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1.
A national critical loads framework for atmospheric deposition effects assessment: I. Method summary
Timothy C. Strickland George R. Holdren Jr. Paul L. Ringold David Bernard Katie Smythe William Fallon 《Environmental management》1993,17(3):329-334
The United States Environmental Protection Agency (EPA), with the assistance of the US Department of Energy (DOE) and the
National Oceanographic and Atmospheric Administration (NOAA) is examining the utility of a critical loads approach for evaluating
atmospheric pollutant effects on sensitive ecosystems. A critical load has been defined as, “a quantitative estimate of an
exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment
do not occur according to present knowledge.” Working in cooperation with the United Nations Economic Community for Europe’s
(UN-ECE) Long Range Transboundary Air Pollution (LRTAP) Convention, the EPA has developed a flexible, six-step approach for
setting critical loads for a range of ecosystem types. The framework is based on regional population characteristics of the
ecosystem(s) of concern. The six steps of the approach are: (1) selection of ecosystem components, indicators, and characterization
of the resource; (2) definition of functional subregions; (3) characterization of deposition within each of the subregions;
(4) definition of an assessment end point; (5) selection and application of models; and (6) mapping projected ecosystem responses.
The approach allows for variable ecosystem characteristics and data availability. Specific recognition of data and model uncertainties
is an integral part of the process, and the use of multiple models to obtain ranges of critical loads estimates for each ecosystem
component in a region is encouraged. Through this intercomparison process uncertainties in critical loads projections can
be estimated.
The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared
at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract #68-C8-0006 with Man Tech Environmental
Technology, Inc. It has been subjected to the agency’s peer and administrative review and approved for publication. Mention
of trade names or commercial products does not constitute endorse ment or recommendation for use. 相似文献
2.
Carolyn Hunsaker Robin Graham Robert S. Turner Paul L. Ringold George R. Holdren Jr. Timothy C. Strickland 《Environmental management》1993,17(3):335-341
The United States Environmental Protection Agency, with support from the US Department of Energy and the National Oceanographic
and Atmospheric Administration, has been evaluating the feasibility of an effects-based (critical loads) approach to atmospheric
pollutant regulation and abatement. The rationale used to develop three of the six steps in a flexible assessment framework
(Strickland and others, 1992) is presented along with a discussion of a variety of implementation approaches and their ramifications.
The rationale proposes that it is necessary to provide an explicit statement of the condition of the resource that is considered
valuable (assessment end point) because: (1) individual ecosystem components may be more or less sensitive to deposition,
(2) it is necessary to select indicators of ecosystem condition that can be objectively measured and that reflect changes
in the quality of the assessment end point, and (3) acceptable status (i.e., value of indicator and quality of assessment
end point at critical load) must be defined. The rationale also stresses the importance of defining the assessment regions
and subregions to improve the analysis and understanding of the indicator response to deposition. Subregional definition can
be based on a variety of criteria, including informed judgment or quantitative procedures. It also depends on the geographic
scale at which exposure and effects models are accurate and on data availability, resolution, and quality.
The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared
at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract #68-C8-0006 with ManTech Environmental
Technology, Inc., and Interagency Agreement #1824-B014-A7 with the US Department of Energy and at Oak Ridge National Laboratory
managed by Martin Marietta Energy Systems, Inc., under Contract DE-AC05-84OR21400 with the US Department of Energy. Environmental
Sciences Division Publication No. 3903. It has been subjected to the agency’s peer and administrative review and approved
for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. 相似文献
3.
Bruce Hicks Robert McMillen Robert S. Turner George R. Holdren Jr Timothy C. Strickland 《Environmental management》1993,17(3):343-353
Methods are discussed for describing patterns of current wet and dry deposition under various scenarios. It is proposed that
total deposition data across an area of interest are the most relevant in the context of critical loads of acidic deposition,
and that the total (i.e., wet plus dry) deposition will vary greatly with the location, the season, and the characteristics
of individual subregions. Wet and dry deposition are proposed to differ in such fundamental ways that they must be considered
separately. Both wet and dry deposition rates are controlled by the presence of the chemical species in question in the air
(at altitudes of typically several kilometers in the case of wet deposition, and in air near the surface for dry). The great
differences in the processes involved lead to the conclusion that it is better to measure wet and dry deposition separately
and combine these quantifications to produce “total deposition” estimates than to attempt to derive total deposition directly.
A number of options for making estimates of total deposition to be used in critical loads assessment scenarios are discussed
for wet deposition (buckets and source receptor models) and for dry deposition (throughfall, micrometeorology, surrogate surfaces
and collection vessels, inference from concentrations, dry-wet ratios, and source-receptor models).
The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared
at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract #68-C8-0006 with ManTech Environmental
Technology, Inc., and Interagency Agreement #1824-B014-A7 with the U.S. Department of Energy and at Oak Ridge National Laboratory
managed by Martin Marietta Energy Systems, Inc., under Contract DE-AC05-84OR21400 with the US Department of Energy. Environmental
Sciences Division Publication No. 3905. It has been subjected to the Agency’s peer and administrative review and approved
for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. 相似文献
4.
An important tool in the evaluation of acidification damage to aquatic and terrestrial ecosystems is the critical load (CL), which represents the steady-state level of acidic deposition below which ecological damage would not be expected to occur, according to current scientific understanding. A deposition load intended to be protective of a specified resource condition at a particular point in time is generally called a target load (TL). The CL or TL for protection of aquatic biota is generally based on maintaining surface water acid neutralizing capacity (ANC) at an acceptable level. This study included calibration and application of the watershed model MAGIC (Model of Acidification of Groundwater in Catchments) to estimate the target sulfur (S) deposition load for the protection of aquatic resources at several future points in time in 66 generally acid-sensitive watersheds in the southern Blue Ridge province of North Carolina and two adjoining states. Potential future change in nitrogen leaching is not considered. Estimated TLs for S deposition ranged from zero (ecological objective not attainable by the specified point in time) to values many times greater than current S deposition depending on the selected site, ANC endpoint, and evaluation year. For some sites, one or more of the selected target ANC critical levels (0, 20, 50, 100μeq/L) could not be achieved by the year 2100 even if S deposition was reduced to zero and maintained at that level throughout the simulation. Many of these highly sensitive streams were simulated by the model to have had preindustrial ANC below some of these target values. For other sites, the watershed soils contained sufficiently large buffering capacity that even very high sustained levels of atmospheric S deposition would not reduce stream ANC below common damage thresholds. 相似文献