Philip W. Johnson

Climate change and geothermal ecosystems: natural laboratories, sentinel systems, and future refugia

Understanding and predicting how global warming affects the structure and functioning of natural ecosystems is a key challenge of the 21st century. Isolated laboratory and field experiments testing global change hypotheses have been criticized for being too small-scale and overly simplistic, whereas surveys are inferential and often confound temperature with other drivers. Research that utilizes natural thermal gradients offers a more promising approach and geothermal ecosystems in particular, which span a range of temperatures within a single biogeographic area, allow us to take the laboratory into nature rather than vice versa. By isolating temperature from other drivers, its ecological effects can be quantified without any loss of realism, and transient and equilibrial responses can be measured in the same system across scales that are not feasible using other empirical methods. Embedding manipulative experiments within geothermal gradients is an especially powerful approach, informing us to what extent small-scale experiments can predict the future behaviour of real ecosystems. Geothermal areas also act as sentinel systems by tracking responses of ecological networks to warming and helping to maintain ecosystem functioning in a changing landscape by providing sources of organisms that are preadapted to different climatic conditions. Here, we highlight the emerging use of geothermal systems in climate change research, identify novel research avenues, and assess their roles for catalysing our understanding of ecological and evolutionary responses to global warming.

Does N2 fixation amplify the temperature dependence of ecosystem metabolism

Variation in resource supply can cause variation in temperature dependences of metabolic processes (e.g., photosynthesis and respiration). Understanding such divergence is particularly important when using metabolic theory to predict ecosystem responses to climate warming. Few studies, however, have assessed the effect of temperature-resource interactions on metabolic processes, particularly in cases where the supply of limiting resources exhibits temperature dependence. We investigated the responses of biomass accrual, gross primary production (GPP), community respiration (CR), and N2 fixation to warming during biofilm development in a streamside channel experiment. Areal rates of GPP, CR, biomass accrual, and N2 fixation scaled positively with temperature, showing a 32- to 71-fold range across the temperature gradient (approximately 7 degrees-24 degrees C). Areal N2-fixation rates exhibited apparent activation energies (1.5-2.0 eV; 1 eV = approximately 1.6 x 10(-19) J) approximating the activation energy of the nitrogenase reaction. In contrast, mean apparent activation energies for areal rates of GPP (2.1-2.2 eV) and CR (1.6-1.9 eV) were 6.5- and 2.7-fold higher than estimates based on metabolic theory predictions (i.e., 0.32 and 0.65 eV, respectively) and did not significantly differ from the apparent activation energy observed for N2 fixation. Mass-specific activation energies for N2 fixation (1.4-1.6 eV), GPP (0.3-0.5 eV), and CR (no observed temperature relationship) were near or lower than theoretical predictions. We attribute the divergence of areal activation energies from those predicted by metabolic theory to increases in N2 fixation with temperature, leading to amplified temperature dependences of biomass accrual and areal rates of GPP and R. Such interactions between temperature dependences must be incorporated into metabolic models to improve predictions of ecosystem responses to climate change.

Use of mine ventilation exhaust as combustion air in gas-fired turbo-electric generators

Methane liberated in coal mines is a potential safety hazard because it is explosive at relatively low concentrations (5-15%) in air. To manage methane, underground mines are ventilated with large quantities of air, and in some cases the gas is also drained with gob wells, and predrained with vertical and horizontal wells. The ventilation air is used to dilute methane emissions to levels well below the explosive limit, and the diluted stream is discharged to the atmosphere. Unfortunately, this waste stream may contain as much as 60% of the total gas energy that was originally in the coal. Also, methane is considered by some to be 24.5 times more detrimental than CO/sub 2/ in contributing to the greenhouse effect. The volume of the waste stream, the high electric power demands of a mine, and the greenhouse effect of methane provide a strong incentive for converting the waste-methane chemical energy to the electrical or mechanical equivalent. A preliminary economic assessment of a proposed test-turbine installation at the Jim Walter Resources No. 5 Mine, shows that such a project makes good sense economically, even without considering the emission-reduction benefits. This unit could produce enough power to drive a ventilation fan, provide a profitable rate of return, and produce a 2% reduction in emissions. A market study indicates that there is the potential to generate 706 to 816 MW of power from mine ventilation gas in the United States.

Recycling of plastic bottles for use as a lightweight geotechnical material

Purpose – Geotechnical fills are used for building roadway embankments, filling in behind retaining walls, and as backfill above buried pipelines. Lightweight fill reduces the load so structures can be built more economically. A new lightweight geo‐material made from recycled plastic bottles glued together in their original post‐consumer form was developed. The purpose of this work is to explore the use of this new material as a lightweight geotechnical fill.Design/methodology/approach – Through a preliminary laboratory and field study, aspects of the physical and mechanical characteristics of the recycled plastic bottle blocks were investigated. This new material is currently undergoing field trials behind a retaining wall on a bicycle path.Findings – It was found that the average density of this new material is very low, at 32.63 kg/m3 (2.04 lb/ft3), with 59.5 percent of a block made up of recycled plastic bottles. The plastic bottle waste stream obtained from a recycling plant is gap‐graded having appr...

