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Critical Load References

This reference list includes published articles and reports that document North American critical loads and supporting information related to the science of critical loads. References are listed by publication year. Documents from other continents are also included if they present information on methods or critical load concepts that are broadly applicable to North America.


  • Driscoll, C.T., T.J. Sullivan, B.P. Baldigo, D.A. Burns. S. Shao. T.C. McDonnell, and G.B. Lawrence. 2020. The Response of Streams to Changes in Atmospheric Deposition of Sulfur and Nitrogen in the Adirondack Mountains. Report 20-19, New York State Energy Research and Development Authority, Albany, NY.
  • McDonnell, T.C., T.J. Sullivan, B. Knees, M. Bell, and E. Felker-Quinn. 2020. Intermodel Comparison of Atmospheric Nitrogen Deposition Estimates for the Conterminous United States and Critical Load Exceedance for Selected National Parks. NPS/NRSS/ARD/NRR—2020/2125. National Park Service, Fort Collins, Colorado.
  • McDonnell, T.C., Reinds, G.J., Wamelink, G.W.W., Goedhart, P.W., Posch, M., Sullivan, T.J., and C.M. Clark. 2020. Threshold effects of air pollution and climate change on understory plant communities at forested sites in the eastern United States. Environmental Pollution 262: 114351.
  • Shao, S., C.T. Driscoll, T.J. Sullivan, D.A. Burns, B.P. Baldigo, G.B. Lawrence, and T.C. McDonnell. 2020. The response of stream ecosystems in the Adirondack region of New York to historical and future changes in atmospheric deposition of sulfur and nitrogen. Sci. Total Environ.
  • Wieder, R.K., Vitt, D.H., Vile, M.A., Graham, J.A., Hartsock, J.A., Popma, J.M., Fillingim, H., House, M., Quinn, J.C., Scott, K.D. and Petix, M., 2020. Experimental nitrogen addition alters structure and function of a boreal poor fen: Implications for critical loads. Science of The Total Environment, p.138619.


  • Belyazid, S., Phelan, J., Nihlgard, B., Sverdrup, H., Driscoll, C., Fernandez, I., … Clark, C. (2019). Assessing the effects of climate change and air pollution on soil properties and plant diversity in northeastern US hardwood forests: Model setup and evaluation. Water Air and Soil Pollution, 230(5), [106].
  • Clark, C. M., Richkus, J., Jones, P. W., Phelan, J., Burns, D. A., de Vries, W., … Watmough, S. A. (2019). A synthesis of ecosystem management strategies for forests in the face of chronic nitrogen deposition. Environmental Pollution, 248, 1046–1058.
  • Clark, C. M., S. M. Simkin, E. B. Allen, W. D. Bowman, J. Belnap, M. L. Brooks, S. L. Collins, L. H. Geiser, F. S. Gilliam, S. E. Jovan, L. H. Pardo, B. K. Schulz, C. J. Stevens, K. N. Suding, H. L. Throop, and D. M. Waller. 2019. Potential vulnerability of 348 herbaceous species to atmospheric deposition of nitrogen and sulfur in the United States. Nature Plants 5:697-705.
  • Geiser, L. H., P. R. Nelson, S. E. Jovan, H. T. Root, and C. M. Clark. 2019. Assessing Ecological Risks from Atmospheric Deposition of Nitrogen and Sulfur to US Forests Using Epiphytic Macrolichens. Diversity 11:87.
  • McDonnell, T.C., J. Aherne, T.J. Sullivan, C. Barton, C. Cotton, and B. Jackson. 2019. Variation in Forest Soil-Nutrient Availability: Dynamic Model Estimates of Past and Future Conditions at Two Sites in the Daniel Boone National Forest, Kentucky, USA. Report Prepared for USDA Forest Service. E&S Environmental Chemistry, Inc., Corvallis, OR.
  • McDonnell, T.C., T.J. Sullivan, and D.L. Moore. 2019. Critical Loads of Atmospheric Nitrogen and Sulfur Deposition for Protection of Sensitive Aquatic and Terrestrial Resources in the Intermountain Region of the USDA Forest Service. Report Prepared for the USDA Forest Service. E&S Environmental Chemistry, Inc., Corvallis, OR.
  • Pardo, L. H., J. A. Coombs, M. J. Robin-Abbott, J. H. Pontius, and A. W. D’Amato. 2019. Tree species at risk from nitrogen deposition in the northeastern United States: A geospatial analysis of effects of multiple stressors using exceedance of critical loads. Forest Ecology and Management 454:117528.
  • Sickman, J. O., A. E. James, M. E. Fenn, A. Bytnerowicz, D. M. Lucero, and P. M. Homyak. 2019. Quantifying atmospheric N deposition in dryland ecosystems: A test of the Integrated Total Nitrogen Input (ITNI) method. Science of the Total Environment 646:1253-1264.
  • Simpson, A. C., D. Zabowski, R. M. Rochefort, and R. L. Edmonds. 2019. Increased microbial uptake and plant nitrogen availability in response to simulated nitrogen deposition in alpine meadows. Geoderma 336:68-80.
  • Symstad, A. J., A. T. Smith, W. E. Newton, and A. K. Knapp. 2019. Experimentally derived nitrogen critical loads for northern Great Plains vegetation. Ecological Applications 29:e01915.
  • Templer, T. Thompson, D. Tong, G. A. Wetherbee, T. H. Whitlow, Z. Wu, Z. Yu, and L. Zhang. 2019. Toward the improvement of total nitrogen deposition budgets in the United States. Science of the Total Environment 691:1328-1352.
  • Van Houtven, G., Phelan, J., Clark, C., Sabo, R., Buckley, J. J., Thomas, Q., … LeDuc, S. (2019). Nitrogen deposition and climate change effects on tree species composition and ecosystem services for a forest cohort. Ecological Monographs.
  • Walker, J. T., M. D. Bell, D. Schwede, A. Cole, G. Beachley, G. Lear, and Z. Wu. 2019. Aspects of uncertainty in total reactive nitrogen deposition estimates for North American critical load applications. Science of the Total Environment 690:1005-1018.
  • Walker JT, Beachley G, Amos HM, Baron JS, Bash J, Baumgardner R, Bell MD, Benedict KB, Chen X, Clow DW, Cole A, Coughlin JG, Cruz K, Daly RW, Decina SM, Elliott EM, Fenn ME, Ganzeveld L, Gebhart K, Isil SS, Kerschner BM, Larson RS, Lavery T, Lear GG, Macy T, Mast MA, Mishoe K, Morris KH, Padgett PE, Pouyat RV, Puchalski M, Pye HOT, Rea AW, Rhodes MF, Rogers CM, Saylor R, Scheffe R, Schichtel BA, Schwede DB, Sexstone GA, Sive BC, Sosa Echeverría R, Templer PH, Thompson T, Tong D, Wetherbee GA, Whitlow TH, Wu Z, Yu Z, Zhang L. Toward the improvement of total nitrogen deposition budgets in the United States. Sci Total Environ. 2019 Nov 15;691:1328-1352.
  • Wieder, R.K., Vitt, D.H., Vile, M.A., Graham, J.A., Hartsock, J.A., Fillingim, H., House, M., Quinn, J.C., Scott, K.D., Petix, M. and McMillen, K.J., 2019. Experimental nitrogen addition alters structure and function of a boreal bog: critical load and thresholds revealed. Ecological Monographs, 89(3), p.e01371.
  • Zarfos, M.R., M. Dovciak, G.B. Lawrence, T.C. McDonnell, and T.J. Sullivan. 2019. Plant richness and composition in hardwood forest understories vary along an acidic deposition and soil-chemical gradient in the northeastern United States. Plant Soil.


