Three-dimensional analysis of coherent turbulent flow structure around a single circular bridge pier

The coherent turbulent flow around a single circular bridge pier and its effects on the bed scouring pattern is investigated in this study. The coherent turbulent flow and associated shear stresses play a major role in sediment entrainment from the bed particularly around a bridge pier where complex vortex structures exist. The conventional two-dimensional quadrant analysis of the bursting process is unable to define sediment entrainment, particularly where fully three-dimensional flow structures exist. In this paper, three-dimensional octant analysis was used to improve understanding of the role of bursting events in the process of particle entrainment. In this study, the three-dimensional velocity of flow was measured at 102 points near the bed of an open channel using an Acoustic Doppler Velocity meter (Micro-ADV). The pattern of bed scouring was measured during the experiment. The velocity data were analysed using the Markov process to investigate the sequential occurrence of bursting events and to determine the transition probability of the bursting events. The results showed that external sweep and internal ejection events were an effective mechanism for sediment entrainment around a single circular bridge pier. The results are useful in understanding scour patterns around bridge piers.     

Bioreduction of nitrate in groundwater using a pilot-scale hydrogen-based membrane biofilm reactor

A long-term pilot-scale H₂-based membrane biofilm reactor (MBfR) was tested for removal of nitrate from actual groundwater. A key feature of this second-generation pilot MBfR is that it employed lower cost polyester hollow fibers and still achieved high loading rate. The steady-state maximum nitrate surface loading at which the effluent nitrate and nitrite concentrations were below the Maximum Contaminant Level (MCL) was at least 5.9 g·N·(m²·d)^?1, which corresponds to a maximum volumetric loading of at least 7.7 kg·N·(m³·d) ^?1. The steady-state maximum nitrate surface area loading was higher than the highest nitrate surface loading reported in the first-generation MBfRs using composite fibers (2.6 g·N·(m²·d)^?1). This work also evaluated the H₂-utilization efficiency in MBfR. The measured H₂ supply rate was only slightly higher than the stoichiometric H₂-utilization rate. Thus, H₂ utilization was controlled by diffusion and was close to 100% efficiency, as long as biofilm accumulated on the polyester-fiber surface and the fibers had no leaks.     

Recovery of Sediment Characteristics in Moraine,Headwater Streams of Northern Minnesota After Forest Harvest1

Merten, Eric C., Nathaniel A. Hemstad, Randall K. Kolka, Raymond M. Newman, Elon S. Verry, and Bruce Vondracek, 2010. Recovery of Sediment Characteristics in Moraine, Headwater Streams of Northern Minnesota After Forest Harvest. Journal of the American Water Resources Association (JAWRA) 46(4): 733-743. DOI: 10.1111/j.1752-1688.2010.00445.x Abstract: We investigated the recovery of sediment characteristics in four moraine, headwater streams in north-central Minnesota after forest harvest. We examined changes in fine sediment levels from 1997 (preharvest) to 2007 (10 years postharvest) at study plots with upland clear felling and riparian thinning, using canopy cover, proportion of unstable banks, surficial fine substrates, residual pool depth, and streambed depth of refusal as response variables. Basin-scale year effects were significant (p < 0.001) for all responses when evaluated by repeated-measures ANOVAs. Throughout the study area, unstable banks increased for several years postharvest, coinciding with an increase in windthrow and fine sediment. Increased unstable banks may have been caused by forest harvest equipment, increased windthrow and exposure of rootwads, or increased discharge and bank scour. Fine sediment in the channels did not recover by summer 2007, even though canopy cover and unstable banks had returned to 1997 levels. After several storm events in fall 2007, 10 years after the initial sediment input, fine sediment was flushed from the channels and returned to 1997 levels. Although our study design did not discern the source of the initial sediment inputs (e.g., forest harvest, road crossings, other natural causes), we have shown that moraine, headwater streams can require an extended period (up to 10 years) and enabling event (e.g., high storm flows) to recover from large inputs of fine sediment.     

Full‐scale in‐situ biobarrier demonstration for containment and treatment of MTBE

The Naval Facilities Engineering Service Center (NFESC), Arizona State University, and Equilon Enterprises LLC are partners in an innovative Environmental Security Technology Certification Program cleanup technology demonstration designed to contain dissolved MTBE groundwater plumes. This full‐scale demonstration is being performed to test the use of an oxygenated biobarrier at Naval Base Ventura County, in Port Hueneme, California. Surprisingly, few cost‐effective in‐situ remedies are known for the cleanup of MTBE‐impacted aquifers, and remediation by engineered in‐situ biodegradation was thought to be an unlikely candidate just a few years ago. This project demonstrates that MTBE‐impacted groundwater can be remediated in‐situ through engineered aerobic biodegradation under natural‐flow conditions. With respect to economics, the installation and operation costs associated with this innovative biobarrier system are at least 50 percent lower than those of a conventional pump and treat system. Furthermore, although it has been suggested that aerobic MTBE biodegradation will not occur in mixed MTBE‐BTEX dissolved plumes, this project demonstrates otherwise. The biobarrier system discussed in this article is the largest of its kind ever implemented, spanning a dissolved MTBE plume that is over 500 feet wide. This biobarrier system has achieved an in‐situ treatment efficiency of greater than 99.9 percent for dissolved MTBE and BTEX concentrations. Perhaps of greater importance is the fact that extensive performance data has been collected, which is being used to generate best‐practice design and cost information for this biobarrier technology. © 2001 John Wiley & Sons, Inc.     

