UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON D.C. 20460
OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD
November 18,2008
EPA-CASAC-09-002
The Honorable Stephen L. Johnson
Administrator
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, N.W.
Washington, D.C. 20460
Subject: Peer Review of EPA 's Integrated Science Assessment (ISA) for Oxides of
Nitrogen and Sulfur - Environmental Criteria (Second External Review
Draft)
Dear Administrator Johnson:
The Clean Air Scientific Advisory Committee (CASAC or Committee) NOX & SOX
Secondary National Ambient Air Quality Standards (NAAQS) Review Panel (Panel) met on
October 1-2, 2008 to review EP A's Integrated Science Assessment for Oxides of Nitrogen and
Sulfur - Environmental Criteria (Second External Review Draft) (EPA/600/R-08/083, August
2008) (see Enclosure 1 for the Panel roster). This letter has been reviewed and approved by the
chartered CASAC at the public conference call on October 30, 2008 (see Enclosure 2 for the
CASAC Roster). Overall, the Panel found the second draft ISA to be much improved and very
comprehensive. In this letter, the CASAC Panel offers general comments and recommendations
to further strengthen the ISA followed by responses to the Agency's charge questions.
Comments from the individual Panel members are provided in Enclosure 3.
1. EPA has done a good job in response to the Panel's concern regarding imbalance in the
discussion of NOX deposition vis-a-vis reactive nitrogen (Nr) deposition and how the
various components of Nr contribute to acidification and nutrient enrichment. (Reactive
nitrogen refers to the sum of NOX, reduced NHX, and organic nitrogen.) However, there
remain instances in the second draft where appropriate adjustments have not been made.
In finalizing the ISA, EPA should carefully consider if references to concentrations of
particular species and/or deposition effect are made correctly, and in particular whether
and when the term "NOX deposition" should be replaced with "Nr deposition" for clarity
and accuracy.
2. The exclusion of the non-ecological welfare effects of NOX and SOX (e.g., effects of
particulate matter on visibility degradation and climate, and materials damage) in this
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NAAQS review process continues to be an area of concern for the Panel. For a document
entitled "Integrated Assessment for Oxides of Nitrogen and Sulfur - Environmental
Criteria" a focus entirely on ecological effects makes its title a misnomer. The Agency
maintains that these effects are discussed in the assessment documents of other criteria
pollutants and consequently a full treatment in the current review is unnecessary. To
ensure that the ISA represents a meaningful assessment of environmental criteria, EPA
should either rename the document "Ecological Criteria" (which is probably not
feasible) or keep "Environmental Criteria," but state clearly in which Agency documents
the omitted NOX/SOX welfare effects are treated and, at a minimum, provide a short
synopsis of the key non-ecological effects in the appendix.
3. Nitrogen is an essential and often limiting plant nutrient. In certain locations, the effects
of increased Nr deposition may be viewed as ecologically and economically beneficial.
The Agency should make certain that the treatment and discussion of the impacts of Nr
deposition in the ISA are balanced.
4. Given the importance of this document as a foundation for further analyses, there remains
a general need to carefully review the draft for editorial integrity, with particular focus on
clarity and accuracy.
Responses to EPA's Charge Questions:
1. We have added an executive summary of the major findings and conclusions to the
second draft ISA. We have also created a "key findings" section that is intended to
provide highlights of these conclusions. We are seeking CASAC panel advice and
comments on these additions to the ISA. To what extent do they provide an
appropriate level of detail and convey the important scientific conclusions of the
assessment?
The Panel is pleased with the inclusion of an Executive Summary in the ISA report and
found the general tone and scope to be appropriate. However, the Panel does recommend that the
current draft of the key findings be merged into the executive summary to create a single
summary document.
The Executive Summary should incorporate additional conclusions from the ISA
regarding the geographical distribution and magnitude of effects of current acidification and
nitrogen deposition in various parts of the United States. An explanation of the implications of
the extent of current acidification and nitrogen enrichment on ecosystems in terms of lost or
degraded ecosystem services (e.g., changes in biodiversity, local species extinction, and lost
habitat) should be considered. The authors should also include further explanatory text on
emissions sources and atmospheric transport and transformation processes that lead to
deposition. Brief statements summarizing recent and long-term trends in both ambient air
concentrations and deposition loads should be clarified because they currently appear
contradictory.
The Panel cautions the Agency about the overly generalized statements in the current
draft ISA that need to be qualified because they are not applicable to all ecosystems and
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locations. Acidification, nitrogen enrichment, and mercury methylation effects are indeed
important for specific sensitive ecosystems within the United States, but generalizations need to
be made more cautiously.
The summary text (and both ISA and REA documents in general) should be carefully
reviewed to determine where total reactive nitrogen is the appropriate term to use rather than
oxides of nitrogen. EPA should also consult the specific wording suggestions provided within the
individual Panel members' written comments.
2. Chapter 1 has been revised to clarify the scope or focus of this assessment on effects
related to the deposition of nitrogen and sulfur compounds. In addition, we have
added a discussion of the framework for evaluation of causality for assessing
ecological effects. Do these revisions adequately characterize the scope of the
assessment? Does the CASAC panel have recommendations for revisions to the
causality framework? Is it appropriately applied in the draft ISA?
The CASAC Panel generally agreed that Chapter 1 provides a clear, concise introduction
to the ISA. The chapter includes an outline of the intended scope of the current assessment, a
brief history of past SOX and NOX NAAQS reviews, and a proposed framework for the
determination of causality in relationships between the pollutants of concern and the resulting
environmental responses.
There have been substantial advances to the scientific evidence since the publication of
the most recent Air Quality Criteria Documents for NOX and SOX in 1993 and 1982, respectively.
Several Panel members recommended expanding the historical summary of secondary SOX and
NOX reviews and associated technical documents to include references to major EPA or
inter-agency publications. A few examples include the 1985 EPA Acidic Deposition
Phenomenon and Its Effects: Critical Assessment Document, the 1990 NAPAP State of Science
and Technology and Integrated Assessment Reports, and the 1995 EPA Acid Deposition
Feasibility Study report to Congress.
The proposed framework for evaluation of causality is logical and clearly presented.
This framework appears to be followed in subsequent chapters (3 and 4), which contain a
number of concise, declarative statements that "the evidence is sufficient to infer a causal
relationship between X causal agent and Y effect." In most cases, the identified causal agents are
usually "acidifying deposition" or "reactive nitrogen deposition," and thus appear to be
non-specific to the traditional NOX and SOX criteria pollutant definitions. It would be helpful to
include some similar statements of causality that relate emissions to air quality to deposition in
Chapter 2. Additionally, expanding this causality framework to include a concept such as a
"significantly contributing factor" as a subset of a "causal factor" (i.e. "the evidence is sufficient
to infer a causal relationship between Nr deposition, for which oxidized N is a significantly
contributing factor, and Y and Z effects") is advised. This concept of a "significantly
contributing factor" could be important in considering effects resulting from pollutant mixtures,
as well as for considering effects which result from or are modified by the cumulative influences
of both current and historical pollutant deposition.
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3. Chapters 2 and 3 from the first draft have been combined. Substantially more
information has been included on NHs emissions, NHs measurement techniques,
NH3 and NH4 concentrations. Additionally, information on NOX and SOX including
ambient concentrations, deposition levels and their spatial and temporal
relationships has been added. Have these revisions to Chapter 2 improved its
assessment of the currently available scientific knowledge on atmospheric sciences
and its relevance to the evaluation of environmental effects presented in later
chapters?
The revisions and additions to Chapter 2 have substantially improved the document.
EPA has been very responsive to the Panel's comments on the previous draft. As a result, this
version is much improved and constitutes a solid scientific basis for the Risk and Exposure
Assessment (REA). However, there are a few areas where additional information could provide
useful context for evaluating the risk and exposure assessment work. In particular, because the
REA relies so heavily on the Community Multiscale Air Quality (CMAQ) model predictions of
deposition, the section on chemical transport model (CTM) models should be augmented with
specific CMAQ model performance statistics on wet- and dry-deposition. Also, comparisons
should be made between measurements and model parameterizations for wet- and
dry-deposition. Some discussion of sensitivity to critical parameters, such as dry deposition
velocity, precipitation intensity, and depositional resistances, is needed as well.
The additional maps were helpful for forming visual links between modeled emissions,
concentration, and deposition. Nevertheless the varying spatial scales and color schemes make
that comparison difficult. These linkages should be made more explicit either with maps in
which the scales or colors are consistent, or with scatter plot comparisons in matched grid cells
(e.g. concentration vs. deposition).
The current title, 'Source to Dose' should be reworded as 'Source to Deposition' or
something similar to reflect the environmental endpoint. Terms that might be unfamiliar to a
more general audience (e.g., compensation point, ozone production efficiency, and nitrogen
cascade) should be defined. Wherever possible, units should be consistent and clearly stated: it
is not always clear if mass S really means mass of sulfur or whether it is really mass of sulfate,
SO42". We recommend the consistent use of mass of sulfur throughout the document, unless
clearly stated otherwise. Also, it is important to note that all deposition flux units should be
presented in kg/ha-yr rather than kg/ha. Similarly, the ISA should express all nitrate deposition
data in units of kg/ha-yr of nitrogen. The summary section of Chapter 2 (Table 2-25) should be
expanded to include information on the regional changes in wet- and dry-deposition in the
western United States.
Finally, the measurement section should include a discussion of passive samplers and
additional discussion on historical emissions and deposition. The Panel recognizes that high
quality historic data on emissions and atmospheric deposition of NOX, NHX, and total reactive
nitrogen are limited, so more discussion as to how these values are currently estimated, both
from field measurements as well as in atmospheric models (e.g., CMAQ), and their relevance to
MAGIC and other water-quality models would be useful. In the interest of trimming some of the
length of the chapter, some material could be put in the appendices: in particular, the
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tropospheric chemistry discussion and the high-time-resolution data (important but less relevant
for ecological time-frames).
4. We removed or eliminated redundancy, added summary sections, added additional
references and reorganized Chapter 3. Revisions to the ecological effects sections are
given below. Have the revisions improved the characterization of the ecological
effects?
a. Consistent with CASAC comments, we expanded our characterization of the
quantification of chemical effects of acidification in aquatic ecosystems, added
new conceptual diagrams, and further discussed interactions between
acidification and plant disease.
The revised Chapter 3 is logically organized and generally well written. It provides
comprehensive information on the ecological effects of NOX, NHX, and SOX deposition in aquatic
and terrestrial ecosystems - including acidification, nutrient enrichment, and sulfur-deposition
induced methylation of mercury. The conceptual diagrams are useful and the discussion of
interactions between acidification and plant disease is well written and up to date.
Important items missing from Chapter 3 include:
• Observation that despite recent decreases in acidifying deposition and some
improvement in surface water acid-base status there are widespread observations
of ongoing soil acidification (i.e., decreases in soil exchangeable base cations);
• Comparison of MAGIC with other watershed models (see Sullivan et al., 2006);
• Recognition that mercury contamination occurs in terrestrial food webs (see
Rimmer et al., 2005); and
• Probable linkage between atmospheric N deposition and biogenic emissions of
NO and VOCs.
b. We expanded the discussion of quantitative relationships between nitrogen
deposition and ecological effects, including published critical loads in the U.S.
and Europe. In addition, the nitrogen enrichment section was expanded to
include new discussions on carbon budgeting, biogenic nitrous oxide and
methane. Information on the linkages between effects and both reduced and
oxidized forms of nitrogen was emphasized, to the extent data were available.
Information on the published critical loads data from Europe is mostly contained in Table
3-24, as adapted from Acherman and Bobbink (2003). This table summarizes biological
indicators and related critical loads for major ecosystem types in Europe and is probably
sufficient for this document. However, the Panel recommends that the recent reports of the
International Cooperative Program (ICP) Forests and ICP Modeling and Maps also be considered
for updated information on critical load modeling efforts in European forests. The summary of
the dose-response curves forN deposition and ecological indicators presented in Table 3-25 is
valuable and should greatly help in developing a large-scale evaluation of critic loads in the US
and their spatial adaptation.
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The section of Chapter 3 dealing with the carbon cycle of the Earth as related to N
deposition is comprehensive and based on recently published studies. EPA staff should make
sure that the presentation recognizes that nitrogen and sulfur are essential to plant growth, and
thus can influence carbon sequestration, with nitrogen often being the limiting nutrient in
terrestrial ecosystems. The evidence presented shows that ambient N deposition can result in
increased atmospheric emission of N2O and CH/t.
c. The section on "other" welfare effects was updated to include information on the
direct phytotoxic effects of nitric acid.
Although a good discussion of direct effects of nitric acid is provided, it should be
emphasized that most of the damaging effects of HNOs have been observed in relatively
short-term exposures at above-ambient concentrations of the pollutant. Long-term effects of
lower air concentrations that more closely approximate ambient levels of HNOs should be
investigated. Similarly, visible injury to plant foliage due to exposure to NO, NC>2 or NH3 have
been demonstrated primarily at concentrations that rarely occur in ambient air.
5. In revising the ISA, we have incorporated additional information on the
indicators of exposure and ecological effects, including increased emphasis on
quantified relationships in the presentation of information of results in tables
and summary discussions in Chapter 4. What are the views of the CASAC panel
on our revisions to focus on quantitative relationships between airborne nitrogen
and sulfur compounds and ecological indicators?
The effort made to perform an analysis of existing literature on ecological indicators
relevant to deposition and acidification is commendable. The meta-analysis appears to be
extensive and appropriate for the ISA. Much literature has been compiled, including a smattering
of studies involving high application of N (up to typical fertilizer levels). A summary of
traditional forest and grassland fertilizer studies could strengthen this study, as well. Much of this
literature is old, but still very relevant - especially the early fertilizer studies by C.O. Tamm et al.
in Sweden. The tradeoffs associated with the use of nitrogen fertilizer in enhancing the
productivity of forests, crops and grasslands versus the deleterious environmental impacts
associated with excess nitrogen being released into the environment, especially surface waters,
should be articulated more clearly.
The analysis of indicators is particularly important since a secondary standard (if
proposed and promulgated) needs to be expressed in terms of SOX, NOX, or NOX + NHX (Nr) and
then properly linked to the effects through the relevant ecological indicators and causality
frameworks. In the summary, it would be desirable to continue fortifying the linkages in the
chain of causation between emission - atmospheric concentration - deposition - dosage - effect
- ecosystem services. An example of such an end-to-end causality illustration would help. A
synchronized array of trend charts for each parameter/indicator in the causality chain could be an
effective way to illustrate the overall framework and key aspects of systems behavior. While it
may not be necessary to have quantitative trend values for each of the parameters in the causality
chain ensemble in the ISA, graphically indicating (e.g., dashed trend lines) the poorly understood
parameters would be a more realistic representation of the current state of the causality
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framework. It is also appropriate to recognize how the causality framework may be used in both
prospective and retrospective analyses.
In summary, with incorporation of the Panel's recommendations to strengthen the
document, this second draft ISA will provide appropriate scientific support for the risk and
exposure assessments. The CAS AC was pleased to review this second draft of the ISA and looks
forward to the Agency's response.
