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81.
Lignins in general have been extensively studied, while beech wood lignin in particular is rarely researched. In the present work, Organosolv isolated lignin from beech wood (OBL) has been characterized. The isolation was done by two methods: (a) by using sulfuric acid at 170 °C and a reaction time of 120 min and (b) at a temperature of 180 °C for 240 min. A range of analytical methods were applied including elemental analysis, FT-IR, UV–Vis, 31P NMR, SEC, Pyrolysis-GC/MS and HPLC to gain information about establish the purity, structure, molecular weight, thermal behavior and to determine carbohydrate residues according to the NREL protocol. FT-IR and UV–Vis spectra of OBL revealed expected typical absorptions for lignins. NREL analysis presented a carbohydrate-free lignin fraction which has not been achieved to date. TGA and DSC are used to study the thermal behavior of the isolated lignins and showed a relatively low glass transition temperatures (Tg: 123 °C) and decomposition temperatures of 348 and 381 °C. The pyrograms generated from the pyrolysis–GC/MS at 550 °C consisted mainly of fragments of syringyl, guaiacyl and hydroxyphenyl units, thereby confirming the results of the NMR analysis. Our findings support Organolsolv as an efficient method to isolate pure lignin fractions from beech wood with practical value in industry. 相似文献
82.
Sorption and fractionation of dissolved organic matter and associated phosphorus in agricultural soil 总被引:1,自引:0,他引:1
Gjettermann B Styczen M Hansen S Borggaard OK Hansen HC 《Journal of environmental quality》2007,36(3):753-763
Mobility of dissolved organic matter (DOM) strongly affects the export of nitrogen (N) and phosphorus (P) from soils to surface waters. To study the sorption and mobility of dissolved organic C and P (DOC, DOP) in soil, the pH-dependent sorption of DOM to samples from Ap, EB, and Bt horizons from a Danish agricultural Humic Hapludult was investigated and a kinetic model applicable in field-scale models tested. Sorption experiments of 1 to 72 h duration were conducted at two pH levels (pH 5.0 and 7.0) and six initial DOC concentrations (0-4.7 mmol L(-1)). Most sorption/desorption occurred during the first few hours. Dissolved organic carbon and DOP sorption decreased strongly with increased pH and desorption dominated at pH 7, especially for DOC. Due to fractionation during DOM sorption/desorption at DOC concentrations up to 2 mmol L(-1), the solution fraction of DOM was enriched in P indicating preferred leaching of DOP. The kinetics of sorption was expressed as a function of how far the solution DOC or DOP concentrations deviate from "equilibrium." The model was able to simulate the kinetics of DOC and DOP sorption/desorption at all concentrations investigated and at both pH levels making it useful for incorporation in field-scale models for quantifying DOC and DOP dynamics. 相似文献
83.
A climatic driver for abrupt mid-Holocene vegetation dynamics and the hemlock decline in New England 总被引:1,自引:0,他引:1
The mid-Holocene decline of eastern hemlock is widely viewed as the sole prehistorical example of an insect- or pathogen-mediated collapse of a North American tree species and has been extensively studied for insights into pest-host dynamics and the consequences to terrestrial and aquatic ecosystems of dominant-species removal. We report paleoecological evidence implicating climate as a major driver of this episode. Data drawn from sites across a gradient in hemlock abundance from dominant to absent demonstrate: a synchronous, dramatic decline in a contrasting taxon (oak); changes in lake sediments and aquatic taxa indicating low water levels; and one or more intervals of intense drought at regional to continental scales. These results, which accord well with emerging climate reconstructions, challenge the interpretation of a biotically driven hemlock decline and highlight the potential for climate change to generate major, abrupt dynamics in forest ecosystems. 相似文献
84.
