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121.
The diamond cartel has remained effective in controlling diamond supplies and prices for a longer period than any other major minerals cartel in the twentieth century. This paper examines the diamond pipeline from mine to the jewellery market. Particular attention is given to the characteristics of diamonds and of the industry structure that make the long-term stability of the cartel possible. The strategies of De Beers Consolidated Diamond Mines in controlling rough gem supplies and prices are examined, and projections are made to 2000. The paper shows that in spite of a projected decrease in the share of total diamond production sold through the De Beers' cartel in the 1990s, the cartel is expected to continue effectively to control supplies and prices. 相似文献
122.
Michael R. Palermo 《补救:环境净化治理成本、技术与工艺杂志》1991,1(4):473-492
This article describes the selection and field evaluation of dredging equipment and techniques for removal of highly contaminated sediments from the upper estuary of the Acusbnet River, a portion of the New Bedford Harbor Supetfund Project. Site conditions as related to dredge selection and operation, factors considered in selection of equipment, and various dredge types considered for use are described. Each of the dredge types is ranked according to the following criteria: availability, safety, potential for sediment resuspension, maneuverability, cleanup precision, cost and production, flexibility, required water depth for operation, ability to access the site, and compatibility with disposal options. A field pilot study comparing three dredge types indicated that dredging could be conducted at the site without a significant increase in the contaminant release from the upper estuary to the lower harbor. 相似文献
123.
Abundance of fecal caliform bacteria is a weak index of the presence of human pathogens in wastewater entering coastal waters.
In spite of this, use of fecal caliform indices for management purposes is widespread. To gain insight into interpretation
of fecal coliform data, we evaluated size of stocks of fecal coliforms in water, sediments, and sea wrack, in Buttermilk Bay,
a coastal embayment in Massachusetts. Sediments contained most of the fecal coliforms. Fecal coliforms in sediments were as
much as one order of magnitude more abundant than in the water column or in sea wrack. The fecal coliforms in sediments of
Buttermilk Bay were so abundant that resuspension of fecal coliforms from just the top 2 cm of muddy sediments could add sufficient
cells to the water column to have the whole bay exceed the federal limit of fecal coliforms for shellfishing.
The major sources of fecal coliforms to the bay were water-fowls, surface runoff, groundwater, and streams. Waterfowl were
the largest source of fecal coliforms during cold months; surface runoff, streams, and groundwater were most important during
warm months. Redirection of surface runoff pipes is unlikely to be a very successful management action since contributions
via this source are insufficient to account for the measured increases in concentrations of fecal coliforms in water. Removal
of waterfowl is also unlikely to be useful, since fecal coliform concentrations leading to closures of shellfish beds and
swimming areas are most frequent during warm months when waterfowl are rarest. Rates of loss of fecal caliform cells from
the water column by death and tidal exchange were high. Mortality of cells was about an order of magnitude larger than losses
by tidal exchange.
The amounts of fecal coliforms brought into the bay by waterfowl, surface runoff, groundwater, and streams are an order of
magnitude smaller than the losses by mortality and tidal removal. This implies that there is an additional source of fecal
coliforms within the bay. We suggest that resuspension of the upper layers of sediments can easily account for the fecal coliforms
present in the water.
Fecal coliform content of water and shellfish were not correlated. In contrast, sediment and shellfish fecal coliform abundances
were significantly related. Monitoring of fecal coliforms in sediments may provide a better assessment of shellfish than sampling
of water.
The large fecal coliform stock in sediments should be the first priority for management. Efforts ought to be directed toward
the reduction of sediment fecal coliform stocks. Lowering nutrient additions to coastal water bodies may be one practical
approach. 相似文献
124.
Environmental degradation, competition for resources, increasing food demands, and the integration of agriculture into the
international economy threaten the sustainability of many food production systems. Despite these concerns, the concept of
sustainable food production systems remains unclear, and recent attempts to appraise sustainability have been hampered by
conceptual inconsistencies and the absence of workable definitions. Six perspectives are shown to underpin the concept. Environmental
accounting identifies biophysical limits for agriculture. Sustained yield refers to output levels that can be maintained continuously.
Carrying capacity defines maximum population levels that can be supported in perpetuity. Production unit viability refers
to the capacity of primary producers to remain in agriculture. Product supply and security focuses on the adequacy of food
supplies. Equity is concerned with the spatial and temporal distribution of products dervied from resource use. Many studies
into sustainable agriculture cover more than one of these perspectives, indicating the concept is complex and embraces issues
relating to the biophysical, social, and economic environments. Clarification of the concept would facilitate the development
of frameworks and analytical systems for appraising the sustainability of food production systems.
LRRC Contribution No. 90–46. 相似文献
125.
126.
