### Guidance on Nitrogen and Sulfur De position Analysis Thresholds

Background The National Park Service (NPS) and the U. S. Fish and Wildlife Service (FWS) have developed criteria for evaluati ng the contribution of additiona l nitrogen (N) or sulfur (S) to deposition within Class I areas. This document describes the equation and process by which Deposition Analysis Thresholds (DATs) have been developed for Class I areas. The NPS and FWS have developed this DAT equation in response to requests by permitting authorities and permit applicants to continue to develop consistent, predictable permit review processes, and to expedite the permit review process. In developing DATs, the NPS and FWS seek to further im prove the process by providing a quantitative method with which to evaluate sulfur deposi tion in Class I areas. DATs for both sulfur and nitrogen have been developed and are presented here.

The Clean Air Act Amendments of 1977 give Federal Land Managers (FLMs) an “affirmative responsibility” to protect air quality and air quality related values (AQRVs) within Class I areas. An AQRV is a resource that may be adversely affected by a change in air quality. The resource may include visibili ty or a specific scen ic, cultural, physical, biological, ecological, or recr eational resource identified by the FLM for a particular area. FLMs are responsible for reviewing ai r quality permit applications from proposed new or modified major sources near Class I ar eas, and determining th e potential impacts, if any, that may result from source emissions . FLMs take into account the particular resources and AQRVs that would be affect ed; the frequency and magnitude of any potential impacts; and the direct, indirect , and cumulative effects of any potential impacts. In making these determinations , FLMs are mandated to err on the side of resource protection.

Deposition-induced changes to AQRVs are of serious concern to FLMs and these thresholds are intended to distinguish where deposition increases may result in potentially adverse ecosystem stresses, as well as where the deposition increases are likely to have a negligible impact on AQRVs.

Deposition Analysis Thresholds

A DAT is the additional amount of N or S deposition within a Class I area, below which estimated impacts from a proposed new or mo dified source are considered insignificant

. The DAT for a park or refuge will be comp ared with the amount of additional deposition resulting from a source, as modeled using CALPUFF or other appropriate models. The N DAT represents total N, including both we t and dry deposition. Total nitrogen includes NO, NO 2 , HNO 3 , NO 3 , NH 3 , and NH 4 . The S DAT represents total S deposition. Total

N and total S were selected in order to be c onsistent with conventions used in deposition loading, to represent the total amount of N a nd S inputs received in an ecosystem and to be compatible with CALPUFF model outputs.

The framework for calculating both the N and S DATs is: DAT = Natural Background Deposition * Va riability Factor * Cumulative Factor2

Using this framework, DATs for N and S ha ve been calculated for the Eastern and Western regions of the United States, and are presented below. A discussion of each component used to develop this equation and DATs is also presented.

Determination of Background Nitrogen (B N ) and Sulfur (B S ) Deposition Natural background deposition was used to determine the DAT because aquatic and terrestrial ecosystems evolved under natural background deposition conditions. Therefore, some fraction of natural background deposition is likely within the range of natural variability for these ecosystems.

The B N values were selected from a range of natural background deposition values published in peer-reviewed scientific lite rature, and from information provided by consultations with researchers (Dentener pers. comm .; Galloway et al . 1995; Galloway et
al . 1996; NAPAP 1991; NADP 2000). The B S values were determined in the same manner (Bates, Lamb 1992; Bates et al. 1992; Dentener pers. comm .; Galloway et al. 1996; Galloway et al . 1982; Galloway, Whepdale 1980). From this range of deposition values, the values of 0.50 kg/ha/yr for the East and 0.25 kg/ha/yr for the West were selected for both N and S, as they fulfilled the requirements of being scientifically valid as well as being conservative. These values represent the low end of the regional range of values that are presented in estimates of regional natural background deposition. This conservatism is necessary in order to fulfill the mandate to err on the side of resource protection, and to protect air qu ality and AQRVs within Class I areas. A reference of all

literature used to determine B N and B S is attached, as well as Supporting Literature references for all sources used in developing both DATs.

Different B N and B S values were developed for the Eastern and Western United States. These separate values are based on the di stinction between east and west natural deposition estimates made through global a nd national scale modeling analyses. The East DAT and West DAT are applicable to Cl ass I areas located ea st and west of the Mississippi River, respectively.

The NPS and FWS do not intend to devise me thodology for assessing exact pre-industrial deposition throughout the United St ates. Currently it is no t possible or necessary to determine natural deposition values for each Cl ass I area. It is most appropriate to

determine the B N and B S values on a large spatial scale, such as the Eastern and Western regions of the United States. This has the added advantage of allowing for a simpler application process for applicants.