Hansen DA Edgerton E Hartsell B Jansen J Burge H Koutrakis P Rogers C Suh H Chow J Zielinska B McMurry P Mulholland J Russell A Rasmussen R 《Journal of the Air & Waste Management Association (1995)》2006,56(10):1445-1458
Measurements of pollutant gases, airborne particulate matter mass and composition, and meteorology have been made at a core site near downtown Atlanta, GA, since August 1998 in support of the Aerosol Research and Inhalation Epidemiology Study (ARIES). This site is one of eight in the Southeastern Aerosol Research and Characterization network. The measurement objective is to provide a long-term, multivariate dataset suitable for investigating statistical associations of respiratory and cardiovascular disease with airborne particulate matter composition, meteorology, and copollutant gases through epidemiologic modeling. Measurements are expected to continue through 2010. Ancillary multiyear measurements at additional sites in the Atlanta metropolitan area and in short-term exposure assessments have been used to estimate the exposure/measurement error associated with using data from a central site to approximate human exposures for the entire area. To date, 13-, 25-, and 53-month air quality datasets have been used in epidemiologic analyses. 相似文献
85.
86.
Water and sustainability 总被引:1,自引:0,他引:1
This inquiry summarizes global water resources and patterns of use, applies indicators of water sustainability in order to identify areas of water stress, and examines prospects for water sustainability in the list century. A long-range conventional development scenario is introduced based on a vision of the future in which the values, consumption patterns and dynamics of the Western industrial society will be progressively played out on a global scale. The scenario is driven by commonly cited projections of population and economic growth, assumes no major changes in water policy and, following historic trends, incorporates progressive improvements in the efficiency of water use. The scenario helps clarify the constraints of a conventional picture of water development, and provides a useful point of departure for examining alternative long-range scenarios and their implications for water and development policy. In the conventional development scenario, there is growing pressure on water resources, particularly in developing regions. Strategies for beginning a transition to a sustainable water development path are summarized . 相似文献
87.
Cease-fires in the Caucasus during the past five years have prevented large-scale life-threatening emergencies and created space for peace negotiations. Yet genuine conflict resolution and normalisation have proven elusive, frustrating the return of uprooted populations and constraining reconstruction. This paper reviews a series of seven strategy sessions held in Moscow and the Caucasus in late 1998 to reflect upon the performance of humanitarian agencies and stimulate greater synergies with diplomatic actors. An experiment in promoting discussion of recently conducted independent policy research throughout the north and south Caucasus, the series resulted in a fresh look at the issues in the region and at agency headquarters. The generic nature of the policy challenges gives the experience potential relevance well beyond the region. 相似文献
88.
Gerald T. Ankley Nelson A. Thomas Dominic M. Di Toro David J. Hansen John D. Mahony Walter J. Berry Richard C. Swartz Robert A. Hoke A. Wayne Garrison Herbert E. Allen Christopher S. Zarba 《Environmental management》1994,18(3):331-337
Due to anthropogenic inputs, elevated concentrations of metals frequently occur in aquatic sediments. In order to make defensible
estimates of the potential risk of metals in sediments and/or develop sediment quality criteria for metals, it is essential
to identify that fraction of the total metal in the sediments that is bioavailable. Studies with a variety of benthic invertebrates
indicate that interstitial (pore) water concentrations of metals correspond very well with the bioavailability of metals in
test sediments. Many factors may influence pore water concentrations of metals; however, in anaerobic sediments a key phase
controlling partitioning of several cationic metals (cadmium, nickel, lead, zinc, copper) into pore water is acid volatile
sulfide (AVS). In this paper, we present an overview of the technical basis for predicting bioavailability of cationic metals
to benthic organisms based on pore water metal concentrations and metal-AVS relationships. Included are discussions of the
advantages and limitations of metal bioavailability predictions based on these parameters, relative both to site-specific
assessments and the development of sediment quality criteria. 相似文献
89.
Dr Peter H. Hansen 《The Environmentalist》1995,15(4):252-256
Worcester Polytechnic Institute's (WPI) unique academic plan enables students to study sustainable development and the environment as part of an international educational experience. As a technological university, WPI requires students to complete an interdisciplinary project on the interaction of science or technology and society. This paper describes the environmental projects completed by WPI students, in Bangkok, Venice and Guayaquil. The lessons from WPI's experience provide a model for environmental education at other institutions. These interdisciplinary projects not only promote environmental awareness among students, but they also provide tangible assistance to regions which are developing strategies for sustainable development. 相似文献
90.