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991.
992.
An assemblage of fossil sockeye salmon was discovered in Pleistocene lake sediments along the South Fork Skokomish River, Olympic Peninsula, Washington. The fossils were abundant near the head of a former glacial lake at 115 m elevation. Large adult salmon are concentrated in a sequence of death assemblages that include individuals with enlarged breeding teeth and worn caudal fins indicating migration, nest digging, and spawning prior to death. The specimens were 4 yr old and 45-70 cm in total length, similar in size to modern sockeye salmon, not landlocked kokanee. The fossils possess most of the characteristics of sockeye salmon, Oncorhynchus nerka, but with several minor traits suggestive of pink salmon, O. gorbuscha. This suggests the degree of divergence of these species at about 1 million yr ago, when geological evidence indicates the salmon were deposited at the head of a proglacial lake impounded by the Salmon Springs advance of the Puget lobe ice sheet. Surficial geology and topography record a complicated history of glacial damming and river diversion that implies incision of the modern gorge of the South Fork Skokomish River after deposition of the fossil-bearing sediments. 相似文献
993.
994.
Suzanne Lesage Susan Brown Kelly Millar Helena Steer 《Ground Water Monitoring & Remediation》2003,23(2):102-110
This paper describes a dual-column laboratory setup consisting of a glass column and a stainless-steel column filled with aquifer material. The setup was used to replicate a ground water recirculation well that serves as an in situ reactor and a combined injection/withdrawal well. The treatment solution consisted of a buffered titanium (III) citrate/vitamin B12 mixture. The first column, representing the well, was made of glass, allowing for visual inspection of the mixing. The stainless-steel column was instrumented with redox (Eh) probes to monitor the changes in redox conditions. The redox measurement showed that, although the sand contained large quantities of iron oxides, the oxidation rate was relatively slow and the titanium solution would remain reduced for some time in the aquifer, continuing to react with the contaminants. This laboratory setup was used to optimize the reagent concentrations and rate of delivery for field implementation. It was found that 4 mM titanium citrate and 3 mg/L vitamin B12 were sufficient to degrade 1,1,2,2-tetrachloroethane and carbon tetrachloride within one day, but not trichloroethylene, which required five days with 10 mM titanium citrate and 5 mg/L vitamin B12 . 相似文献
995.
Susan W. Hardwick 《The Professional geographer》2005,57(1):21-27
Early career geography faculty in colleges and universities in the United States are positioned at the leading edge of a challenging period of change in higher education. Demands brought on by new technologies, new administrative and research pressures, and an increasingly competitive campus climate, may make it difficult to balance teaching, research, and service while also trying to maintain a personal life. This article argues that many geographers could benefit from the support of mentoring. Using ideas generated by participants in the Association of American Geographers' recent project, the Geography Faculty Development Alliance, I provide both pragmatic and personal suggestions for establishing these all‐important mentoring relationships to help cope with the pressures facing early career faculty. 相似文献
996.
Michael Emch James W. Quinn Marc Peterson Mark Alexander 《The Professional geographer》2005,57(2):256-267
Measuring land‐cover change is an essential part of sustainable conservation planning. This project uses Landsat MSS and ETM+ data to document forest cover change in the Toledo District, Belize, from 1975 to 1999 and provides an initial assessment of why these changes took place. Supervised and subpixel classification methods were employed. The results showed an aggregate forest loss of almost 10 percent, which is approximately 36,000 ha. Deforestation expanded significantly in the most populous Mayan areas of central Toledo District and along the Guatemalan border. Subpixel classification results showed that in 1999 the most densely forested areas were in northern Toledo District in the Maya Mountains. 相似文献
997.
Rats were raised on a variety of isotopically controlled diets comprising 20% C3, C4 or marine protein and C3 and/or C4 non-protein or energy (i.e. sucrose, starch and oil) macronutrients. Compound specific stable carbon isotope (δ13C) analysis was performed on the cholesterol isolated from the diet (n=7 ) and bone (n=15 ) of these animals and the values compared with bulk δ13C measurements of bone collagen and apatite. The dietary signals reflected by these three bone biochemical components were investigated using linear regression analysis. δ13C values of bone cholesterol were shown to reflect whole diet δ13C values, collagen to reflect mainly dietary protein values and apatite to reflect whole diet values. Further correlations between dietary protein-to-energy spacings (Δ13Cprot-engy = δ13Cprotein - δ13Cenergy) and whole diet-to-bone component fractionations (Δ13Cbcomp-wdiet = δ13Cbone component - δ13Cwhole diet) indicates that for hypothetical diets where protein δ13C values are equal to energy values, fractionations between whole diet and bone biochemical fractions are -3.3‰ for cholesterol, +5.4‰ for collagen and +9.5‰ for apatite. Moreover, the narrow range of variation observed in apatite-to-cholesterol spacings (Δ13Capat-bchol) suggests that cholesterol δ13C values can potentially also be used as an independent test for the isotopic integrity of apatite δ13C values. These insights into bone cholesterol, collagen and apatite dietary signals, diet-to-bone fractionations and bone component-to-bone component spacings provide the basis for more accurate interpretations of the dietary behaviour of archaeological populations and food webs when the δ13C analysis of bone is employed. 相似文献
998.
Megan R. Johnson Susan L. Williams Carolyn H. Lieberman Arne Solbak 《Estuaries and Coasts》2003,26(1):106-115
Changes in environmental conditions can be accompanied by shifts in the distribution and abundances of organisms. When physical factors become unsuitable for growth ofZostera marina (eelgrass), which is a dominant seagrass species in North America, other more ruderal seagrass species, includingRuppia maritima (widgeongrass), often increase in abundance or replace the dominant species. We report the proliferation of widgeongrass into eelgrass beds in Mission Bay and San Diego Bay in San Diego, California, during the 1997 to 1998 El Niño Southern Oscillation (ENSO). Widgeongrass persisted in these eelgrass beds at least one year after a return to non-ENSO conditions and an increase in eelgrass density. We suggest that a warming of the water in two bays in San Diego by 1.5–2.5°C could result, in a permanent shift in the local seagrass vegetation from eelgrass to widgeongrass. This shift, could, have substantial ecosystem-level ramifications. 相似文献
999.
Effective risk communication is central to good environmental risk management. While studies have shown that newspapers are the primary source of information to the public regarding environmental issues, little is known about how environmental news is used as a risk‐communication tool. This article explores the role of local information systems in risk communication, using newspaper content analysis as well as in‐depth interviews with journalists and community residents to develop a case study of an environmental assessment process for a nonhazardous industrial‐waste landfill. Results indicate that risk messages were chosen and shaped by journalists on the basis of their own exigencies. In addition, while newspapers were a major source of risk information, their impact was mitigated by resident distrust and access to other information sources, most notably their own personal information networks. These results have implications for environmental policy, as decision makers often use—either passively or actively—print media as a risk‐communication tool. 相似文献
1000.