Use of a Variability Factor Once natural background deposition numbers ar e determined, FLMs ha ve a responsibility to determine what fraction of this depositi on could be added to existing natural and anthropogenic deposition amounts within an ecosystem and still be considered insignificant. The NPS and FWS selected very c onservative natural background numbers from the range of values presented in scientific literature, and have determined that all combined anthropogenic sources could contribute up to 50% of this co nservative natural3

background value without triggering concerns regarding resource imp acts. Rationale for this decision came from looking at the mode led historical deposition scenarios in the scientific literature, where the range of estim ates for any given area are often + or – 50% or more between various studies. Furthermore, the range of natural variability associated with annual natural background deposition at any given site is unknown, but 50% above or below the historical mean is plausible dur ing any given year due to fluctuations in climate, biotic productivity, bacterial decomposition, lightning occurrence, fire, volcanic activity, sea spray, and other factors.

The NPS and FWS have determined that a tota l increase in deposition, from all sources over time, greater than fifty percent of natural background deposition would trigger management concerns. Therefor e, the natural background value (B N or B S ) is multiplied by 0.5, or 50%.

Use of a Cumulative Factor There is an FLM concern that, over time, cu mulative deposition from emissions sources may produce impacts upon Class I areas. It is beneficial to the FLMs, the permitting authority, and the applicant to determine what amount, if any, a new source could contribute to total deposition while having a reasonable assurance that cumulative deposition from all new sources would not exceed 50% of natural background. In developing the 1996 proposal for New Source Re view Reform, the U.S. Environmental Protection Agency (EPA) determined that, as long as no individual source contribution exceeds 4% of a Class I increment, it is un likely that the accumulation of sources over

time will exceed that increment. The FLMs have applied the 4% value used in Class I increment significant impact levels to thes e new deposition analys is thresholds. By incorporating this value into the DAT equa tions, new sources whose modeled deposition amounts are below the DATs are not likely to significantly contribute to cumulative impacts from N or S deposition.

Deposition Analysis Threshold Equation The DAT for a specific Class I area is calculated as: Nitrogen DAT = B N (0.5) * 0.04

Sulfur DAT = B S (0.5) * 0.04

Where: B N = natural background nitr ogen deposition value.

Eastern Class I areas: B N = 0.50 kg/ha/yr

Western Class I areas: B N = 0.25 kg/ha/yr

B S = natural background sulfur deposition value.

Eastern Class I areas: B S = 0.50 kg/ha/yr

Western Class I areas: B S = 0.25 kg/ha/yr 0.5 = Variability Factor

0.04 = Cumulative Factor

This equation incorporates a 0.5 Variability Factor and a 0.04 Cumulative Factor. The value of 0.04 represents a four percent safe ty factor to protect Class I areas from cumulative deposition impacts. B N or B S is multiplied by 0.5 to result in a value that is fifty percent of the natural background deposition. The NPS and FWS consider an4

increase in deposition (resulting from all s ources over time) that is greater than fifty percent of the B N or B S value to be a threshold that tr iggers management concerns. The use of both factors is explai ned in more detail below.

Therefore, DATs for nitrogen and sulfur in Eastern and Western Class I parks and refuges are: East DAT: (0.50 kg/ha/yr N or S * 0.5) * 0.04 = 0.010 kg/ha/yr N or S West DAT: (0.25 kg/ha/yr N or S * 0.5) * 0.04 = 0.005 kg/ha/yr N or S

Discussion The DAT is a deposition thres hold, not necessarily an adve rse impact threshold. The DAT is the additional amount of deposition that triggers a management concern, not necessarily the amount that constitutes an adve rse impact to the environment. Both the NPS and the FWS utilize a case-by-case appr oach to permit review. Adverse impact determinations will be considered on a case-by-case basis for modeled deposition values that are higher than the DAT. This approach considers the best scientific information available for each park or refuge to assess exis ting as well as potential future deposition impacts. The magnitude of the deposition that an individual source would contribute as well as the sensitivity of the ecosystem must be considered. At present there is no equation that would, in all situations, allow an FLM to determine whether or not a source of N or S deposition would cause or contribut e to an adverse impact. Therefore, FLMs

will continue to use scientific data and information, in conjunction with modeling, to evaluate whether or not an adverse impact would occur. FLMs must also take into account site-specific information for each Class I area. This would include evaluating the potential deposition impacts from a source not just in relation to the DAT, but with other factors as well, such as whether adverse impacts resulting from deposition have been documented, or are suspected, in that specific Class I area.

Coastal ecosystems have evolved under natu rally higher sulfur de position rates due to

contribution from oceanic sources. This f actor will be considered by the NPS and FWS when making the case-by-case determination as to whether S deposition from a proposed source will adversely impact a Class I area containing coastal ecosystems.

While the values used in the DAT equati on reflect current NPS/FWS guidance and the scientific information available, it is important to note that these values could be updated as new changes in effects-related informa tion becomes available. These DATs replace any previous screening level values or deposit ion thresholds that may have been utilized by the NPS or FWS prior to the development of these DATs. The NPS and FWS will work closely with permit applicants to implement these DATs, and applicants are encouraged to contact the NPS or FWS at all stages of the application process.5



### References

Literature used to determine the B N 

### values:

Dentener, F. J. Personal communication with Tamara Blett, National Park Service. Globally modeled nitrogen maps for 1860. April 19, 2001.