Sincerely,
/Signed/
Dr. Armistead (Ted) Russell, Chair
CASAC NOX & SOX Secondary
NAAQS Review Panel
/Signed/
Dr. Jonathan M. Samet, Chair
Clean Air Scientific Advisory Committee
Enclosures
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Enclosure 1: Roster of CASAC NOX & SOX Secondary NAAQS Review Panel
U.S. Environmental Protection Agency
Clean Air Scientific Advisory Committee
NOX& SOX Secondary NAAQS Review Panel
CHAIR
Dr. Armistead (Ted) Russell, Professor, Department of Civil and Environmental Engineering,
Georgia Institute of Technology, Atlanta, GA
PANEL MEMBERS
Dr. Praveen Amar, Director, Science and Policy, NESCAUM, Boston, MA
Dr. Andrzej Bytnerowicz, Senior Scientist, Pacific Southwest Research Station, USDA Forest
Service, Riverside, CA
Ms. Lauraine Chestnut, Managing Economist, Stratus Consulting Inc., Boulder, CO
Dr. Douglas Crawford-Brown, Professor Emeritus, Department of Environmental Sciences and
Engineering, University of North Carolina at Chapel Hill, Chapel Hill, NC
Dr. Charles T. Driscoll, Jr., Professor, Environmental Systems Engineering, College of
Engineering and Computer Science, Syracuse University, Syracuse, NY
Dr. Paul J. Hanson, Distinguished R&D Staff Member, Environmental Sciences Division, Oak
Ridge National Laboratory, Oak Ridge, TN
Dr. Rudolf Husar, Professor and Director, Mechanical Engineering, Engineering and Applied
Science, Center for Air Pollution Impact & Trend Analysis (CAPITA), Washington University,
St. Louis, MO
Dr. Dale Johnson, Professor, Department of Environmental and Resource Sciences, College of
Agriculture, University of Nevada, Reno, NV
Dr. Naresh Kumar, Senior Program Manager, Environment Division, Electric Power Research
Institute, Palo Alto, CA
Dr. Myron Mitchell, Distinguished Professor and Director, College of Environmental and
Forestry, Council on Hydrologic Systems Science, State University of New York, Syracuse, NY
Mr. Richard L. Poirot, Environmental Analyst, Air Pollution Control Division, Department of
Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT
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Mr. David J. Shaw, Director, Division of Air Resources, New York State Department of
Environmental Conservation, Albany, NY
Dr. Kathleen Weathers, Senior Scientist, Institute of Ecosystem Studies, Millbrook, NY
SCIENCE ADVISORY BOARD STAFF
Ms. Kyndall Barry, Designated Federal Officer, 1200 Pennsylvania Avenue, NW
1400F, Washington, DC, Phone: 202-343-9868, Fax: 202-233-0643, (barry.kyndall@epa.gov)
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Enclosure 2: Roster of the chartered CAS AC
U.S. Environmental Protection Agency
Clean Air Scientific Advisory Committee
CHAIR
Dr. Jonathan M. Samet, Professor and Chair, Department of Preventive Medicine, University
of Southern California, Los Angeles, CA
MEMBERS
Dr. Joseph Brain, Philip Drinker Professor of Environmental Physiology, Department of
Environmental Health, Harvard School of Public Health, Harvard University, Boston, MA
Dr. Ellis B. Cowling, University Distinguished Professor At-Large Emeritus, Colleges of
Natural Resources and Agriculture and Life Sciences, North Carolina State University, Raleigh,
NC
Dr. James Crapo, Professor of Medicine, Department of Medicine, National Jewish Medical
and Research Center, Denver, CO
Dr. H. Christopher Frey, Professor, Department of Civil, Construction and Environmental
Engineering, College of Engineering, North Carolina State University, Raleigh, NC, USA
Dr. Donna Kenski, Data Analysis Director, Lake Michigan Air Directors Consortium,
Rosemont, IL
Dr. Armistead (Ted) Russell, Professor, Department of Civil and Environmental Engineering,
Georgia Institute of Technology, Atlanta, GA
SCIENCE ADVISORY BOARD STAFF
Dr. Holly Stallworth, Designated Federal Officer, 1200 Pennsylvania Avenue, NW,
Washington, DC, Phone: 202-343-9867, Fax: 202-233-0643, (stallworth.holly@epa.gov)
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Enclosure 3: Compilation of Individual Panel Member Comments on EPA's Integrated Science
Assessment (ISA) for Oxides of Nitrogen and Sulfur - Environmental Criteria (Second External
Review Draft)
Comments received:
Dr. Praveen Amar 12
Dr. Andrzej Bytnerowicz 14
Ms. Lauraine Chestnut 17
Dr. Ellis Cowling 19
Dr. Douglas Crawford-Brown 24
Dr. Charles T. Driscoll 28
Dr. Paul J. Hanson 43
Dr. Rudolf Husar 46
Dr. Dale Johnson 49
Dr. Donna Kenski 53
Dr. Myron J. Mitchell 55
Mr. Richard L. Poirot 71
Mr. David Shaw 73
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Dr. Praveen Amar
Question # 3: Chapters 2 and 3 from the first draft have been combined. Substantially more
information has been included on NH3 emissions, NH3 measurement techniques, NH3 and NH4
concentrations. Additionally, information on NOx and SOx including ambient concentrations,
deposition levels, and their spatial and temporal relationships has been added. Have these
revisions to Chapter 2 improved its assessment of the currently available scientific knowledge of
atmospheric sciences and its relevance to the evaluation of environmental effects presented in
the later chapter si
Response:
I would like to note that the previous Chapters 2 and 3, now combined in current Chapter 2, is a
great improvement over the first ISA Draft. It is quite clear that very useful and relevant
information has been included on reduced form of nitrogen (ammonia emissions, measurement
techniques to estimate ambient levels of ammonia and inter comparison of these techniques, as
well as concentrations of nitrate in particulate form). Equally useful is the more clear
presentation on NOx and SOx (concentrations, deposition levels, trends in these levels, as well as
spatial and temporal character of these two pollutants). EPA staff needs to be commended for
this.
I have several specific comments that are outlined below:
1.1 think the Title of the Chapter needs to change from "Source to Dose" to "Source and
Exposure," or something similar. This is because this Chapter is NOT about dose. In fact, a quick
"search" shows that the word "dose" appears only once in this Chapter of more than 200 pages
(page 2-116 to be exact). This is not surprising because this Chapter talks about emissions,
concentrations, measurement techniques, trends, etc. but does not talk about dose. In fact,
Chapter 3 is about "dose-response" and the word 'dose" appears in that Chapter frequently and
correctly.
2. On page 2-2, please describe N cascade of Galloway in a little more detail since this is an
important concept and not widely understood.
3. Page 2-19:1 do not understand "compensation point" of ammonia. Needs some clarification.
What is being compensated? Ammonia?
4. Page 2-20: Line 10:1 do not think "biogenic production" of ammonia from agriculture (chiefly
from livestock) is the right word. It is as anthropogenic as it can get!
5. P (O3): Ozone Production Efficiency: It is an important concept. However, I do not think it is
clearly defined in the document (as number of molecules of ozone produced per molecule of
NOx over a certain time period and over a spatial extent, etc.). I suggest it should be explicitly
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defined first time it appears. Just like N cascade, it is important concept and needs to be
explained clearly.
6. Page 2-20: Para under the Figure: I had made this comment on the first ISA Draft. Ammonia
emission totals are dominated by livestock/fertilizer operations because they simply are. They
are dominant source of ammonia in their own right and not because mobile sources are not.
Please drop the words "for these reasons..." on line 9.
7.1 have not thoroughly read the section on Halogen Chemistry (page 2-41). Please make sure it
is improvement on the version included in first draft and that it is integrated with the general
theme of its relationship with, and effect on, SOx/NOx/NH3 chemistry.
8. A general comment: please be consistent and clear that you mean to give quantitative values
of nitrogen and sulfur deposition in the units of "N" and "S" for kg of N/ha/yr, and kg of
S/ha/yr., etc. If they are given in terms of sulfate (SO4) or nitrate (NO3), they should be clearly
labeled as such. I recommend "N" and "S". To be inserted
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Dr. Andrzej Bytnerowicz
Question 4. Have the revisions improved the characterization of the ecological effects?
In general, Chapter 3 presents comprehensive information on ecological effects of SOx and
NOx. The chapter is logically organized, contains current knowledge supported by large number
of informative tables and figures. Good examples of very informative tables are Table 3-12
presenting summary of knowledge on the effects of fire on nutrient concentrations in forests in
California and Nevada and Table 3-15 summarizing N effects on forest carbon cycling. In
summary - the revisions improved characterization of the ecological effects in the document.
Summaries in the end of each sub-sections are very useful. Remark - summaries from Section
3.2 are not listed in the Table of Contents.
References in the text and list of citations are not always matching. Some of them are not cited
properly. Examples of this deficiency are the references of Bytnerowicz et al., or Temple and
Taylor (1983), incorrectly cited in the text as Temple (1983).
Remark - careful technical editing of a final version of this document is recommended.
Question 4a. Chemical effects of acidification in aquatic ecosystems
Information on acidifying effects of NOx and SOx aquatic ecosystems is comprehensive.
Conceptual diagrams for this section have been correctly chosen. Examples of such diagrams are
Figure 3.1 presenting fluxes of major ions associated with S depositions or Figure 3-5 showing
the effects of acidic deposition on Ca supply in trees, their physiology, growth and resistance to
environmental stresses.
Discussion of interactions between acidification and plant disease is well written and up to date.
Interaction of acidity with foliar, membrane-associated calcium, which influences responses of
trees to changing environmental conditions, such as cold temperatures and winter injury, is very
well described. Remark - a reference to Figure 3-5 should be made in the text.
Question 4b. Quantitative relationships between nitrogen deposition and ecological effects
Information on the published critical loads data from Europe is mostly contained in Table 3-24
adapted from Acherman and Bobbink (2003). The table summarizes biological indicators and
related critical loads for major ecosystem types in Europe and is probably sufficient for this
document. However, I would like to recommend that the recent reports of the ICP Forests and
ICP Modeling and Maps are also considered for updated information on CL modeling efforts in
the European forests. Summary of the dose-response curves for N deposition and ecological
indicators presented in Table 3-25 is valuable and should greatly help in developing a large-scale
evaluation of critical loads in the U.S and its spatial extrapolation.
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The nitrogen enrichment section has been expanded and contains discussion on carbon
budgeting, and fluxes of biogenic nitrous oxide and methane. Section on the carbon budget as
related to N deposition is comprehensive and based on the recent scientific literature. Figure 3-35
shows interactions between the N and C cycles while Table 3-15 summarizes N effects on forest
carbon cycling in Europe and North America. The section is well organized and written and is
supported by informative graphs and summary tables. Specific remark - page 3-136, citation of
Sutton et al (2008) does not seem to be correct. Section on methane and nitrous oxide flux is
based on the meta-analysis of the recently published studies. The presented evidence shows that
N deposition results in higher concentrations of these greenhouse gases in the atmosphere.
Question 4c. Other welfare effects
Good discussion of direct effects of nitric acid is provided. However, it should be emphasized
that the described damaging effects of HNOs have been demonstrated in controlled experiments
for relatively short-term exposures at highly elevated concentrations of the pollutant. Long-term
effects of lower, closer to ambient, levels of HNOs, should be investigated. Similarly, visible
injury to plant foliage due to NO, NO2 or NH? exposures have been demonstrated only at very
high concentrations (controlled studies, industrial spills), at the levels that normally do not occur
in ambient air.
Table 3-28 on direct effects of SO2 should be moved closer to the text describing these effects.
Remark - please see my above comments regarding a need for correct citation of references in
this sub-section.
Executive Summary
Although it generally adequately summarizes the ISA document, there are several deficiencies
that should be resolved:
1. In the Introduction, or in a footnote to it, it should be noted that 1 ppm = 1000 ppb. Readers
less familiar with science may not know this fact, and both units are used throughout the text.
2. In the section "Current concentrations and deposition in the US", there are some statements
that are not correct. For instance, on page 2, last paragraph of the first column, a statement is
made that the highest mean N deposition of about 9 kg/ha/yr totals is in the Ohio River valley.
This value seems to be too low -1 suspect that this is only the wet portion of N deposition. On
the same page, the second paragraph of the second column, states that the model-predicted
values in some regions of the Adirondacks are >20 kg N/ha/yr. In southern California the
model-predicted total N deposition can be as high as 32 kg N/ha/yr. Actually, according to Fenn
(2008), the highest values can be as high as > 100 kg N/ha/yr on the western slopes of the San
Bernardino Mountains. However, that high deposition mostly results from deposition of HNOs,
NH? and particulate NOs" and NH4+, not NO and NO2 as the Executive Summary states.
3. In the section "Ecological effects of N deposition" a clear statement is needed that ecological
effects of NOX and SOX should be considered in a context of often unpredictable climate changes.
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Ecological effects of NOX and SOX will also depend on other stressors, such as elevated
background levels of ambient ozone, drought, insect and pathogens outbreaks, etc.
4. On Page 6, 3rd paragraph of the first column - a statement "Exposures of NO2, nitric oxide
(NO), peroxyacetyl nitrate (PAN) and nitric acid (HNO3) cause similar forms of plant injury and
decreased growth" is not true. Characteristics of foliar injury caused by these various compounds
are actually quite different (please see Bytnerowicz et al., 1998 for discussion of this issue).
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Ms. Lauraine Chestnut
Charge Question 1: Executive summary and key findings
The Executive Summary (ES) is a useful addition to the document, but it needs a little more
detail to communicate more effectively the nature and magnitude of current harmful effects on
ecosystems from N and S deposition in the US. As currently written, it describes the effects that
can happen but says too little about the extent to which these are currently happening. The "key
findings" document is largely redundant with the ES, but uses some nice formatting and boxes to
highlight key points. I suggest merging these into one summary document and making use of text
boxes to highlight some of the key conclusions.
The "Scope" section needs a paragraph or two explaining the transport of emissions and their
interaction in the atmosphere that result in N and S deposition. The first paragraph in Section 4-1
on page 4-1 in the conclusions section provides a description of this at a level of detail that
would be useful in the ES.
A paragraph or two on the major sources of emissions that lead to N and S deposition would be
helpful in this section. This information is well described in Chapter 2.
The "Current concentrations" section needs to reconcile the information about declines in
ambient concentrations from 1990 to 2005 versus the "10-fold increase" in deposition in the past
100 years. It would be appropriate here and in the Introduction chapter to mention the Acid Rain
Program (Title IV) as one of the main reasons for the decrease in emissions (especially 862)
from 1990 to 2005 and to note that the reductions from this program are now close to fully
implemented and are leveling off. This program is not part of the NAAQS process, but it seems
odd not to mention such a major program that was motivated by concern about the effects of acid
deposition.
In the section on "Ecological effects of acidification" there needs to be more descriptive
information about the effects and their current extent and significance in the US. I'm not sure it
comes through clearly that certain species offish, particularly ones that people like to catch, have
died off and cannot live in these acidified lakes and streams. I'm not sure the words "decline in
fish species richness" quite gets the significance across. The discussions of the Adirondacks and
Shenandoah and expectations of future acidification conditions at current deposition levels are
good and are examples of the kinds of descriptive implications appropriate for the ES.
In the section on "Ecological effects of N deposition" there needs to be more descriptive
information about the extent and significance of eutrophication of estuarine ecosystems in the
US. How many of the major estuaries in the US show significant eutrophication? What is the
extent of losses to fisheries and habitat?
The "key findings" section will go away if merged into the ES, but material that is not
duplicative should be brought into the ES. In that light here are some specific comments on the
key findings:
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• The first box would be better labeled "main effects" than key findings. It describes the
types of effects, but does not say how widespread or significant these effects are in the
US at current deposition levels.
• In the first paragraph after the first box, the parenthetical phrase after "secondary" is
confusing. Ecological effects are public welfare effects, as I understand the language of
the Clean Air Act. It would be more straightforward to just explain here that this ISA is
focusing on ecological effects of deposition, and other welfare effects of PM, SO2 and
NOx are dealt with elsewhere.
• In the first set of bullets under effects of acidification, it would be helpful to distinguish
between ecosystems that are sensitive and those that are experiencing significant effects
on ecosystem functions at current deposition levels.
• The second bullet on deposition levels is good, but seems out of place in this list. A little
more location dimension to these numbers would be useful—perhaps a map.
• It might be easier to for the reader if the sections on effects of acidification and N
deposition were both subdivided into aquatic and terrestrial subsections.
• The acidification section needs more description of where and how significant are current
effects on ecosystems. The last paragraph in this section is good, but the heading needs to
be qualified—some ecosystems that are currently experiencing harmful effects....
• Bullets under effects of nitrogen deposition: Separate the points about effects, deposition
levels, and monitoring. The monitoring points need some explanation of why these
monitoring limitations are problematic. Add some location information on the deposition
rates.
• In the section on effects of N deposition add information on where there are significant
observed effects in the US now, and describe the extent of the effects.
• The figure on interactions between carbon and nitrogen cycles needs some discussion. It
in not clear what the implications are.
Charge Question 2: Chapter 1
Some discussion of how Title IV (Acid Rain Program) fits into this history would be appropriate.
Also some mention of the 1995 "Acid deposition standard feasibility study" report to Congress
would be appropriate as part of the background.
Charge Question 4: Chapter 3
Chapter 3 does a much better job now in describing the significance of the effects on ecosystems
and of using the "case studies" as examples of these effects. Section 3.3.9 on ecosystem services
affected by N deposition is good and helps set the stage for what comes in the REA. It would be
useful if something similar were done for acidification in section 3.2.
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Dr. Ellis Cowling
General Comments on the New NAAQS Review Processes
Before dealing with the details of my specific assignments during the October 1-2, 2008 meeting
of CASAC I would like to offer a few general comments about the current efforts to streamline
the NAAQS review processes and how these changes in process are playing out in the case
of the CASAC Review of the Secondary (public-welfare based) NAAQS for NOx and SOx.
Many of us in CASAC have been very pleased that EPA has recently shown increased
willingness to think more holistically - and in more fully integrated ways - about both the
policy-relevant science and the practical arts of air quality management aimed at protection of
both public welfare and public health. These shifts in both emphasis and approach have
included:
1) Increased emphasis on scientific questions that are as directly relevant as possible to
well-defined policy questions of concern to EPA. This shift to greater policy relevancy
in our scientific discussions within CASAC will increase efficiency in the preparation
and CASAC review of NAAQS documents, and also help streamline the NAAQS review
Process. For example, the following policy-defining statement was recommended as a
guide during NAAQS review processes:
"What scientific evidence and/or scientific insights have been developed since the last
review to indicate if the current public-health based and/or the current public-welfare
based NAAQS need to be revised or if alternative levels, indicators, statistical forms, or
averaging times of these standards are needed to protect public health with an
adequate margin of safety and to protect public welfare?"
2) More frequent discussion about both public-welfare and public-health impacts of
mixtures of air pollutants;
3) Separation of the preparation and review of documentation for a Secondary
(public-welfare-based) NAAQS from the (previously always dominating) Primary
(public-health-based) NAAQS review processes,
4) The decision by the Science Advisory Board (SAB) of EPA in January 2007 to establish
a special Integrated Nitrogen Committee (INC) with the following set of objectives:
a) Identify and analyze, from a scientific perspective, the problems nitrogen presents
in the environment and the links among them,
b) Evaluate the contribution an integrated nitrogen management strategy could make
to environmental protection,
c) Identify additional risk management options for EPA's consideration, and
d) Make recommendations to EPA concerning improvements in nitrogen research to
support risk reduction,
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5) The unprecedented decisions by EPA to undertake an integrated [simultaneous]
review of the Secondary NAAQS for two Criteria Pollutants at the same time
[Oxides of Nitrogen (NOx) and Oxides of Sulfur (SOx)], and to facilitate the
required CAS AC and public reviews of:
i) an Integrated Science Assessment (ISA) for NOx and SOx — to be issued in
December 2008,
ii) a Risk/Exposure Assessment (R/EA) - to be completed by July 2009,
iii) a Policy Assessment/Rulemaking document prepared in the form of an Advanced
Notice of Proposed Rule Making (ANPR) — by August 2009, and thus to
achieve
iv) Final Rule Making — prior to a court-ordered deadline of October 19, 2010.
