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721.
Prenatal monitoring of three pregnancies at risk of Morquio's disease type A by determination of N-acetylgalactosamine 6-sulphate sulphatase activity in cultured amniotic cells is reported. In one pregnancy prenatal diagnosis of one affected fetus was made. Enzyme determinations in tissues of the aborted fetus confirmed the prenatal diagnosis. 相似文献
722.
Veska Toncheva An Van Den Bulcke Etienne Schacht Joris Mergaert Jean Swings 《Journal of Polymers and the Environment》1996,4(2):71-83
Poly (-caprolactone) (PCL), poly (-valerolactone) (PVL), poly (-caprolactone-co--valerolactone) [P(CL-co-VL)], and poly (-caprolactone-co-ethylene oxide-co--caprolactone) (PCL-PEO-PCL) were synthesized by ring-opening and diol-initiated polymerization of -caprolactone and -valerolactone. The degradation of the samples by chemical hydrolysis and in a soil burial test was evaluated. It was found that PCL, PVL, and P(CL-co-VL) degrade mainly enzymatically. The rate of degradation depends on their molecular weight, chemical structure, composition, and morphology. PCL-PEO-PCL block copolymers exhibit a repelling effect to the microorganisms in the soil, which depends on the molecular weight and relative amount of PEO block in the copolymer. 相似文献
723.
724.
Patrick R. Zimmerman Maribeth Price Changhui Peng William J. Capehart Karen Updegraff Patrick Kozak Lee Vierling Elaine Baker Fred Kopp Genet Duke Chandan Das 《Mitigation and Adaptation Strategies for Global Change》2005,10(2):307-331
The C-Lock system was developed to address the need for an improved method of quantifying and certifying project-level carbon emission reduction credits (CERC). It was designed to enable individual landowners to efficiently quantify, certify, pool, market and trade CERCs generated by agricultural management practices. We provide a general overview of the C-Lock system as it has been implemented for the USA State of South Dakota. C-Lock is comprised of four linked components: a web interface, a client database, a Geographic Information System (GIS) database of soil, climate and generalized land use history parameters, and the CENTURY soil carbon model. The user-friendly interface elicits generalized land-use and crop history information from the client from 1900 through 1989, then explicit annual information from 1990 onward. A climate-zone level landuse and crop management database is used to fill in gaps in the client-provided data. These data are used to drive the CENTURY model, which estimates annual changes in soil carbon stocks. Monte Carlo simulation is used to estimate uncertainty bounds, and these are applied to the CENTURY outputs in order to provide probabilistic estimates of accrued CERCs in a manner that is transparent and verifiable. In a demonstration application, CERCs are estimated for three different land-use scenarios on a representative field in eastern South Dakota: reduced tillage or conservation (no-till) management of a corn (maize)/wheat/soybean rotation, and enrollment in the Conservation Reserve Program, which entails establishing permanent grass cover. The credits are based on a business-asusual scenario of conventional tillage. 相似文献
725.
For decades, trees have been exposed to atmospheric S pollution (acid rains). They can thus fulfil their S requirements not only via the roots, but also via their needles. However, whether leaf-absorbed S has a different fate from that of root-absorbed S, or may be toxic to the plant, remains uncertain. Norway spruce trees have been contaminated with (35)SO(4)(2-) either via a nutrient solution, or via a spray, and their (35)S distribution has been analysed. In the case of foliar contamination, a high percentage of (35)S(-) was present in the form of SO(4)(2-), both on the surface and inside the youngest needles. In the case of root contamination, the (35)S of the youngest leaves was mainly incorporated into insoluble organic compounds. Older needles showed a different S distribution. 相似文献
726.
To evaluate the effect of potentially toxic compounds on soil fauna mediated carbon and other mineral fluxes in poplar litter, a terrestrial micro-ecosystem (MES) was developed, with the isopod Porcellio scaber as a representative soil fauna species. An experiment was conducted, in which MES with isopods were compared to MES without isopods. Potassium fluoride was used as a model compound. The isopods influenced the microbial respiration negatively. No effect was found for the isopods on the nitrogen and phosphorus mineralization. After the first four weeks of the experiment the total respiration of the MES was increased and the phosphate concentration decreased at the highest fluoride concentration. After nine weeks, fluoride decreased ammonium, nitrate and phosphate concentrations in the litter. It is concluded that nitrogen and phosphorus mineralization in the MES are more sensitive to effects of fluoride that microbial respiration. The no observed effect concentrations for net mineralization of ammonium, nitrate and phosphorus were, respectively, 17, 5.3 and 53 micromol fluoride per gram dry weight of litter. Fluoride seems to be toxic for microbial processes at concentrations found in moderately polluted areas. 相似文献
727.
