Sheep grazing effects on Mojave Desert vegetation and soils

Some effects of domestic sheep grazing on vegetation and soils were measured at four sites in the western Mojave Desert. Although sheep have grazed the Mojave Desert for the past 50–100 years, the effects of grazing on the desert ecosystem are largely unknown.The results reflect only short-term effects of grazing, because fenced control areas were not available for study. Heavy grazing caused a 60% reduction in the above-ground biomass under creosote bushes (Larrea tridentata), and sheep trampling caused an increase in soil strength and decreased intershrub annual densities 24 and 28% in two areas. The average area per individual (cover) of burrobush (Ambrosia dumosa) decreased 16–19% and the cover of spiny hop-sage (Grayia spinosa) decreased 29% under grazing pressure. The volumes of individual Ambrosia were 21 and 65% less in two heavily grazed areas than in two lightly grazed areas; the volume of goldenhead (Acamptopappus sphaerocephalus) was 68% less in one heavily grazed area.These changes indicate that the range quality of the Mojave Desert is deteriorating under sheep grazing pressures. Trampling reduces annual cover and disrupts the soil surface, thus promoting wind erosion. The loss of annual biomass and shrub cover should adversely affect reptiles and rodents by removing food sources and protection. Soil strength increases may retard future growth of annuals, further contributing to erosion and food source losses. Studies should be initiated to determine the long-term effects of grazing in the Mojave Desert.     

Driver-training and emergency brake performance in cars with antilock braking systems

The purpose of this study was to assess the effects of a two-day post-license driver-training program on brake performance in cars with antilock braking systems (ABS). A trainee group (n = 26) and a control group (n = 13) participated in the experiment. The trainee group were enrolled in a two-day training course that included instruction in a braking technique that may be used in cars with and without ABS. All participants performed emergency brake tests from 80 and 100 km h⁻¹ in an instrumented car before and after the training period. Results indicated the post-training group used a smoother braking profile, were less reliant on ABS activation, had enhanced postural stability, but took about one car length longer to stop from 100 km h⁻¹ compared with the control group. Implications of these results for braking in cars with and without ABS, and for driver education programs in general are discussed.     

“If you treat me right,I reciprocate”: examining the role of exchange in organizational survey response

Survey nonresponse can pose a major threat to the generalizability of organizational survey findings. This paper examines whether organizational members' evaluations of their organizational experiences affect survey response to organizationally sponsored surveys. In particular, we hypothesized that perceived organizational support, social exchange, procedural justice and an individual's inclination to feel exploited in social relationships predicted organizational members' compliance with organizations' requests for survey completion. A longitudinal field experiment conducted in collaboration with the Office of Institutional Research at a large university (sample: n = 622 university students) supported the hypotheses. Organizational members who consciously decided to not participate in organizational surveys perceived their organization as less procedurally just and less supportive. They also reported negative perceptions of their social exchange relationship with their organization, and were more inclined to feel exploited in relationships. Hence, an exchange‐oriented theoretical framework grounded in organizational citizenship behavior theory seems appropriate for the study of survey nonresponse. Implications for survey practice include that survey‐based findings are unlikely to generalize to specific groups of nonrespondents, and that techniques commonly used to increase response rates may not be effective in reaching these groups of nonrespondents. Copyright © 2006 John Wiley & Sons, Ltd.     

Modeling obsolete computer stock under regional data constraints: An Atlanta case study

In this paper, we report on our efforts to develop a research framework that can be used to quantify waste flows for different geographical areas in the face of limited waste data availability. We demonstrate this framework in our case study of obsolete computers in the Atlanta metropolitan area. We develop computer obsolescence rates at the national metropolitan level, and couple this data with economic information at the census tract level to generate product inventory estimates (PIE) of the stock of obsolete computers from both business and household sectors in the Atlanta metropolitan area. We seek to improve the accuracy of waste flow estimates for specific geographic areas over those of previous studies, provide an easily replicable and cost effective methodology, highlight the ensuing spatial implications for collection and recycling systems using GIS, and demonstrate the potential economic benefits from diverting electronic wastes within a region. The modeling framework we have developed is intended to be applicable to other regions and to other medium range durable goods discarded by households, businesses, or obtained from buildings.     