In view of this demanding series of deadlines following our October 1-2 CASAC meeting, it is
obvious that EPA and CASAC now have only about:
i) 3 months to complete the Final ISA for NOx and SOx, and
ii) 11 months in which to complete reviews of both the First and Second External
Review Drafts and then to prepare a Final Draft R/EA for NOx and SOx.
But we now have the considerable advantage that the new NAAQS review process envisions
preparation of much more concise and much more policy-focused ISA and R/EA documents
for the present Integrated Secondary NAAQS for NOx and SOx than has historically been
achieved in the encyclopedic Criteria Documents that have been prepared during the years
since 1970.
Specific Comments on the ISA for the Secondary Nitrogen and Sulfur Pollution NAAQS
Standards
The present Second Draft ISA is a very huge volume which consists of:
Chapter 1 - an appropriately short (10 page) "Introduction,"
Chapter 2 - an exhaustive (202 page) analysis of "Source to Dose" relationships for both
NOx and SOx,,
Chapter 3 - a similarly exhaustive (237 page) analysis of Ecological and Other Welfare
Effects. This chapter is appropriately focused on five critically important impacts of
atmospherically deposited reactive nitrogen and sulfur compounds - acidification and
nutrient enrichment of aquatic and terrestrial ecosystems and sulfur induced increase in
methylation of mercury,
Chapter 4 - a reasonably short (33 page) Summary and Conclusions chapter that includes
many statements of conclusion from the science that is reviewed Chapters 2 and 3,
Glossary - a very neat set of definitions for many of the specialized terms used in Chapters
1-4,
References - an exhaustive (124 page) list of (nearly 3000 scientific literature citations!)
most of which are relevant to the possible revision of the current NAAQS standards for
nitrogen and sulfur pollution. It would be very valuable to identify a limited number of
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these documents that are especially significant in terms of the policy purpose for which
this ISA was written.
Having carefully reviewed all of these several parts of this Second Draft ISA, I was:
1) Generally satisfied with the parts of Chapters 1-3 that deal with oxides of nitrogen
and sulfur, but was disappointed that much less attention continues to be given in
Chapters 2 and 3 to the quantitative importance and significant biological impacts
of chemically reduced forms of total reactive nitrogen. This is true with regard to
both acidification and nutrient enrichment of aquatic and terrestrial ecosystems.
2) In spite of the 'relatively less attention' comment mentioned in comment 1 (above), I
was very pleased to read in Chapter 4 the 23 bold-face-type statements regarding
the "sufficiency of evidence to infer a causal relationship between 'acidifying
deposition' and/or 'Nr deposition'" and each of the many adverse acidification and
nutrient enrichment effects of atmospheric deposition reactive nitrogen and sulfur
pollution on aquatic and terrestrial ecosystems that are discussed in Chapters 2 and
3.
3) At the same time, however, I was disappointed that almost all of the
non-bold-faced-type conclusions among the Summary and Conclusions statements
in Chapter 4 were notably lacking in specific articulation of the quantitative
importance and significant biological impacts of chemically reduced and organic
forms of reactive nitrogen in both terrestrial and aquatic ecosystems.
4) This lack of specific articulation of the quantitative importance and significant
biological impacts of chemically reduced and organic forms of reactive nitrogen was
especially worrisome in the final "Conclusion" statement in the Executive Summary
of this ISA.
Specific Comments on the Executive Summary of the ISA
This final Conclusion in the Executive Summary includes the following two statements
both of which are incorrect and misleading in terms of their relevance to the policy
purpose for which this ISA is being written:
"Acidification is driven by the deposition resulting from NOx and SOx pollution."
"In addition to acidification, deposition resulting from NOx, along with other
sources of reactive nitrogen (e.g., fertilizers, waste water, and atmospheric
ammonia deposition), causes a suite of ecological problems including biodiversity
losses, disease, eutrophication, and harmful algal blooms."
Permit me to offer the following improved and more accurate wording of the final
Conclusion of the Executive Summary (please note especially the explicit recognition of
both reduced and oxidized forms of reactive nitrogen — both of these chemical forms of
nitrogen are significant "Pollutants of Concern" as well as causal factors in both
acidification and nutrient enrichment:
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Conclusion
The three main effects of nitrogen and sulfur pollution presented in this ISA are
acidification, nitrogen enrichment, and methylation of mercury. Acidification of
ecosystems is driven primarily by atmospheric deposition of NOx, NHx, and SOx.
These three pollutants cause a cascade of effects that harm both aquatic and terrestrial
ecosystems including localized extinction offish populations and other aquatic species,
and slower growth and injury to forests. In addition to acidification, atmospheric
deposition resulting from NOx and NHx emissions, along with other sources of reactive
nitrogen (e.g., fertilizers and waste waters) cause a suite of ecological problems including
biodiversity losses, disease in aquatic and terrestrial organisms, as well as eutrophication
and harmful algal blooms in both fresh water, estuarine, and ocean ecosystems. Both
gaseous sulfur compounds and particulate sulfate can interact with methanogenic bacteria
to produce methyl mercury, a powerful toxin that can bioaccumulate to toxic amounts in
food webs at higher trophic levels (e.g., otters, king fishers.)
Specific Comments on the Value of the Recently-Posted Document Titled
'•'•Selected Recommendations and Findings from the Integrated Nitrogen
Committee" and
an earlier Resolution by the Integrated Nitrogen Committee of EPA's Science
Advisory Board
As many of us on the CAS AC NOx/SOx Secondary NAAQS Panel will recall, during our
October 30, 2007 CAS AC meeting, the following Resolution was received from the SAB's
Integrated Nitrogen Committee.
Resolution from the Integrated Nitrogen Committee of the Science Advisory Board ~
for Consideration by the CASAC Secondary NAAQS NOx and SOx Review Panel
During the ongoing meeting of the EPA Science Advisory Board's Integrated Nitrogen
Committee (INC) - meeting at SAB Headquarters in Washington DC on October 29-31, 2007 --
the several members and Chair of the INC, Dr. James Galloway of the University of Virginia,
asked me (as the CASAC-designated liaison person to the Science Advisory Board's Integrated
Nitrogen Committee) to present the following Resolution (which was developed and approved
by the INC) for consideration during the CASAC review of the NAAQS for NOx and SOx
during our CASAC Conference Call Consultation on October 30, 2007.
Resolution
The current air pollution indicator for oxides of nitrogen, NOx, is an inadequate measure of
reactive nitrogen in the atmospheric environment. The SAB's Integrated Nitrogen
Committee recommends that inorganic reduced nitrogen (ammonia plus ammonium) and total
oxidized nitrogen, NOy, be monitored as indicators of total chemically reactive nitrogen.
This Resolution is an important part of the scientific foundation and rationale behind my concern
that the "Second External Review Draft of the ISA for Oxides of Nitrogen and Sulfur -
Environmental Criteria" and the First Draft of the "Risk and Exposure Assessment for Review of
the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of
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Sulfur" are not consistent with the central idea of this Resolution - that both chemically reduced
and chemically oxidized forms of reactive nitrogen must be considered in the current round of
reviews of the NOx/SOx Secondary NAAQS Standards.
Further justification for these ideas — and policy recommendations that derive from the extended
deliberations of the SAB's Integrated Nitrogen Committee — are contained in a recently
completed Summary Document titled: "Selected Recommendations and Findings from the
Integrated Nitrogen Committee." This document was recently posted on the SAB website and
thus is available for public review at the following URL:
http://yosemite.epa.gov/sab/sabproduct.nsf/MeetingCal/EFB3E4663E2143F88525746
5006C5B32?OpenDocument
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Dr. Douglas Crawford-Brown
I am charged primarily with Question 1, and so my comments are primarily on that question.
However, since this Charge Question covers the Executive Summary and a "key findings"
section, the review makes reference to other chapters where these materials are found. The
specific Charge Question addressed is:
1. We have added an executive summary of the major findings and conclusions to the
second draft ISA. We have also created a "key findings" section that is intended to provide
highlights of these conclusions. We are seeking CAS AC panel advice and comments on these
additions to the ISA. To what extent do they provide an appropriate level of detail and convey
the important scientific conclusions of the assessment?
The short answer is yes and yes. They provide the appropriate level of detail (with a few caveats
noted below) and convey the most important conclusions from other chapters. As I will note
below, however, it is less clear where this "key findings" section is located. Given the Charge
Question, I had expected to find it in the Executive Summary or listed in the Table of Contents.
It is in neither.
In the Executive Summary on Page 1, there is a segue-way needed between gas and deposition
effects. The first section ends by saying that the existing NAAQS were set on the basis of direct
exposure to gases. Then the next paragraph begins by stating that this document focuses on
deposition of NOx and SOx, which will be dominated by the particulate phase. A reader will
wonder whether the current document is therefore a supplement to the previous NAAQS, or has
changed the focus of concern - and if so, why.
Then in the same area of the document, the authors state that understanding the ecological effects
requires considering many reduced forms of N. While I agree with this, the statement does not
say "in addition to the oxidized forms", and so the reader will again be confused, wondering if
the NAAQS has changed completely to deposition rather than gas phase, and to reduced rather
than oxidized forms. It is simply a problem with the way this sentence is structured, not with the
list of forms shown or the intent of the sentence.
In the next paragraph, there is a discussion of the extent of decrease in NOx and SOx. The
numbers are correct given data in later chapters, but there needs to be clarity as to what the 35%
and 50% figures refer to. Are these mean annual levels measured at monitors; mean levels of
exposure (perhaps population-weighted)? Something else? A few words of explanation would
resolve this problem.
And then later, the comment is made (correctly) that N deposition has been increased 10 fold
over the past century. The problem with this statement is that it seems to contradict the finding
that ambient levels have been in fact going down over the past decade. The problem lies, of
course, in specifying the different periods of time over which the trends are being discussed.
Surely N deposition has been going down as ambient levels have gone down, even if they went
up quite a bit more prior to the recent decline. Or, is the difference between the two sections that
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the first refers specifically to NOx and the latter to all forms of N deposition, with perhaps the
reduced forms continuing to go up (I doubt this is the case, but just want to be sure)? If I am
confused, the average reader probably will be as well.
I fully support the conclusion on the inadequacy of the current monitoring network for
deposition. Some more comment is needed on how that system might be better structured to
resolve the specific areas of uncertainty found in the ISA.
I believe the later chapters support the conclusion that "available evidence is sufficient to infer a
causal relationship between acidifying deposition at current levels and effects on the following
aspects of ecosystem structure and function:
(1) biogeochemistry related to terrestrial and aquatic ecosystems;
(2) biota in terrestrial and aquatic ecosystems."
As with the previous ISA, however, I remain less convinced that we can quantify this causal
relationship sufficiently to determine an ambient concentration that would be judged to produce
an acceptable level of impact, and nothing in the subsequent chapters makes me more
comfortable with this task. Surely the ecosystem effects must be treated somewhat like the
human health effects, where a change in some measure of health is not in itself evidence of
unacceptably high adversity of effect. At some point, the changes noted in ecosystem measures
of health do become high enough to consider not just present but adverse, but the ISA is not yet
able to establish where that might be in most cases. I suspect this will drive the regulatory
process to rely on the primary standards, with the secondary effects providing supporting
evidence for the need to further lower ambient levels - even if it cannot specify how far they
should be lowered.
With respect to climate change, I disagree with the way the following statement is introduced
and phrased: "N deposition often increases primary productivity. This does not necessarily
increase C sequestration. C budgets are complicated by numerous factors that influence carbon
exchange (e.g. climate)." The problem with the phrase is that in later chapters, the argument is
made that nitrogen oxides can contribute to climate change both by being greenhouse gases and
by reducing carbon storage in flora. The phrase "This does not necessarily increase C
sequestration" is correct, but I would suggest that on average the increase in primary productivity
will offset the adverse effects on plant growth. Perhaps I am wrong in this, but the later chapters
don't provide any data to suggest the correct answer one way or the other, and so the statement
in the Executive Summary strikes me as an off-hand way to disarm a possibility that runs counter
to the story being told (that NOx is bad for climate change). A much better scientific analysis is
needed in the document to provide any firm conclusions one way or the other, or the impression
will be left that the EPA staff have deliberately chosen only some aspects of the N-climate
change connection to bolster their case.
I agree completely with the focus on acidification and nitrogen enrichment as the two primary set
of effects. There is sufficient evidence in later chapters to infer a causal relationship between
current ambient levels in some geographic areas and adverse ecological effects. But I am less
convinced by the methyl mercury argument. I don't mean I don't believe the case is made for
sulfate leading to methyl mercury, but rather that I don't see sufficient evidence to suggest that
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current levels of sulfate are causing methyl mercury concentrations that are of concern. I suppose
the argument could be made that any methyl mercury increase is too much given current levels
of methyl mercury in the food chain, but this argument isn't made or supported in later chapters.
On the issue of causal relationships, found in Chapter 1, the authors have done a good job of both
classifying the causal categories and explaining the criteria for judging causality. As with
previous ISAs, however, it is much less clear that any formal framework has been used to
determine whether a given body of evidence does or does not satisfy these criteria, or how the
criteria are to be balanced when one is satisfied but not another. The result is a purely subjective
judgment of the strength of causality. I would agree that all judgments are in the end subjective,
but there are judgments where the basis for that subjectivity is reached in a systematic fashion
clearly elucidated, and judgments that result from reflection in a way that can't be - or isn't -
described. I believe the current ISA falls into the latter group. I suspect, therefore, that different
stakeholders would come to different judgments even when faced with the same information.
Having said that, I still support the particular judgments of causality made in the ISA even if the
document doesn't let me see clearly the thinking that led to them.
A significant problem I continue to have is that the causal judgments are too generic. The
question that seems to be asked is whether there is a causal connection between deposition and
effect at some level of deposition, rather than at the levels of deposition that currently exist or
might exist under alternative NAAQS. I always take it for granted that any substance will
produce adverse effects at some level of exposure, and so I was looking for a bit more
policy-relevant judgments of causal connections in the current document. The levels of
deposition at which the causal connection has been established needs to be specified for each
effect.
With respect to the Key Findings section, I am generally comfortable that this reflects the major
findings as described in other parts of the document. However, this section shares a problem I
already noted above: that the claims of effects make little or no reference to the loadings and
ambient concentrations at which the effects may be considered both causal and adverse. As a
result, the reader is left with the impression that all of these effects may be taking place under the
current NAAQS and would be alleviated with a lower NAAQS, neither of which is actually
established elsewhere in the ISA. I think this problem is especially acute in the discussion of
methyl mercury production, where I would disagree that evidence presented elsewhere in the
ISA does not support a claim that sulfates currently are causing any of the fish advisories
mentioned.
As to the quantified relationships on page 4,1 am not sure I would call these relationships. They
are instead levels at which effects have been noted. But it also is the case that the effects are not
shown to be of levels considered adverse in any sense of that word defined in the ISA.
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Finally, there is a policy issue I would like to raise. I believe the ISA lays the appropriate
groundwork for assessing whether current levels of N and S deposition are protective, and draws
the right scientific conclusions on this issue. However, it is necessary to ask whether any
continuing effects are due to the need for a lower NAAQS, or from a failure to fully enforce the
current NAAQS. I see no discussion of that point, and would expect at least a sentence or two on
this important issue. The policy solution is quite different depending on the answer.
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Dr. Charles T. Driscoll
The second draft of the ISA is an improvement over the first draft. There are still many
mistakes and errors that need to be fixed. Although the authors indicate they have eliminated
redundancy, I find the document continues to be highly repetitive.
I would like to see the units of deposition expressed as kg/ha-yr.
I do not like the term acidifying deposition. Why introduce a new term? I understand where
the authors are coming from, but we have three decades of acid or acidic deposition; why create
unnecessary confusion?
Many references cited do not include the et al.
I had difficulty with units and many of the figures. It would be very helpful to clarify the mass
basis of concentrations, emissions, deposition (e.g., mass as S vs. mass as 804). I had difficulty
in the atmosphere section with English units. It is difficult to relate these to the metric units in
the effects section. If it is necessary to present English units please also present their metric
equivalent.
I found several of the figure and tables very difficult to read due to small fonts. I understand
that space is an issue but anything hat could be done to help this situation would be helpful.
Sometimes there is a difference in the balance of the summary comments. Some comments are
emphasized in the summary sections but are barely mentioned in the body of the text. I have
tried to point these out in my specific comments.
Specific comments:
Executive Summary
I liked the Executive Summary. I think it could be improved by adding some context to the
beginning of the executive summary.
Page 1, para 1, line 2 Concise? Please give me a break.
Page 1, para 2, line 6 nitrogen
Page 1, para 2, line 10 Define Nr
Page 2, para 4, line 3 and 8 Change to... limited data exist
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Page 3, para 4, line 18
Page 3, para 4, line 18
Page 3, para 4, line 20
Page 3, para 5, line 3
Page 4, para 4, line 6
Page 5, para 2, line 1
Page 6, para 1, line 8
Page 6, para 4, line 16
Chapter 1. Introduction:
Page 1-1, line 1
Page 1-4, line 19
Chapter 2:
Change to... S deposition is generally the primary cause of chronic
acidification with secondary contributions from nitrate due to N
deposition.
Change to... 1980s and 1990s
Change to... were no longer acidic during baseflow in the...
