Modeling of Vertical Solute Dispersion in a Sediment Bed Enhanced by Wave‐Induced Interstitial Flow1

Abstract: Mass (solute) transport in a stream or lake sediment bed has a significant effect on chemical mass balances and microbial activities in the sediment. A “1D vertical dispersion model” is a useful tool to analyze or model solute transfer between river or lake water and a sediment bed. Under a motionless water column, solute transfer into and within the sediment bed is by molecular diffusion. However, surface waves or bed forms create periodic pressure waves along the sediment/water interface, which in turn induce flows in the pores of the sediment bed. The enhancement of solute transport by these interstitial periodic flows in the pores has been incorporated in a 1D depth‐dependent “enhanced dispersion coefficient (D_E).” Typically, D_E diminishes exponentially with depth in the sediment bed. Relationships have been developed to estimate D_E as a function of the characteristics of sediment (particle size, hydraulic conductivity, and porosity) and pressure waves (wave length and height). In this paper, we outline and illustrate the calculation of D_E as well as the penetration depth (d_p) of the flow effect. Sample applications to illustrate the computational procedure are provided for dissolved oxygen transfer into a stream gravel bed and release of phosphorus from a lake bed. The sensitivity of the results to input parameter values is illustrated, and compared with the errors obtained when interstitial flow is ignored. Maximum values of D_E near the sediment surface can be on the order of 1 cm²/s in a stream gravel bed with standing waves, and 0.001 cm²/s in a fine sand lake bed under progressive surface waves, much larger than molecular diffusion coefficients.     

Forecasting Resilience in Arctic Societies: Creating Tools for Assessing Social–Hydrological Systems1

Altaweel, Mark R., Lilian N. Alessa, and Andrew D. Kliskey, 2009. Forecasting Resilience in Arctic Societies: Creating Tools for Assessing Social–Hydrological Systems. Journal of the American Water Resources Association (JAWRA) 45(6):1379‐1389. Abstract: Arctic communities are increasingly faced with social–ecological changes that act at variable speeds and spatial scales. Such changes will affect vital resources, particularly water supplies. Currently, there are few computational tools that integrate multiple social and environmental processes in order to aid communities’ adaptation to change through decision support systems. This paper proposes a modeling and simulation approach that can integrate such processes at different spatiotemporal scales in order to address issues affecting community water supplies. In this paper, a modeling and simulation tool is developed and applied to a case study on the Seward Peninsula. Initial results, using both field observations and computation, show projected patterns of water use, perceptions of water availability, and long‐term consumption trends. More broadly, the paper demonstrates the need for developing tools that address issues at the community level for better understanding human and hydrological interactions and policy decisions affecting water supplies.     

“Safety is everyone's job:” The key to safety on a large university construction site

Problem

Construction risk management is challenging.

Method

We combined data on injuries, costs, and hours worked, obtained through a Rolling Owner-Controlled Insurance Program (ROCIP), with data from focus groups, interviews, and field observations, to prospectively study injuries and hazard control on a large university construction project.

Results

Lost-time injury rates (1.0/200,000 hours worked) were considerably lower than reported for the industry, and there were no serious falls from height. Safety was considered in the awarding of contracts and project timeline development; hazard management was iterative. A top-down management commitment to safety was clearly communicated to, and embraced by, workers throughout the site.

Discussion and Impact

A better understanding of how contracting relationships, workers' compensation, and liability insurance arrangements influence safety could shift risk management efforts from worker behaviors to a broader focus on how these programs and relationships affect incentives and disincentives for workplace safety and health.     

A comparison of web-based and telephone surveys for assessing traffic safety concerns, beliefs, and behaviors

Introduction

The purpose of this investigation was to compare the results of a web-based and a telephone interview survey measuring driver concerns about a variety of traffic safety issues, their beliefs, and specific driving behaviors.

Method

State-wide, annual random digit-dial telephone surveys and web-based surveys were conducted in Maryland. A total of 1,700 drivers were surveyed by telephone and 6,806 took a web survey.

Results

Telephone respondents were more likely to be female and older. Web respondents were more likely to be white and not Latino/Hispanic. After controlling for demographic differences, telephone survey respondents were more likely to be concerned about traffic safety. They were more likely to believe that sobriety checkpoints reduce drunk driving (OR = 2.18, 95% CI 1.94, 2.45), they would be ticketed for not wearing a seat belt (OR = 1.26, 95% CI 1.12, 1.43), and they would be stopped by the police if they drove after drinking too much (OR = 1.17, 95% CI 1.03, 1.32). They were less likely to report a variety of risky behaviors including using a cell phone while driving (OR = .54, 95% CI .48, .61) and driving 10+ mph over the speed limit (OR = .81, 95% CI .72, .91), but were more likely to report having been ticketed for a moving violation in the last month (OR = 2.22, 95% CI 1.70, 2.90). Suggestions are offered for overcoming potential sources of sampling bias.

Impact on Industry

Web-based surveys produce substantially different results than random-digit-dial telephone surveys, when used for public assessments of traffic safety concerns and behaviors.     