W. Michael. Aust Russ Lea James D. Gregory 《Journal of the American Water Resources Association》1991,27(1):111-116
ABSTRACT: A palustrine water tupelo (Nyssa aquatica L.)-baldcy-press (Taxodium distichum (L.) Rich.) swamp in southwestern Alabama was subjected to three types of disturbance, including helicopter logging, rubber-tired skidder logging simulation, and helicopter logging followed by an herbicide application. An adjacent undisturbed stand served as a control area. Post-harvest collection of sedimentation data revealed that the herbaceous and woody vegetation regrowth within the helicopter and skidded clearcut areas trapped more sediments than did the control or herbicide treatment areas. Clearcutting, followed by plant regrowth, improved the wet-land's capacity to remove sediments from overbank flow flood waters. 相似文献
127.
Myron A. Peck Paul E. Fell Elizabeth A. Allen Jennifer A. Gieg Carl R. Guthke Michael D. Newkirk 《Environmental management》1994,18(2):283-293
Macroinvertebrates were examined on an impounded valley marsh in Stonington, Connecticut, that has changed from aTypha-dominated system to one with typical salt-marsh vegetation during 13 years following the reintroduction of tidal exchange.
Animal populations on this restored impounded marsh were evaluated by comparing them with populations on a nearby unimpounded
valley marsh of roughly the same size. Populations of the high marsh snail,Melampus bidentatus Say, were quantitatively sampled along transects that extended from the water-marsh edge to the upland; those of the ribbed
mussel,Geukensia demissa Dillwyn, were sampled in low marsh areas on transects along the banks of creeks and mosquito ditches. The occurrence of other
marsh invertebrates also was documented, but their abundance was not measured. The mean density ofMelampus was 332±39.6 SE/m2 on the restored impounded marsh and 712±56.0 SE/m2 on the unimpounded marsh. However, since snails were larger on the restored impounded marsh, the difference in snail biomass
was less pronounced than the difference in snail density. MeanMelampus biomass was 4.96±0.52 SE g dry wt/m2 on the restored impounded marsh and 6.96±0.52 SE g dry wt/m2 on the unimpounded marsh. On the two marshes, snail density and biomass varied in relation to plant cover and other factors.
The density and biomass ofGeukensia at the edge of the marsh were comparable on the restored impounded and unimpounded marshes. Mean mussel densities ranged
from 80 to 240/m2 and mean mussel biomass varied from 24.8–64.8 g dry wt/m2 in different low marsh areas. In contrast, below the impoundment dike, meanGeukensia density was 1100±96.4 SE/m2 and meanGeukensia biomass was 303.6±33.28 SE g dry wt/m2. A consideration of all available evidence leads to the conclusion that the impounded marsh is in an advanced phase of restoration. 相似文献
128.
In this paper, the energy and environmental dimensions of several proposed energy strategies for Senegal are explored. An analytical framework to compare the energy and measurable environmental impacts of a set of scenarios is developed, and the limitations of the quantitative approach are discussed. It is found that policies to promote substitution of liquid petroleum gas (LPG) for charcoal use in households may actually reduce greenhouse gas emissions, while also improving more important near-term environmental problems. Substitution of LPG for charcoal would not necessarily lead to a significant increase in Senegal's oil import bill, since other petroleum product usage will continue to dominate. Despite past industrial sector initiatives, considerable potential for energy efficiency investment remains, and presents additional opportunities for minimizing environmental impacts. 相似文献
129.
Michael Pacione 《Journal of Environmental Planning and Management》1985,28(2):65-69
Government responses to the problems of the inner city currently focus on comprehensive programmes of positive discrimination. The first and most extensive is the G.E.A.R. project in Glasgow. Regular monitoring of the effectiveness of such large‐scale initiatives is essential. If the physical and social aims of such policies are to be realised, assessments must utilise both objective and subjective indicators. 相似文献
130.
Jy S. Wu Ellis L. King Michael Wang 《Journal of the American Water Resources Association》1985,21(3):417-421
Traditionally, identification of the Muskingum routing coefficients has been based on observations of the linearity of a loop formed by graphically plotting a forward and a reverse path. This graphical procedure is time-consuming and may not minimize the error of estimation. A procedure was developed to improve the drawbacks of the graphical method. This procedure calls for (a) the use of least square regression on the forward and reverse paths to determine their respective slopes, and (b) the use of statistical t-test to evaluate the hypothesis that these two slopes are equal. The computational procedure is repeated, using incremental values of the flow weighting coefficient, x. A graph of the computed t-value versus x can be constructed. The optimal value of x, as read from the graph, occurs at the minimum computed t-value. The procedure has been demonstrated superior to the graphical method for three illustrative examples, resulting in a reduction of the error squares by factors ranging from 5 to 6. 相似文献