MODELING ACID MINE DRAINAGE ON A WATERSHED SCALE FOR TMDL CALCULATIONS1

ABSTRACT: The Cheat River of West Virginia is impaired by acid mine drainage (AMD). Fifty‐five of its river segments were placed on the 303(d) list, which required calculations of total maximum daily load (TMDL) to meet the water quality criteria for pH, total iron, aluminum, manganese, and zinc. An existing watershed model was enhanced to simulate AMD as nonpoint source load. The model divided a watershed into a network of catchments and river segments. Each catchment was divided into soil layers, which could contain pyrite, calcite and other minerals. A kinetic expression was used to simulate pyrite oxidation as a function of oxygen in the soil voids. Oxygen in the soil voids was consumed by pyrite oxidation and replenished by earth breathing. The by‐products of pyrite oxidation were calculated according to its mass action equations. Chemical equilibrium was used to account for the speciation of ferrous and ferric irons and precipitation of metal hydroxides. Simulated hydrology and water quality were compared to available data. The USEPA used the calibrated model to calculate the TMDLs in the Cheat River Watershed.     

Computational modeling and analysis of thoracolumbar spine fractures in frontal crash reconstruction

Abstract

Objective: This study aimed to reconstruct 11 motor vehicle crashes (6 with thoracolumbar fractures and 5 without thoracolumbar fractures) and analyze the fracture mechanism, fracture predictors, and associated parameters affecting thoracolumbar spine response.

Methods: Eleven frontal crashes were reconstructed with a finite element simplified vehicle model (SVM). The SVM was tuned to each case vehicle and the Total HUman Model for Safety (THUMS) Ver. 4.01 was scaled and positioned in a baseline configuration to mimic the documented precrash driver posture. The event data recorder crash pulse was applied as a boundary condition. For the 6 thoracolumbar fracture cases, 120 simulations to quantify uncertainty and response variation were performed using a Latin hypercube design of experiments (DOE) to vary seat track position, seatback angle, steering column angle, steering column position, and D-ring height. Vertebral loads and bending moments were analyzed, and lumbar spine indices (unadjusted and age-adjusted) were developed to quantify the combined loading effect. Maximum principal strain and stress data were collected in the vertebral cortical and trabecular bone. DOE data were fit to regression models to examine occupant positioning and thoracolumbar response correlations.

Results: Of the 11 cases, both the vertebral compression force and bending moment progressively increased from superior to inferior vertebrae. Two thoracic spine fracture cases had higher average compression force and bending moment across all thoracic vertebral levels, compared to 9 cases without thoracic spine fractures (force: 1,200.6 vs. 640.8 N; moment: 13.7 vs. 9.2?Nm). Though there was no apparent difference in bending moment at the L1–L2 vertebrae, lumbar fracture cases exhibited higher vertebral bending moments in L3–L4 (fracture/nonfracture: 45.7 vs. 33.8?Nm). The unadjusted lumbar spine index correctly predicted thoracolumbar fracture occurrence for 9 of the 11 cases (sensitivity?=?1.0; specificity?=?0.6). The age-adjusted lumbar spine index correctly predicted thoracolumbar fracture occurrence for 10 of the 11 cases (sensitivity?=?1.0; specificity?=?0.8). The age-adjusted principal stress in the trabecular bone was an excellent indicator of fracture occurrence (sensitivity?=?1.0; specificity?=?1.0). A rearward seat track position and reclined seatback increased the thoracic spine bending moment by 111–329%. A more reclined seatback increased the lumbar force and bending moment by 16–165% and 67–172%, respectively.

Conclusions: This study provided a computational framework for assessing thoracolumbar fractures and also quantified the effect of precrash driver posture on thoracolumbar response. Results aid in the evaluation of motor vehicle crash–induced vertebral fractures and the understanding of factors contributing to fracture risk.     

Improvements in Fluvial Stability Associated with Two‐Stage Ditch Construction in Mower County,Minnesota

Water quality and stream habitat in agricultural watersheds are under greater scrutiny as hydrologic pathways are altered to increase crop production. Agricultural drainage ditches function to remove water quickly from farmed landscapes. Conventional ditch designs lack the form and function of natural stream systems and tend to be unstable and provide inadequate habitat. In October of 2009, 1.89 km of a conventional drainage ditch in Mower County, Minnesota, was converted to an alternative system with a two‐stage channel to investigate the improvements in water quality, stability, and habitat. Longitudinal surveys show a 12‐fold increase in the pool‐riffle formation. Cross‐sectional surveys show an average increase in bankfull width of approximately 10% and may be associated to an increased frequency in large storm events. The average increase in bankfull depth was estimated as 18% but is largely influenced by pool formation. Rosgen Stability Analyses show the channel to be highly stable and the banks at a low risk of erosion. The average bankfull recurrence interval was estimated to be approximately 0.30 years. Overall, the two‐stage ditch design demonstrates an increase in fluvial stability, creating a more consistent sediment budget, and increasing the frequency of important instream habitat features, making this best management practice a viable option for addressing issues of erosion, sediment imbalance, and poor habitat in agricultural drainage systems.     