  • Clark, C.M., Phelan, J., Doraiswamy, P., Buckley, J., Cajka, J.C., Dennis, R.L.,Lynch, J., Nolte, G.N., & Spero, T.L. 2018. Atmospheric deposition and exceedances of critical loads from 1800-2025 for the conterminous United States. Ecological Applications, 28(4), 2018, pp. 978–1002.
  • Fenn, M.E, Bytnerowicz, A, Schilling, S.L., Vallanob, D.M., Zavaleta, E.S., Weiss, S.E., Morozumi, C., Geiser, H.G., & Hanks, K. 2018. On-road emissions of ammonia: An underappreciated source of atmospheric nitrogen deposition Science of the Total Environment 625 (2018) 909–919.
  • Horn, K. J., Thomas, R. Q., Clark, C. M., Pardo, L. H., Fenn, M. E., Lawrence, G. B., … Watmough, S. 2018. Growth and survival relationships of 71 tree species with nitrogen and sulfur deposition across the conterminous U.S. PLoS One, 13(10).
  • McDonnell, T.C., S. Belyazid, T.J. Sullivan, M. Bell, C. Clark, T. Blett, T. Evans, W. Cass, A. Hyduke, and H. Sverdrup. 2018. Vegetation dynamics associated with changes in atmospheric nitrogen deposition and climate in hardwood forests of Shenandoah and Great Smoky Mountains national parks, USA. Environmental Pollution. 237:662-674.
  • McDonnell, T.C., Reinds, G.J., Sullivan, T.J., Clark, C.M., Bonten, L.T.C., Mol-Dijkstra, J.P., Wamelink, G.W.W., and M. Dovciak. 2018. Feasibility of coupled empirical and dynamic modeling to assess climate change and air pollution impacts on temperate forest vegetation of the eastern United States. Environmental Pollution 234: 902-914. doi:10.1016/j.envpol.2017.12.002
  • McDonnell, T.C., T.J. Sullivan, and C.M. Beier. 2018. Influence of climate on long-term recovery of Adirondack Mountain lakewater chemistry from atmospheric deposition of sulfur and nitrogen. Adir. J. Environ. Stud. 22:20-45.
  • McDonnell, T.C., W.A. Jackson, B.J. Cosby, and T.J. Sullivan. 2018. Atmospheric Deposition Effects Modeling for Resource Management on Southern Appalachian National Forests. Report prepared for USDA Forest Service, Asheville, NC. E&S Environmental Chemistry, Inc., Corvallis, OR.
  • Pardo, Linda H.; Duarte, Natasha; Van Miegroet, Helga; Fisher, L. Suzanne; Robin-Abbott, Molly J. 2018. Critical loads of sulfur and nitrogen and modeled effects of deposition reduction for forested ecosystems of Great Smoky Mountains National Park. Gen. Tech. Rep. NRS-180. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 26 p.
  • Sullivan, T.J., M.R. Zarfos, M. Dovciak, T.C. McDonnell, and G.B. Lawrence. 2018. Effects of Acid Deposition on the Biodiversity of Forest Understory Plant Communities in the Northern Hardwood Forests of the Adirondack Mountain Region. Final Technical Report 18-17. New York State Energy Research and Development Authority (NYSERDA), Albany, NY.
  • Whitfield, C.J., Phelan, J.N., Buckley J., Clark, C.M., Guthrie, S, & Lynch, JA. 2018. Estimating Base Cation Weathering Rates in the USA: Challenges of Uncertain Soil Mineralogy and Specific Surface Area with Applications of the PROFILE Model. Water Air Soil Pollution (2018) 229:61


