Multi-decadal changes in tundra environments and ecosystems: synthesis of the International Polar Year-Back to the Future project (IPY-BTF)

Understanding the responses of tundra systems to global change has global implications. Most tundra regions lack sustained environmental monitoring and one of the only ways to document multi-decadal change is to resample historic research sites. The International Polar Year (IPY) provided a unique opportunity for such research through the Back to the Future (BTF) project (IPY project #512). This article synthesizes the results from 13 papers within this Ambio Special Issue. Abiotic changes include glacial recession in the Altai Mountains, Russia; increased snow depth and hardness, permafrost warming, and increased growing season length in sub-arctic Sweden; drying of ponds in Greenland; increased nutrient availability in Alaskan tundra ponds, and warming at most locations studied. Biotic changes ranged from relatively minor plant community change at two sites in Greenland to moderate change in the Yukon, and to dramatic increases in shrub and tree density on Herschel Island, and in subarctic Sweden. The population of geese tripled at one site in northeast Greenland where biomass in non-grazed plots doubled. A model parameterized using results from a BTF study forecasts substantial declines in all snowbeds and increases in shrub tundra on Niwot Ridge, Colorado over the next century. In general, results support and provide improved capacities for validating experimental manipulation, remote sensing, and modeling studies.     

Ammonia assessment from agriculture: U.S. status and needs

Recent studies suggest that human activities accelerate the production of reactive nitrogen on a global scale. Increased nitrogen emissions may lead to environmental impacts including photochemical air pollution, reduced visibility, changes in biodiversity, and stratospheric ozone depletion. In the last 50 yr, emissions of ammonia (NH3), which is the most abundant form of reduced reactive nitrogen in the atmosphere, have significantly increased as a result of intensive agricultural management and greater livestock production in many developed countries. These agricultural production practices are increasingly subject to governmental regulations intended to protect air resources. It is therefore important that an accurate and robust agricultural emission factors database exist to provide valid scientific support of these regulations. This paper highlights some of the recent work that was presented at the 2006 Workshop on Agricultural Air Quality in Washington, D.C. regarding NH3 emissions estimates and emission factors from agricultural sources in the U.S. and Europe. In addition, several best management practices are explored as the scientific community attempts to maximize the beneficial use of reactive nitrogen while simultaneously minimizing negative environmental impacts.     

The ozone productivity of n-propyl bromide: Part 2--An exception to the Maximum Incremental Reactivity Scale

In an earlier paper the ozone-forming potential of n-propyl bromide (NPB) was studied with a new methodology designed to address issues associated with a marginal smog-forming compound. However, the U.S. Environmental Protection Agency (EPA) subsequently revised its policy and now recommends using the Maximum Incremental Reactivity (MIR) scale to rank the ozone-forming potential of all volatile organic compounds (VOCs), including those of marginal ozone productivity. Nevertheless, EPA contemplated exceptions to the box-model-derived MIR scale by allowing use of photochemical grid-model simulations for case specific reactivity assessments. The California Air Resources Board (CARB) also uses the MIR scale and CARB has a Reactivity Scientific Advisory Committee that can consider exceptions to the MIR scale. In this study, grid-model simulations that were recommended by EPA are used to evaluate the incremental ozone impacts of NPB using an update to the chemical mechanism developed in an earlier paper. New methods of analysis of the grid-model output are further developed here to quantify the relative reactivities between NPB and ethane over a wide range of conditions. The new grid-model-based analyses show that NPB is significantly different and generally less in ozone-forming potential (i.e., reactivity) than predicted by the box-model-based MIR scale relative to ethane, EPA's "bright-line" test for non-VOC status. Although NPB has low reactivity compared to typical VOCs on any scale, the new grid-model analyses developed here show that NPB is far less reactive (and even has negative reactivity) compared to the reactivity predicted by the MIR scale.     

Valuing the benefits of the urban forest: a spatial hedonic approach

This paper measures the benefits of the urban forest by examining its effect on housing prices. A Geographic Information System is used to develop a measure of the urban forest, the Normalised Difference Vegetation Index, from satellite imagery and to construct other variables from a variety of sources. Spatial hedonic housing price models for the Indianapolis/Marion County area are estimated. The models indicate that greener vegetation around a property has a positive, significant effect on housing price, holding everything else constant. This effect is dominated by measures at the neighborhood level. These findings indicate that property owners value the urban forest, at least in part, by the premium they pay to live in neighborhoods with greener, denser vegetation. These findings also indicate that public action to maintain and enhance the urban forest may be warranted. Planners and urban foresters can use these findings to inform public and policy debates over urban forestry programs and proposals.     

Body mass index and serum chlorinated dibenzo-p-dioxin and dibenzofuran levels

Several studies have found that current levels of 2,3,7,8 tetrachlorodibenzo-p-dioxin in serum lipids are related to age with older persons generally having higher levels. To account for this age pattern, reference ranges based on national samples have been established in order to allow determination of background levels for regional studies. In several studies, body mass index (BMI), has also been associated with current 2,3,7,8 tetrachlorodibenzo-p-dioxin levels with increasing body mass index related to increasing levels. We measured lipid-adjusted serum levels for all 2,3,7,8-substituted dioxins and furans in 62 chemical manufacturing workers with chlorophenol exposures and 36 workers without chlorophenol exposures employed at the same location. We then assessed the impact of age and BMI on the serum levels of all these compounds in the presence of other potential confounders. We found that both factors are important independent determinants of serum levels of 2,3,7,8-substituted dioxins and furans. Specifically, age and BMI are both important factors for assessing background levels of 2,3,7,8 tetrachlorodibenzo-p-dioxin, 1,2,3,7,8 pentachlorodibenzo-p-dioxin and the calculated total toxic equivalency. BMI, but not age, is important for assessing background levels of higher chlorinated dioxins and some hexachlorofurans. We conclude that age and BMI are both important considerations when comparing a potentially exposed group to a referent group, or to national norms. Further, age and BMI may also be important in epidemiology studies where back-extrapolation from current dioxin levels is used to assess historical chlorophenol exposure.     