Change to... Northeast, Southeast and Mountain West
between 5.5 and 10 kg N/ha-yr
Lichens are among the ...
This statement is misleading. Watersheds with high production
of methyl mercury have been widely observed, not only the
Northeast.
Rewrite sentence. Paniculate sulfate interact with methanogenic
bacteria. This sentence is not correct and doesn't make sense.
How about the activity of sulfate reducing bacteria generates
methyl mercury?
Eliminate concise
Define PM
Unfortunately I did not have an opportunity to review this section in detail and so therefore I do
not have any detailed comments.
I would like to see some discussion on values of deposition prior to the Industrial Revolution
(background deposition). This would include sulfate, nitrate, ammonium, chloride, calcium,
magnesium, sodium and potassium. This information is critical to ecosystem effects models.
It would also be good to see some discussion of historical emissions from about 1850 forward.
This is critical to ecosystem effects models.
Finally, in the spirit of making suggestions to simplify the document I would ask the EPA to
consider that this atmospheric chapter is to support the effects section. Ecological effects
largely occur via deposition and over the time scale of decades. As a result the focus of chapter
3 could be largely on long-term deposition patterns. Seasonal deposition is really not important
in ecosystem effects. If it was desired a considerable portion of this material could be shifted to
the annex.
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Chapter 3:
This section covers most of the major issues concerning ecological effects of air pollutants. It
is comprehensive and generally well done. There are a few sections that are emphasized in the
summary section but really were not discussed in the body of the chapter. For example there is
now some literature suggesting that there is a compensatory response of dissolved organic
carbon to changes in acidic deposition. I think the science is still developing here but this is an
important point and it should be mentioned in the body of the chapter, possibly as a short section
in3.2.3.1.
There is an analysis of the extent of N limitation in remote lakes that is presented in Chapter 4.
This is an analysis of the stoichiometry of water chemistry from the National Surface Water
Survey. This analysis helps quantify the extent of N limitation. I would urge that this analysis
be presented in 3.3.3.3 or another section of chapter 3.
MAGIC is an important tool used in the REA. I would like to see some text discussing how the
structure of MAGIC affects prediction. This could include a comparison of MAGIC with other
watershed models. For example see Sullivan et al. (2006).
The science is emerging on mercury contamination in terrestrial food chains (e.g., Rimmer et al.
2005). There should probably be some mention of mercury contamination in the terrestrial
food chain.
Finally a question. Is it worthwhile to mention the linkage of atmospheric N deposition and
biogenic emissions of NO and VOCs? I don't think the literature is compelling here but there
may be some linkages between N deposition and soil emissions of NO and between foliar N and
VOC emissions. Is this a welfare effect? It is a linkage with atmospheric chemistry.
Page 3-4, line 25 I don't understand the line at the end about wetlands. Aren't
wetlands included in other ecosystem services described above?
Page 3-6, line 2 hydrogen ion
Page 3-6, line 7 eastern U.S.
Page 3-8, line 20 H+
Page 3-8, line 30 southeastern
Page 3-10, line 1 northeastern
Page 3-10, line 8 You should mean oxidizing NH4+
Page 3-11, line 9 section ?
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Page 3-12, line 14 This statement is not correct. Under conditions of low soil base
saturation (<20%) and elevated concentrations of strong acid
anions, Al is mobilized from soil to drainage water (Cronan and
Schofield 1990).
Page 3-14 You discuss episodic acidification but fail to discuss chronic
acidification. This seems a bit out of place without a discussion
of chronic acidification.
Page 3-16, figure title Italics in-situ
Page 3-17, line 12 above 0 jieq/L
Page 3-17, line 13 Italics in-situ
Page 3-24, line 8 Do you mean N deposition?
Page 3-24, line 17 than forests
Page 3-24, line 25 by oxidizing NH4+
Page 3-25, line 16 pool of exchangeable base cations
Page 3-26, line 13 northeastern U.S.
Page 3-26, line 18 cite DeHayes et al. 1999
Page 3-29, line 1 northeastern U.S.
Page 3-30, 1st paragraph You should probably reference the study of St. Clair et al. (2005)
who document a relationship between enzyme antioxidant levels in
sugar maple foliage and soil and foliar calcium.
Page 3-31, line 4 eastern U.S.
Page 3-33, line 13 eastern North America
Page 3-36, line 26 Acid neutralizing capacity is the most readily...
Page 3-40, line 2 northeastern U.S.
Page 3-42, line 3 and 32 eastern U.S.
Page 3-45, line 17 is typically decreased by acidic deposition
Page 3-46, line 16 I could not find Sullivan et al. in press in the references
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Page 3-48, line 34 northeastern U.S.
Page 3-49, line 6 I question the statement that recent soil acidification appears to be
modest. I refer the authors to (Likens et al. 1996, Bailey et al.
1996, Bailey et al. 2005). I am also attaching a recently accepted
paper Warby et al. (in press). The rates of soil nutrient cation lost
are high.
Page 3-49, line 12 northeastern U.S.
Page 3-51, line 1 What is meant by "pre-disturbance"?
Page 3-51, line 2 This sentence seems to be inconsistent with the text in 3-90.
Page 3-51, line 6 The authors should look at Gbondo-Tugbawa and Driscoll (2003)
who evaluate historical forest cutting and soil and water
acidification.
Page 3-52, lines 26-28 The first two bullet points are at odds with the text in 3-90 and
Zhai et al. (2008).
Page 3-54, table 3.7 This table does not include Zhai et al. 2008, Chen et al. 2005b, c,
Driscoll et al. 2001 among others.
Page 3-55, line 19 eastern U.S.
Page 3-55, line 22 an indication of acid base status
Page 3-56, line 17 eastern U.S.
Page 3-57, line 8 eastern U.S.
Page 3-57, line 15 northeastern U.S.
Page 3-57, line 28 Italics in-situ
Page 3-66, line 25, Page 3-67, line 3-4
Up to this point in the text, I have not seen any literature on effects
on birds and now it is mentioned in the summary. This does not
seem appropriate. If it is not important enough to be discussed in
the body of the text, it probably should not be in the summary.
There was a paper by Hames et al. 2002 on acid rain effects on
songbirds in the Northeast.
32
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Page 3-74, line 5 What is mildly acidic? Give an ANC value?
Page 3-83, line 2 that further reductions in acidic deposition
Page 3-83, line 25 Do you mean suitable?
Page 3-87, line 11 As shown in Figure 3-22, N retention actually has been increasing
in the Adirondacks. Correct statement.
Page 3 -103, line 24 Define GHG
Page 3-117, line 27 Space after wetlands
Page 3-118, line 7 Missing reference
Page 3-127, line 26 Section?
Page 3-138, line 7 Should this be °C?
Page 3-139, line 8 northern U.S.
Page 3-139, line 10 table
Page 3-143, line 1 Missing space
Page 3-144, line 20 italics in-situ
Page 3-144, line 22 Usually this is referred to as the Experimental Lakes Area (ELA).
Page 3-145, line 2 period
Page 3-149, line 4 Change to... algal detritus
Somewhere in 3.3.4 I believe studies have shown increased biogenic NOX emissions in
response to N additions. Isn't this a relevant consideration and
shouldn't it be included in the review? Also, I believe that foliar
VOCs emissions are a function of foliar N which is influenced by
atmospheric N deposition. Should this effect be addressed in this
section?
Page 3-153, line 19 methanotrophic
Page 3-158, line 7 denitrifying
Page 3-161, line 19 Is positive relationship correct? This seems inconsistent with the
remainder of the section.
33
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Page 3-169, line 2 Who is they?
Page 3-176, line 1 eastern U.S.
Page 3-176, line 11 northern U.S.
Page 3-176, line 13 table
Page 3-176, lines 2 and 26 These sentences are identical. Do you really want the same
sentences on the same page?
Page 3-177, line 16 bioindicator
Page 3-180, lines 4, 5 italics in-situ
Page 3-182, line 17 italics in-situ
Page 3-184, line 4 Change to... Among the most sensitive...
Page 3-185, line 12 eastern U.S.
Page 3-185, line 25 In the West,
Page 3-186, line 12 NH4+ twice
Page 3-192, lines 14, 15 Northeastern
Page 3-196, line 6 italics in-situ
Page 3-200, line 4 and elsewhere
Control should be changed to reference
Page 3-206, line 26 Aren't changes in biodiversity changes in structure?
Page 3-209, line 7 period
Page 3-216, line 15 table
Page 3-218, line 19 Change to... all fish consumption advisories
Page 3-225, line 5 Methylation is prevalent in ecosystem in other regions besides the
Northeast. This sentence should be changed.
34
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Page 3-227, somewhere in here
Studies have also shown elevated concentrations of Hg in
songbirds and bats via the terrestrial food chain. This should be
mentioned (e.g., Rimmer et al. 2005).
Page 3-228, 2nd paragraph You change the symbol for methyl mercury here. The text should
be changed to be consistent.
Page 3-232, lines 10, 11 The first letter of several of the names are in lower case.
Page 3-236, line 1 H+
Chapter 4
Page 4-1, line 12 role in transporting N
Page 4-4, line 19 Define p NO3"
Page 4-4, line 23 Define FRM
Page 4-5, line 4 is very sparse over
Page 4-6, line 7 and throughout the document
I do not like the term acidifying deposition. Change to acidic or
acid deposition.
Page 4-6, line 13 energy by oxidizing NH4+ to N(V
Page 4-6, line 17 (see Table 4-1), including soil base saturation, aluminum
concentration and C:N ratio.
Page 4-6, line 21 are increasingly neutralized by
Page 4-7, line 8 toxicity, decreased ability of plant roots to take up nutrient cations,
and elevated leaching of Ca2+ from needles
Page 4-9, line 15 eastern U.S.
Page 4-9, line 17 western U.S.
Page 4-10, line 6 eastern U.S.
Page 4-10, line 9 indicator of acid-base status
Page 4-10, line 11 pH, Ca, SO42" and
35
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Page 4-10, line 20 Southern Appalachian Mountains
Page 4-11, line 1, 17 eastern U.S.
Page 4-11, line 19 the Central and Southern Appalachian Mountains
Page 4-11, line 24 northeastern U.S.
Page 4-13, bullet 1 Were effects on birds really discussed in Section 3? If not it
probably should not be emphasized here.
Page 4-14, line 30 Change to... were on average 30 jieq/L.
Page 4-15, line 1 Change to: would need on average to recover
Page 4-15, line 16 northeastern U.S.
Page 4-15, line 23 Was DOC change discussed in Section 3? This is an important
issue and probably deserves a paragraph in Section 3.
Page 4-16, line 26 Change to... to a state more removed from a condition of N
saturation.
Page 4-18, lineS West
Page 4-18, line 27 western U.S.
Page 4-20, line 27 western U.S.
Page 4-23, line 3 southwestern U.S.
Page 4-23, line 4 Sonoran Desert
Page 4-23, line 20 Isn't reducing biodiversity altering ecosystem structure?
Page 4-26, lines 10, 15 eastern U.S.
Page 4-27, line 3 dissolved inorganic N?
Page 4-27, line 4 phosphorus
Page 4-27, 1st paragraph Was this analysis of lake stoichiometry in the ELS discussed in
Section 3? If not it should be as it is an important conclusion.
Page 4-27, line 13 eastern and western U.S.
36
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Page 4-29, line 6 western U.S.
Page 4-31, line 12 eastern U.S.
Page 4-32, paragraph 2 Should these units be metric?
Page 4-34, line 10 This statement is incorrect. Methylation is a widespread
phenomenon. It occurs in many areas besides the Northeast and
southeastern Canada.
References:
Bailey, S. W., J. W. Hornbeck, C. T. Driscoll, and H. E. Gaudette. 1996. Calcium inputs and
transport in a base-poor forest ecosystem as interpreted by Sr isotopes (Paper
95WR03642). Water Resources Research 32:14.
Bailey, S. W., S. B. Horsley, and R. P. Long. 2005. Thirty years of change in forest soils of the
Allegheny Plateau, Pennsylvania. Soil Science Society of America Journal 69:681-690.
Cronan, C. S., and C. L. Schofield. 1990. Relationships between aqueous aluminum and acidic
deposition in forested watersheds of North America and Northern Europe. Environmental
Science and Technology 24:1100-1105.
DeHayes, D. H., P. G. Schaberg, G. J. Hawley, and G. R. Strimbeck. 1999. Acid rain impacts on
calcium nutrition and forest health. BioScience 49:789-800.
Gbondo-Tugbawa, S. S., and C. T. Driscoll. 2003. Factors controlling long-term changes in soil
pools of exchangeable basic cations and stream acid neutralizing capacity in a northern
hardwood forest ecosystem. Biogeochemistry 63:161-185.
Hames, R. S., K. V. Rosenberg, J. D. Lowe, S. E. Barker, and A. A. Dhondt. 2002. Adverse
effects of acid rain on the distribution of the Wood Thrush Hylocichla mustelina in North
America. Proceedings of the National Academy of Sciences of the United States of
America 99:11235-11240.
Likens, G. E., C. T. Driscoll, and D. C. Buso. 1996. Long-term effects of acid rain: Response and
recovery of a forest ecosystem. Science 272:244-246.
Rimmer, C. C., K. P. McFarland, D. C. Evers, E. K. Miller, Y. Aubry, D. Busby, and R. J.
Taylor. 2005. Mercury concentrations in Bicknell's Thrush and other insectivorous
passerines in montane forest of northeastern North America. Ecotoxicology 14:223-240.
37
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St. Clair, S. B., J. E. Carlson, and J. P. Lynch. 2005. Evidence for oxidative stress in sugar maple
stands growing on acidic, nutrient imbalanced forest soils. Oecologia 145:258-269.
Warby, R. A. F., C. E. Johnson, and C. T. Driscoll. (in press). Continuing acidification of organic
soils across the northeastern USA: 1984 - 2001. Soil Science Society of America Journal.
Zhai, J., C. T. Driscoll, T. J. Sullivan, andB. J. Cosby. 2008. Regional application of the
PnET-BGC model to assess historical acidification of Adirondack lakes. Water
Resources Research 44, W01421:doi:10.1029/2006WR005532.
38
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KEY FINDINGS
The mam effects evaluated in the ISA are
acidification, nitrogen enrichment and
mercury methylation.
Acidification is driven by deposition of
nitrogen oxides and sulfur oxides, and results
in a cascade of effects that harm terrestrial and
aquatic ecosystems, including slower growth
and injury to forests, and localized extinction
of fishes and other aquatic species.
Nutrient enrichment results from deposition of
nitrogen oxides^ along with other sources of
reactive nitrogen (e.g.. fertilizers, wastewaterr
and atmospheric ammonia deposition), and it
causes a suite of ecological problems
including biodiversity losses, disease.
eutrophication, and harmful algal blooms.
Particular sulfate can interact with
methanogemc bacteria to produee
methylnaercnrft a powerful toxin that can
bioaccumulare to toxic amounts in higher
trophic levels (e.g. otters, and kingfishers).
This draft Integrated Science Assessment is a
concise synthesis and evaluation of the most
policy-relevant science to help form the
scientific foundation for the review of the
secondary (ecological or welfare-based)
national ambient air quality standards for
nitrogen oxides and sulfur oxides.
Ecological effects of acidification
Deposition of seme nitrogen and sulfur species
can cause acidification, altering
biogeochemistry and affecting biota in^
terrestrial and aquatic ecosystems across the
U.S. Major effects on biota include a decline in
some forest tree species, such as red spruce and
sugar maple: and a loss of biodiversity of
fishes, zooplankton. and macroinvertebrates.
• The sensitivity of terrestrial and aquatic
ecosystems to acidification from sulfur and
nitrogen deposition is predominantly
governed by surficial geology.
• Deposition of inorganic nitrogen and
sulfur species routinely measured was as
high as 9.6 kg N/ha/yr and 21.3 kg S.-'ha/yr,
respectively, in the U.S. in 2004-2006.
• Areas most sensitive to terrestrial effects
from acidifying deposition include forests
in the Adirondack Mountains of New York,
the Green Mountains of Vermont, the White
Mountains of New Hampshire, the
Allegheny Plateau of Pennsylvania, and
high-elevation forest ecosystems in the
.southern Appalachians.
• Many of the most acid sensitive sxirface
waters in the U.S. are in the Northeast (see
figure below) and mountainous West.
* 01' ftr IM«l»4t* *•!! £|M«M UHIt
-
Regions of the eastern U.S. that contain
appreciable numbers of lakes and streams
sensitive to deleterious effects from acidifying
deposition, (Source: Stoddard et aL 2003)
Biogeochemical effects
AekKfyme^deposition alters biogeochemistry
in terrestrial and aquatic ecosystems,
• In terrestrial ecosystems, ecological
effects are linked to changes in soil
chemistry, including soil base saturation.
inorganic aluminum concentration in soil
water, and soil carbon-to-nitrogen ratio.
• In aquatic ecosystems, ecological effects
are linked to changes in surface water
chemistry, including sulfate concentration.
nitrate concentration, sum of base cations.
acid neutralizing capacity, surface water
39
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inorganic aluminum concentration, and
surface water pHA
Examples of biogeochemical indicators of effects
fi'om ntidifSing^ deposition oo ecosystems
Ecosvstem
Terresnial
Aquatic
Biogeochemical Indicator
• Soil base saturation
• Inorganic Aimmmirn concentration
in soi£ wa;er
• Soil carbou-to-rjitroaea ratio
• Sutfate
• Nitrate
• Base cations
• Acid neutralizing capacity
• Surface water inorganic Aluminum
• pH
Biological effects
Acidifying,deposition alters ecosystem
structure.