  • Bell, M.D., Phelan, J., Blett, T.F., Landers, D., Nahlik, A.M., Van Houtven, G., Davis, C., Clark, C.M., and J. Hewitt. 2017. A framework to quantify the strength of ecological links between an environmental stressor and final ecosystem services. Ecosphere 8(5):e01806.
  • Clark, C.M., Bell, M.D., Boyd, J.W., Compton, J.E., Davidson, E.A., Davis, C., Fenn, M.E., Geiser, L., Jones, L., and T.F. Blett. 2017. Nitrogen-induced terrestrial eutrophication: cascading effects and impacts on ecosystem services. Ecosphere 8(7):e01877.
  • Crowley, K.F., and G.M. Lovett. 2017. Effects of nitrogen deposition on nitrate leaching from forests of the northeastern United States will change with tree species composition. Canadian Journal of Forest Research 47(8): 997-1009.
  • Fakhraei, H., Driscoll, C.T., Kulp, M.A., Renfro, J.R., Blett, T.F., Brewer, P.F., and J.S. Schwartz. 2017. Sensitivity and uncertainty analysis of PnET-BGC to inform the development of Total Maximum Daily Loads (TMDLs) of acidity in the Great Smoky Mountains National Park. Environmental Modelling & Software 95: 156-167.
  • Irvine, I.C., Greaver, T., Phelan, J., Sabo, R.D., and G. Van Houtven, 2017. Terrestrial acidification and ecosystem services: effects of acid rain on bunnies, baseball, and Christmas trees. Ecosphere 8(6):e01857.
  • Lawrence, G.B., T.C. McDonnell, T.J. Sullivan, M. Dovciak, S.W. Bailey, M.R. Antidormi, and M.R. Zarfos. 2017. Soil base saturation combines with beech bark disease to influence composition and structure of sugar maple-beech forests in an acid rain-impacted region. Ecosystems 191:19-27.
  • Lawrence, G.B., T.J. Sullivan, T.C. McDonnell, M. Dovciak, S.W. Bailey, M.R. Antidormi, and M.R. Zarfos. 2017. Soil Acidification and Beech Bark Disease: Influencing the Composition and Structure of Sugar Maple/Beech Forests. Summary Report 17-26 prepared for the New York State Energy Research and Development Authority. E&S Environmental Chemistry, Inc., Corvallis, OR.
  • Nanus, L., McMurray, J.A., Clow, D.W., Saros, J.E., Blett, T., and J.J. Gurdak. 2017. Spatial variation of atmospheric nitrogen deposition and critical loads for aquatic ecosystems in the Greater Yellowstone Area. Environmental Pollution 223: 644-656.
  • O’Dea, C.B., Anderson, S., Sullivan, T., Landers, D., and C.F. Casey. 2017. Impacts to ecosystem services from aquatic acidification: using FEGS-CS to understand the impacts of air pollution. Ecosphere 8(5):e01807.
  • Rhodes, C., Bingham, A., Heard, A.M., Hewitt, J., Lynch, J., Waite, R., and M.D. Bell. 2017. Diatoms to human uses: linking nitrogen deposition, aquatic eutrophication, and ecosystem services. Ecosphere 8(7):e01858
  • Robin-Abbott, M.J., and L.H. Pardo. 2017. How Climatic Conditions, Site, and Soil Characteristics Affect Tree Growth and Critical Loads of Nitrogen for Northeastern Tree Species. Gen. Tech. Rep. NRS-172. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 143 p.
  • Sullivan, T.J. 2017. Air Pollution and its Impacts on U.S. National Parks. CRC Press. 680 pp. (link)
  • Sullivan, T.J., T.C. McDonnell, G.B. Lawrence, M. Dovciak, and M.R. Zarfos. 2017. Acidification and Forest Understory Plant Communities in the Adirondack Mountains. Summary Report. 17-27. New York State Energy Research and Development Authority, Albany, NY.
  • Valliere, J.M., Irvine, I.C., Santiago, L., and E.B. Allen. 2017. High N, dry: experimental nitrogen deposition exacerbates native shrub loss and nonnative plant invasion during extreme drought. Global Change Biology.
  • Williams, J.J., Chung, S.H., Johansen, A.M., Lamb, B.K., Vaughan, J.K., and M. Beutel. 2017. Evaluation of atmospheric nitrogen deposition model performance in the context of U.S. critical load assessments. Atmospheric Environment 150: 244-255.
  • Williams, J., and S.G. Labou. 2017. A database of georeferenced nutrient chemistry data for mountain lakes of the Western United States. Scientific Data.
  • Williams, J. J., J. A. Lynch, J. E. Saros, and S. G. Labou. 2017. Critical loads of atmospheric N deposition for phytoplankton nutrient limitation shifts in western U.S. mountain lakes. Ecosphere 8(10):e01955.


