Response of Organic and Inorganic Carbon and Nitrogen to Long-Term Grazing of the Shortgrass Steppe

We investigated the influence of long-term (56 years) grazing on organic and inorganic carbon (C) and nitrogen (N) contents of the plant–soil system (to 90 cm depth) in shortgrass steppe of northeastern Colorado. Grazing treatments included continuous season-long (May–October) grazing by yearling heifers at heavy (60–75% utilization) and light (20–35% utilization) stocking rates, and nongrazed exclosures. The heavy stocking rate resulted in a plant community that was dominated (75% of biomass production) by the C₄ grass blue grama (Bouteloua gracilis), whereas excluding livestock grazing increased the production of C₃ grasses and prickly pear cactus (Opuntia polycantha). Soil organic C (SOC) and organic N were not significantly different between the light grazing and nongrazed treatments, whereas the heavy grazing treatment was 7.5 Mg ha^–1 higher in SOC than the nongrazed treatment. Lower ratios of net mineralized N to total organic N in both grazed compared to nongrazed treatments suggest that long-term grazing decreased the readily mineralizable fraction of soil organic matter. Heavy grazing affected soil inorganic C (SIC) more than the SOC. The heavy grazing treatment was 23.8 Mg ha^–1 higher in total soil C (0–90 cm) than the nongrazed treatment, with 68% (16.3 Mg ha^–1) attributable to higher SIC, and 32% (7.5 Mg ha^–1) to higher SOC. These results emphasize the importance in semiarid and arid ecosystems of including inorganic C in assessments of the mass and distribution of plant–soil C and in evaluations of the impacts of grazing management on C sequestration.     

A Proactive Approach Can Make Site Remediation Less Expensive

Without any incentive to clean up a contaminated site, remediation is often delayed until the site owner is compelled to act by regulatory agencies. In such a context, the selected technology is typically the one that will reach the remediation goals as quickly as possible. Unfortunately, this criterion is often met by overly expensive technologies, resulting in high and sometimes unaffordable total remediation costs, leading to a remediation with a negative net benefit. This study examines the effects of time constraint and benefit value on the optimal remediation strategy for a diesel-contaminated site. This strategy is developed using the technico-economic model METEORS, which takes into account the technology’s effectiveness, the uncertainty of the level of contamination, and the possibility of reducing this uncertainty through either an additional characterization (before selecting and applying a technology) or the monitoring of the remediation technology (during its use). Results of simulations with both economic and temporal constraints support a proactive approach to site remediation.     

Mutagenic and carcinogenic potency of extracts of diesel and related environmental emissions: Study design, sample generation, collection, and preparation

A major diesel emissions research program has been initiated by the U.S. Environmental Protection Agency to assess the human health risk associated with increased use of diesel automobiles. This program is intended to establish the mutagenic and carcinogenic potency of complex organics associated with diesel particles as well as comparative particle-bound organics from other environmental emissions for which human epidemiological data are available. The mobile source samples selected for this study were collected from a heavy-duty diesel engine, a series of light-duty diesel passenger cars, and a gasoline catalyst automobile. The comparative source samples incorporated into the study were cigarette smoke condensate, coke oven emissions, roofing tar emissions, and benzo(a)pyrene. The samples were tested using three mutagenic assays and four carcinogenic assays as prescribed by a test matrix. This report describes the study design, particle generation, and sample collection and preparation. A brief summary of the bioassays is also included.     

Fate of oil from two major oil spills: Role of microbial degradation in removing oil from the Amoco Cadiz and IXTOC I spills

The fate of oil was examined in intertidal sediments impacted by the Amoco Cadiz spill in Brittany, France, and in surface waters contaminated by the IXTOC I well blowout in the Bay of Campeche, Mexico. The role of microbial degradation in removing the contaminating hydrocarbons was assessed by laboratory determinations of numbers of hydrocarbon utilizing microorganisms, measurement of microbial hydrocarbon biodegradation potentials, by chemical analyses of samples incubated under controlled conditions and by examination of the evolution of the hydrocarbon mixture in field samples collected after the spill. Analyses included the use of ¹⁴C radiolabelled hydrocarbon tracers, glass capillary-gas chromatography and mass spectrometry. Numbers of hydrocarbon utilizing microorganisms were found to be elevated by several orders of magnitude in oil contaminated samples. Numbers of hydrocarbon utilizing microorganisms appear to provide a useful index of environmental hydrocarbon contamination. However, environmental constraints on microbial processes appear to be most important in determining actual rates of biodegradation rather than numbers of available hydrocarbon utilizing microorganisms. Very high rates of degradation were found in intertidal sediments impacted by the Amoco Cadiz spill. In contrast, rates of degradation in the Gulf of Mexico were found to be much lower, partly due to nutrient limitations and partly due to the formation of large masses of oil-water emulsion or mousse.     

Spectral analysis of forest model time series

The use of spectral analysis to elucidate the cyclic behavior in time series generated by a forest stand growth simulation model is discussed. A stand-level simulator, FORET, for an Appalachian deciduous forest is described. An estimate of the power spectral density of the total biomass time series is calculated. The power spectral density estimate indicates a dominant cyclic behavior with a period of about 200 years. In addition the spectral density is approximately bandlimited. This characteristic makes possible the application of the sampling theorem for analysis of sampling rates.     

ENHANCING EVACUATION WARNING COMPLIANCE: SUGGESTIONS FOREMERGENCY PLANNING*

This review of incentives to evacuate is meaningful largely in the context of planning for and managing the consequences of the impact of riverine floods. Of course, incentives do not constitute an emergency plan. At best, they should be seen as suggestions for structuring some elements of a plan. Furthermore, the enumeration of incentives presented here is meant to be suggestive rather than exhaustive. A primary objective of this paper has been to underscore the importance of advance planning in coping with hazards and to argue that, even though limited, existing research can be productively used in the planning process. The incentives described here are based upon or drawn from empirical research on people's performance under flood disaster conditions. This reflects the view that it is important to build emergency planning around people's known reaction patterns. Too often emergency plans which are administratively devised turn out to be based upon misconceptions of how people react (cf. Drabek and Stephenson, 1971, p. 202; Dynes et al., 1972, p. 31) and, therefore, potentially create more difficulties than they solve. One must be cautioned, however, that although our data indicate that people say they would support the idea of various evacuation incentives examined here, these are attitudinal data and not performance data. Thus, the real test of evacuation incentives lies in their implementation and in evaluation data on pilot programs which, unfortunately, do not presently exist. The outlook for the feasibility of developing and utilizing evacuation incentives appears to be positive, though, judging from responses to our interviews. In the final analysis, it would appear to be wise to develop emergency plans which guide and channel citizen actions into complementary and productive protection behavior patterns. The present discussion of incentives to evacuate is intended to encourage data-based emergency planning.