• Biological effects of acidification in
terrestrial ecosystems are generally linked
to aluminum toxicity and decreased ability'
of plant root* to take up base cations.
• Decreases in acid neutralizing capacity
and pH and increases in inorganic
aluminum concentration contribute to
declines in zooplankton.
macromvertebrates. and fish species
richness in aquatic ecosystems.
Examples of biological indicators of effects from
acidifying deposition on ecosystems.
Indicator
Terrestrial ecosystems
• Rjed spruce *
• Sugar maple •
Aquatic ecosystems
• Fishes. «
zooplaiiktcu. «
crustaceans, *
rotifers
Measure
Percent dieback of
canopy Tees
Dead basal area, crovvu
vigor index, fine ting
dieback
Presence •' absence
Fish condidon factor
Biodiversity
Ecosystems will continue to be acidified by
current ernissions.^or example, in the
Adirondacks, the current rates of nitrogen
and sulfur deposition exceed the amount that
would allow recovery of the most acid
sensitive lakes. In the Shenandoah
Mountains, historically deposited sulfate lias
accumulated in the soil and is slowly released
from the soil into stream water where it
causes acidification and makes parts of this
region sensitive to current loading. Numeric
models suggest that the number of acidic
streams will increase under the current
deposition rates..
Ecological effects of nitrogen
deposition
Nitrogen deposition causes ecosystem
enrichment and eutrophication that alters
biogeochemical cycles and harms biota, such
as native lichens, and alters biodiversity of
ecosystems, such as grasslands and
meadows. Nitrogen deposition contributes to
eutrophication of estuaries and the associated
effects including, toxic algal blooms and fish
mortality.
• Multiple forms of reactive nitrogen (e.g..
ammonia, ammonium ion: nitrogen oxides.
nitric acid, nitrous oxide, nitrate, urea.
amines, proteins, and nucleic acids)
contribute to the ecological effects of
nitrogen enrichment. However, most
ecological experiments have deposition data
for only a subset of the total of reactive
nitrogen chemical species.
• Deposition of inorganic nitrogen species
was as high as 9.6 kg Nlia-yr in 2004-2006.
• At least one important component of N.
ammonia, is not measured routinely in any
national network,, but may account for
greater than 80° o of total reduced nitrogen
deposition.
• Existing monitoring networks are
inadequate to characterize the full extent of
regional heterogeneity in nitrogen and
sulfur deposition, and very likely
underestimate the total nitrogen deposition
across wide areas of the U.S.
• Ecological effects can occur at nitrogen
deposition rates as low as 2 kg/l
40
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Biogeochemical effects
Reactive nitrogen deposition alters the
biogeochemical cycling of nitrogen.
• Atmospheric nitrogen deposition is the
main source of new mtiogen to terrestrial
ecosystems. Hie onset of nitrate leaching
from soils is an indicator of excess nitrogen
in these systems and is calculated to begin
at values ranging froin~5 to 10 kgN;'ha'yr
for forests in the eastern U.S. ^mportautly,
nitrogen deposition can profoundly affect
ecosystems prior to the onset of nitrate
leaching.
• The contribution of atmospheric nitrogen
deposition to total nitrogen loads varies by
wetland-type: freshwater bogs are the most
sensitive, and salt marshes are the least
sensitive. Nitrogen mineralization increases
with nitrogen addition, which can increase
nitrogen export from wetland to adjacent
surface waters.
• Atmospheric nitrogen deposition is the
mam source of nitrogen to headwater
streams, lower order streams, and high
elevation lakes. Elevated surface water
NO;" concentrations due to nitrogen
deposition occur in both the eastern and
western U.S.
Examples of biogeochetnical indicators of effects
from reactive nitrogen deposition on ecosystems
Ecosystem
Terrestrial
and Wetland
Freshwater
and Estuarine
Aquatic
Biogeocheinica] Indicator
« NO 3" leaching
• Kilnficanoa-demaiflcation
• N:0 emission
* CHj emission
• Soil C: nitrosen ratio
• Fohar.'plant tissue [N]. C:N. K:Me.
K:P
• Soil water [KO31
• Soil pore water [NHj*]
• Chlorophyll a
• Water [NO 3']
• Dissolved inorsanic nitrogen
• Dissolved oxygen
• K:P ratio
the most highly eutrophic estuaries in the
U.S.. including the Chesapeake Bay.
N deposition affects primary productivity.
thereby altering biogeochemical cycling of
carbon.
• Nitrogen deposition can accelerate plant
growth and change carbon allocation
patterns (see figure below), which can
increase their susceptibility to severe fires.
drought, and wind.
• Nitrogen deposition causes changes in
ecosystem carbon budgets. However.
whether nitrogen deposition increases or
decreases ecosystem carbon-sequestration
remains unclear. For example, a limited
number of studies suggest that nitrogen
deposition may increase carbon-
sequestration in forests, but has no apparent
effect on carbon-sequestration in non-forest
ecosystems.
• Productivity of many freshwater
ecosystems and most estuaries and coastal
water ecosystems is nitrogen limited.
Nitrogen deposition can cause
eutrophication of aquatic ecosystems^
• The contribution from atmospheric
nitrogen deposition can be greater than
30° o of total nitrogen loadings in some of
interactions between the carbon and
nitrogen cycles.
Methane and nitrous oxide are green house
gases that have biogenic sources and sinks.
Nitrogen deposition alters methane and^
nitrous oxide fluxes in terrestrial and
transitiona^ecosystems.
41
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• Nitrogen addition increases the flux of
nitrous oxide from soils to the atmosphere
in coniferous forests, deciduous forests,
grasslands, and wetlands.
• Nitrogen addition can reduce methane
uptake in coniferous and deciduous forest.
In wetlands, nitrogen addition can increase
methane production, but has no apparent
effect on methane uptake.
Biological effects
Multiple biological indicators have shown that
nitrogen deposition alters ecosystem
structure.
• Addition of nitrogen to most ecosystems
causes changes in primary productivity and
growth of plants and algae, which can alter
competitive interactions among species.
Some species grow more than^thers.
leading to shifts in population dynamics,
species composition, and community
structure. The most extreme effects include
a shift of ecosystem type in terrestrial
ecosystems, and hyposic zones that are
devoid of life in aquatic ecosystem.^ which
typically results from nitrogen loading from
multiple sources.
Examples of biological indicators of effects from
nitrogen deposition on ecosystems
Ecosystem
Terrestrial
and
Wetlands
Aquatic
Biological Indicators
« Altered community composition.
biodiversity and /or population
decline. Tasa affected include:
diatoms, lichen, niycorrhiza.
moss, grasses and other
herbaceous plant-;.
• Plant root: shoot ratio
• Terrestrial plant
bioma ss.'prc duction
* Phytoplaukton
biomass-'prodiiction
* Toxic or nuisance algae blooms
« Submerged aquatic vegetation
« Fauna from higher trophic levels
occurring at 3 kg N/ha/yr in the Pacific
Northwest and Southern California.
• The onset of declining biodiversity was
found to occur at levels of 5 kg N-lia^yr and
above within grasslands in Minnesota and
in Europe.
• Altered species composition of ^.pine
ecosystems and forest encroachment into
temperate grasslands was found at 10 kg
X ha/yr and above in both the U.S. and
Canada. A brief list of deposition levels
and associated effects is shown below.
Examples of quantified relationship-; between
deposition levels and ecological effect?
Kg
>7ha.vi
-1.5
3.1
4
Ecological effect
Altered diatom connuuaities in high
elevation freshwater lakes and elevated
nitrogen in tree leaf issue high elevation
forests la the U.S.
Decline of some lichen species in the
Wc'iccm.U.S. (critical load)
Altered growth aad coverage of alpine
pSaut species inp.S.
5 Onset of decliae of species richness in
grasslaads of the U.S. aad U.K.
5.3^- 10' Onset of nitrate leachiaa in Eastern
forests of the U.S. t
5-;S Multiple effects m tundra, boss aad
freshwater lakes in Europe (critical loads)
5-15
Multiple effects in arctic, alpiae.
subaipine aad scrub habitats in Europe
(critic alloads)
Sulfate effects on mercury
methylation
Mercury is highly neurotoxic and enters the
food web in its methylated form. Because
sulfate can stimulate bacterial production of
methyl mercury, sediments and biota 111
wetlands and other aquatic ecosystems can
have elevated concentrations of methyl
mercury. In 2006, 3,0SO fish advisories, were
issued in the U.S. due to the prcicncc^of
methvl mercurv in fish.
Quantified relationships between deposition
levels and ecological effects
• Lichens are^he most sensitive terrestrial
taxa to nitrogen with clear adverse effects
42
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Dr. Paul J. Hanson
I found the second draft of the Integrated Science Assessment (ISA) to be greatly
improved. Panel suggestions on the first draft appear to have been incorporated for the most part.
The requested Executive Summary is well crafted and a nice introduction to the ISA, but some
wording changes may still be in order. My specific comments and editorial suggestions are
listed below.
Specific comments and suggested edits:
Executive Summary
Page two, second column: Change to "Numerical modeling experiments can help fill in
these data gaps and suggest that local and even regional areas of high concentration and
deposition may exist where measured data are unavailable. Subscript the 2 in NC>2.
Page 4 last paragraph: The last statement is not correct. The onset of leaching is not a fixed
constant that applies to all eastern forests. This text should be changed to indicate that such a
threshold applies to a defined set of sensitive eastern forests.
Page 5: Change the first two sentences to: "N deposition often increases primary
productivity, but may not lead to enhanced carbon sequestration'' In the first paragraph
change "However, alteration..." to 'Alteration...' I would add the word possible to the
following: "The increase in growth is greater for some species than others, leading to possible
shifts in population dynamics, species composition, community structure and, in extreme
instances, ecosystem type." Growth changes are not a guarantee of cascading effects. The
paragraph on lichens seemed too general. Are the limits for lichen response true for all
ecosystems, or only sensitive ones?
Page 5 last paragraph: Should organisms be animals? Elemental mercury is taken up by plants.
Page 6 third paragraph: Change to "Acute exposures to NC>2,...." Delete the word "Overall".
Page 6 last paragraph: Consider the following changes:
".. .deposition resulting from NOx and SOx pollution. It causes a cascade of effects that
harm susceptible terrestrial and aquatic ecosystems, including slower growth and injury
to forests, and localized extinction of fishes and other aquatic species. In addition to
acidification, deposition resulting from NOx, along with other sources of reactive
nitrogen (e.g., fertilizers, wastewater, and atmospheric ammonia deposition), causes a
suite of ecological changes within sensitive ecosystems including biodiversity losses,
disease, eutrophication, and harmful algal blooms. Particulate sulfate can interact with
methanogenic bacteria to produce methylmercury, a powerful toxin that can
bioaccumulate to toxic amounts in higher trophic levels (e.g. otters and kingfishers).
Chapter 1: No comments.
43
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Chapter 2
The font size for the text within figures on pages 2-96 through 2-100 is too small. These
figures need to be adjusted.
Figures 2-41 , 2,42, 2-43, and 2-44: Using the same color scheme for an alternate range of
concentrations in the comparison of Total vs. background concentrations masks what should be
the main message of these figures. Background levels are very, very low. The need to
visualize where background levels are highest over a range from very-low to low seems
unnecessary. If the authors really want this specificity they should choose an alternate color
scheme for the background map.
Chapter 3
Tables 3-11 to 3-26 within Section 3.3 provide an appropriate and site-specific level of
detail to allow the readers to understand the indicators and levels of deposition of importance for
specific ecosystems and the responses being highlighted.
Chapter 4
For the bolded conclusion statements on pages 4-17 through 4-31 determine if you can
change "alteration" to a statement of directional change if the data warrant (e.g., change
alteration to increase in the statement of N deposition effects on N2O emissions).
Comments on the Key Findings draft (1 October 2008):
Page 1 first yellow box:
In the third paragraph I recommend changing the word "problems" to 'changes' to avoid the
judgmental nature of the first term. As with many other locations in the document it is
important that this statement not be interpreted as applying equally to all ecosystems throughout
the United States.
Second yellow box:
While the statement may be factually correct it tends to imply that acidification leading to
adverse effects is taking place in all ecosystems. I don't believe this is true. One size doesn't
fit all and levels of deposition, acidification, and adverse effects are not consistent across the US.
The bullets at the top right portion of page 1 are just right in my opinion. They contain the
detail needed for the reader to draw the appropriate conclusion.
Right hand column of Page 2 - yellow box:
I would change the first lines to "Nitrogen deposition causes ecosystem element
enrichment and eutrophication...."
Page 2, second column, first bullet:
Modify the text to read "... .nitrogen enrichment. However, most ecological experiments and
observations have "
44
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Page 2, second column, third bullet:
Is Ammonia always 80% of total reduced N or only in locations with high N deposition totals?
Page 2, second column, last bullet:
Add the words 'insensitive ecosystems' to the end of the bullet.
Page 3, column 1, first bullet:
I don't believe that this statement is true in natural ecosystems dominated by nitrogen
fixing species (alder thickets/forests; and perhaps early successional oldfields). The last
statement of this bullet needs further expansion. I'm not clear on the intent.
Page 4, first column, first bullet under the Biological Effects heading:
Near the end of the statement the terms 'terrestrial ecosystems' is too general. This is
not true for all terrestrial ecosystems.
Page 4:
Bullets ending column 1 and beginning column 2 are well worded.
Page 4, second column, yellow box:
The statement suggesting that 5.6 to 10 kgN/ha/y drives the onset of nitrate leaching in
eastern forests is wrong. It only applies to specific systems and locations within eastern US
forests.
I agree with the suggestion of one panel member (can't remember who) that spatially explicit
information on the areal extent of acidification, nitrogen enrichment, and sulfate effects on
mercury methylation might all be made clear in the executive summary.
45
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Dr. Rudolf Husar
These comments pertain primarily to Charge Question 5 with brief comments on other sections.
ISA Charge Question 5. In revising the ISA, we have incorporated additional information on the
indicators of exposure and ecological effects, including increased emphasis on quantified relationships in
the presentation of information of results in tables and summary discussions in Chapter 4. What are the
views of the CASAC panel on our revisions to focus on quantitative relationships between airborne
nitrogen and sulfur compounds and ecological indicators?
• It is commendable that effort was made to perform an analysis of existing literature on
indicators relevant to deposition and acidification. The meta-analysis appears to be
extensive and appropriate for the ISA
• The analysis of indicators is particularly important since the a secondary standard (if
proposed and promulgated) needs to be expressed in terms of Sox / Nox and then
properly linked to the effects through the indicators and a causality framework.
• It would be desirable to continue fortifying the linkages in the causality chain between
emission - atmospheric concentration - deposition - dosage - effect - ecosystem
services.
• An example of such an end-to-end causality illustration would help. A synchronized
array of trend charts for each parameter/indicator in the causality chain could be an
effective way to illustrate the overall framework and key aspects of systems behavior.
• In the ISA it may not be necessary the have quantitative trend values for each of the
parameters in the causality chain ensemble. In fact, graphically indicating (say dashed
trend lines) the poorly understood parameters would be a more realistic representation of
the current state of the causality framework.
A recurring general concern regarding the ISA, voiced by several panel members over multiple
meetings, is the near-complete avoidance of the non-ecological welfare effects of NOX and
SOX, such as particle effects on visibility and climate, materials damage etc. It is understood
that some of these effects are discussed in other assessment documents and full treatment of
these in this ISA is not necessary.
This document is titled "Integrated Assessment for Oxides of Nitrogen and Sulfur -
Environmental Criteria" but by design, it focuses on the ecological effects. Fine, no problem
here. However, since Environment includes air, land, water, biota I see two possibilities:
• Either rename the document to 'Ecological Criteria' - probably not feasible
• Or keep "Environmental Criteria" but state it clearly
o in which docs other NOx/Sox welfare effects of are being treated
o provide a short synopsis of the key non-ecological effects in the
appendix, so this ISA document can meaningfully represent an
assessment of Environmental Criteria.
46
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Detailed Comments on Specific Sections of ISA Document
Page 1-3: The schematic Figure on the biogeochemical cycles of NOx and SOx is good.
However, during the June 2008 CASAC it was suggested that such a general Figure should
be fortified by adding magnitudes to the flows represented by the arrows. The transfer
rates, say over the US, can be estimated from the model runs, or based on the empirical
evidence. There is ample literature on biogeochemical cycles that estimates the magnitude
and importance of the various flow rates.
Page 2-47: Figure 2-20 is again a qualitative schematic of the sulfur flows in the and out of
the atmosphere. At the minimum, estimating the magnitude of dry and wet deposition
would be most helpful.
Page 2-47: Multi-phase SOx chemistry is reviewed in considerable detail including the
relative humidity effects on deliquescence. It is puzzling why this detailed behavior of
particles is relevant for ISI which is to support ecological effects and not the atmospheric
effects of particles.
Page 2-54: Same comment as above. Why discuss deliquescence of nitrate particles when
atmospheric effects of particles are not considered.
Page 2-56: Section 2.6.5 "Transport-Related Effects" is a rather haphazard collection of
references that neither explain the general features of S and N transfer in the atmosphere nor
is a comprehensive list of literature. Calling it Transport Effects is misleading, since the
section covers transport processes and phenomena, not effects.
In addition to Transport Phenomena a statement on the general role of meteorological
processes shaping pollutant transport, governing thermodynamics (e.g. gas-particle
equilibrium and reaction kinetics) and removal processes. Shoving the precipitation pattern
would provide considerable explanatory support to the pattern of S and N deposition and the
resulting effects. An explicit discussion of the atmospheric life time of various sulfur and
nitrogen species would be most helpful.