  • Allen, E.B., Egerton-Warburton, L.M., Hilbig, B.E., and J.M. Valliere. 2016. Interactions of arbuscular mycorrhizal fungi, critical loads of nitrogen deposition, and shifts from native to invasive species in a southern California shrubland. Botany 94: 425–433,
  • Baldigo, B.P., Roy, K.M., and C.T. Driscoll. 2016. Response of fish assemblages to declining acidic deposition in Adirondack Mountain lakes, 1984-2012. Atmospheric Environment 146: 223-235.
  • Beier, C.M., Caputo, J., Lawrence, G.B., and T.J. Sullivan. 2016. Loss of ecosystem services due to chronic pollution of forests and surface waters in the Adirondack region (USA). Journal of Environmental Management.
  • Bingham, A.H. and M. F. Cotrufob. 2016. Organic nitrogen storage in mineral soil: Implications for policy and management. Science of The Total Environment 551–552: 116–126.
  • Bytnerowicz, A., Fenn, M., Allen, E.B., and Cisneros, R. 2016. Atmospheric Chemistry, pp. 107-128, In H. Mooney and E. Zavaleta (Eds.), Ecosystems of California-A Sourcebook. University of California Press. Berkeley, California. (link)
  • Caporn, S., Field, C., Payne, R., Dise, N., Britton, A., Emmett, B., Jones, L. Phoenix, G., Power, S., Sheppard, L., and Stevens, C. 2016. Assessing the effects of small increments of atmospheric nitrogen deposition (above the critical load) on seminatural habitats of conservation importance. Natural England Commissioned Reports, Number 210.(link)
  • Caputo, J., Beier, C.M., Sullivan, T.J., and G.B. Lawrence. 2016. Modeled effects of soil acidification on long-term ecological and economic outcomes for managed forests in the Adirondack region (USA). Science of the Total Environment 565: 401-411.
  • Cathcart, H., Aherne, J., Jeffries, D.S., and K.A. Scott. 2016. Critical loads of acidity for 90,000 lakes in northern Saskatchewan: A novel approach for mapping regional sensitivity to acidic deposition. Atmospheric Environment 146: 290-299.
  • DeWalle, D.R., Boyer, E.W., and A.R. Buda. 2016. Exploring lag times between monthly atmospheric deposition and stream chemistry in Appalachian forest using cross-correlation. Atmospheric Environment 146: 206-214.
  • Dibble, A.C., Hinds, J.W., Perron, R., Cleavitt, N., Poirot, R.L., and L.H. Pardo. 2016. Monitoring air quality in class I wilderness areas of the northeastern United States using lichens and bryophytes. Gen. Tech. Rep. NRS-165. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 44 p. (link)
  • Engel, B.J., Schaberg, P.G., Hawley, G.J., Rayback, S.A., Pontius, J., Kosiba, A.M., and E.K. Miller. 2016. Assessing relationships between red spruce radial growth and pollution critical load exceedance values. Forest Ecology and Management 359: 83–91. doi:10.1016/j.foreco.2015.09.029
  • Fakhraei, H., Driscoll, C.T., Renfro, J.R., Kulp, M.A., Blett, T.F., Brewer, P.F., and J.S. Schwartz. 2016. Critical loads and exceedances for nitrogen and sulfur atmospheric deposition in Great Smoky Mountains National Park, United States. Ecosphere 7(10):e01466.
  • Heard, A. M., and J. O. Sickman. 2016. Nitrogen assessment points: development and application to high-elevation lakes in the Sierra Nevada, California. Ecosphere 7(11):e01586. 10.1002/ecs2.1586
  • Hernandez, D.L., Vallano, D.M., Zavaleta, E.S., Tzankova, Z., Pasari, J.R., Weiss, S., Selmants, P.C., and C. Morozumi. 2016. Nitrogen pollution is linked to US listed species declines. BioScience 66: 213–222.
  • Kenkel, J.A., Sisk, T.D., Hultine, K.R., Sesnie, S.E., Bowker, M.A. and N.C. Johnson. 2016. Indicators of vehicular emission inputs into semi-arid roadside ecosystems. Journal of Arid Environments 134: 150-159.
  • Morrison, E.W., Frey, S.D., Sadowsky, J.J., van Diepen, L.T.A., Thomas, W.K., and A. Pringle. 2016. Chronic nitrogen additions fundamentally restructure the soil fungal community in a temperate forest. Fungal Ecology 23: 48-57.
  • Phelan, J., S. Belyazid, P. Jones, J. Cajka, J. Buckley, and C. Clark. 2016. Assessing the Effects of Climate Change and Air Pollution on Soil Properties and Plant Diversity in Sugar Maple–Beech–Yellow Birch Hardwood Forests in the Northeastern United States: Model Simulations from 1900 to 2100. Water, Air, & Soil Pollution 227(3): 1-30.
  • Simkin, S.M., E.B. Allen, W.D. Bowman, C.M. Clark, J. Belnap, M.L. Brooks, B.S. Cade, S.L. Collins, L.H. Geiser, F.S. Gilliam, S.E. Jovan, L.H. Pardo, B.K Schulz, C.J. Stevens, K.N. Suding, H.L. Throop, and D.M. Waller. 2016. Conditional vulnerability of plant diversity to atmospheric nitrogen deposition across the United States. Proceedings of the National Academy of Sciences of the United States of America, online in advance of print.
  • Stevens, C.J. 2016. How long do ecosystems take to recover from atmospheric nitrogen deposition? Biological Conservation 200: 160–167.
  • Valliere, J.M., and E.B. Allen. 2016. Interactive effects of nitrogen deposition and drought-stress on plant-soil feedbacks of Artemisia californica seedlings. Plant and Soil 403: 277-290.
  • Valliere, J.M., and E.B. Allen. 2016. Nitrogen enrichment contributes to positive responses to soil microbial communities in three invasive plant species. Biological Invasions: 1-16.
  • Whitfield, C.J., Mowat, A.C., Scott, K.A., and S.A. Watmough. 2016. A modified approach for estimating the aquatic critical load of acid deposition in northern Saskatchewan, Canada. Atmospheric Environment 146: 300-310.
  • Wilkins, K., Aherne, J., and A. Bleasdale. 2016. Vegetation community change points suggest that critical loads of nutrient nitrogen may be too high. Atmospheric Environment 146: 324-331.
  • Williams, J.J., M. Beutel, A. Nurse, B. Moore, S.E. Hampton, J.E. Saros. 2016. Phytoplankton responses to nitrogen enrichment in Pacific Northwest, USA Mountain Lakes. Hydrobiologia, pp. 1-16.
  • Williston, P., Aherne, J., Watmough, S., Marmorek, D., Hall, A., de la Cueva Bueno, P., Murray, C., Henolson, A., and J.A. Laurence. 2016. Critical levels and loads and the regulation of industrial emissions in northwest British Columbia, Canada. Atmospheric Environment 146: 311-323.