Spatial and temporal trends of precipitation chemistry in the United States, 1985-2002 总被引:1,自引:0,他引:1
Lehmann CM Bowersox VC Larson SM 《Environmental pollution (Barking, Essex : 1987)》2005,135(3):347-361
A Seasonal Kendall Trend (SKT) test was applied to precipitation-weighted concentration data from 164 National Atmospheric Deposition Program National Trends Network (NADP/NTN) sites operational from 1985 to 2002. Analyses were performed on concentrations of ammonium, sulfate, nitrate, dissolved inorganic nitrogen (DIN, sum of nitrogen from nitrate and ammonium), and earth crustal cations (ECC, sum of calcium, magnesium, and potassium). Over the 18-year period, statistically significant (p< or =0.10) increases in ammonium concentrations occurred at 93 sites (58%), while just three sites had statistically significant ammonium decreases. Central and northern Midwestern states had the largest ammonium increases. The generally higher ammonium concentrations were accompanied by significant sulfate decreases (139 sites, 85%), and only one significant increase which occurred in Texas. In the west central United States there were significant nitrate increases (45 sites, 27%), while in the northeastern United States there were significant decreases (25 sites, 15%). Significant DIN decreases were observed in the northeastern United States (11 sites, 7%); elsewhere there were significant increases at 75 sites (46%). ECC decreased significantly at 65 sites (40%), predominantly in the central and southern United States, and increased at 11 sites (7%). The concentrations of sulfate, nitrate, and ammonium in precipitation have changed markedly over the time period studied. Such trends indicate changes in the mix of gases and particles scavenged by precipitation, possibly reflecting changes in emissions, atmospheric chemical transformations, and weather patterns. 相似文献
728.
Roekens E Bleyen C Van Grieken R 《Environmental pollution (Barking, Essex : 1987)》1989,57(4):289-298
The sulphite and sulphate concentrations in weathering products of limestone and in wet and total deposition samples were measured by the modified West-Gaeke method and by ion chromatography. The sulphite content in the weathering crust and in the runoff rainwater of two historical buildings in Belgium, was always much lower than the sulphate content. The maximum sulphite to sulphate ratio was 2.5%. The sulphite concentration in wet and total deposition samples was in the low or sub ppm range except during two misty periods when the sulphite concentration was 6.8 and 21 mg litre(-1). In those samples a high sulphate concentration was also found (nl. 57 and 137 mg litre(-1), respectively). 相似文献
729.
Van Assche F Cardinaels C Clijsters H 《Environmental pollution (Barking, Essex : 1987)》1988,52(2):103-115
Toxic doses of zinc and cadmium inhibit shoot growth but increase the capacity of several leaf enzymes in dwarf beans (Phaseolus vulgaris L.). Both effects were studied as a function of the metal concentration applied to the plant. There was a linear relationship between the metal content of the primary leaf and the nutrient solution. When leaf metal content exceeded a toxic threshold value, shoot growth became inhibited and an increase in capacity of the following enzymes was measured in the leaf: glucose-6-phosphate dehydrogenase, glutamate dehydrogenase, isocitrate dehydrogenase, malic enzyme, glutamate-oxaloacetate transminase, peroxidase. The threshold values were similar for growth inhibition as well as for enzyme capacity induction. Both effects were strongly correlated to each other, especially under conditions of toxic zinc treatment. Measurement of enzyme capacity might therefore provide a useful criterion for the evaluation of the phytotoxicity of soils, contaminated by zinc and/or cadmium. 相似文献
730.
Wipfler EL Ness M Breedveld GD Marsman A Van Der Zee SE 《Journal of contaminant hydrology》2004,72(1-4):47-66
Enhanced understanding of light non-aqueous phase liquid (LNAPL) infiltration into heterogeneous porous media is important for the effective design of remediation strategies. We used a 2-D experimental facility that allows for visual observation of LNAPL contours in order to study LNAPL redistribution in a layered porous medium. The layers are situated in the unsaturated zone near the watertable and they are inclined to be able to observe the effect of discontinuities in capillary forces and relative permeabilities. Two experiments were performed. The first experiment consisted of LNAPL infiltration into a fine sand matrix with a coarse sand layer, and the second experiment consisted of a coarse sand matrix and a fine sand layer. The numerical multi-phase flow model STOMP was validated with regard to the experimental results. This model is able to adequately reproduce the experimental LNAPL contours. Numerical sensitivity analysis was also performed. The capillarity contrast between sands was found to be the main controlling factor determining the final LNAPL distribution. 相似文献