Page 4-1: Chapter 4, "Summary and Conclusions" supposed to summarize the content of
Chapter 2 (Emissions, Atmospherics) and Chapter 3 (Ecological Effects) of NOx and SOx.
The way in which Chapter 4 has been written, only about 10% of the 40 page summary deals
with the emissions, ambient concentrations, transport and deposition. 90% is about the
effects and associated summary tables. Table 4-4 for N is useful and similar compilation for
S would be useful as well. Given the sizable effort invested in the compilations this
Chapter appears to be an integration Chapter rather than just a Summary Chapter.
Page 4-1 Line 11: Section 4.1.1 " Relevant Chemical Families and Constituent Species"
is a single paragraph, loaded with inaccuracies and dubious rationale. Examples:
"particulate nitrate is .... not a member of the oxidized N family of species" . So,
particulate nitrate is not an oxidized N? Line 17: "Only SO2 is present in concentrations
47
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relevant for atmospheric chemistry and environmental exposures. " So, the 10,000
excess death per year, mostly from sulfate are not relevant?
Page 4-2 Line 1: Stating that the 2001 US NOx emissions were approximately "~23.19 Tg"
is misleading since it implies that the accuracy of US NOx emissions is known with better
than 1% accuracy. For most of us the NOx emission accuracy is not better than 20% , i.e.
23+7 - 2 Tg.
Page 4-2 Line 5: "Biogenic NOx sources include biomass burning, lightning, and
soils". I wonder which biota in the sky are responsible for lightning??
Page 4-2 Line 5: "Biogenic NOx sources are substantially smaller than anthropogenic ".
On global scale anthropogenic and natural nitrogen emissions to the atmosphere are
comparable (http://www.visionlearning.com/library/module_viewer.php?mid=98).
Page 4-5 Line 1: It is true that the measurements of particulate NO3 and NH4 are subject to
positive and negative errors. However, the measurement of parti culate sulfate is among the
most accurate and reliable among the sampling methods.
Page 4-5 Line 5: "This assessment concludes that...". This complicated sentence is
incomprehensive.
Page 4-10 Line 26: "However, there is no apparent relationship between recent trends in N
deposition and trends in NO3 concentrations in these surface waters." This statement has
significant consequences regarding the conclusions as stated below.
Page 4-27 Line 8: "The evidence is sufficient to infer a causal relationship between N
deposition and the alteration of biogeochemical cycling of N in fresh water aquatic
ecosystems". Is this consistent with the statement that N deposition trends are not matched
by corresponding N concentration trends?
48
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Dr. Dale Johnson
This draft is an improvement in some ways but I believe that it needs to include assessments of
the possibility of beneficial effects of N deposition. It now contains detailed descriptions of N
and S cycles and recognized the fact that nitrogen (but not sulfur) is often a limiting nutrient. It
now considers the potential for N deposition to enhance production and C sequestration
specifically within the body of the text - and then summarily dismisses such a possibility and
mentions nothing of it in summary statements. It appears that the treatment of the potential
benefits of sulfur are discussed much more extensively than those for nitrogen (although I fully
recognize that N deposition is probably not important for crop systems, given how much they are
fertilized).
Specific comments:
p. 3-7, lines 1-3: In addition to these studies, are the very detailed studies of Richter and
Markewitz (2001) which show long-term soil acidification due to both tree uptake and
atmospheric deposition. The fourth resampling of Walker Branch Watershed will also soon be
published (Johnson et al., 2008) and I will send a copy. It documents continued declines in
exchangeable Ca2+ and Mg2+ with the exception of cases where decomposing logs enrich Ca2+.
The Ca declines are attributed mostly to uptake where the Mg2+ declines attributed mostly to
leaching, augmented by acid deposition.
p. 3-12:1 do not think the study by Bailey et al is by any means the most thorough resampling
study in the US. The Richer and Markewitz study is much more comprehensive and detailed, and
fully deals with the causes of soil change in a quantitative manner, which the Bailey study does
not. As noted in my last review, while Bailey did evaluate the role of uptake in causing the soil
changes they observed, they have grossly overestimated the potential role of acidic deposition in
the soil changes they observed - it would have taken a prolonged S deposition rate of something
like 200 kg ha-1 yr-1 for many decades, for example, to produce such changes as they saw in
some cases. It is simply not logical to blame acidic deposition for that magnitude of change. I
wrote a letter to the editor on this (Johnson, D.W. 2006. Comments on "Thirty years of change in
forest soils of the Allegheny Plateau, Pennsylvania." Soil Sci. Soc. Amer. J. 69: 2077.), to which
they responded, which the authors of this document should look at if they intend to highlight the
Bailey studies as hallmark studies showing soil acidification by acid deposition. I noted this in
my last review of this document, but this comment was apparently overlooked. The authors may
choose to dismiss my letter and accept Bailey's conclusions, but they should at least
acknowledge the controversy.
p. 3-13, line 33 to p. 3-14, line 1: Once acidified, it is unlikely that Al levels in soils will decline
again unless the soils are limed.
p. 3-26, lines 6-12: What about the effects of N on N-deficient sytems?
p. 3-43, line 5: The base cation decline could be explained as a simple consequence of charge
balance.
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p. 3-75, lines 1-17: This is amazing. So we do not even know if our forests are growing at a
faster or a slower rate. A fundamental piece of knowledge that is missing while we speculate
about effects.
p. 3-104, lines 17-23: The beginning of this paragraph acknowledges thatN can be both
beneficial and detrimental - so I would add to the end of it something like the following: " or
on the other hand, improved forest health by alleviation of N deficiency, increased productivity
and C sequestration".
p. 3-115: Good segment on disturbance - there are also many other references on the effects of
fire, including effects on water quality - see references below.
p. 3-131, lines 1-11: It is very common in commercial fertilizer studies as well as pollution N
addition studies for trees to take up only a fraction of applied N unless it is applied to foliage.
Even so, as noted on lines 9-11, growth increases to this small proportion of plant uptake are
common.
p. 3-133, lines 1-8: Of course it is true that when you add a limiting nutrient you will run up
against the next limiting nutrient - this is very well known. Is this then a wholly bad thing or was
the addition of the limiting nutrient "good" to start with?
p. 3-133, lines 9-12 through p. 3-133, lines 1-10: By my reading, there were 6 positive responses
to N listed in Table 3-15, and some were at the "moderate to high" levels of N addition. I count
three negative responses, including the one by McNulty which is so prominently highlighted, and
three which showed both positive and negative responses, depending on time and which species
was being looked at. AND, I will wager that if you included fertilization studies in commercial,
fast-growing forests, you would find a very high proportion of positive growth responses indeed.
p. 3-135, Regional Trends.... It is a shame that we do not have the data to know whether forest
growth has increased, decreased, or stayed the same from the forest inventory system. The
Europeans have this, yet we seem not to. That being the case, apparently, I do not find this
segment particularly illuminating, although it may the best we can do.
p. 3-136, lines 3-17:1 am glad that the authors included a discussion of the Magnini paper - even
though they do dismiss it rather easily. I am not sure I agree with that - nitrogen is, as is
acknowledged in this document - a limiting nutrient and it seems highly probable that adding it
will cause increased growth. The authors opinions obviously differ from mine. At least it was
discussed.
p. 3-162, Trees: The view here seems to be that there is nothing good about "altered growth
rates". Can't altered growth rates be a "good" thing if they are in the positive direction and in, for
example, commercial forests? Does this not bear even the slightest mention?
3-163 to 3-175: A very good review of N effects from the pollutant point of view. Do traditional
forest fertilization studies tell us anything more?
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3-164 Grasslands: It would be good to mention the cheatgrass issue in the Great Basin here.
Cheatgrass is a nitrophile and increased N deposition will undoubtedly facilitate the spread of
this noxious species also.
p. 3-191, line 13:1 would add "increased growth" after "sensitive"
p. 3-206, lines 4 and 8-18: "forest yields" is mention in the headlines, but no mention of
increased timber yield is mentioned in the following paragraph - all is negative.
p. 3-212 to 3-218: A very good, thorough and objective treatment of sulfur.
General References
Johnson, D.W., D.E. Todd, C.F. Trettin, and PJ. Mulholland. 2008. Changes in Soil
Exchangeable K+, Ca2+, and Mg2+in Forests of Walker Branch Watershed, 1972-2004. Soil
Sci. Soc. Amer. J. (in press)
Richter, D.D., and D. Markewitz. 2001. Understanding Soil Change: Soil Sustainability over
Millennia, Centuries, and Decades. Cambridge University Press. 255p
Richter, D.D., D. Markewitz, H.L. Allen, R. April, P.R. Heine, and R. Urrego. 1994. Soil
chemical change during three decades in an old-field loblolly pine (Pinus taeda L.)
ecosystem. Ecology 75:1463-1473.
Trettin, C.A., D.W. Johnson, and D.E. Todd, Jr. 1999. Forest nutrient and carbon pools: a
21-year assessment. Soil Sci. Soc. Amer. J. 63: 1436-1448.
References on the effects of fire:
Adams, M.A., Iser, J., Keleher, A.D., and D.C. Cheal. 1994. Nitrogen and phosphorus
availability and the role of fire in heathlands at Wilsons Promontory. Aust. J. Bot.
42:269-281.
Baird, M., Zabowski, D., and R.L. Everett. 1999. Wildfire effects on carbon and nitrogen
in inland coniferous forests. Plant Soil 209:233-243.
Bayley, S.E., Schindler, D.W., Parker, B.R., Stainton, M.P., andK.G. Beaty. 1992.
Effects of forest fire and drought on acidity of a base-poor boreal forest stream:
similarities between climatic warming and acidic precipitation. Biogeochem. 17:191-204.
Certini, G. 2005. Effects of fire on properties of forest soils: a review. Oecologia 143: 1-10.
Chorover, J., Vitousek, P.M., Everson, D.A., Esperanza, A.M., and D. Turner. 1994.
Solution chemistry profiles of mixed-conifer forests before and after fire. Biogeochem.
26:115-144.
DeBano, L.F. and C.E. Conrad. 1978. The effect of fire on nutrients in a chaparral
51
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ecosystem. Ecology. 59(3):489-497.
Dyrness, C.T., Van Cleve, K., and J.D. Levison. 1989. The effect of wildfire on soil
chemistry in four forest types in interior Alaska. Can. J. For. Res. 19:1389-1396.
Grier, C.C. 1975. Wildfire effects on nutrient distribution and leaching in a coniferous
ecosystem. Can. J. For. Res. 5:599-607.
Hauer, F.R., and C.N. Spencer. 1998. Phosphorus and nitrogen dynamics in streams
associated with wildfire: a study of immediate and longterm effects. Int. J. Wildland
Fire 8(4): 183-198.
Khanna, P.K. and RJ. Raison. 1986. Effect of fire intensity on solution chemistry of
surface soil under a Eucalyptuspauciflora forest. Aust. J. Soil Res. 24:423-434.
Khanna, P.K., Raison, R.J., and Falkiner, R.A. 1994. Chemical properties of ash derived
from Eucalyptus litter and its effects on forest soils. For. Ecol. Manage. 66:107-125.
Knight, H. 1966. Loss of nitrogen from the forest floor by burning. For. Chron.
42(2): 149-152.
Neary, D.G., C.C. Klopatek, L.F DeBano, PF. Ffolliot. 1999. Fire effects on belowground
sustainability: a review and synthesis. For. Ecol. Managem. 122: 51-71.
Raison, RJ. and J.W. McGarity. 1980. Some effects of plant ash on the chemical
properties of soils and aqueous suspensions. Plant Soil 55:339-352.
Rashid, G.H. 1987. Effects of fire on soil carbon and nitrogen in a Mediterranean oak
forest of Algeria. Plant Soil 103:89-93.
Trabaud, L. 1994. The effect of fire on nutrient losses and cycling in a Quercus cocci/era
garrigue (southern France). Oecologia, 99: 379-386.
Williams, M.R. and J.M. Melack. 1997. Effects of prescribed burning and drought on the
solute chemistry of mixed-conifer forest streams of the Sierra Nevada, California.
Biogeochem. 225-253.
52
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Dr. Donna Kenski
Overarching comments:
There is an impressive amount of new material in this new draft. EPA has been very responsive
to the panel's comments on the previous draft. As a result this version is much improved and
constitutes a solid scientific basis for the REA. I find only one major shortcoming, and that is
in its discussion of CMAQ' s performance characteristics. After reviewing the REA and noting
its reliance on CMAQ, it seems more important than ever to thoroughly describe CMAQ's
performance especially with respect to modeling wet and dry deposition. The ISA includes
plenty of useful new information on CMAQ, all of which is a welcome addition, including the
Tampa Bay modeling exercise (although the accompanying Figs. 2-29 through 2-37 are so small
as to be practically unreadable). The existing text on CTM deposition performance (Sec.
2.8.3.2) compares results for 23 different models (including CMAQ?), but no CMAQ specific
data are given. Is the factor-of-2 performance of these models for wet deposition adequate for
supporting the REA analyses and the standard-setting process? Dry deposition performance is
probably even more variable. Section 2.8.4 has some limited statistics on RADM performance
- but the REA doesn't propose any applications of RADM, so do we really need this? A more
thorough discussion of these deposition uncertainties, specific to CMAQ as much as possible, is
still needed.
Charge Questions:
Exec. Summary: This was a great addition that was just the right length and tone. I liked the
simple summaries of causal evidence and the emphasis on current concentrations.
Chap 1: Addition of the causality framework was helpful. The way the causal judgments
were carried through the document was great - i.e., in the summary, throughout Chapt. 3, and in
the conclusions in Chap. 4.
Chap 2: Nice review of NH3 measurement methods. Expanded information on CTM models,
especially CMAQ, is well written and very helpful, although still more is needed on CMAQ
performance with respect to wet and dry deposition. The additional tables on various
monitoring programs are nice (although hard to read - the font size in all tables has shrunk a
little too much). I also like the new maps and the source attribution summary. All in all, this
is a much stronger section than it was.
Chap 4: Like the executive summary, I thought this summary chapter was just about the right
length and struck the right tone.
Specific comments, typos, etc:
p. 2-2, Table 2-1: Improved formatting and detail in this table makes it much easier to read.
p. 2-4, line 4; remove 'the'
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p. 2-4, lines 5-8: It seems more appropriate to consider all electricity generation together for
this analysis, rather than split it into utility and industrial categories. Then it's clear that
electricity generation is almost equal to mobile sources in NOX emissions.
p. 2-4 thru 2-6: the added maps, figures 2-1 through 2-4, are very nice.
p. 2-7, lines 29-30: marine transport is 60% of land-based NOx in Europe? Can that be true?
p. 2-20, lines 3-5: although vehicle NH3 is only 8% of total NH3, it can be locally significant
(i.e., in cities). This is evident in Fig. 2.12 but bears noting in the text as well.
p. 2-27, Figure caption. Good clarification and explanation of this figure!
p. 2-30, top of page: 2NO2O5 should be N2O5
p. 2-30, line 13: what is 'organic coating' referring to? Organic compounds on the particle
surface? Not clear.
p. 2-34, line 30: instantiations?
p. 2-37, line 4: incomplete sentence.
p. 2-38, line 35: should snow be soot?
p. 2-95, Fig. caption 2-27 is garbled.
p. 2-96, line 2: predations ->predictions
p. 2-101, line 9: incomplete sentence
p. 2-122, line 14: change first 'and' to 'by'
p. 2-122, lines 17-21: Note that SEARCH makes continuous NH3 measurements at several
sites (not all of the network though). Discussion of their denuder difference method might be
added to the text.
p. 2-155, Fig. 2-75: Isn't this a map of particle NO3 concentration (not gas phase)?
p. 2-161: Figure 2-80 is the same as Figure 2-74
p. 2-199, line 15: Section 0?
p. 4-1, line 14: typical/y
54
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Dr. Myron J. Mitchell
General Comments (For these general comments my responses are in italics.)
Be consistent in the order of multiple citations throughout the document. Either cite by date or
alphabetically. Within the document the citations are not complete or consistent including the
need to use letters for multiple citations by the same author and same year. It would be helpful to
have unified and consistent units throughout the document. There is a mixture of English and
metric units (i.e., SI) in the current document. The correct SI abbreviations and units should be
used throughout the document. If English units are used, the equivalent values using SI units
provided in parenthesis would be helpful.
Responses to Charge to the CASAC NO /SO Secondary Review Panel
1. We have added an executive summary of the major findings and conclusions to the second
draft ISA. We have also created a "key findings" section that is intended to provide highlights of
these conclusions. We are seeking CASAC panel advice and comments on these additions to the
ISA. To what extent do they provide an appropriate level of detail and convey the important
scientific conclusions of the assessment?
In general the information level in the executive summary is suitable. However, the executive
summary and key findings need to be placed in the broader context of other environmental issues
including climate change, invasion of exotics, extreme events, changes in CO 2 concentration etc.
These other environmental affects can dampen and/or amplify the environmental effects
associated with SOX andNOx. Some changes related to other effects are suggested within my
detailed comments. Within the key findings there are a number of issues that need to be
addressed and these are provided within my detailed comments.
2. Chapter 1 has been revised to clarify the scope or focus of this assessment on effects related to
the deposition of nitrogen and sulfur compounds. In addition, we have added a discussion of the
framework for evaluation of causality for assessing ecological effects. Do these revisions
adequately characterize the scope of the assessment? Does the CASAC panel have
recommendations for revisions to the causality framework? Is it appropriately applied in the draft
ISA?
The information provided in Chapter 1 seems appropriate with respect to the overall approach.