  • BassiriRad, H., Lussenhop, J.F., Sehtiya, H.L., and K.K. Borden. 2015. Nitrogen deposition potentially contributes to oak regeneration failure in the Midwestern temperate forests of the USA. Oecologia 177: 53–63.
  • Burns, D.A., and T.J. Sullivan, 2015, Critical Loads of Atmospheric Deposition to Adirondack Lake Watersheds: A Guide for Policymakers, NYSERDA Technical Report, Albany, NY, 16 p. (link)
  • Bytnerowicz, A., Johnson, R.F., Zhang, L., Jenerette, G.D., Fenn, M.E., Schilling, S.L., and Gonzalez-Fernandez, I. 2015. An empirical inferential method of estimating nitrogen deposition to Mediterranean-type ecosystems: The San Bernardino mountains case study. Environ. Pollut. 203: 69-88.
  • Cleavitt, N. L., Hinds, J. W., Poirot, R. L., Geiser, L. H., Dibble, A. C., Leon, B., Perron, R., Pardo, L. H. 2015. Epiphytic macrolichen communities correspond to patterns of sulfur and nitrogen deposition in the northeastern United States. The Bryologist 118(3), 304-324.
  • Clow, David W., Heidi A. Roop, Leora Nanus, Mark E. Fenn, Graham A. Sexstone. 2015. Spatial patterns of atmospheric deposition of nitrogen and sulfur using ion-exchange resin collectors in Rocky Mountain National Park, USA. Atmospheric Environment 101 (2015) 149-157.
  • Lawrence, G.B., Sullivan, T.J., Burns, D.A., Bailey, S.A., Cosby, B.J., Dovciak, M., Ewing, H.A., McDonnell, T.C., Minocha, R., Quant, J., Rice, K.C., Siemion, J., and Weathers, K.C., 2015, Acidic deposition along the Appalachian Trail corridor and its effects on acid-sensitive terrestrial and aquatic resources: Results of the Appalachian Trail atmospheric deposition effects MEGA-transect study, Natural Resource Report NPS/NRSS/ARD/NRR—2015/996. National Park Service, Fort Collins, Colorado, 241 p. (link)
  • Leavitt, S. D., & Clair, L. L. S. (2015). Bio-monitoring in Western North America: What Can Lichens Tell Us About Ecological Disturbances?. In Recent Advances in Lichenology (pp. 119-138). Springer India. (link)
  • Fenn, M.E., J.S. Fried, H.K. Preisler, A. Bytnerowicz, S. Schilling, S. Jovan, and O. Kuegler. 2015. Remeasured FIA plots reveal tree-level diameter growth and tree mortality impacts of nitrogen deposition on California’s forests. Proceedings of the 2015 FIA Symposium. Gen. Tech. Rep. PNW-GTR-931. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station.
  • Mast, M. Alisa, David W. Clow, Jill S. Baron, and Gregory A. Wetherbee. 2015. Links between N Deposition and Nitrate Export from a High-Elevation Watershed in the Colorado Front Range. Environmental Science Technology
  • McMurray, J. A., Roberts, D. W., & Geiser, L. H. (2015). Epiphytic lichen indication of nitrogen deposition and climate in the northern rocky mountains, USA. Ecological Indicators, 49, 154-161.
  • Pardo, L.H., Blett, T., Clark, C.M., and L.H. Geiser. 2015. Impacts of nitrogen pollution on terrestrial ecosystems in the United States. EM: Air and Waste Management Association’s Magazine for Environmental Managers 65: 24-30. (link)
  • Pardo, L. H., Robin-Abbott, M. J., Fenn, M. E., Goodale, C. L., Geiser, L. H., Driscoll, C. T., … & Dennis, R. L. (2015). Effects and Empirical Critical Loads of Nitrogen for Ecoregions of the United States. In Critical Loads and Dynamic Risk Assessments (pp. 129-169). Springer Netherlands.
  • Root, H. T., Geiser, L. H., Jovan, S., & Neitlich, P. (2015). Epiphytic macrolichen indication of air quality and climate in interior forested mountains of the Pacific Northwest, USA. Ecological Indicators, 53, 95-105.
  • Will-Wolf, S., Jovan, S., Neitlich, P., Peck, J. E., & Rosentreter, R. (2015). Lichen-based indices to quantify responses to climate and air pollution across northeastern USA. The Bryologist, 118(1), 59-82.
  • Zhou, Q., Driscoll, C.T., Moore, S.E., Kulp, M.A., Renfro, J.R., Schwartz, J.S., Cai, M., and J. A. Lynch. 2015. Developing critical loads of nitrate and sulfate deposition to watersheds of the Great Smoky Mountains National Park, USA. Water Air and Soil Pollution 226:255


