Environmental management of the Colorado River within the Grand Canyon

Irreversible environmental changes are occurring along the Colorado River in the Grand Canyon as a result of regulation of the river flow by the Glen Canyon Dam. The questions of primary importance in managing this great natural resource are 1) in what manner and how rapidly are the physical and ecological adjustments taking place, and 2) is the increased use of the river for recreational boating contributing to the degradation? Human use along the Colorado River is limited, for the most part, to the relic, pre-dam fluvial deposits colloquially called “beaches.” With the new river regime these deposits are positioned well above the present high-water stage, 27,000 cubic feet/second (cfs), or 765 cubic meters/second (cms), so they are not replenished periodically as they were prior to construction of the dam in 1963. The dominant natural processes now are aeolian sand transport and mass wasting. The float-trip passengers use the river beaches for hiking, camping, and. lunch stops. At the most desirable sites thirty to forty people camp on the beaches each night over a four to five month season. Human impact includes incorporation of campsite litter, burial of chemically treated waste, and the direct stress associated with people walking on the vegetation and unstable sedimentary deposits. Results of our investigations indicate that the rate of degradation at the most heavily used sites exceeds the capacity of aeolian processes to reestablish natural landscapes. Therefore, careful management of float trjps is needed if these environments are to be maintained in a natural state rather than a “sand-box” state.     

Recreational impacts on Colorado River beaches in Glen Canyon,Arizona

Recreational impact was measured on eight beaches in Glen Canyon National Recreation Area and 15 beaches in Grand Canyon National Park using permanently located transects and plots. Recreational impact indices included densities of human trash and charcoal and a measure of sand discoloration due to charcoal. Significant increases in the indices occurred on several Glen Canyon beaches over a seven-month period. Sand discoloration became significantly higher over all Glen Canyon beaches during the same time period. All indices were significantly higher in Glen Canyon than on similar Grand Canyon beaches. These differences are probably due to differences in: (a) level of impacts tolerated by the respective management regimes and, (b) in the number of user days among the two National Park Service administrative units. Management alternatives are presented for reversing the present trends of recreational impact on Glen Canyon beaches.     

Vegetation changes associated with barrier-dune construction on the outer banks of North Carolina

Manmade dunes are used to stabilize the barrier islands of the mid-Atlantic coast of the United States so that they are more amenable to development. Although this strategy has stabilized extensive sections of the barrier-island substrate, it has also caused significant ecological changes. The rate and pattern of the resulting vegetation changes along the Outer Banks of North Carolina were determined using sequential aerial photography. Successional trends have been altered in favor of more stable woody communities.     

Footstep-induced sediment displacement in the Grand Canyon

The Glen Canyon Dam has severely altered the riparian zone of the Colorado River in the Grand Canyon. One result of the controlled river discharge is more efficient prediction of water stages at the major rapids, leading to higher visitor use. Increased visitation results in heavy foot traffic, trampling along the river banks, erosion of the campsite soils, and the destruction of vegetation. Erosion occurs when the surfaces are roughened, exposing them to wind transport and runoff. In addition, each footstep physically displaces sand downhill.The results of a field experiment designed to measure the amount of sand displaced by footsteps show that each year trampling alone displaces 230 m³ of sand downslope and into the river. With the controlled river flow, no natural processes exist to replace the lost sediment.     

An evaluation of factors affecting alumina selectivity for the isomer specific determination of 2,3,7,8-tetrachlorodibenzodioxin

Fully activated basic alumina has previously been shown to have the ability to give quantitative separation of tetrachlorodibenzo-p-dioxins (TCDDs) from polychlorinated biphenyls (PCBs) using a 12% chloroform in hexane solution. Further separation of 2,3,7,8-TCDD from other tetra isomers can be accomplished by use of 100% n-butyl chloride, 15% methylene chloride in hexane or 40% chloroform in hexane. A more complete comparison of basic alumina with acidic and neutral alumina has now been carried out. Additionally, an evaluation of this procedure for use with the other 2,3,7,8- substituted furans and dioxins has been made. Lewis base oxygen sites of the dioxin and furan molecules were used to explain the interactions observed. The alumina surface is believed to provide randomly spaced aluminum sites which act as Lewis acids in the adsorption process.     

Stress and mental strain in hospital work: Exploring the relationship beyond personality

This study focuses on the relationship between job stressors and mental strain in hospital work, adjusting for differences in personality traits. Questionnaires were obtained from 760 full-time employees. Fourteen scales of job stressors were clustered into four factors: professional latitude, clinical demands, workload problems and role difficulties. A mental strain index was derived from the addition of three sub-scales: depression, anxiety and irritation. Two personality traits were measured: Locus of Control (Rotter) and Striver-Achiever (Sales). The four job demand factors were dichotomized into high-low grouping variables. A 2⁴ factorial analysis of covariance was conducted, using the two personality traits as covariates, in order to test and adjust for trait-related strain. Results show that Locus of Control adjusted differences in mental strain appear significantly related to work stressors. A direct relationship was found with role difficulties, professional latitude and workload problems. Moreover, high levels of role difficulties and low levels of professional latitude interact significantly with adjusted levels of mental strain. The Striver-Achiever trait, however, appears most strongly correlated with workload problems but not with mental strain. We believe that this exploratory analysis suggests that the stressor-strain relationship might be best conceived as a combination of direct and complex pathways, relating facets of both job demands and of personality with outcomes, under a cognitive and conditional paradigm.     

European union system for the evaluation of substances: the second version

This publication presents major changes in the assessment of the risks of chemicals to human health and the environment as implemented in the second version of the European Union System for the Evaluation of Substances, EUSES 2.0. EUSES is a harmonised quantitative risk assessment tool for chemicals. It is the PC-implementation of the technical guidelines developed within the framework of EU chemical legislation for industrial chemicals and biocides. As such, it is designed to support decision making by risk managers in government and industry and to assist scientific institutions in the risk assessment for these substances. The development of EUSES 2.0 is a co-ordinated project of the European Chemicals Bureau, EU Member States and the European chemical industry. Several model concepts, the technical background and the user interface of EUSES have been improved considerably. Major changes in the environmental assessment such as the implementation of emission scenario documents for industrial chemicals and biocides, the addition of the marine risk assessment, the enhancement of the regional model to include global scales, and improvements in the secondary poisoning and environmental effects modelling will be discussed. The update of the human risk assessment module in EUSES focuses on the risk characterisation for both threshold and non-threshold substances with, among others, the introduction of assessment factors. The performance of EUSES is illustrated in an example showing the human and environmental risk assessment of a sanitation disinfectant for private use.