3. Chapters 2 and 3 from the first draft have been combined. Substantially more information has
been included on NHa emissions, NHa measurement techniques, NHa and NH4+ concentrations.
Additionally, information on NOX and SOX including ambient concentrations, deposition levels
and their spatial and temporal relationships has been added. Have these revisions to Chapter 2
improved its assessment of the currently available scientific knowledge on atmospheric sciences
and its relevance to the evaluation of environmental effects presented in later chapters?
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There is certainly more detail on atmospheric chemistry in Chapter 2.1 am not certain whether
all of this detail including issues related to analytical technique, artifacts, differences in
instrumentation, etc. are necessary with respect to having sufficient information to set standards.
I would suggest placing some of these details in an appendix. More explicit linkages need to be
made on what we know as well as what we do not know and how this information is needed for
setting standards for NOX and SOx. The details provided in this section are somewhat
overwhelming including extensive graphics and results from specific sites. A clear summary of
what is known related to setting NO and SO standards would help bring all of this information
into focus. In particular the issues relating to the estimates of deposition velocities need to have
a central place in this document. One example that I am aware of is for the Egbert, Ontario site
in Canada where both concentration measurements and deposition values were compared using
CASTNET and CAPMoN approaches. The concentration data are almost identical, but the
deposition estimates are quite different. The issue related to confidence in modeled deposition
velocities needs to be placed in the context of the CMAQ predictions. The flow of information
could be improved with better use of headings to direct the reader to the content of major
sections. Also, some further discussion is warranted about how other factors such as climate
change, extreme events (e.g. fire, hurricanes, ice storms), invasion of exotics, etc. can also have
a major impact on ecosystem response and can have a major influence on the expression of
acidic deposition impacts on ecosystems. These results need to be placed in an historical
framework since for the effects analyses the longer time scales (i.e., decades) are most relevant.
4. We removed or eliminated redundancy, added summary sections, added additional references
and reorganized Chapter 3. Revisions to the ecological effects sections are given below. Have the
revisions improved the characterization of the ecological effects?
This section has many problems in the citations and references. Some of the sections in this
chapter are redundant. For example in section 3.2.1.3 there is a review of N accumulation and
nitrate leaching and in section 3.3.2 there is a section on N enrichment effects on N cycling. A
major challenge is placing the nitrogen atmospheric deposition concerns in the context of other
environmental issues including wastewater treatment and fertilizer contributions to the nitrogen
loading to surface waters. It is clear that there are often quite different current conditions and
responses among regions such as the Rocky Mountain West versus the Northeast especially with
respect to nitrogen. The need for different standards or approaches needs to be considered that
focus on specific types of ecosystems (e.g., alpine, northern hardwoods, etc.). It would be helpful
to have some better comparisons among model predictions (e.g., MAGIC versus PnET-BGC as
well as other models). Also, some better use of the PIRLA I andPIRLA II results in showing the
historical patterns of acidic deposition.
a. Consistent with CASAC comments, we expanded our characterization of the
quantification of chemical effects of acidification in aquatic ecosystems, added new
conceptual diagrams, and further discussed interactions between acidification and plant
disease.
Certainly more details are provided. However, there is considerable redundancy in the
document. A clearer delineation of particular areas of focus is needed.
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b. We expanded the discussion of quantitative relationships between nitrogen deposition
and ecological effects, including published critical loads in the U.S. and Europe. In
addition, the nitrogen enrichment section was expanded to include new discussions on
carbon budgeting, biogenic nitrous oxide and methane. Information on the linkages
between effects and both reduced and oxidized forms of nitrogen was emphasized, to the
extent data were available.
The more you can do to pull together information from these divergent informational sources
and provide those points that indicate divergence or divergence related to deposition and
ecological effects will improve this document.
c. The section on "other" welfare effects was updated to include information on the direct
phytotoxic effects of nitric acid.
The inclusion of additional information on the direct phytotoxic effects of nitric acid was helpful.
5. In revising the ISA, we have incorporated additional information on the indicators of exposure
and ecological effects, including increased emphasis on quantified relationships in the
presentation of information of results in tables and summary discussions in Chapter.
This revised version certainly is more complete than the previous version. A major challenge is
placing the issues related to NOX and SOX effects in the context of other ecosystem changes
including effects due to climate change, invasion of exotics, extreme events. There is also
substantial reliance on a variety of models that are used to predict a variety of parameters.
These models have different spatial and temporal resolutions. Also, some clearer delineation is
needed on the overall model performance and the confidence of predictions. How does this
confidence effect the ability to make accurate assessments of the effects ofNOx and SOx?
Specific Comments
For Key Findings the following issues need to be addressed:
This statement is not true:
Particulate sulfate can interact with methanogenic bacteria to produce methylmercury.
This relationship is for sulfate in soil and wetlands not "paniculate sulfate ".
For the statement:
The sensitivity of terrestrial and aquatic ecosystems to acidification from sulfur and nitrogen
deposition is predominantly governed by surficial geology.
Change to include regional differences.
For the statement:
In aquatic ecosystems, ecological effects are linked to changes in surface water chemistry,
including sulfate concentration, nitrate concentration, sum of base cations, acid neutralizing
capacity, surface water inorganic aluminum concentration, and surface water pH.
Also indicate these effects are influenced by historical inputs to these systems.
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For the statement:
At least one important component of N, ammonia, is not measured routinely in any national
network, but may account for greater than 80% of total reduced nitrogen deposition.
This statement gives impression that N deposition is greatly under estimated without the inclusion
ofNHs. Provide clarification on the degree of the relative importance ofNHs deposition across
the U.S.
For the statement:
Existing monitoring networks are inadequate to characterize the full extent of regional
heterogeneity in nitrogen and sulfur deposition, and very likely underestimate the total nitrogen
deposition across wide areas of the U.S.
Indicate where the actual geographical problems occur.
The following statement is not true:
Atmospheric nitrogen deposition is the main source of new nitrogen to terrestrial ecosystems.
Across terrestrial ecosystems for the total U.S. N fertilizers are the dominant form of input.
Clarify that N atmospheric deposition's relative importance varies among regions.
For the following statement:
Nitrogen deposition causes changes in ecosystem carbon budgets. However, whether nitrogen
deposition increases or decreases ecosystem carbon-sequestration remains unclear. For example,
a limited number of studies suggest that nitrogen deposition may increase carbon-sequestration
in forests, but has no apparent effect on carbon-sequestration in non-forest ecosystems.
Clarify that these effects are highly spatially variable including whether there are decreases or
increases in C sequestration.
For the following statement:
Productivity of many freshwater ecosystems and most estuaries and coastal water ecosystems is
nitrogen limited.
This suggests that N is the major limiting nutrient for freshwater systems. This is not generally
true. This statement needs to be placed in context ofP which often as important than N as a
limiting nutrient for freshwater systems.
For the following statement and related section:
Biological effects, Multiple biological indicators have shown that nitrogen deposition alters
ecosystem structure.
This section needs to be placed in the context of other agents of change including climate, exotic
introductions, extreme events, etc.
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Page Line Comment
xvii Change to "chloride ion."
xviii Change to "fluoride ion"
1 Within the body of the text "Nitrogen" should be changed to "nitrogen".
1 Throughout the text corrections need to be made for subscripts that are lacking in
some cases (e.g., NO3 should be NO3, NO2 should be NO2, SOX should be SOX,
etc.).
1 Change to "In the years 2004-2006, S deposition in the United States."
2 Change "inferred" to "modeled."
2 Change to "Although deposition in most areas of the United States was dominated
by wet deposition, there were some exceptions, including parts of California here
N deposition was primarily dry."
2 Change to "The sparse coverage of monitoring sites in many areas, especially in
the rural West, results in little or no data on deposition totals in a substantial
number of potentially sensitive places."
2 Change to "Numerical modeling efforts can help fill-in these data gaps and may
suggest that local and even regional areas of high concentration and deposition
exist where currently no data exist.
4 Some of most severe acidification may also occur during the summer after periods
of drought especially in those watersheds with substantial portions of wetlands.
These rewetting episodes are associated with acidification due to the oxidation of
previously reduced sulfides.
2-1 8-18 Isn't there some merit in changing the definition of nitrogen oxides to be the same
as that used by atmospheric scientists and air quality control experts?
2-4 2 Change "Roughly" to "Approximately"
2-6 6 Change to "The N content in fossil fuels and chemical forms1 vary strongly."
2-6 7 Change "running" to "operating conditions".
2-7 35 I thought that the effect of "stack height" effect was relatively minor with respect
to the overall dispersion distance of pollutants from combustion.
2-8 16 Change to "of the various products of N transformations."
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2-8 22 Change to "synthetic and organic TV fertilizers."
2-8 29 Change to "N metabolism in soils is strongly dependent on soil substrate
concentrations of both N and labile carbon constituents as well as physical."
2-8 30 Change to "Where available N."
2-9 11-12 Change to "such as the differences between shortgrass and tallgrass prairie for
example."
2-9 18-19 Change to "Local contributions to soil NOX can be greater per unit area than the
global average."
2-10 28 Delete extra "," in "(e.g.,,." Note this occurs twice in this line.
2-11 14-16 This statement is a little confusing. It suggests there a combination of both
atmospheric residency time as well as heat trapping efficiency that produces this
value of 300? These two parameters need to be clearly separated. Isn't the heat
trapping capacity on a per molecule 310 times that of carbon dioxide?
2-11-12 Reword as follows: However, N2O is an intermediate product along with NO
from the complex soil metabolism described in Section 2.2.2.1. A brief
description of N2O emissions and its contribution to the U.S. GHGs is described
below.
2-12 16-17 Delete: These emissions resulted from the fuel combustion, industrial practices,
and stimulation of biogenic sources through agricultural practices enumerated
above.
2-12 18-19 Change to "From 1990 and 1998 "
2-12 23 Change to "Biogenic production of NiOfrom soil accounted for > 75%."
2-12 27 Change to "may be affectedly environmental conditions."
2-12 28-29 Change to "enhancing denitrification, and potentially increasing N2O emissions."
2-13 8 Change to "emissions originated from."
2-13 10 Change to "either as SO2 or SO3."
2-13 14 Change to "can not accurately be used to calculate the contribution of local
sources to selected environmental."
2-13 18-19 Delete "with most counties east of the Mississippi River in warmer colors (greater
emissions densities) than most counties in the West."
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2-15 6 Change to "98 and 160 tons total 862 per square mile, respectively."
2-18 4 In addition to carbon-bonded S (amino acid) there is also inorganic sulfate.
2-22 1-3 This is a confusing sentence that needs to be reworded.
2-22 10 Change to "have been performedyor a number."
2-22 12 Change to "it can be treated conservatively on these scales."
2-23 30 Change to "may have been underestimated or were increasing."
2-24 6 Change to "proved useful for estimating.'"
2-25 11 Change to "volatility. This pattern, however, has not appeared in previous
emissions factors and inventories."
2-26 10 Change to "available in numerous references (Seinfeld."
2-26 11 Change to "recounted here with special attention to."
2-26 12-13 Change to "are schematized in Figure 2-15. NO2, itself an oxidant, can react to
form."
2-26 16-17 Change to "to HNOs and can contributing to the acidity of cloud, fog, and rain
water."
2-27 Figure Caption 2-15 As stated previously it would be helpful to have the
definitions of "NOX" and "NOy" be consistent with the atmospheric science
literature.
2-29 2 Delete "highways."
2-29 7 Change to "Reaction 7:."
2-29 14 Delete "schematic."
2-29 17 Change to "this chapter are:."
2-30 2 Change to "NO3:." Note I would suggest that if reactions are provided after a
statement this statement should end with a ":" throughout the document.
2-32 15-16 Be consistent in the order of multiple citations throughout the document. Either
cite by date or alphabetically.
2-34 4 Change to "decomposition ranges."
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2-34 6 Change to "uptake by vegetation."
2-34 7 Change to "Reaction 21/s thermally."
2-34 11 Change to "concentrations of their precursors."
2-34 12 Change to "found in most environments, ranging from remote."
2-34 14 Change to "downtown metropolitan areas, especially."
2-35 5 Change to "because many factors important for P(O3) are omitted."
2-35 6 Change to "VOCs that are mostly absent during early morning hours."
2-35 11-12 Delete "at a monitoring site in Shenandoah National Park, VA."
2-35 18 Change "from commercial aircraft are very similar."
2-35 20 Delete "included in model calculations."
2-35 27 Change to "(1998, 2001)."
2-35 32 What is implied by the use of the term "correlation patterns"? See also page 2-36,
line 1.
2-36 7 Change to "2001 , 2003)."
2-37 10 Change to "Brown et al. (2006) found."
2-38 1-2 Change to "available for reaction thus increasing P(C>3)."
2-38 5 Change to "amounts. However, only."
2-38 8-11 Change to: "It is important to recognize that the studies of both Schultz et al.
(2000) and Singh et al. (1996) involved aircraft sampling at high altitude that can
significantly under-represent sea salt aerosols. These aerosols are important
contributors to total NOs (defined to be HNOs + pNOs) and large fractions of
NOY(Huebert, 1996)."
2-38 12 Change to "budgets based upon their studies"
2-38 14 Change to "domine, 2002) that."
2-38 19 Change to "Hence, HNO3 recycling."
2-38 33 Delete "observed."
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2-38 34 Change "(React!on 18) constitutes a."
2-39 6 Change to "and kerosene soot, and found that."
2-39 16 Delete "observed.".
2-39 18 Change to "Longfellow etal. (1999)."
2-39 20 Change to "NO3/N2O5 and HO2/HO2NO2"
2-40 11-12 Change to "Daytime observations of HNO2, when rapid photolysis depletes
ambient concentrations to very low levels, implies large sources of
photoinduced."
2-48 4 Change to "Jacobson (2002)."
2-48 12 Change to "~5 x 10'3 with."
2-50 6-7 Is there still a quantifiable plum "further downwind". Why are conditions even
"more oxidizing than in background air"?
2-55 18 The correct abbreviation for moles is "mol" not "M".
2-56 2 Change to "throughout the Earth's boundary layer."
2-56 8-9 Does the term "reservoir species" imply chemical species with larger "T"?
2-56 19-20 Change to "Photochemical activity is enhanced by higher temperatures and
sunlight."
2-57 1 Change to "distances from their sources."
2-59 26-27 The format here is mixed up and needs a ")" at the end.
2-60 1 Change to "(2007)". There are two 2007 references that need to be designated
with letters.
2-60 1 Delete "parts per billion" and "[]".
2-60 7 See other comment about Dunlea et al. references.
2-60 2-34 Change to "The daily average interference for an episode during the summer of
2002 was modeled. Concentration fields for NOZ species and conversion
efficiencies for NOZ species ranged from -20% in Baltimore to -80% in Madison,
VA.
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2-61 1 Change to "activity was highest."
2-61 2 Change to "compounds were greatest"
2-61 7 Delete "On the whole."
2-61 10 What is meant by "can be changing rapidly"? Do you mean changing rapidly in
the literature
2-65 7 Change to "normal" to "typical."
2-65 12-17 These statements are important in relating the results to actual needs and
determination of standards. Similar types of statements are needed throughout the
document to focus the results on those issues which are policy relevant.
2-66 4-5 This sentence needs to be reworded since "and of the particles against deposition"
does not make sense. See also line 9.
2-66 11-13 Delete the term "standard" in these statements. There is no actual standard
configuration for these devices.
2-69 1 Clarify what is meant by "In addition to the elevation by EPA."
2-69 2 Delete "and reported by."
2-69 3-6 Change to "The methods included the use of a tunable diode laser (TDL)
absorption spectrometer, a wet scrubbing long-path absorption photometer
(LOPAP), a wet effusive diffusion denuder (WEDD), an ion mobility
spectrometer (IMS), a Nitrolux laser acousto-optical absorption analyzer, and a
modified CL analyzer."
2-69 11-13 Change to: "Hence comparisons of ambient NHa instruments have confirmed that
no single technique has yet been identified that provides automated, high quality
results for continuously determining NH at low concentrations."
2-71 5 Be more explicit in using the term "positive artifact" here and elsewhere. Does
this mean to suggest that there are overestimates of concentration measurements?
Would a better term be something like artifacts resulting in overestimates.
2-71 11 See the comment above and modify to avoid confusion I the term "negative
interference."
2-78-81 This section could benefit with more focus on the issues related to evaluating SOX
and NOX at the scales important for this assessment with respect to chemical
transport models CTMs.
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2-81-83 Is this review of global scale issue important for the issues associated with
regional/local situations. At a minimum this section could be reduced playing
particular attention to those global aspects that can have regional implications.
2-87 3 In the Picketering et al. citations remove ";". These format errors need to be
corrected throughout the document.
2-88 The previous pages (2-78 to 2-87) need to have a clearer linkage to this deposition
section.
2-89 9-13 Certainly a major issue that needs focus are the errors and problems with
estimating dry deposition and a considerable amount of these concerns related to
the calculations of deposition velocities.
2-90 13-15 The statement that "Deposition rates are independent of leaf area or stomatal
conductance, implying that deposition occurs to branches, soil, and the leaf cuticle
as well as leaf surfaces" is misleading since leaf area and stomatal conductance
are important, but that other factors also need to be included.
2-93-95 The section on "Air Quality Model Evaluation" is a critical part of this document.
2-94 3-5 These errors can lead to erroneous predictions especially with respect to those
associated with future air quality estimates.
2-101-202 Figures 2-38 and 2-39 suggest that the model results are quite different than those
for the NADP network sites. Doesn't this bring into question the model validity
for predicting these wet deposition amounts?
