 112 559, £12.99

Citizen Science: a study of people, expertise and sustainable development. Alan Irwin, 1995, London, Routledge, ISBN 0 415 130 107, £13.99

The True Costs of Road Transport. David Maddison, David Pearce, Olof Johansson, Edward Calthrop, Todd Litman & Eric Verhoef, 1996, London, Earthscan, 242 pp. ISBN 185 383 2685, £10.95

Car Dependence: a report for the RAC Foundation for Motoring and the Environment. RAC Foundation for Motoring and the Environment, 1995, London, 154 pp. ISBN 086211355 5

Local Sustainability: turning sustainable development into practical action in our communities. Roger Few (Ed.), Leicester Environment City Trust, 1996, Leicester, Environ Trust, 100 pp., £28.00, [Available from: Environ Parkfield, Western Park, Leicester, LE3 6HX, UK]

Successful Environment Management in a Week. Mark Yoxon, 1996, London, Hodder & Stoughton, 96 pp. ISBN 0 340 66374 X, £6.99

Principles of Environmental and Resource Economics. H. Folmer, H. Landis Gabel & H. Opschoor (Eds), 1995, Aldershot, Edward Elgar, 512 pp. ISBN 1 85898 224 3, £85.00

The Contingent Valuation of Environmental Resources: methodological issues and research needs. David Bjornstad & James R. Khan (Eds), 1996, Cheltenham, UK and Brookfield USA, Edward Elgar, ISBN 1 858983215

Towards Sustainability. Peter Martin & Colin Hutchinson, 1996, London, Office for Public Management, £5.45

Conservation and the Consumer: understanding environmental concern. Paul Hackett, 1995, London, Routledge, 229 pp. ISBN 0 415 08096 7, £45.00     

The use of invertebrates to detect small-scale habitat heterogeneity and its application to restoration practices

Recent conceptual and technological solutions to biodiversityassessment allow large numbers of invertebrate specimens to beprocessed rapidly and provide researchers and practitioners with a unique tool for characterizing habitats. One applicationof these advances is the ability to detect and monitor small-scale habitat heterogeneity and so provide a measure of ecosystem restoration. This case study presents a test of theefficacy of using invertebrates to assess and monitor ecologicalrestoration following bush regeneration. Eight contiguous habitatpatches within a suburb of northern Sydney, Australia, were selected to represent areas that had undergone different bushregeneration techniques. A nearby and relatively undisturbed area of bushland was also sampled. A total of 57 806 ground-active invertebrate specimens from 35 different orders were collected in pitfall traps. 1 246 ant (Formicidae) specimens were further sorted into 46 ant morphospecies from20 genera. Analyses of the three taxonomic data sets, includingtwo different data transformations, demonstrated that: (i) invertebrate communities successfully characterized different sites, providing a high degree of differentiation among sites;(ii) ordinations of the sites allowed visual assessment of theimpact of each management technique on the habitat relativeto undisturbed habitats; and (iii) characterization of sitescould be achieved using abundance classes or binary countsof ant morphospecies, representing potential cost and timesavings. The project duration was a total of three personweeks and cost less than US$3,000 (1999 prices) to complete.Measurement of invertebrate assemblages will provide a toolfor both rapid assessment of management decisions and ameans by which to implement adaptive management and restoration.     

Establishing the Canadian Community Monitoring Network

Community-based ecosystem monitoring activities in Canada are increasing in response to a number of factors including: (i) the needs of decision-makers for timely information on local environmental changes; (ii) limited use of government monitoring data and information by decision makers; (iii) government cuts to monitoring programs; (iv) the increasingly recognized need to include stakeholders in planning and management processes; and (v) the desire of citizens to contribute to environmental protection. To date there has been no network coordination of community based monitoring in Canada. This paper reports on the establishment of the Canadian Community Monitoring Network by Environment Canada's Ecological Monitoring and Assessment Network Coordinating Office and the Canadian Nature Federation. Information on research prepared in support of network establishment is presented along with a discussion of the potential of the network.     

A terrain-based paired-site sampling design to assess biodiversity losses from eastern hemlock decline

Biodiversity surveys are often hampered by the inability tocontrol extraneous sources of variability introduced intocomparisons of populations across a heterogenous landscape. If not specifically accounted for a priori, this noisecan weaken comparisons between sites, and can make itdifficult to draw inferences about specific ecologicalprocesses. We developed a terrain-based, paired-sitesampling design to analyze differences in aquaticbiodiversity between streams draining eastern hemlock (Tsuga canadensis) forests, and those draining mixedhardwood forests in Delaware Water Gap National RecreationArea (USA). The goal of this design was to minimize variancedue to terrain influences on stream communities, whilerepresenting the range of hemlock dominated streamenvironments present in the park. We used geographicinformation systems (GIS) and cluster analysis to define andpartition hemlock dominated streams into terrain types basedon topographic variables and stream order. We computedsimilarity of forest stands within terrain types and usedthis information to pair hemlock-dominated streams withhardwood counterparts prior to sampling. We evaluated theeffectiveness of the design through power analysis and foundthat power to detect differences in aquatic invertebratetaxa richness was highest when sites were paired and terraintype was included as a factor in the analysis. Precision ofthe estimated difference in mean richness was nearly doubledusing the terrain-based, paired site design in comparison toother evaluated designs. Use of this method allowed us tosample stream communities representative of park-wide forestconditions while effectively controlling for landscapevariability.     

Spatial patterns in forest composition and standing dead red spruce in montane forests of the Adirondacks and northern Appalachians

The decline of red spruce (Picea rubens Sarg.) in montane forests of the northeastern United States has been previously reported. The objective of this study was to assess spatial patterns, if any, in standing dead red spruce stems in the Adirondacks of New York and northern Appalachians of Vermont, New Hampshire, and Maine. A stratified random sample of 19 mountains along a west to east transect in the Adirondacks and the northern Appalachians showed that the live basal area of all species was highest in the White Mountains (34.6 m² ha^–1) and lowest in the Adirondack Mountains (23.7 m² ha^–1) in the Green Mountains was significantly lower than in any other region. Intact standing dead red spruce in the Adirondack and Green Mountains (30%) was significantly higher than that in the three eastern clusters (14%). The amount of intact standing dead red spruce trees increased with elevation in only the western part of the region. With the exception of the Adirondacks, there was a greater average percent dead red spruce on the west side than on the east side of each mountain. The sum of standing dead for other tree species (average 13%) showed no statistically significant patterns with region, elevation or aspect, and was significantly lower than the amount of total dead red spruce (average 42%). The standing dead red spruce patterns we observed cannot be associated with any specific causal factors at this time.     

Field methods and example applications for the Min-Trap® mineral sampler

Important reactive minerals are commonly created during in situ groundwater remediation activities; for example, iron sulfides formed during enhanced reduction approaches can abiotically degrade many chlorinated solvents. However, cost-effective tools to evaluate these treatment processes in field applications are limited and the collection of samples to evaluate in situ mineral formation is costly due to drilling requirements. The new passive Min-Trap sampler is a simple and cost-effective tool that can directly measure the formation of reactive minerals in situ without the need for additional drilling or soil core collection. The methods presented here describe how Min-Traps deployed in conventional monitoring wells can measure reactive minerals and how these minerals can be identified through commercially available analytical methods. Several examples are presented that show how Min-Traps can be used to characterize the rate and spatial variability of reactive mineral precipitation and these data may support operation and optimization decisions.