Effects of four decades of fire manipulation on woody vegetation structure in Savanna

The amount of carbon stored in savannas represents a significant uncertainty in global carbon budgets, primarily because fire causes actual biomass to differ from potential biomass. We analyzed the structural response of woody plants to long-term experimental burning in savannas. The experiment uses a randomized block design to examine fire exclusion and the season and frequency of burn in 192 7-ha experimental plots located in four different savanna ecosystems. Although previous studies would lead us to expect tree density to respond to the fire regime, our results, obtained from four different savanna ecosystems, suggest that the density of woody individuals was unresponsive to fire. The relative dominance of small trees was, however, highly responsive to fire regime. The observed shift in the structure of tree populations has potentially large impacts on the carbon balance. However, the response of tree biomass to fire of the different savannas studied were different, making it difficult to generalize about the extent to which fire can be used to manipulate carbon sequestration in savannas. This study provides evidence that savannas are demographically resilient to fire, but structurally responsive.     

Modelling the effects of trade-offs between long and short-term objectives in fisheries management

Fisheries management is typically a complex problem, from both an environmental and political perspective. The main source of conflict occurs between the need for stock conservation and the need for fishing community well-being, which is typically measured by employment and income levels. For most fisheries, overexploitation of the stock requires a reduction in the level of fishing activity. While this may lead to long-term benefits (both conservation and economic), it also leads to a short-term reduction in employment and regional incomes. In regions which are heavily dependent on fisheries, short-term consequences of conservation efforts may be considerable. The relatively high degree of scientific uncertainty with respect to the status of the stocks and the relatively short lengths of political terms of office, generally give rise to the short-run view taking the highest priority when defining policy objectives. In this paper, a multi-objective model of the North Sea is developed that incorporates both long-term and short-term objectives. Optimal fleet sizes are estimated taking into consideration different preferences between the defined short-term and long-term objectives. The subsequent results from the model give the short-term and long-term equilibrium status of the fishery incorporating the effects of the short-term objectives. As would be expected, an optimal fleet from a short-term perspective is considerably larger than an optimal fleet from a long-run perspective. Conversely, stock sizes and sustainable yields are considerably lower in the long-term if a short-term perspective is used in setting management policies. The model results highlight what is essentially a principal-agent problem, with the objectives of the policy makers not necessarily reflecting the objectives of society as a whole.     

Spatial variability of unpaved road dust PM10 emission factors near El Paso, Texas

The testing re-entrained aerosol kinetic emissions from roads technique is compared with distance-based emission factors (EFs; g/VKT) measured downwind of a dirt road by using towers instrumented with real-time meteorological and particle sensors at multiple heights. The emission potential (EP), defined as the EF divided by the vehicle speed (m/sec), and weight index permits the intercomparison of emissions from multiple roadways surveyed by the TRAKER vehicle. A survey of 72 km of unpaved roads on the Ft. Bliss Military Base near El Paso, Texas, indicated that 60% of all measured EPs fell between 6.7 (g/VKT)/(m/sec) and 9.6 (g/VKT)/(m/sec). The EP measured across the base was approximately 50% lower than those collected in the vicinity of the instrumented towers. This implies that EFs measured for other vehicles on the same test section should be reduced by 50% to more accurately represent EFs for the entire military base. Using geographic information system-based soil maps, the inferred EFs are related to differences in soil types over the survey area. Variations among five different soil types accounted for <10% of variation in EP. Individual measurements using the testing re-entrained aerosol kinetic emissions from roads technique did show larger spatial variations in EP; however, these were not effectively captured by the soil classifications, partly because of the comparatively coarse spatial classification used in the soil survey data.     