Stakeholder Willingness to Pay for Watershed Restoration in Rural Bolivia1

Abstract: Two CVM surveys were administered to 211 urban households and 188 rural farmer‐irrigators in the Comarapa watershed in Bolivia, South America, to estimate stakeholder willingness to pay (WTP) for a proposed upper watershed restoration program. Mean monthly household WTP to improve drinking water was $1.95 (65% of current charges), while mean annual WTP among farmer‐irrigators to improve irrigation water was $17 per hectare (34% of current costs). Aggregated to the entire population of households and farmer‐irrigators total WTP is $77,400 per year, which is 77% of the minimum cost to implement a watershed restoration program.     

A Proposed Aquatic Plant Community Biotic Index for Wisconsin Lakes

The Aquatic Macrophyte Community Index (AMCI) is a multipurpose tool developed to assess the biological quality of aquatic plant communities in lakes. It can be used to specifically analyze aquatic plant communities or as part of a multimetric system to assess overall lake quality for regulatory, planning, management, educational, or research purposes. The components of the index are maximum depth of plant growth; percentage of the littoral zone vegetated; Simpson's diversity index; the relative frequencies of submersed, sensitive, and exotic species; and taxa number. Each parameter was scaled based on data distributions from a statewide database, and scaled values were totaled for the AMCI value. AMCI values were grouped and tested by ecoregion and lake type (natural lakes and impoundments) to define quality on a regional basis. This analysis suggested that aquatic plant communities are divided into four groups: (1) Northern Lakes and Forests lakes and impoundments, (2) North-Central Hardwood Forests lakes and impoundments, (3) Southeastern Wisconsin Till Plains lakes, and (4) Southeastern Wisconsin Till Plains impoundments, Driftless Area Lakes, and Mississippi River Backwater lakes. AMCI values decline from group 1 to group 4 and reflect general water quality and human use trends in Wisconsin. The upper quartile of AMCI values in any region are the highest quality or benchmark plant communities. The interquartile range consists of normally impacted communities for the region and the lower quartile contains severely impacted or degraded plant communities. When AMCI values were applied to case studies, the values reflected known impacts to the lakes. However, quality criteria cannot be used uncritically, especially in lakes that initially have low nutrient levels.     

CALCIUM CARBONATE PRECIPITATION AND TURBIDITY MEASUREMENTS IN OTISCO LAKE,NEW YORK1

ABSTRACT: Calcium carbonate precipitate, known as “whiting,” forms in a large number of hard water lakes and reservoirs, and thus contributes to turbidity measurements in these systems. Here we document the occurrence of “whitings,” and the associated impact on turbidity, in Otisco Lake, New York. A simple, potentially broadly applicable, technique, measurement of turbidity before and after acidification, successfully quantified this component of turbidity in the lake. Calcium carbonate represented 32 percent of the turbidity in the upper waters of Otisco Lake for a three-month period, and at times was as much as 70 percent. Routine monitoring of this component of turbidity in raw water sources, where it is significant, should provide insight into water quality management and treatment plant operations.     

Physical characteristics of conditioned anaerobic digested sludge – A fractal, transient and dynamic rheological viewpoint

The changes in the physical characteristics of unconditioned and conditioned anaerobic digested sludge (ADS) biosolids, such as capillary suction time (CST), yield stress, average size and fractal dimensions, were investigated through a CST test, transient and dynamic rheological test and image analysis. The results showed that the optimum polymer dose range was observed when CST or its reciprocal value was employed as an indicator. There were good correlations between the yield stresses determined from both a controlled shear stress test and a strain amplitude sweep test. The yield stress and storage modulus (G′) increased as the polymer dose increased in most cases. A frequency sweep test revealed that polymer conditioning could extend the frequency sweep ranges for their elastic behaviors over viscous behaviors as well as the gel-like structure in the linear viscoelastic range. These results implied that more deformation energy was stored in this rigid structure, and that elastic behavior became increasingly dominant with the addition of the polymer in most cases. In addition, both the average sizes and two-dimensional fractal dimensions for conditioned ADS biosolids presented a similar up-climax-down variation trend as the polymer doses increased, whereas the critical polymer doses at the highest average sizes or two-dimensional fractal dimensions, were different. Correlation analysis revealed that the conditioned ADS dewaterability was not correlated with the yield stresses, while the average sizes or the two-dimensional fractal dimensions for conditioned ADS biosolids could be taken as the indication parameters for ADS dewaterability.