Galloway, J.N., W.H. Schlesinger, H. Levy II, A. Michaels, and J.L. Schnoor. 1995. Nitrogen fixation: Anthropogenic enhancem ent – environmental response. Global Biogeochemical Cycl es 9(2): 235-252.

Galloway, J.N., W.C. Keene, and G.E. Likens. 1996. Processes controlling the composition of precipitation at a remote Sout hern hemisphere locat ion: Torres del Paine National Park, Chile. Journal of Geophysical Research 101(D3): 6883-6897.

National Atmospheric Deposition Program (N RSP-3)/National Trends Network 2000. Illinois State Water Survey. NADP/NTN Coor dination Office, 2204 Griffith Drive, Champaign, IL 61820.

U.S. National Acid Precipitation Assessmen t Program: Acidic Deposition: State of Science and Technology. 1991. P.M. Irving, e d. Volume I: Emissions, Atmospheric Processes and Deposition. Washington D.C.



### Literature used to determine the B S 

### values:

Bates, T.S. and B.K. Lamb. 1992. Natural sulf ur emissions to the atmosphere of the

continental United States. Global Bi ogeochemical Cycles, Vol 6(4):431-435.

Dentener, F. J. Personal communication with Tamara Blett, National Park Service. Modeling data for global sulfur deposition in 1860. July 9, 2001.

Galloway, J.N., W.C. Keene, and G.E. Likens. 1996. Processes controlling the composition of precipitation at a remote southern hemispheric location: Torres del Paine National Park, Chile. Journal of Geophysic al Research Vol. 101(D3): 6883-6897.

Galloway, J.N., G. E. Likens, W.C. Keene, and J.M. Miller. 1982. The composition of precipitation in remote areas of the World. Journal of Geophysical Research Vol. 87(11):

8771-8786.

Galloway, J.N., and D.M. Whepdale. 1980. An atmospheric sulfur budget for Eastern North America. Atmospheric Environment Vol. 14: 409-417.6

National Atmospheric Deposition Program (N RSP-3)/National Trends Network 2000. Illinois State Water Survey. NADP/NTN Coor dination Office, 2204 Griffith Drive, Champaign, IL 61820.



### Supporting Literature used in developing N and S DATs:

Bates, T.S., B.K. Lamb, A. Guenther, J. Dignon, and R.E. Stoiber. 1992. Sulfur emissions to the atmosphere from natural sources. Journal of Atmospheric Chemistry 14:315-337.

Bower, J.L. and I. Valiela. 2001. Historical changes in atmospheric nitrogen deposition to Cape Cod, Massachusetts, USA. Atmospheric Environment 35: 1039-1051.

Dentener, F.J. and P.J. Crutzen. 1994. A globa l 3D model of the ammonia cycle. Journal of Atmospheric Chemistry 19: 331-369.

Fenn, M.E., M.A. Poth, J.D. Aber, J.S. Bar on, B.T. Bormann, D.W. Johnson, A.D. Lenly, S.G. Mcnulty, D.F. Ryan and R. Stottlemey er. 1998. Nitrogen excess in North American ecosystems: Predisposing factors, ecosystem responses, and management strategies. Ecological Applicat ions 8(3): 1039-1051.

Hedin, L.O., J.J. Amestro, and A.H. J ohnson. 1995. Patterns of nutrient loss from unpolluted old growth temperate forests: Evaluation of biogeochemical theory. Ecology 76(2): 493-509.

Holland, E.A., B.H. Braswell, T.F. Lamasque, A. Townsend, T. Sulzman, T.F. Muller, F. Dentener, G. Brasseur, H. Levy II, T.E. Penne r, and G.T. Roelofs. 1997. Variations in the predicted spatial distribution of atmospheric nitrogen deposition and their impact on carbon uptake by terrestrial ecosystems. Journal of Geophysical Research, 102(D13):15849-15866.

Kasgnoc, A.D. 1998. A time averaged inventory of subaerial volcanic sulfur emissions. Journal of Geophysical Re search 103(25):251-262.

Lelieveld, J.and F. Dentener. 2000. What c ontrols tropospheric ozone? Journal of Geophysical Research: 3531-3551.

U.S. National Acid Precipitation Assessment Program: Acidic Deposition: State of Science and Technology. 1991. P.M. Irving, e d. Volume I: Emissions, Atmospheric Processes and Deposition. Washington D.C.

Van Aardenne, J. A., F.J. Dentener, C.G.M. Klijn Goldewijk, J. Lelieveld, and J.G. J.

Olivier. A 1  ̊ -1  ̊ resolution dataset of hi storical anthropogenic trace gas emissions for the period 1890-1990. Submitted to Global Biogeochemical Cycles, 1999.

Vitousek, P.M., J. Piber, R.W. Howarth, G.E. Likens, P.A. Matson, D.W. Schindler, W.S. Scheslinger, and G.D. Tilman. 1997. Human Alteration of the Global Nitrogen Cycle:7

Causes and Consequences. Issues in Ecology (1), Spring 1997. Ecological Society of

America.