Management Objective Importance in Fisheries: An Evaluation Using the Analytic Hierarchy Process (AHP)

In determining the importance of criteria in the management of fisheries, two key issues stand out—the definition of a succinct set of criteria and the determination of which interest groups play a defining role in the management development process. This is indeed the case for all natural resource management problems, and many other environmental problems as well. The analytic hierarchy process (AHP) provides an effective framework for such an analysis. The AHP is generally used to evaluate importance amongst criteria based on the concept of paired comparison. This paper considers the development of a representative criteria hierarchy, and uses data obtained from a pairwise comparison survey based on the UK fisheries of the English Channel to investigate priorities that exist among different interest groups in the fisheries. The implementation of the AHP in this application provides a useful tool for analysis of criteria amongst groups involved in the management process with diverse interests.     

Effects of different pretreatment methods on anaerobic mixed microflora for hydrogen production and COD reduction from palm oil mill effluent

Effects of different pretreatment methods on sludge inocula were evaluated with respect to hydrogen (H₂) production enhancement using palm oil mill effluent (POME) in a batch system. The experimental results showed that the pretreatment methods (chemical, acid, heat-shock, freezing and thawing, and base) at 35 °C and initial pH 5.5 had a positive influence on H₂ production yield and chemical oxygen demand (COD) removal efficiency during the fermentative H₂ production as compared to the control experiments (without pretreatment). Heat-shock pretreatment method was shown to be a simple and useful method for enhancing both H₂ producing and COD removal processes from POME with highest H₂ yield and COD removal efficiency at 0.41 mmol H₂/g COD and 86%, respectively.     

Modelling temporal and spatial changes of PCBs in fish tissue from Lake Huron

A model has been developed to assess temporal and spatial changes in the concentration of polychlorinated biphenyl (PCB) contaminant in whole fish from Lake Huron during the years 1980 to 2004. The model uses log PCB concentration as the response variable and includes time trend, within-lake variability and dependence on age, weight and length as explanatory variables. A preliminary examination of the data revealed that some values are recorded as below detection limits (thus leading to the left censoring), and the PCB concentration appears to show declines in latter years. To this end, parametric log-location-scale regression models used in survival analysis were employed. It has been found that the Weibull model yields a better fit than the log-logistic or the log-normal models. The analysis provides strong evidence that, starting in 1996, the level of PCB concentration showed steady decline, which is most contributed by the Canadian and US governments?? actions carried out earlier to reduce the load of toxic contaminants to the Great Lakes. Spatially, fish from the north of the lake is less contaminated than fish from the south. The pattern and magnitude of the estimated spatial and temporal trends can provide useful information regarding the safety of fish consumption, the setting of regularity limits, the identifiability of PCB sources and the effects of remedial actions in the future. In addition, the developed model is not restricted to the current application but could be used for the analysis of other contaminants.     

Defining the Reference Condition for Wadeable Streams in the Sand Hills Subdivision of the Southeastern Plains Ecoregion,USA

The Sand Hills subdivision of the Southeastern Plains ecoregion has been impacted by historical land uses over the past two centuries and, with the additive effects of contemporary land use, determining reference condition for streams in this region is a challenge. We identified reference condition based on the combined use of 3 independent selection methods. Method 1 involved use of a multivariate disturbance gradient derived from several stressors, method 2 was based on variation in channel morphology, and method 3 was based on passing 6 of 7 environmental criteria. Sites selected as reference from all 3 methods were considered primary reference, whereas those selected by 2 or 1 methods were considered secondary or tertiary reference, respectively. Sites not selected by any of the methods were considered non-reference. In addition, best professional judgment (BPJ) was used to exclude some sites from any reference class, and comparisons were made to examine the utility of BPJ. Non-metric multidimensional scaling indicated that use of BPJ may help designate non-reference sites when unidentified stressors are present. The macroinvertebrate community measures Ephemeroptera, Plecoptera, Trichoptera richness and North Carolina Biotic Index showed no differences between primary and secondary reference sites when BPJ was ignored. However, there was no significant difference among primary, secondary, and tertiary reference sites when BPJ was used. We underscore the importance of classifying reference conditions, especially in regions that have endured significant anthropogenic activity. We suggest that the use of secondary reference sites may enable construction of models that target a broader set of management interests.     