  • Blett, T.F., J.A.Lynch, L.H. Pardo, C. Huber, R Haeuber, R. Pouyat. 2014. FOCUS: A pilot study for national-scale critical loads development in the Unites States. Environmental Science and Policy. 38:225-236.
  • Cox, R. D., K. L. Preston, R. F. Johnson, R. A. Minnichc, E. B. Allen. 2014. Influence of landscape-scale variables on vegetation conversion to exotic annual grassland in southern California, USA. Global Ecology and Conservation 2 190–203. doi:10.1016/j.gecco.2014.09.008
  • Cummings, T., T. Blett, E. Porter, L. Geiser, R. Graw, J. McMurray, S. Perakis and R. Rochefort. 2014. Thresholds for protecting Pacific Northwest ecosystems from atmospheric deposition of nitrogen: State of knowledge report. Natural Resource Report NPS/PWRO/NRR—2014/823. National Park Service, Fort Collins, Colorado. (link)
  • McDonnell T.C., S. Belyazid, T.J. Sullivan, H. Sverdrup, W.D. Bowman, E.M. Porter. 2014 Modeled subalpine plant community response to climate change and atmospheric nitrogen deposition in Rocky Mountain National Park, USA. Environmental Pollution 187.
  • McDonnell, T.C., and T.J. Sullivan. 2014. Comparison of Regional Stream ANC Predictions for the George Washington National Forest Using Spatial and Non-Spatial Regression Modeling. Final Report USDA Forest Service, Asheville, NC. E&S Environmental Chemistry, Inc. pp. 37. (link)
  • McDonnell, T. C., T. J. Sullivan. 2014. Total Atmospheric Nitrogen and Sulfur Deposition in Forest Service Wildernesses and National Forests Throughout the Conterminous United States. E&S Environmental Chemistry, Inc. Corvallis, OR (link)
  • McDonnell, Todd C., Timothy J. Sullivan, Paul F. Hessburg, Keith M. Reynolds, Nicholas A. Povak, Bernard J. Cosby, William Jackson, and R. Brion Salter. 2014. Steady-state sulfur critical loads and exceedances for protection of aquatic ecosystems in the U.S. southern Appalachian Mountains. Journal of Environmental Management, Volume 146, 15 December 2014, Pages 407–419, doi:10.1016/j.jenvman.2014.07.019
  • McMurray, J. A., D. W. Roberts, L. H. Geiser. 2014. Epiphytic lichen indication of nitrogen deposition and climate in the northern rocky mountains, USA. Ecological Indicators 49 154–161. doi:10.1016/j.ecolind.2014.10.015
  • New York State Energy Research and Development Authority (NYSERDA). 2014. Critical Loads for Air Pollution: Measuring the Risks to Ecosystems. NYSERDA Report 14-24. Prepared by the Wildlife Conservation Society and E&S Environmental Chemistry. (link)
  • Phelan, Jennifer, Salim Belyazid, Daniel Kurz, Scott Guthrie, James Cajka, Harald Sverdrup, Randall Waite. 2014. Estimation of Soil Base Cation Weathering Rates with the PROFILE Model to Determine Critical Loads of Acidity for Forested Ecosystems in Pennsylvania, USA: Pilot Application of a Potential National Methodology. Water Air Soil Pollut (2014) 225:2109, doi:10.1007/s11270-014-2109-4
  • Povak, N. A., P. F. Hessburg, T. C. McDonnell, K. M. Reynolds, T. J. Sullivan, R. B. Salter, and B. J. Cosby. 2014. Machine learning and linear regression models to predict catchment-level base cation weathering rates across the southern Appalachian Mountain region, USA, Water Resour. Res., 50,
  • Root, H. T., McCune, B., & Jovan, S. (2014). Lichen communities and species indicate climate thresholds in southeast and south-central Alaska, USA.The Bryologist, 117(3), 241-252.doi:10.1639/0007-2745-117.3.241
  • Scheffe, R. D J. A. Lynch, A. Reff, J. T. Kelly, B. Hubbell, T. L. Greaver, J. T. Smith. 2014. The Aquatic Acidification Index: A New Regulatory Metric Linking Atmospheric and Biogeochemical Models to Assess Potential Aquatic Ecosystem Recovery. Water Air Soil Pollution 225:1838.
  • Schirokauer, D., L. Geiser, A. Bytnerowicz, M. Fenn, and K. Dillman. 2014. Monitoring air quality in Southeast Alaska’s National Parks and Forests: Linking atmospheric pollutants with ecological effects. Natural Resource Technical Report NPS/SEAN/NRTR—2014/839. National Park Service, Fort Collins, Colorado (link)
  • Shaw G. D., R. Cisneros, D. Schweizer, J. O. Sickman, M. E. Fenn. 2014. Critical Loads of Acid Deposition for Wilderness Lakes in the Sierra Nevada (California) Estimated by the Steady-State Water Chemistry Model. Water Air Soil Pollution (2014) 225:1804.
  • Sheibley, R. W, M. Enache, P. W. Swarzenski, P. W. Moran, J. R. Foreman. 2014. Nitrogen Deposition Effects on Diatom Communities in Lakes from Three National Parks in Washington State. Water Air Soil Pollution (2014) 225:1857.
  • Watmough, Shaun A., Colin J. Whitfield , Mark E. Fenn. 2014. The importance of atmospheric base cation deposition for preventing soil acidification in the Athabasca Oil Sands Region of Canada. Science of the Total Environment 493 (2014) 1–11.


  • Clark, C.M., Morefield, P.E., Gilliam, F.S., and Pardon, L.H. 2013. Estimated losses of plant biodiversity in the United States from historical N deposition (1985-2010). Ecology, 94: 1441-1448.
  • Duarte, N., L. H. Pardo and M. J. Robin-Abbott. 2013. Susceptibility of Forests in the Northeastern USA to Nitrogen and Sulfur Deposition: Critical Load Exceedance and Forest Health. Water Air Soil Pollution (224).
  • R. A. Ellis, D. J. Jacob, M. P. Sulprizio, L. Zhang, C. D. Holmes, B. A. Schichtel, T. Blett, E. Porter, L. H. Pardo, and J. A. Lynch. 2013. Present and future nitrogen deposition to national parks in the United States: critical load exceedances. Atmos. Chem. Phys., 13, 9083-9095.
  • G.M. Lovett. 2013. Critical issues for critical loads. Proceedings of the National Academy of Sciences 110 (3): 803-809. 10.1073/pnas.1219007110
  • McDonnell, T.C., T.J. Sullivan, B.J. Cosby, W.A. Jackson, and K. Elliott. 2013. Effects of climate, land management, and sulfur deposition on soil base cation supply in national forests of the Southern Appalachian Mountains. Water Air Soil Pollution 224:1733.
  • R.J. Payne, N.B. Dise, C.J. Stevens, D.J. Gowing, and BEGIN Partners. 2013. Impact of nitrogen deposition at the species level. Proceedings of the National Academy of Sciences 110 (3): 984-987.
  • Povak, N.A., P.F. Hessburg, K.M. Reynolds, T.J. Sullivan, T.C. McDonnell, and R.B. Salter. 2013. Machine learning and hurdle models for improving regional predictions of stream water acid neutralizing capacity. Water Resources Research 49.
  • Sullivan, T.J., G.B. Lawrence, S.W. Bailey, T.C. McDonnell, and G.T. McPherson. 2013. Effects of acidic deposition and soil acidification on sugar maple trees in the Adirondack Mountains, New York. NYSERDA Report No. 13-04. New York State Energy Research and Development Authority, Albany, NY. (link)
  • Sullivan, T.J., G.B. Lawrence, S.W. Bailey, T.C. McDonnell, C.M. Beier, K.C. Weathers, G.T. McPherson, and D.A. Bishop. 2013. Effects of acidic deposition and soil acidification on sugar maple in the Adirondack Mountains, New York. Environmental Science & Technology.