Translocal anti-fracking activism: an exploration of network structure and tie content

ABSTRACT

In order to develop conceptual models that reflect the realities of networked communicative processes scholars must examine both the underlying network structure and the content of these ties. Using mixed methods, I apply a relational perspective to the role of digital technologies in transnational organizing, using activism against high-volume hydraulic fracturing as a case study. In-depth interviews are combined with social network analysis of hyper-linkages between organizations supporting a day of action calling for a ban on fracking, Global Frackdown. Analysis shows that activism against unconventional fossil fuels brings together very localized concerns about environmental risks associated with extractive industries with more abstract global concerns. I apply the concept of translocal to examine environmental organizations and movements. This conceptual shift focuses on the brokerage role of global-minded local groups in mediating global issues back to the hyper-local scale. While international NGOs play a coordinating role, local groups with a global worldview can connect transnational movements to the hyper-local scale by networking with groups that are too small to appear in a transnational network.     

Assessment of phenylurea herbicides sorption on various Mediterranean soils affected by irrigation with wastewater

The retention values of two herbicides, chlorotoluron and isoproturon, in five Mediterranean soils were assessed by two different approaches, a dynamic method, using a batch technique (BT) and a static method, using a soil saturated paste (SP). The SP method led in all cases to lower herbicide sorption when compared with BT, although pesticide distribution constants from both methods were linearly related for the set of used soils (R² ? 0.99) showing that both methods similarly reflected the behaviour of the different soils. Low-quality water, evaluated by employing recycled urban wastewater, did not modify herbicide sorption when compared with high quality water, in any soil and with any method.     

饮用水中苯系物的检测方法研究概况

苯系物通常包括苯,甲苯,乙苯,邻、间、对二甲苯,异丙苯和苯乙烯等化合物,它们是重要的化工原料,可以通过各种途径污染饮用水进而严重威胁人类健康。通过对近十几年来国内饮用水中苯系物检测方法地综述及这些方法优缺点地比较,为进一步研究提供有益的参考,并对饮用水中苯系物检测方法的发展趋势进行了展望。     

When are historical data sufficient for making watershed-level stream fish management and conservation decisions?

Addressing landscape-level threats to stream fishes such as habitat and hydrological alterations requires adequate watershed-level species inventories. Where watershed-level ichthyofaunal surveys are prohibitively expensive, existing (historical) data sources may provide an option for compiling species lists. However, it is critical that managers consider potential biases or limitations of species lists compiled from existing data. Here we assess the suitability of species lists compiled from existing data sources for making watershed-level fish management and conservation decisions. For nine Great Lakes watersheds, we developed existing species lists by compiling all available federal and state agency and museum fish survey data. We then compared the size and species composition of existing species lists to current species lists compiled from intensive field surveys, conducted in 2002, of the same watersheds. Species lists compiled from commonly available existing data sources, such as state and federal agency and museum data, missed many species detected during our 2002 field surveys. In most watersheds, more than 10 species were missed (range 5–21) on existing lists. Sampling over multiple years and seasons increased the size of both current (field) and existing species lists. Existing species lists compiled from surveys conducted over multiple years and seasons included an average of 15 species not captured during the 2002 field surveys. However, such multiyear existing datasets are rare and not available for many watersheds. In addition, species lists compiled from older existing surveys (e.g., before 1984) did not accurately represent current species composition of the watersheds and our results indicate several apparent misidentifications or errors on these lists. Lastly, while most game species were detected on existing lists, migratory species and recently introduced species were commonly missed on these lists. We conclude with recommendations for using existing data for watershed-level stream fish management and conservation decisions.     

Book Reviews

Books reviewed: John Twigg and Mihir R. Bhatt, eds, Understanding Vulnerability Joachim von Braun, Tesfaye Teklu and Patrick Webb, Famine in Africa: Causes, Responses, and Prevention C. Emdad Haque, Hazrads in a Fickle Environment: Bangladesh Walter Gillis Peacock, Betty Hearn Morrow and Hugh Gladwin, eds, Population and Food: Global Trends and Future Prospects Roy Gutman and David Rieff, eds, Crimes of War: What the Public Should Know     

An overview of systems analysis methods in delineating environmental quality indices

Environmental quality indices (EQIs) have been developed for a variety of purposes ranging from enforcement of environmental standards, to analysis of trends of environmental degradation or improvement, to scientific research. EQIs currently in use are not organized within an integrated framework and thus it has been difficult to analyze adequately complex, multidisciplinary, large-scale, global phenomena. In this paper we compare four different approaches to developing EQIs within a systems perspective. Our analysis suggests that: (1) non-linear regression models that represent an ecosystem's response to different impacts within a stress-response framework (method of response functions) are useful tools for analysis of environmental data; (2) non-equilibrium thermodynamics models based on the concept of exergy, which represents the free energy a system possesses in relation to its environment, provide a common basis for representing many aspects of ecosystem development and response to environmental impacts as a single measure; (3) diagram models based on the concept of emergy, which represents both environmental values and economic values with a single measure, provide a common basis for integrating economic development and environmental protection values into one index; and (4) complex systems simulation models based on general systems theory, which use the methodologies of systems analysis and simulation to identify, quantify, and interrelate EQIs within a dynamic systems context, provide explicit linkages between causes and effects (vertical integration) and identify cross-linkages among different environmental issues (horizontal integration).