Change in zooxanthellae and mucocyte tissue density as an adaptive response to environmental stress by the coral, <Emphasis Type="Italic">Montastraea annularis</Emphasis>

Results from controlled in situ experimentation conducted on the leeward reef tract of Curaçao, Netherlands Antilles, indicate that the coral Montastraea annularis exhibits a complex, yet consistent, cellular response to increasing sea surface temperature (SST) and decreasing irradiance. This was determined by simultaneously quantifying and tracking the tissue density of zooxanthellae and mucocytes using a novel technique that integrates the lectin histochemical stain wheat germ agglutinin (WGA) with high-resolution (200 nm) optical epifluorescence microscopy. Coral colonies growing at 6-m water depth (WD) and an irradiance of 100.2 ± 6.5 μmol m^?2 s^?1 were treated with a shading experiment for 11 days that reduced irradiance to 34.9 ± 6.6, 72.0 ± 7.0 and 90.1 ± 4.2 μmol m^?2 s^?1, respectively. While a significant decrease in the density of both zooxanthellae and mucocytes were observed at all shade levels, the largest reduction occurred between the natural non-shaded control (44,298 ± 3,242 zooxanthellae cm^?2; 4,853 ± 346 mucocytes cm^?2) and the highest shading level (13,982 ± 1,961 zooxanthallae cm^?2; 2,544 ± 372.9 mucocytes cm^?2). Colonies were also sampled during a seasonal increase in SST of 1.5°C, where the density of zooxanthellae was significantly lower (from 54,710 ± 1,755 to 34,322 ± 2,894 cells cm^?2) and the density of mucocytes was significantly higher (from 6,100 ± 304 to 29,658 ± 3,937 cells cm^?2). These observations of coral cellular response to environmental change provide evidence to support new hypotheses for coral survival and the complex role played by mucus in feeding, microbial associations and resilience to increasing SST.     

Post-Perturbation Genetic Changes in Populations of Endangered Virgin River Chubs

A 34-kilometer reach of the Virgin River, Utah-Arizona-Nevada, was poisoned with rotenone in an attempt to eradicate non-native red shiners ( Cyprinella lutrensis ), a species implicated in the decline of native fish populations in the American West. An error in detoxification resulted in lethal concentrations of piscicide passing through an additional 50 kilometers of stream. We used allozyme electrophoresis to analyze genetic variation among pre- and post-poison samples of endangered Virgin River chubs ( Gila seminuda ). Pre-poison samples indicated a single panmictic population in the river. In contrast, fish subsequently produced through natural recruitment in poisoned reaches exhibited deviations from the original pattern of genetic variation. A genetic bottleneck caused by severe reduction in the number of spawning adults was indicated. The altered pattern persisted 2.5 years post-poisoning, indicating unexpectedly slow recolonization from the unpoisoned reach upstream. Genetic variation among hatchery-produced young was similarly unrepresentative of the original pattern because of the small number of brood fish used in propagation. Because of their small numbers and/or restricted distribution, endangered species are particularly vulnerable to natural or anthropogenic catastrophes. Assessment of the genetic impact of such events is essential but requires that baseline data are available.     

Evaluating Causes of Population Change in North American Insectivorous Songbirds

Although the North American Breeding Bird Survey (BBS) is a principal source of information regarding populations of most North American bird species, many features of the survey complicate analysis of population change. Correlation studies based on BBS data cannot be used to define cause and effect relationships unambiguously. Recently, Böhning-Gaese et al. (1993) presented an analysis of population trends in insectivorous songbirds using data from the BBS. They concluded that predation has played an important role in influencing population trends. We review aspects of the analysis methods for estimating population trends (e.g., observer effects, data subset) and for associating mean trends with species attributes (e.g., confounding of attributes). Using alternative analyses of the same BBS data, we demonstrate that the evidence that predation is associated with population declines is weaker than they suggested. Based on our analyses the only factor among those tested that was consistently associated with population trends was migration status (short-distance migrant/resident versus long-distance migrant) during the period 1978–1987. Also, we present evidence that the harsh winters of the mid-1970s severely depressed populations of short-distance migrant species and may have been responsible for the observed associations between migration status and population trends.     

A Framework for Understanding and Improving Environmental Decision Making

This paper presents a framework for understanding and improving public sector environmental decision making. Within the framework, four interrelated components are discussed: (1) the environmental and cultural context-understanding this context includes understanding what people consider to be environmental problems, the goals and values that they bring to environmental problems and decision processes, specialized and common knowledge about environmental problems, and the institutional settings within which problems are addressed; (2) planning and appraisal activitiesthese activities include forecasting and monitoring exercises, evaluations of past decisions, and decisions that processes ought to be launched to solve specific environmental problems; (3) decision-making modes-these include six typical ways of conducting an environmental problem-solving process, modes which, in the framework, are called emergency action, routine procedures, analysis-centred, elite corps, conflict management and collaborative learning; (4) decision actions-these include five generic steps that are undertaken, formally or intuitively, in virtually any decision-making situation: issue familiarization; criteria setting; option construction; option assessment; and reaching a decision. In the course of describing the framework, we show a decision-making process can be adapted to incorporate sustainability concerns, including fostering sustainable environmental and social systems, meeting obligations to future generations, and searching for robust and reasonable (rather than rigidly optimal) decisions. The framework also helps to illuminate intriguing questions regarding institutional responsibility, decision process complexity and paradigms for environmental decision making.