Increased resource use efficiency amplifies positive response of aquatic primary production to experimental warming

Climate warming is affecting the structure and function of river ecosystems, including their role in transforming and transporting carbon (C), nitrogen (N), and phosphorus (P). Predicting how river ecosystems respond to warming has been hindered by a dearth of information about how otherwise well-studied physiological responses to temperature scale from organismal to ecosystem levels. We conducted an ecosystem-level temperature manipulation to quantify how coupling of stream ecosystem metabolism and nutrient uptake responded to a realistic warming scenario. A ~3.3°C increase in mean water temperature altered coupling of C, N, and P fluxes in ways inconsistent with single-species laboratory experiments. Net primary production tripled during the year of experimental warming, while whole-stream N and P uptake rates did not change, resulting in 289% and 281% increases in autotrophic dissolved inorganic N and P use efficiency (UE), respectively. Increased ecosystem production was a product of unexpectedly large increases in mass-specific net primary production and autotroph biomass, supported by (i) combined increases in resource availability (via N mineralization and N2 fixation) and (ii) elevated resource use efficiency, the latter associated with changes in community structure. These large changes in C and nutrient cycling could not have been predicted from the physiological effects of temperature alone. Our experiment provides clear ecosystem-level evidence that warming can shift the balance between C and nutrient cycling in rivers, demonstrating that warming will alter the important role of in-stream processes in C, N, and P transformations. Moreover, our results reveal a key role for nutrient supply and use efficiency in mediating responses of primary producers to climate warming.

Shifts in community size structure drive temperature invariance of secondary production in a stream-warming experiment

A central question at the interface of food-web and climate change research is how secondary production, or the formation of heterotroph biomass over time, will respond to rising temperatures. The metabolic theory of ecology (MTE) hypothesizes the temperature-invariance of secondary production, driven by matched and opposed forces that reduce biomass of heterotrophs while increasing their biomass turnover rate (production : biomass, or P:B) with warming. To test this prediction at the whole community level, we used a geothermal heat exchanger to experimentally warm a stream in southwest Iceland by 3.8°C for two years. We quantified invertebrate community biomass, production, and P : B in the experimental stream and a reference stream for one year prior to warming and two years during warming. As predicted, warming had a neutral effect on community production, but this result was not driven by opposing effects on community biomass and P:B. Instead, warming had a positive effect on both the biomass and production of larger-bodied, slower-growing taxa (e.g., larval black flies, dipteran predators, snails) and a negative effect on small-bodied taxa with relatively high growth rates (e.g., ostracods, larval chironomids). We attribute these divergent responses to differences in thermal preference between small- vs. large-bodied taxa. Although metabolic demand vs. resource supply must ultimately constrain community production, our results highlight the potential for idiosyncratic community responses to warming, driven by variation in thermal preference and body size within regional species pools.

Inadequate Design Management Compared with Unprecedented Technical Issues as Causes for Engineering Failure

This paper stems from research in the University of Alabama’s Department of Civil, Construction, and Environmental Engineering. Engineering design failures fall into two broad categories, those that occur because of a hitherto unknown or unprecedented technical cause, and those that occur because of a known cause that was overlooked during the design process. The latter can be considered a failure of design management, and the purpose of this paper is to compare and contrast inadequate design management to unprecedented technical issues as a cause for engineering failures. Failures that occur to improper maintenance or abuse are not the scope of this paper. Two approaches were taken, namely: (1) evaluation of current and historical engineering failures for instances of inadequate design management and/or unprecedented technical issues; and (2) review of filed claims data for design errors and omissions to determine whether inadequate design management is a substantial issue. This research may provide useful information in understanding how both categories limit the success of the design process.

Using Design-Based Change Orders as a Lessons Learned Metric in University Dormitory Construction

The enrollment at The University of Alabama has increased substantially in recent years and the University is expanding to meet the growing demands. The expansion includes four dormitory complexes built within the past 5 years. Change orders considerably influenced the final cost of the first and second dormitory projects and the University initiated the current study to follow-up on a global change order study that previously examined new construction on campus. The current study analyzed the reasons for the change and what Construction Specifications Institute (CSI) Division the change represented. While it was determined that the largest source of change orders on dormitory projects were owner initiated, these changes have not been targeted for reduction since they are at the discretion of the University and can be beneficial to the project. To gauge the performance of the change management program currently in place at the University, the direct impact on the total project cost due to changes resulting from design errors were analyzed for all four dormitory projects. The author hopes that the recommendations in this study will aid universities and colleges by providing a means to gather, track, and analyze changes that occur during the construction of dormitory projects and show how the lessons learned from the change orders during these projects can potentially reduce costs on future projects.

Calculating immobile gas saturations

We present a simple, fast, analytical expression which can be used to estimate the reservoir pressure as a function of gas saturation, for gas saturations between zero and the critical gas saturation. Use of the relation also makes it extremely easy to assess the local recovery factor as a function of pressure from the bubble point down to the pressure at which the critical gas saturation is reached.

Determination of transient drainage across lease boundaries

Abstract A technique which simplifies the determination of how much oil or gas flows across a linear segment during the transient flow period of the reservoir is presented. The technique is based on two definite integrals which result from application of the line-source solution of flow in an infinite-acting reservoir combined with the fundamental definition of flow across a plane. The theory, the outline of a methodology, and several examples are provided. The examples, one which determines the flow across a lease line for transient flow in an oil reservoir, one using the method for a bounded lease, and one using the method to assess the well spacing in a tight-gas reservoir, show that the technique can be applied to a variety of practical problems. Graphical solutions to the definite integrals are given to facilitate application of the method.