2-104 12-13 Suggesting that Ext-RADM provides "good" agreement when R2 values are
between 0.4 to 0.7 for most species is misleading since at lower values less than
50% of the variation is being explained.
2-105 1-4 These statements suggest a better Ext-RADM result. Is this due to the value
representing a larger spatial unit and also an estimate for a longer period?
2-108 1-4 I am not sure of the rationale for including in PRB the anthropogenic sources
outside of U.S., Canada and New Mexico.
2-120 Are the measurement protocols in State and Local Air Monitoring Systems
(SLAMS) networks sufficiently similar for these measurements to be comparable
to CASTNET.
2-131 10 Incomplete sentence.
2-198-202 Having this summary is helpful in placing the large amount of information
provided in the document in context. Some further inclusion of statements relating
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to problems with respect to dry deposition estimates including the issues
associated with estimating deposition velocities needs to be included.
2-199 18-21 This sentence needs to reworded and likely separated into a series of sentences.
3-4 25-26 Why are wetlands given special attention here?
3-7 Figure 3-2 caption. Change to "Diagram illustrates soil horizons commonly
found".
3-9 8 Change to "(Shanley et al, 2005)."
3-9 14-15 References are not cited correctly (these are multiple authors) including a need for
a letter designation for Driscoll et al. (2001)
3-9 20 See comment above regarding citation. It appears that this section has many cases
where the references are not cited correctly including the absence of showing that
the references are multiple authors.
3-11 9 Section "0"?
3-12 17 Another line with incorrect referencing being used.
3-12 30 Another line with incorrect referencing being used.
3-16 Figure 3-3 needs a reference.
3-17 Figure 3-4 needs a reference.
3-19 3-9 Even in the West the nitrate in surface waters during snowmelt is mostly
microbially derived and is not from direct atmospheric input. These statements
confuse this issue.
3-22 4 There are also large differences in tree species to tolerance of different levels of
Al. Note this is indicated later in line 14. A clear statement is needed of the
major factors associated with Al toxicity.
3-22 14 Figure 3-5 does not clear depict that Al stress varies with species as suggested
with this reference.
3-25 2-5 The term buffering is not correctly used here. Reword to : Once base saturation
decreases to a critical level (approximately 15-20%), inputs of H2SO4 and
result in exchange of inorganic Al.
3-25 9-10 Change to " If the C:N ratio of soils falls below about 20 to 25, nitrification is
stimulated resulting in net nitrification and increased acidity'."
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3-27 Figure 3-6 needs a reference.
3-34 18-21 Also grasslands tend to be found on soils with relatively high pH and % base
saturation. Aren't grassland associated with acidic soils less common?
3-39 16 Change to "in most affected."
3-39 22 Delete "to a greater extent than SO42"."
3-39 23-24 Delete "The importance of NOs as an agent of acidification varies by region." -
3-39 29 Delete "Average."
3-40 1 Change to "Surface water NO concentrations have changed over time and these i
trends vary by regions".
3-40 19 Change "outbreak of gypsy moths, which consumed foliage" to "gypsy moth
defoliation."
3-40 20-21 Delete " in affected watersheds."
3-40 32-33 Change to "annual air temperatures were strongly related to average annual NO3.
concentrations in stream water".
3-41 5-6 Was it really suggested that an increase in pH stimulated primary productivity? If
this is the case this should be attributed to the authors of the article.
3-41 9 Change to "between recent temporal trends."
3-42 1-2 Change to "(Aber, 2003). Moreover, spatial patterns of NOs concentrations in
surface water across the Northeastern U.S. are consistent with atmospheric N
deposition values although there is considerable variation in these concentrations
based upon watershed attributes.
3-42 15-16 Change to "Within western Virginia and in Shenandoah National Park,
concentrations of base cations in streams did not exhibit significant temporal
trends from 1988 to 2001"
3-42 16-17 If sulfate concentrations did not change indicate this explicitly versus an indirect
reference to the role of sulfate adsorption.
3-43 1-2 See comment above regarding the results from Virginia.
3-43 6-7 Delete "The pH of water quantifies the hydrogen ion concentration, which is toxic
to many forms of aquatic life."
3-43 12 Explain the derivation of these three pH reference levels.
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3-43 22 Change to "southwestern Adirondacks acidified more compared to other lakes in
the Adirondacks since preindustrial time."
3-44 6 Should this be "(0.18 ueq/L/yr)"?
3-45 1 Be explicit in referring to this study. I assume this is Stoddard et al. (2003).
3-45 18 Do you mean by more stable that ANC is not affected by ambient CC>2
concentrations? Make this more explicit.
3-45 29 Explain these three cutoff values for ANC.
3-45 33 Change to "the oxidation of chemically reduced S-containing minerals."
3-47 11-14 Delete "ANC can be measured in the laboratory by Gran titration or calculated on
the basis of the difference between the base cation sum and the mineral acid anion
sum. Acidic waters are defined as those having ANC less than or equal to zero
ueq/L".
3-48 33 Not sure the term "limited" is appropriate.
3-50-51 References are needed in this text to support the statements.
3-52 The following study provides additional information on ANC patterns within the
Adirondacks using a mass balance approach: Ito, M. MJ. Mitchell, C.T. Driscoll
and K.M. Roy. 2005. Factors affecting acid neutralizing capacity in the
Adirondack region of New York: a solute mass balance approach. Environmental
Science and Technology 39:4076-4081.
3-54 I believe some PnET-BGC simulations by Driscoll's group have also been done
that would provide other estimates of the recovery of ANC.
3-56 8 Change to "rain events."
3-76 32-33 References needed to support this statement.
3-79 1-2 A major problem in making wide scale regional projections is that it is well
known that the response even within relatively small areas (e.g. almost adjacent
watersheds) that the response to acidic deposition can be quite marked.
3-79 3-6 It needs to be emphasized that the water pathways and soil depth can be very
important in the capacity to neutralize the effects acidic inputs.
3-79 13 It should also be stated that this is a threshold which is generally necessary, but
does not always result in enhanced nitrate loss.
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3-80-81 Some inclusion of issues associated with how biotic response can also be altered
by other factors such as climate change, invasion of exotics, extreme events (e.g.,
drought, ice storms, hurricanes, etc.)
3-87 Figure 3-19. Why not cite NADP/NTN as the source versus Sullivan et al.
(2006a). Also, the more recent data should be included.
3-88 In reviewing the results from the Adirondacks focus on those findings specific to
the Adirondacks versus generalities associated with acidification of ecosystems.
3-89 The PIRLAI and PIRLA II projects provided some of the most definitive
evidence of historical changes in acidification of the Adirondacks. Inclusion of
some of the figures produced from this project would strengthen the document.
3-89-90 The inclusion of figures showing side by side comparison of MAGIC and
PnETBCG hind casting would be instructive especially if placed in the context of
the PIRLA reconstructions.
3-90 8 Provide figures or tables clearly showing similarities and differences between the
MAGIC and PnET-BGC simulations.
3-91 Table 3-10. Reference needed
3-102-123 The structure of the document results in redundancy with some of the information
in this section also being presented in previous sections of Chapter 3.
3-127 9 Certainly atmospheric deposition is an important contributor, but it also needs to
be stated that other forms of N input generally exceed that from the atmosphere.
3-127 23 Even for those watersheds exhibiting substantial nitrate loss the vast majority of
the N inputs are either being stored or being denitrified within these watersheds.
3-128 1-2 Change to "higher rates of deposition with some of these watersheds showing
little nitrate losses."
3-128 12-19 Wetlands can also be sources of nitrogen due to nitrogen fixation such as that
associated with alders.
3-128 23-24 The case for freshwater eutrophication is not strong. The strongest evidence is
associated with changes in the biotic assemblages of lakes especially in the
Mountain West.
3-129 1-4 A more conservative statement is warranted with respect to the contribution of
atmospheric deposition so that it is clear that in general this is not the dominant
source of N input that is causing eutrophication.
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3-129 19-25 It should be emphasized that there is also an issue of transient effects where over
the short term the additional N results in additional C fixation (e.g. enhanced
primary productivity) but this will not continue as other factors limit production
over extended periods.
3-130 21 Change to "beech."
3-130 25-31 This affect on frost hardiness needs to be linked to issues of red spruce dieback at
high elevations.
3-133 6-7 Some further elaboration is needed related to results in Europe that have shown
that experimental N additions have resulted in higher forest growth and this high
growth resulted in other nutrient deficiencies especially in the form of Mg.
3-133-136 This discussion on "N Deposition Effects on Productivity and C Budgets in
Terrestrial Ecosystems" is generally well done and provides a good synopsis of
existing information.
3-142 1-13 The discussion on the historical aspects of N limitation in North American lakes
is interesting, but it is important to ascertain which is the type of lake nutritional
status are the goals of any regulatory programs. It is not likely that there would be
a strong mandate to return to pre-Columbian conditions. This situation may be
different with respect to desirable endpoints between the eastern and western U.S.
3-146 14-15 This needs to reworded so as not to give the impression that the N is the major
limiting nutrient for most lakes. Clear articulation of differences between more
pristine versus more developed regions is likely required.
3-147-151 The section on estuaries is generally thorough a provides a good review of the
influence of N availability on productivity and other aspects of importance to
biogeochemical and biotic responses.
3-162 10 Change to "100 y.'
3-166 16 Change to "documented."
3-152 33-34 It needs to be explicitly stated that atmospheric N loadings is not the sole
contributor to the increased N loading in estuaries.
R-30 There are two Dunlea et al. (2007) references that need to be designated "a" and
"b" respectively.
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Mr. Richard L. Poirot
These comments pertain primarily to Charge Question 2 and Chapter 1 of the 2nd draft ISA.
Question 2. Chapter 1 has been revised to clarify the scope or focus of this
assessment on effects related to the deposition of nitrogen and sulfur compounds. In
addition, we have added a discussion of the framework for evaluation of causality
for assessing ecological effects. Do these revisions adequately characterize the scope
of the assessment? Does the CASAC panel have recommendations for revisions to
the causality framework? Is it appropriately applied in the draft ISA?
Chapter 1 provides a clear, concise introduction to the ISA, including a brief history of past
NAAQS reviews, an outline of the intended scope of the current assessment, and a proposed
framework for the determination of causality in relationships between the pollutants of concern
and the resulting ecological responses. Overall I think this chapter looks good, and my
comments are mostly minor.
While the scope of the assessment is relatively broadly defined - to include for example
consideration of ecological effects resulting from N-nutrient enrichment from deposition of both
oxidized and reduced nitrogen - there still seems to be a rather intentional avoidance of
questions of how such effects or environmental effects may be related to alternative kinds of
NAAQS air-quality-related indicators. This question does get taken up to some extent in
Chapter 8 of the Risk and Exposure Assessment. However, it might also be useful to add some
discussion and display of the inter-relationships among various air quality, deposition and effects
metrics as part of the ISA. It would be useful to know up front if deposition-based or critical
load-type NAAQS are a possibility, or are we stuck with SO2 and NO2, again?
As indicated in previous comments, I think its unfortunate that the scope of this assessment was
narrowed to exclude consideration of visibility effects from aerosol phase sulfur and nitrogen
compounds. I think it would have been possible to copy/paste the same discussion of these
effects in both the SOx/NOx and PM secondary NAAQS ISAs (and then decide which NAAQS -
if any - would be most effective for addressing all the welfare effects of S & N emissions). In
the current case it might also have led to consideration of useful alternative NAAQS indicators -
which consideration of aerosol concentrations & effects would help justify. It can also be noted
that the working definitions of NOx and SOx are somewhat awkward here, as NOx is taken to
include nitric acid and aerosol nitrate, while SOx includes only the gaseous oxidized sulfur
compounds.
The historical summary of the secondary SOx and NOx NAAQS reviews is exceedingly brief,
and it seems incomplete for example to mention the 1984 EPA Acid Deposition Critical
Assessment Document without also mentioning the 1990 NAPAP State of the Science and
Technology and Integrated Assessment Reports, the 1990 CAA Amendments (Title IV), and
1995 EPA Acid Deposition Standard Feasibility Study Report to Congress. Granted, these
were not part of the NAAQS review per se, but the 1996 decisions not to revise the secondary
SOx or NOx NAAQS were related to these other activities, and represented a clear decision that
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the environmental effects of these pollutants were better addressed by other regulatory
mechanisms.
The proposed framework for evaluation of causality is logical and clearly presented. So far as I
can tell, it appears to be appropriately (and effectively) applied elsewhere in the document -
where chapters 3 and 4 contain a number of clear, persuasive statements that "the evidence is
sufficient to infer a causal relationship between .. .X and Y". With the exception of a few
such statements on direct vegetation effects from exposures to specific gaseous S and N
compounds, the identified "causal agents" are almost always either "acidifying deposition" or
"reactive nitrogen deposition", and thus appear to be intentionally non-specific to the
traditional criteria pollutant definitions. I think this is fine - even preferable - if secondary
NAAQS are being considered that might be deposition-based, combine S&N or combine
oxidized and reduced nitrogen. If such alternative metrics are not being considered, than maybe
some of these bullets might be rephrased in more pollutant-specific terms. Also perhaps there
could be some causality conclusions in chapter 2, in which causal relationships might be inferred
between (current and historical) emissions, ambient air concentrations and deposition of various
S and N compounds.
Possibly also, the concept of a "significantly contributing factor" could be introduced here (and
used later) as a sort of subset of a "causal factor" (i.e. "the evidence is sufficient to infer a causal
relationship between Nr, for which oxidized N is a significantly contributing factor, and Z
effects..."). This concept of significant contributing factor could be important in considering
effects resulting from pollutant mixtures, as well as for considering effects which result from or
are modified by the cumulative influences of both current and historical pollutant deposition.
I think the description of the 2-step process in the causality framework could be more clearly
presented. There's a bit of a logic problem with saying first we will determine the causal
relationship and then we will determine what effect has been caused. In reality, the process
seems to be more one of starting with identifying rather broad, general causal relationships (for
example between total Nr deposition and alteration of terrestrial species richness) and then in
step 2 winnowing this down to identify more pollutant-specific and/or species-specific
relationships at specific ranges of concentrations/exposures. Additional confusion is introduced
by apparent inconsistencies between the 2 steps in the causality framework as described in lines
4 and 5 page 1-7, and the subsequent discussion of 2 steps in sections 1.6.1 and 1.6.2. In the
first case, step 2 refers narrowly to the determination of whether levels of exposure can be
defined at which effects of concern can be observed (kind of a yes/no threshold answer). In the
second case (section 1.6.2), step 2 is more broadly and comprehensively defined to consider
effects over a range of exposure conditions with evaluation of the shapes of exposure-response or
concentration-response functions. Presumably this would also include consideration of
estimated future ecological responses to changes (increases or decreases) in pollutant
concentration and deposition. For the most part, this ISA seems much more focused on step 1
type conclusions - although there are some very useful tabular presentations of quantitative
relationships between N deposition levels and specific ecological effects such as in Table 4-4.
I wonder if the intent is to intentionally focus on step 1-type conclusions in the ISA and then
develop more detailed quantitative evaluations of ecological response (i.e. step 2) in the Risk and
Exposure Assessment. If this is the intent, why not make it clear?
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Mr. David Shaw
General Comments
The executive summary is an excellent contribution to the ISA. This addresses some of my
previous concerns regarding a clear message of the document.
Executive Summary, Page 2:
The paragraph which begins with "Expanding urbanization..." has a last sentence explaining
heterogeneous deposition. This last sentence might be benefited by the addition transport.
It seems that it would serve the assessment better to have Section 1.7 (page 1-10) appear at the
beginning of Chapter 1.
Charge Questions
Chapter 1 has been revised to clarify the scope or focus of this assessment on effects related to
the deposition of nitrogen and sulfur compounds. In addition, we have added a discussion of
the framework for evaluation of causality for assessing ecological effects. Do these revisions
adequately characterize the scope of the assessment? Does the CASAC panel have
recommendations for revisions to the causality framework? Is it appropriately applied in the
draft IS A?
I feel that the scope has been properly modified to include both oxidized and reduced forms of
nitrogen. Furthermore, I am pleased at the use of "acidifying deposition" throughout the
document. This reflects the actual concern of this type of deposition.
Section 1.1, Page 1-3:
I still feel that particulate matter should not be omitted from this document. As my previous
comments state:
PM plays a significant role in nitrogen and sulfur deposition. I feel that separating out the
effects of gas- versus aerosol-phase S/N will be difficult, since wet and dry deposition can
include both phases, and atmospheric chemistry and transport affect both phases. The ISA
clearly states that "particulate NOX and SOX will be addressed with the secondary PM NAAQS
review," and it therefore becomes crucial that these two review process tracks are highly
consistent with each other. One cannot proceed independently of the other track.
Section 1.6, Table 1-1:
While the causality framework does seem appropriate, it is unclear as to how much weight is
given to each aspect. I do appreciate that it clearly states that that scientific evidence will not
have to meet all of the aspects of causality, but it might benefit the group to understand how each
will be considered in the weighting process (i.e. if no consistency then not used).
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Section 1.6.1, Table 1-2:
Again, while the descriptors for weight of evidence seem appropriate, I wonder if these could
somehow be associated with the causality aspects. For example, given a "weight" in the form
of a number for each aspect, add all the aspect numbers for a total. When this total is
calculated, apply to the weight of evidence table. Perhaps "sufficient to infer a causal
relationship" is used for aspect numbers of 30 or higher (depending on how the number scheme
is set).
Misc.
Page 1-6, line 16:
Should read "... analyses used appropriately and..."
Executive Summary
There is inconsistency in how NOX and SOX is typed.
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