Lack of evidence for nepotism by workers tending queens of the polygynous termite <Emphasis Type="Italic">Nasutitermes corniger</Emphasis>

Kin selection theory predicts that workers in social insect colonies should preferentially aid close relatives over less related or unrelated individuals if such behaviors increase inclusive fitness. For example, a worker in a polygynous (multiple-queen) colony is predicted to tend its own mother rather than an unrelated queen if this nepotistic behavior increases its mother’s reproductive success in excess of costs. Despite predictions, experimental tests conducted in the social Hymenoptera have found no clear evidence of nepotism. No tests for nepotism have been carried out in the Isoptera (termites), another major insect taxon showing highly developed sociality. We tested for nepotistic behavior in the termite Nasutitermes corniger by determining if workers preferentially fed and groomed their mothers in a laboratory assay. We collected workers from nine naturally occurring multiple-queen colonies as they tended queens and determined their parentage using highly variable microsatellite markers. Our results provide no evidence that workers tend their mothers in preference to co-occurring queens. The absence of evidence for nepotism is consistent with previous results reported from numerous studies of eusocial hymenopterans.     

Conceptual development of a harmonised method for tracking change and evaluating policy in the agri-environment: The Agri-environmental Footprint Index

An aggregated farm-level index, the Agri-environmental Footprint Index (AFI), based on multiple criteria methods and representing a harmonised approach to evaluation of EU agri-environmental schemes is described. The Index uses a common framework for the design and evaluation of policy that can be customised to locally relevant agri-environmental issues and circumstances. Evaluation can be strictly policy-focused, or broader and more holistic in that context-relevant assessment criteria that are not necessarily considered in the evaluated policy can nevertheless be incorporated. The Index structure is flexible, and can respond to diverse local needs. The process of Index construction is interactive, engaging farmers and other relevant stakeholders in a transparent decision-making process that can ensure acceptance of the outcome, help to forge an improved understanding of local agri-environmental priorities and potentially increase awareness of the critical role of farmers in environmental management. The structure of the AFI facilitates post-evaluation analysis of relative performance in different dimensions of the agri-environment, permitting identification of current strengths and weaknesses, and enabling future improvement in policy design. Quantification of the environmental impact of agriculture beyond the stated aims of policy using an ‘unweighted’ form of the AFI has potential as the basis of an ongoing system of environmental audit within a specified agricultural context.     

Application of Biobarriers for Groundwater Containment at Fractured Bedrock Sites

Biological barriers are a beneficial application of biofilms that aim at reducing the hydraulic conductivity (K) in geological formations. Several studies have shown the potential benefits of creating such barriers either by stimulating the indigenous microbial community (biostimulation) or injecting bacteria (bioaugmentation). For example, laboratory experiments show that groundwater microorganisms attached to a ceramic surface and generated a biofilm as thick as 1,100 μm. In a limestone fracture, this bacterial community clogged a single fracture up to 99.2 percent within 22 days. At the field scale, applications in porous aquifers led to a five‐fold decrease in K after 2.5 days of biostimulation, and a bioaugmentation with a starved, adapted bacterial culture decreased K by 99.4 percent. One promising development of the biobarrier concept is a field application at a fractured bedrock site. Using a multidisciplinary approach and focusing on a well‐characterized fracture system, a field trial was undertaken in Southern Ontario to measure the extent of bioclogging and the stability over time. This article focuses on the literature pertinent to the preparation of this field trial and presents the innovative approach selected to monitor the bioclogging in such a challenging environment.     

Estimation of septic tank setback distances based on transport of E. coli and F-RNA phages

Setback distances between septic tank systems and the shorelines of Lake Okareka, New Zealand were determined from model simulations for a worst-case scenario, using the highest hydraulic conductivity and gradient measured in the field, removal rates of the microbial indicators (Escherichia coli and F-RNA phages) determined from a column experiment, and maximum values of the design criteria for the disposal system, and assuming an absence of an unsaturated zone, a continuous discharge of the raw effluent from a failed or non-complying treatment system (both indicators at concentrations of 1x10(7) counts/100 ml) into the groundwater and no sorption of pathogens in the aquifer. Modelling results suggest that the minimal setback distances were 16 m to satisfy the New Zealand Recreational Water Quality Guidelines for E. coli <126 per 100 ml (Ministry for the Environment, 1999) and 48 m to meet the Drinking-Water Standards for New Zealand 2000 for enteric virus <1 per 100 l (Ministry of Health, 2000). These distances may be applicable for other lakeshores in pumice sand aquifers with groundwater velocities <7 m/day. Findings of laboratory column and batch experiments provided an insight into the microbial attenuation and transport processes in pumice sand aquifers. Bacterial removal was predominately through filtration (87-88%) and partially by die-off (12-13%), while viral removal was by both die-off (45%) and filtration (55%). In addition, microbial die-off in groundwater without aquifer material (i.e., free microbes) was much lower than die-off in groundwater with aquifer material (i.e., sorbed microbes) and contributed only 2-6% to the total removal. This implies that the setback distances estimated from die-off rates for the free microbes, determined in the laboratory without considering aquifer media and other removal processes, which are often reported in the literature, could be larger than necessary.