  • W.D. Bowman, J. Murgel, T. Blett, and E. Porter. 2012. Nitrogen critical loads for alpine vegetation and soils in Rocky Mountain National Park. Journal of Environmental Management 103: 165-171. doi:10.1016/j.jenvman.2012.03.002
  • Fenn, M.E., K.F. Lambert, T.F. Blett, D.A. Burns, J.H. Pardo, G.M. Lovett, R.A. Haeuber, D.C. Evers, C.T. Driscoll and D. S. Jefferies. 2011. Setting limits: Using air pollution thresholds to protect and Restore U.S. Ecosystems. Issues in Ecology. Report No. 14. 21 pages. (pdf)
  • McDonnell, T.C., Cosby, B.J., Sullivan, T.J. 2012. Regionalization of soil base cation weathering for evaluating stream water acidification in the Appalachian Mountains, USA. Environmental Pollution 162: 338-344.
  • Miller, E. 2012. Steady-State Critical Loads and Exceedance for Terrestrial and Aquatic Ecosystems in the Northeastern United States. Technical Report to the Mulit-Agency Critical Loads Project of CLAD, NADP. (link)
  • L. Nanus, D.W. Clow, J.E. Saros, V.C. Stephens, and D.H. Campbell. 2012. Mapping critical loads of nitrogen deposition for aquatic ecosystems in the Rocky Mountains, USA. Environmental Pollution 166: 125-135.
  • Phelan, J.N. 2012. Review of Models to Evaluate Interactive Impacts of Nitrogen Deposition and Climate Change on Ecosystems and Ecosystem Services. Final Report prepared by RTI International for Chris Clarke, EPA Office of Research and Development, National Center for Environmental Assessment. 61pp. Available by request from Chris Clark (
  • Porter, E., H. Sverdrup, and T.J. Sullivan. 2012. Estimating and mitigating the impacts of climate change and air pollution on alpine plant communities in national parks. Park Science 28(2): 58-64. (link)
  • Reynolds K.M., Hessburg P.F., Sullivan T., Povak N.A., McDonnell T., Cosby B., Jackson W. 2012. Spatial Decision Support for Assessing Impacts of Atmospheric Sulfur Deposition on Aquatic Ecosystems in the Southern Appalachian Region. Hawaii International Conference on System Sciences 45: 1-10.
  • Sullivan, T.J. 2012. Combining ecosystem service and critical load concepts for resource management and public policy. Water 4:905-913.
  • Sullivan, T.J., B.J. Cosby, C.T. Driscoll, T.C. McDonnell, and A.T. Herlihy. 2011. Target loads of atmospheric sulfur deposition protect terrestrial resources in the Adirondack Mountains, New York against biological impacts caused by soil acidification. Journal of Environmental Studies and Sciences 1(4): 301-314.
  • Sullivan, T.J., B.J. Cosby, C.T. Driscoll, T.C. McDonnell, A.T. Herlihy, and D.A. Burns. 2012. Target loads of atmospheric sulfur and nitrogen deposition for protection of acid sensitive aquatic resources in the Adirondack Mountains, New York. Water Resource Research 48 (W01547): 1-16.
  • Sullivan, T.J., B.J. Cosby, T.C. McDonnell, E.M. Porter, T. Blett, R. Haeuber, C.M. Huber, and J. Lynch. 2012. Critical loads of acidity to protect and restore acid-sensitive streams in Virginia and West Virginia. Water Air Soil Pollution 223:5759-5771.
  • Sullivan, T.J., ed. 2012. USDA Forest Service National Protocols for sampling air pollution-sensitive waters. Gen. Tech Rep. RMRS-GTR-278WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 334 p. (pdf)
  • Sullivan, T.J. and T.C. McDonnell. 2012. Application of Critical Loads and Ecosystem Services Principles to Assessment of the Effects of Atmospheric Sulfur and Nitrogen Deposition on Acid-Sensitive Aquatic and Terrestrial Resources. Pilot Case Study: Central Appalachian Mountains. Report prepared for the U.S. Environmental Protection Agency, in association with Systems Research and Applications Corporation. E&S Environmental Chemistry, Inc., Corvallis, OR.
  • Sverdrup, H., T.C. McDonnell, T.J. Sullivan, B. Nihlgard, S. Belyazid, B. Rihm, E. Porter, W.D. Bowman, L. Geiser. 2012. Testing the feasibility of using the ForSAFE-VEG model to map the critical load of nitrogen to protect plant biodiversity in the Rocky Mountains Region, U.S.A. Water Air Soil Pollution 223: 371-387.