About bridges and bonds: community responses to the 2000 floods in Mabalane district, Mozambique

Massive floods hit Mozambique in 2000.1 Many of the affected regions benefited from external aid. This paper investigates how the floods impacted on two communities in the interior of the Limpopo Valley, which did not receive significant assistance during the event and in the immediate aftermath. Drawing on the livelihood approach, it focuses on the role of two types of local resources: knowledge and social capital. The paper shows that the scale of the 2000 floods surpassed the response capacity of these resources and looks at how wealth and gender influenced access by households to the local support mechanisms that enhance survival and recovery. It appears that the floods mainly affected wealthier households, as these more frequently lost houses and cattle. The paper points to the importance of ploughs and cattle for local support mechanisms, which, in turn, most likely reduced the capacities of communities to recover from the disaster.     

Impacts of weathered tire debris on the development of Rana sylvatica larvae

Highway runoff has the potential to negatively impact receiving systems including stormwater retention ponds where highway particulate matter can accumulate following runoff events. Tire wear particles, which contain about 1% Zn by mass, make up approximately one-third of the vehicle derived particulates in highway runoff and therefore may serve as a stressor to organisms utilizing retention ponds as habitat. In this study, we focused on the potential contribution of tire debris to Zn accumulation by Rana sylvatica larvae and possible lethal or sublethal impacts resulting from exposure to weathered tire debris during development. Eggs and larvae were exposed to aged sediments (containing either ZnCl2 or tire particulate matter, both providing nominal concentrations of 1000 mg Zn kg(-1)) through metamorphosis. Water column Zn was elevated in both the ZnCl2 and tire treatments relative to the control treatment, indicating that aging allowed Zn leaching from tire debris to occur. Tissue Zn was also elevated for the ZnCl2 and tire treatments indicating that Zn in the treatments was available for uptake by the amphibians. Exposure to both ZnCl2 and tire treatments increased the time for larvae to complete metamorphosis in comparison with controls. We also observed that the longer the organisms took to complete metamorphosis, the smaller their mass at metamorphosis. Our results indicate that Zn leached from aged tire debris is bioavailable to developing R. sylvatica larvae and that exposure to tire debris amended sediments can result in measurable physiological outcomes to wood frogs that may influence population dynamics.     

Biodegradation of mono-alkyl phthalate esters in natural sediments

Mono-alkyl phthalate esters (MPEs) are primary metabolites of di-alkyl phthalate esters (DPEs), a family of industrial chemicals widely used in the production of soft polyvinyl chloride and a large range of other products. To better understand the long term fate of DPEs in the environment, we measured the biodegradation kinetics of eight MPEs (-ethyl, -n-butyl, -benzyl, -i-hexyl, -2-ethyl-hexyl, -n-octyl, -i-nonyl, and -i-decyl monoesters) in marine and freshwater sediments collected from three locations in the Greater Vancouver area. After a lag period in which no apparent biodegradation occurred, all MPEs tested showed degradation rates in both marine and freshwater sediments at 22 °C with half-lives ranging between 16 and 39 h. Half-lives increased approximately 8-fold in incubations performed at 5 °C. Biodegradation rates did not differ between marine and freshwater sediments. Half-lives did not show a relationship with increasing alkyl chain length. We conclude that MPEs can be quickly degraded in natural sediments and that the similarity in MPE degradation kinetics among sediment types suggests a wide occurrence of nonspecific esterases in microorganisms from various locations, as has been reported previously.     

Fate of Bacillus thuringiensis (Bt) Cry3Bb1 protein in a soil microcosm

Transgenic crops expressing insecticidal, crystalline (Cry) Bacillus thuringiensis (Bt) proteins were commercialized in the US in 1996. There is little information in the peer-reviewed literature on the environmental fate of the coleopteran-active Bt Cry3Bb1 protein expressed in event MON863 corn. The exposure characterization of Bt proteins is unique in that the fate of the protein in soil and in crop residue must be considered. To date, the significance of macrodecomposing organisms, such as earthworms, isopods, and springtails, to the dissipation of Bt proteins present in crop residue has not been assessed. In addition, the input of Bt proteins into soil through leaching from post-harvest crop residue has not been examined. Two laboratory microcosm studies were conducted to determine the fate of Bt Cry3Bb1 in decomposing MON863 corn residue and to determine whether Bt proteins can enter soil by leaching from crop residue. In addition, the importance of macrodecomposing organisms to the degradation of Bt proteins in corn residue was assessed. Laboratory microcosms containing MON863 corn leaf, root, and stalk with and without macrodecomposers were used to examine the fate of Bt Cry3Bb1 in post-harvest MON863 corn residue. A half-life of less than five days was found for Bt Cry3Bb1 protein in decomposing MON863 corn residue. There was a trend of increasing half-life of Cry3Bb1 in microcosms containing macrodecomposers, however, this trend was only significant (p<0.05) for Bt Cry3Bb1 in MON863 leaf tissue and this increase is not likely relevant for non-target exposure. The recovery of Bt Cry3Bb1 protein from soil extracts was either below the limit of quantification (9 ng g(-1) soil) or below the limit of detection (0.7 ng mL(-1)) at all time points during the study. Based on the results from this study, Bt protein leaching from post-harvest crop residue is not a significant contributor to Bt protein input into soil.     

