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471.
472.
The United States Environmental Protection Agency (USEPA) Region V Clean Lakes Program employs artificial and modified natural
wetlands in an effort to improve the water quality of selected lakes. We examined use of wetlands at seven lake sites and
evaluated the physical and institutional means by which wetland projects are implemented and managed, relative to USEPA program
goals and expert recommendations on the use of wetlands for water quality improvement. Management practices recommended by
wetlands experts addressed water level and retention, sheet flow, nutrient removal, chemical treatment, ecological and effectiveness
monitoring, and resource enhancement. Institutional characteristics recommended included local monitoring, regulation, and
enforcement and shared responsibilities among jurisdictions. Institutional and ecological objectives of the National Clean
Lakes Program were met to some degree at every site. Social objectives were achieved to a lesser extent. Wetland protection
mechanisms and appropriate institutional decentralization were present at all sites. Optimal management techniques were employed
to varying degrees at each site, but most projects lack adequate monitoring to determine adverse ecological impacts and effectiveness
of pollutant removal and do not extensively address needs for recreation and wildlife habitat. There is evidence that the
wetland projects are contributing to improved lake water quality; however, more emphasis needs to be placed on wetland protection
and long-term project evaluation. 相似文献
473.
Electron microscopy-energy dispersive spectroscopy (EM/EDS) can be used to determine the elemental composition of individual particles. However, the accuracy with which atmospheric particle compositions can be quantitatively determined is not well understood. In this work we explore sources of sampling and analytical bias and methods of reducing bias. Sulfuric acid [H2SO4] and ammonium sulfate [(NH4)2SO4] particles were collected on beryllium, silicon, and carbon substrates with similar deposition densities. While [(NH4)2SO4] particles were observed on all substrates, [H2SO4] and ammonia-treated [H2SO4] particles could not be found on beryllium substrates. Interactions between the substrate and sulfuric acid particles are implicated. When measured with EM/EDS, [H2SO4] particles exposed to ammonia overnight were found having lower beam damage rates (0.000 ± 0.002 fraction s−1) than those without any treatment (0.023 ± 0.006 fraction s−1) For laboratory-generated [C10H6(SO3Na)2] particles, the composition determined using the experimental k-factors evaluated from independent particle standards of similar composition and size shows an error less than 20% for all constituents, while greater than 78% errors were found when k-factors were calculated from the theory. This study suggests (1) that sulfate beam damage can be reduced by exposure of atmospheric particle samples to ammonia before analysis, (2) that beryllium is not a suitable substrate for atmospheric particle analysis, and (3) calibration (k-factor determination) using particle standards of similar size and composition to particles present in the atmosphere shows promise as a way of improving the accuracy of quantitative EM analysis. 相似文献
474.
Meckenstock RU Morasch B Griebler C Richnow HH 《Journal of contaminant hydrology》2004,75(3-4):215-255
The assessment of biodegradation in contaminated aquifers has become an issue of increasing importance in the recent years. To some extent, this can be related to the acceptance of intrinsic bioremediation or monitored natural attenuation as a means to manage contaminated sites. Among the few existing methods to detect biodegradation in the subsurface, stable isotope fractionation analysis (SIFA) is one of the most promising approaches which is pronounced by the drastically increasing number of applications. This review covers the recent laboratory and field studies assessing biodegradation of contaminants via stable isotope analysis. Stable isotope enrichment factors have been found that vary from no fractionation for dioxygenase reactions converting aromatic hydrocarbons over moderate fractionation by monooxygenase reactions (epsilon=-3 per thousand) and some anaerobic studies on microbial degradation of aromatic hydrocarbons (epsilon=-1.7 per thousand) to larger fractionations by anaerobic dehalogenation reactions of chlorinated solvents (epsilon=between -5 per thousand and -30 per thousand). The different isotope enrichment factors can be related to the respective biochemical reactions. Based on that knowledge, we discuss under what circumstances SIFA can be used for a qualitative or even a quantitative assessment of biodegradation in the environment. In a steadily increasing number of cases, it was possible to explain biodegradation processes in the field based on isotope enrichment factors obtained from laboratory experiments with pure cultures and measured isotope values from the field. The review will focus on the aerobic and anaerobic degradation of aromatic hydrocarbons and chlorinated solvents as the major contaminants of groundwater. Advances in the instrumental development for stable isotope analysis are only mentioned if it is important for the understanding of the application. 相似文献
475.
McDonald JD Zielinska B Sagebiel JC McDaniel MR Mousset-Jones P 《Journal of the Air & Waste Management Association (1995)》2003,53(4):386-395
The chemical mass balance source apportionment technique was applied to an underground gold mine to assess the contribution of diesel exhaust, rock dust, oil mists, and cigarette smoke to airborne fine (<2.5 microm) particulate matter (PM). Apportionments were conducted in two locations in the mine, one near the mining operations and one near the exit of the mine where the ventilated mine air was exhausted. Results showed that diesel exhaust contributed 78-98% of the fine particulate mass and greater than 90% of the fine particle carbon, with rock dust making up the remainder. Oil mists and cigarette smoke contributions were below detection limits for this study. The diesel exhaust fraction of the total fine PM was higher than the recently implemented mine air quality standards based on total carbon at both sample locations in the mine. 相似文献
476.
