Representing general theoretical concepts in structural equation models: the role of composite variables

Structural equation modeling (SEM) holds the promise of providing natural scientists the capacity to evaluate complex multivariate hypotheses about ecological systems. Building on its predecessors, path analysis and factor analysis, SEM allows for the incorporation of both observed and unobserved (latent) variables into theoretically-based probabilistic models. In this paper we discuss the interface between theory and data in SEM and the use of an additional variable type, the composite. In simple terms, composite variables specify the influences of collections of other variables and can be helpful in modeling heterogeneous concepts of the sort commonly of interest to ecologists. While long recognized as a potentially important element of SEM, composite variables have received very limited use, in part because of a lack of theoretical consideration, but also because of difficulties that arise in parameter estimation when using conventional solution procedures. In this paper we present a framework for discussing composites and demonstrate how the use of partially-reduced-form models can help to overcome some of the parameter estimation and evaluation problems associated with models containing composites. Diagnostic procedures for evaluating the most appropriate and effective use of composites are illustrated with an example from the ecological literature. It is argued that an ability to incorporate composite variables into structural equation models may be particularly valuable in the study of natural systems, where concepts are frequently multifaceted and the influence of suites of variables are often of interest.     

Carbonation of brine impacted fractionated coal fly ash: implications for CO2 sequestration

Coal combustion by-products such as fly ash (FA), brine and CO(2) from coal fired power plants have the potential to impact negatively on the environment. FA and brine can contaminate the soil, surface and ground water through leaching of toxic elements present in their matrices while CO(2) has been identified as a green house gas that contributes significantly towards the global warming effect. Reaction of CO(2) with FA/brine slurry can potentially provide a viable route for CO(2) sequestration via formation of mineral carbonates. Fractionated FA has varying amounts of CaO which not only increases the brine pH but can also be converted into an environmentally benign calcite. Carbonation efficiency of fractionated and brine impacted FA was investigated in this study. Controlled carbonation reactions were carried out in a reactor set-up to evaluate the effect of fractionation on the carbonation efficiency of FA. Chemical and mineralogical characteristics of fresh and carbonated ash were evaluated using XRF, SEM, and XRD. Brine effluents were characterized using ICP-MS and IC. A factorial experimental approach was employed in testing the variables. The 20-150 μm size fraction was observed to have the highest CO(2) sequestration potential of 71.84 kg of CO(2) per ton of FA while the >150 μm particles had the lowest potential of 36.47 kg of CO(2) per ton of FA. Carbonation using brine resulted in higher degree of calcite formation compared to the ultra-pure water carbonated residues.     

Factors leading to the evolution and maintenance of a male ornament in territorial species

Male ornamentation is assumed to have evolved primarily from selection by female mate choice. Yet this is only one possible reason for ornament evolution. Ornaments might also be useful in aggressive competition by improving opponent assessment between males, or they might function to enhance signal detection by making males more conspicuous in the environment. We tested both these ideas in territorial Anolis lizards in which female choice is either absent or secondary to males competing for territories that overlap female home ranges. Male tail crests only evolved in species in which territory neighbors were distant, consistent with the signal detection hypothesis. Once the tail crest had evolved, however, it seems to have become a signal in itself, with variation in the frequency and size of tail crests within species correlating with variables predicted by the aggressive competition hypothesis. Our study presents an apparent example of a male ornament in which the selection pressure leading to variation among species in ornament expression is different from the selection pressure acting on variation within species. The Anolis tail crest is therefore likely to be an exaptation. We caution that conclusions made on the evolution of male ornaments are dependent on the phylogenetic perspective adopted by a study. Studies restricted to single species are useful for identifying selection pressures in contemporary settings (i.e., the current utility of traits), but may lead to erroneous conclusions on the factors that initially lead to the origin of traits.     

Physical impact of waterjet‐based sediment remediation on benthic organisms

Adding activated carbon to sediments has been shown to be an effective means of reducing the bioavailability of certain contaminants. The current state of the practice is to mechanically mix activated carbon to a target concentration of 3 percent at depths of approximately 30 cm using a rotovator or similar construction equipment. Waterjets have been used to cut hard material using a mixture of water and an abrasive. If activated carbon is substituted for the abrasive, waterjets have the potential to use surface injection as a replacement for mechanical mixing during sediment remediation. A perceived benefit of waterjet‐based sediment remediation is that there may be a reduced potential for benthic organism mortality related to amendment delivery. A set of waterjet parameters were identified that have the potential to achieve amendment placement goals, and a series of waterjet tests were conducted to evaluate the potential impact on the benthic community. The tests included mortality testing using a swimming macroinvertebrate and a burrowing invertebrate, benthic artifacts such as shells, and craft foam as a surrogate for living organisms. The results indicated that the immediate survivability was typically greater than 50 percent, and that empirical relationships between two variables (waterjet nozzle diameter and the water column height between the nozzle and the target) and the depth of cut in the foam could be established. Data are not available in the literature for direct comparison of organism survivability immediately after mechanical mixing, but the results of this study provide motivation for the further evaluation of waterjets on the basis of the low observed mortality rates. Future waterjet work may address field‐scale characterization of mixing effectiveness, resuspension potential, technical feasibility, and cost. © 2011 Wiley Periodicals, Inc.     

Traditional management and conservation of shea trees (<Emphasis Type=Italic>Vitellaria paradoxa</Emphasis> subspecies <Emphasis Type=Italic>nilotica</Emphasis>) in Uganda

Traditional practices are universally recognised as a basis for conservation of biodiversity. However, such practices are often not included in natural resource conservation policies. This study assessed local conservation practices of shea trees (Vitellaria paradoxa) within different farming systems in Uganda and developed conservation guidelines for the species. The assessment involved 300 respondents, 15 focus groups and 41 key informants. Content analysis was used to identify the most important management and conservation practices. Local uses were categorised on the basis of shea tree products while differences in conservation practices were analysed using the Friedman test. The results show that eight shea tree products are used for 36 different purposes. Respondents’ age significantly influenced their knowledge about the shea tree. Traditional conservation practices include on-farm retention during cultivation and the use of folklore (mainly taboos), customs and rituals. Traditional management practices include weeding, bush burning, pollarding and pruning. Based on the current management and traditional conservation practices, a framework for the conservation of shea trees is proposed for integration into conservation policy decisions.     

Forecasting peak daily ozone levels: part 2--A regression with time series errors model having a principal component trigger to forecast 1999 and 2002 ozone levels

A modified time series approach, a Box-Jenkins regression with time series errors (RTSE) model plus a principal component (PC) trigger, has been developed to forecast peak daily 1-hr ozone (O3) in real time at the University of Wisconsin-Milwaukee North (UWM-N) during 1999 and 2002. The PC trigger acts as a predictor variable in the RTSE model. It tries to answer the question: will the next day be a possible high O3 day? To answer this question, three PC trigger rules were developed: (1) Hi-Low Checklist, (2) Discriminant Function Approach I, and (3) Discriminant Function Approach II. Also, a pure RTSE model without including the PC trigger and a persistence approach were tested for comparison. The RTSE model with DFA I successfully forecast the only two 1-hr federal exceedances (124 ppb), one in 1999 and one in 2002. In terms of the O3 100-ppb exceedances, 60-80% of the incorrect forecasts occurred with incorrect PC decisions. A few others may have been caused by unexpected O3-weather relations. When the three approaches used UWM-N data to forecast a 100-ppb exceedance somewhere in the Milwaukee, WI, metropolitan area, their performance was dramatically improved: the false alarm rate was reduced from 0.89 to 0.44, and the probability of detection was increased from 0.71 to 0.88.