Rapid Geomorphic and Habitat Stream Assessment Techniques Inform Restoration Differently Based on Levels of Stream Disturbance

Visual‐based rapid assessment techniques provide an efficient method for characterizing the restoration potential of streams, with many focusing on channel stability and instream habitat features. Few studies, however, have compared these techniques to see if they result in differing restoration priorities. Three rapid assessment techniques were contrasted at three wild trout streams in western New York with different amounts of channel disturbance. Two methods focused only on geomorphic stability, whereas the third addressed physical habitat condition. Habitat assessment scores were not correlated with scores for either geomorphic assessment method and they varied more between channels with different degrees of disturbance. A model based on dynamic equilibrium concepts best explains the variation among the streams and techniques because it accounts for a stream's capacity to maintain ecological integrity despite some inherent instability. Geomorphic indices can serve as effective proxies for biological indices in highly disturbed systems. Yet, this may not be the case in less disturbed systems, where geomorphic indices cannot differentiate channel adjustments that impact biota from those that do not. Dynamically stable streams can include both stable and unstable reaches locally as characterized by geomorphic methods and translating these results into restoration priorities may not be appropriate if interpretations are limited to the reach scale.     

Detection and visualization of storm hydrograph changes under urbanization: an impulse response approach

Urbanization often alters catchment storm responses, with a broad range of potentially significant environmental and engineering consequences. At a practical, site-specific management level, efficient and effective assessment and control of such downstream impacts requires a technical capability to rapidly identify development-induced storm hydrograph changes. The method should also speak specifically to alteration of internal watershed dynamics, require few resources to implement, and provide results that are intuitively accessible to all watershed stakeholders. In this short paper, we propose a potential method which might satisfy these criteria. Our emphasis lies upon the integration of existing concepts to provide tools for pragmatic, relatively low-cost environmental monitoring and management. The procedure involves calibration of rainfall-runoff time-series models in each of several successive time windows, which sample varying degrees of watershed urbanization. As implemented here, only precipitation and stream discharge or stage data are required. The readily generated unit impulse response functions of these time-series models might then provide a mathematically formal, yet visually based and intuitive, representation of changes in watershed storm response. Nominally, the empirical response functions capture such changes as soon as they occur, and the assessments of storm hydrograph alteration are independent of variability in meteorological forcing. We provide a preliminary example of how the technique may be applied using a low-order linear ARX model. The technique may offer a fresh perspective on such watershed management issues, and potentially also several advantages over existing approaches. Substantial further testing is required before attempting to apply the concept as a practical environmental management technique; some possible directions for additional work are suggested.     

Wilderness forms and their implications for global environmental policy and conservation

With the intention of securing industry-free land and seascapes, protecting wilderness entered international policy as a formal target for the first time in the zero draft of the Post-2020 Global Biodiversity Framework under the Convention on Biological Diversity. Given this increased prominence in international policy, it is timely to consider the extent to which the construct of wilderness supports global conservation objectives. We evaluated the construct by overlaying recently updated cumulative human pressure maps that offer a global-scale delineation of industry-free land as wilderness with maps of carbon stock, species richness, and ground travel time from urban centers. Wilderness areas took variable forms in relation to carbon stock, species richness, and proximity to urban centers, where 10% of wilderness areas represented high carbon and species richness, 20% low carbon and species richness, and 3% high levels of remoteness (>48 h), carbon, and species richness. Approximately 35% of all remaining wilderness in 2013 was accessible in <24 h of travel time from urban centers. Although the construct of wilderness can be used to secure benefits in specific contexts, its application in conservation must account for contextual and social implications. The diverse characterization of wilderness under a global environmental conservation lens shows that a nuanced framing and application of the construct is needed to improve understanding, communication, and retention of its variable forms as industry-free places.