  • Baron, J.S., C.T. Driscoll, J.L. Stoddard, and E.E. Richer. 2011. Empirical critical loads of atmospheric nitrogen deposition for nutrient enrichment and acidification of sensitive U.S. Lakes. BioScience 61(8): 602-613. (10.1890/10-2341.1)
  • Lampman, G., G.B. Lawrence, T.J. Sullivan, K.C. Weathers, B.J. Cosby, and T.C. McDonnell. 2011. Comparison of methods for estimating critical loads of acidic deposition in the Western Adirondack region of New York. New York State Energy Research and Development Authority. (pdf)
  • Pardo, L.H., M.J. Robin-Abbott, and C.T. Driscoll. 2011. Assessment of nitrogen deposition effect and empirical critical loads of nitrogen for ecoregions of the Untied States. Gen.Tech. Rep. NRS-80. U.S. Department of Agriculture, Forest Service Northern Research Station. 291 pp.(link)
  • Pardo, L.H. Fenn, M., Goodale, C.L., Geiser, L.H., Driscoll, C.T., Allen E., Baron, J. Bobbink, R. Bowman, W.D., Clark, C., Emmett, B., Gilliam, F.S., Greaver, T., Hall, S.J., Lilleskov, E.A., Liu, L., Lynch, J., Nadelhoffer, K., Perakis, S., Robin-Abbott, M.J., Stoddard, J., Weathers, K., Dennis, R.L. 2011. Effects of nitrogen deposition and empirical critical loads for nitrogen for ecoregions of the United States. Ecological Applications 21(8): 3049-3082. (10.1890/10-2341.1)
  • Hessburg et al. 2011. Predicting Acid Neutralizing Capacity and Base Cation Weathering in the Southern Appalachian Mountains. Final Report
  • Sullivan, T.J., B.J. Cosby, and W.A. Jackson. 2011. Target loads of atmospheric deposition for the protection and recovery of acid-sensitive streams in the Southern Blue Ridge Province. Journal of Environmental Management 30: 1-8. (link)
  • Sullivan, T.J., B.J. Cosby, W.A. Jackson, K.U. Snyder, and A.T. Herlihy. 2011. Acidification and prognosis for future recovery of acid-sensitive streams in the Southern Blue Ridge Province. Water, Air, Soil Pollution 219: 11-26. (link)


  • Fenn, M.E., E.B. Allen, S.B. Weiss, S. Jovan, L.H. Geiser, G.S. Tonnesen, R.F. Johnson, L.E. Rao, B.S. Gimeno, F. Yuan, T. Meixner, and A. Bytnerowicz. 2010. Nitrogen critical loads and management alternative for N-impacted ecosystems in California. Journal of Environmental Management 91: 2404- 2423.
  • Geiser, L.H., S.E Jovan, D.A. Glavich, and M.K. Porter. 2010. Lichen-based critical loads for atmospheric nitrogen deposition in Western Oregon and Washington Forests U.S.A. Environmental Pollution 158: 2412-2421. (pdf)
  • McDonnell, T.C., B.J. Cosby, T.J. Sullivan, S.G. McNulty, and E.C. Cohen. 2010. Comparison among model estimates of critical loads of acidic deposition using different sources and scales of input data. Environmental Pollution. 158:2934-2939.
  • McNulty, S.G., and Boggs, J.L. 2010. A conceptual framework: Redefining forest soil’s critical acid loads under a changing climate. Environmental Pollution 158: 2053-2058.
  • Sullivan, T.J., B.J. Cosby, and T.C. McDonnell. 2010. Aquatic critical loads and exceedances in acid-sensitive portions of Virginia and West Virginia. E&S Environmental Chemistry, Inc. Final Report: 1-91 (pdf)


  • Saros, Jasmine. 2009. Determining critical N loads to subalpine lakes in the Pacific Northwest. Climate Change Institute, University of Maine. Final Report: 1-11. (pdf)


  • Burns, D.A., T. Blett, R. Haeuber, and L.H. Pardo. 2008. Critical loads as a policy tool for protecting ecosystems from the effects of air pollutants. Frontiers in Ecology and the Environment 6(3): 156-159.


  • Li, H. and S.G. McNulty. 2007. Uncertainty analysis on simple mass balance model to calculate critical loads for soil acidity. Environmental Pollution 149: 315-326. (link)
  • McNulty, S.G., E.C. Cohen, J.A. Moore Myers, T.J. Sullivan, and H. Li. 2007. Estimates of critical acid loads and exceedances for forest soils across the conterminous United States. Environmental Pollution 149: 281-292. (link)
  • Porter, E., S. Johnson. 2007. Translating science into policy: Using ecosystem thresholds to protect resources in Rocky Mountain Nation Park. Environmental Pollution 149: 268-280. doi:10.1016/j.envpol.2007.06.060


  • Baron, Jill S. 2006. Hindcasting nitrogen deposition to determine an ecological critical load. Ecological Applications 16(2): 433-439. (pdf)
  • Groffman, P.M., J.S. Baron, T. Blett, A.J. Gold, I. Goodman, L.H. Gunderson, B.M. Levinson, M.A. Palmer, H.W. Pearl, G.D. Peterson, N.L. Poff, D.W. Rejeski, J.F. Reynolds, M.G. Turner, K.C. Weathers, and J. Wiens. 2006. Ecological Thresholds: The key to successful environmental management or an important concept with no practical application. Ecosystems 9: 1-13. doi:10.1007/s10021-003-0142-z


  • Dupont J., Clair, T.A., Gagnon, C., Jeffries, D.S., and Kahl, J.S. 2005. Estimation of critical loads of acidity for lakes in northeastern United States and eastern Canada. Environmental Monitoring and Assessment 109: 275-291. (pdf)
  • Porter, E., T. Blett, D.U. Potter, and C. Huber. 2005. Protecting resources on federal lands: Implications of critical loads for atmospheric deposition of nitrogen and sulfur. BioScience 55(7): 603-612. doi:10.1641/0006-3568

Before 2004

  • Baron, J.S., H.M Rueth, A.M. Wolfe, K.R. Nydick, E.J. Allstott, J. T. Minear, and B. Moraska. 2000. Ecosystem responses to nitrogen deposition in the Colorado Front Range. Ecosystems 3: 352-368.
  • Fenn, M.E., J.S. Baron, E.B. Allen, H.M. Rueth, K.R. Nydick, L. Geiser, W.D. Bowman, J.O. Sickman, T. Meixner, D.W. Johnson, and P. Neitlich. 2003. Ecological effects of nitrogen deposition in the Western United States. BioScience 53(4): 404-420.