Alfalfa nutritive quality for ruminant livestock as influenced by ambient air quality in west-central Alberta

Alfalfa (Medicago sativa) nutritive quality response to ambient ozone (O(3)), sulfur dioxide (SO(2)) and oxides of nitrogen (NO(x)) were assessed at three locations in west-central Alberta, Canada (1998-2002). Yield data were segregated into high and low relative to overall median yield. Ozone concentrations (hourly median and 95th-percentile) and precipitation (P) contributed 69 and 29%, respectively, to the variability in crude protein (CP) concentration in low-yielding alfalfa, whereas mean temperature (T) and relative humidity (RH) collectively influenced 98% of the variation in CP in high-yielding alfalfa. Three-fourths of the accounted variation in relative feed value (RFV) of low-yielding alfalfa was attributable to P, T and RH, whereas median and 95th-percentile hourly O(3) concentrations and SO(2) and NO(x) exposure integrals contributed 25%. In contrast, air quality, (mainly O(3)) influenced 86% of the accounted variation in RFV of high-yielding alfalfa, and T and P collectively contributed 14%.     

Management commitment to safety as organizational support: relationships with non-safety outcomes in wood manufacturing employees

INTRODUCTION: Employee perceptions of management commitment to safety are known to influence important safety-related outcomes. However, little work has been conducted to explore non-safety-related outcomes resulting from a commitment to safety. METHOD: Employee-level outcomes critical to the effective functioning of an organization, including attitudes such as job satisfaction and commitment to the organization, were included on surveys given to 641 hourly production employees at three wood products manufacturing facilities. Participants' were asked about perceptions of management commitment to safety and job-related variables such as perceived dangerousness of their position, organizational commitment, and withdrawal behaviors. Supervisors also rated the performance of each of their hourly subordinates. RESULTS: Results suggest that employee outcomes differ based on perceptions of management's commitment to safety. Specifically, management commitment to safety was positively related to job satisfaction, organizational commitment, and job-related performance. We also found a negative relationship between commitment to safety and employee withdrawal behaviors. CONCLUSIONS: Our results suggest that increasing employee perceptions of management's personal concern for employee well-being through a dedication to safety will result in positive outcomes beyond improved safety performance. These results also imply that there is a type of social exchange between employees and management that may affect employees similarly to perceived organizational support. IMPACT ON INDUSTRY: Results further reinforce the value of a commitment to safety by a firm's management. Organizations with a strong commitment to safety may enjoy not only a reduction in safety-related events but also increases in desirable employee attitudes and behaviors.     

Young people driving after drinking and riding with drinking drivers: drinking locations--what do they tell us?

OBJECTIVE: The present study investigated the extent to which drinking in specific locations and heavy drinking mediated the effects of overall alcohol use on driving after drinking (DD) and riding with drinking drivers (RWDD) among young people. Additionally, this study examined the relationships among ethnicity, gender, drinking in specific locations, and DD and RWDD. METHOD: Using random-digit dialing procedures, participants were recruited to take part in a telephone survey in California, United States of America. Participants were 1,534 youth, ages 15-20 years (mean age = 17.6). Latinos, African Americans, and Asian Americans were over-sampled to allow cross-group comparisons. Along with background characteristics, overall alcohol use, heavy drinking, drinking in specific locations, DD, and RWDD were measured. RESULTS: Latent variable structural equation modeling showed that European Americans, males, older adolescents, those who have a driver license, and those who drive more often were more likely to report drinking alcohol in the past year. Heavy episodic drinking and drinking in cars increased both DD and RWDD. Drinking in restaurants also increased DD. The effects of overall alcohol consumption on DD were entirely mediated through heavy episodic drinking and drinking in restaurants and cars. Alcohol consumption had both direct and indirect effects on RWDD. With the exception of being Latino and frequency of driving, the effects of the background variables on RWDD were all entirely mediated through alcohol consumption. CONCLUSIONS: Heavy drinking and drinking in specific locations appeared to be important unique predictors of both DD and RWDD. In light of the relationship between drinking in restaurants and in cars, and DD, prevention programs and policies aimed at underage drinking should focus on developing more effective responsible beverage service programs, increasing compliance with laws limiting alcohol sales to youth, and enforcing graduated driver licensing and zero tolerance laws.