Morrill PL Lacrampe-Couloume G Slater GF Sleep BE Edwards EA McMaster ML Major DW Sherwood Lollar B 《Journal of contaminant hydrology》2005,76(3-4):279-293
Stable isotope analysis of chlorinated ethene contaminants was carried out during a bioaugmentation pilot test at Kelly Air Force Base (AFB) in San Antonio Texas. In this pilot test, cis-1,2-dichloroethene (cDCE) was the primary volatile organic compound. A mixed microbial enrichment culture, KB-1, shown in laboratory experiments to reduce chlorinated ethenes to non-toxic ethene, was added to the pilot test area. Following bioaugmentation with KB-1, perchloroethene (PCE), trichloroethene (TCE) and cDCE concentrations declined, while vinyl chloride (VC) concentrations increased and subsequently decreased as ethene became the dominant transformation product. Shifts in carbon isotopic values up to 2.7 per thousand, 6.4 per thousand, 10.9 per thousand and 10.6 per thousand were observed for PCE, TCE, cDCE and VC, respectively, after bioaugmentation, consistent with the effects of biodegradation. While a rising trend of VC concentrations and the first appearance of ethene were indicative of biodegradation by 72 days post-bioaugmentation, the most compelling evidence of biodegradation was the substantial carbon isotope enrichment (2.0 per thousand to 5.0 per thousand) in ?13C(cDCE). Fractionation factors obtained in previous laboratory studies were used with isotope field measurements to estimate first-order cDCE degradation rate constants of 0.12 h(-1) and 0.17 h(-1) at 115 days post-bioaugmentation. These isotope-derived rate constants were clearly lower than, but within a factor of 2-4 of the previously published rate constant calculated in a parallel study at Kelly AFB using chlorinated ethene concentrations. Stable carbon isotopes can provide not only a sensitive means for early identification of the effects of biodegradation, but an additional means to quantify the rates of biodegradation in the field. 相似文献
477.
McKelvie JR Lindstrom JE Beller HR Richmond SA Sherwood Lollar B 《Journal of contaminant hydrology》2005,81(1-4):167-186
In situ biodegradation of benzene, toluene, and xylenes in a petroleum hydrocarbon contaminated aquifer near Fairbanks, Alaska was assessed using carbon and hydrogen compound specific isotope analysis (CSIA) of benzene and toluene and analysis of signature metabolites for toluene (benzylsuccinate) and xylenes (methylbenzylsuccinates). Carbon and hydrogen isotope ratios of benzene were between -25.9 per thousand and -26.8 per thousand for delta13C and -119 per thousand and -136 per thousand for delta2H, suggesting that biodegradation of benzene is unlikely at this site. However, biodegradation of both xylenes and toluene were documented in this subarctic aquifer. Biodegradation of xylenes was indicated by the presence of methylbenzylsuccinates with concentrations of 17-50 microg/L in three wells. Anaerobic toluene biodegradation was also indicated by benzylsuccinate concentrations of 10-49 microg/L in the three wells with the highest toluene concentrations (1500-5000 microg/L toluene). Since benzylsuccinate typically accounts for a very small fraction of the toluene present in groundwater (generally <1 mol%), the signature metabolite approach works best at higher toluene concentrations when it is not constrained by detection limits. In wells with lower toluene concentrations (410-640 microg/L), carbon and hydrogen isotopic values were enriched by up to approximately 2 per thousand for delta13C and approximately 70 per thousand for delta2H. This evidence of isotopic fractionation verifies the effects of biodegradation in these low concentration wells where metabolites may already be below detection limits. The combined use of signature metabolite and CSIA data is particularly valuable given the challenge of verifying biodegradation in subarctic environments where degradation rates are typically much slower than in temperate environments. 相似文献
478.
Section 305(b) of the United States’ Clean Water Act (CWA) requires states to assess the overall quality of waters in the
states, while Section 303(d) requires states to develop a list of the specific waters in their state not attaining water quality
standards (a.k.at impaired waters). An integrated, efficient and cost-effective process is needed to acquire and assess the data needed to
meet both these mandates. A subset of presentations at the 2002 Environmental Monitoring and Assessment Program (EMAP) Symposium
provided information on how probability data, tools and methods could be used by states and other entities to aid in development
of their overall assessment of condition and list of impaired waters. Discussion identified some of the technical and institutional
problems that hinder the use of EMAP methods and data in the analysis to identify impaired waters as well as development needs
to overcome these problems. 相似文献
479.
480.