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Title:2015 Summary of Critical Load Maps
Author(s):National Atmospheric Deposition Program; Critical Loads of Atmospheric Deposition (CLAD) Science Committee
Subject(s):Air pollution
Environmental impact of atmospheric deposition
Sulfur deposition
Nitrogen deposition
Critical loads
Geographic Coverage:North America
Abstract:2015 Summary of Critical Load Maps On the cover: Surface Water Critical Loads for Acidity. Average aggregation for 12 km2 grid cell with S + N (McDonnell et al. 2014; Scheffe et al. 2014; Sullivan et al. 2014; unpublished data). Use Condition and Citation; please use the following: The intended use of this database is for scientific, policy-related, or educational purposes. Any published use of the CLAD database information must acknowledge the original sources for the data used. Each critical load value in the database can be linked to its origin using the RefID field. The proper citations for each RefID can be found in Table 7 of the database (Citation for all critical load values). In addition, whenever a data user presents and/or publishes research based on critical load values in the database, CLAD and NADP must be acknowledged. A suggested acknowledgement is: "We acknowledge the Critical Loads of Atmospheric Deposition (CLAD) Science Committee of the National Atmospheric Deposition Program (NADP) for their role in making available CLAD_CL_ACID_v2.5 and CLAD_CL_N_v2.5accdb datasets.” 1 Contents Background ..................................................................................................................................... 2 About the Maps and National Critical Load Database (NCLD) ..................................................... 4 Surface Water Critical Loads for Acidity ........................................................................................ 6 Forest Ecosystem Critical Loads for Acidity ................................................................................. 14 Empirical Critical Loads for Nitrogen ........................................................................................... 18 Cited References ........................................................................................................................... 23 2 Background In April 2010, the National Atmospheric Deposition Program (NADP) Executive Committee formed the Critical Loads of Atmospheric Deposition Science Committee (CLAD). This committee evolved from an ad hoc group originally formed in 2006.The purpose of CLAD is to discuss current and emerging issues regarding the science and use of critical loads for effects of atmospheric deposition on ecosystems in the United States. The goals of CLAD are to: •Facilitate technical information sharing on critical load topics within a broad multi-agency/entity audience; •Fill gaps in critical loads development in the US; •Provide consistency in development and use of critical loads in the US; •Promote understanding of critical load approaches through development of outreach and communications materials. For more information regarding CLAD, please visit the NADP-CLAD web page at http://nadp.sws.uiuc.edu/committees/clad/. Starting in 2010, the “FOCUS Pilot Study” project gathered and synthesized both empirical and calculated critical loads data and information from dozens of regional- and national-scale projects (See Blett et al. 2014). CLAD members submitted data to this cooperative effort as a productive and meaningful way to share information to improve methods for estimating, calculating, mapping, interpreting, and refining critical loads. The first round of critical load data synthesis formed the foundation for an informal, unofficial submission to the UNECE Coordinating Center on Effects (CCE) in 2011. This unofficial submission to the European critical loads community represented a maturing of interest in the United States’ critical loads science community. What is a critical load? Air pollution emitted from a variety of sources is deposited from the air into ecosystems. These pollutants may cause ecological changes, such as long-term acidification of soils or surface waters, soil nutrient imbalances affecting plant growth, and loss of biodiversity. The term “critical load” is used to describe the threshold of air pollution deposition that causes change to sensitive resources in an ecosystem. A critical load is technically defined as “the quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment are not expected to occur according to present knowledge” (Nilsson and Grennfelt 1988). Critical loads are typically expressed in terms of kilograms per hectare per year (kg/ha/yr) or equivalents per hectare per year (eq/ha/yr) of wet or total (wet + dry) deposition. Critical loads can be developed for a variety of ecosystem responses, including shifts in microscopic aquatic species, increases in invasive grass species, changes in soil chemistry affecting tree growth, and lake and stream acidification to levels that can no longer support fish. When critical loads are exceeded, the environmental effects can extend over great distances. For example, excess nitrogen can change soil and surface water chemistry, which 3 in turn can cause eutrophication of downstream estuaries. Critical loads describe the point at which a natural system is impacted by air pollution. For ecosystems that have already been damaged by air pollution, critical loads help determine how much improvement in air quality would be needed for ecosystem recovery to occur. In areas where critical loads have not been exceeded, critical loads can identify levels of air quality needed to protect ecosystems in the future. U.S. scientists, air regulators, and natural resource managers are currently developing critical loads for areas across the United States and collaborating with scientists developing critical loads in Europe and Canada. Once critical loads are established, they can then be used to assess ecosystem health, inform the public about natural resources at risk, evaluate the effectiveness of emission reduction strategies, and guide a wide range of management decisions. This summary is a collection of critical load maps for the U.S., developed by CLAD members using critical load data that are publically available as part of the NADP CLAD National Critical Load Database (NLCD). The full set of critical load maps can be downloaded at the following link: http://nadp.sws.uiuc.edu/committees/clad/db/ 4 About the Maps and National Critical Load Database (NCLD) The critical load maps provided here represent a compilation of empirical and calculated critical load values from a variety of regional- and national-scale projects. The intended uses of these maps are for scientific, policy-related, or educational purposes. These maps illustrate critical loads in the National Critical Load Database (NCLD) and help to identify spatial gaps in information, as well as additional research needs.
Issue Date:2015-10
Publisher:Illinois State Water Survey
Series/Report:ISWS Miscellaneous Publication MP-204
NADP Data Report 2015-02
Genre:Technical Report
Type:Text
Language:English
URI:http://hdl.handle.net/2142/103675
Publication Status:published or submitted for publication
Peer Reviewed:is peer reviewed
Rights Information:Copyright ... University of Illinois Board of Trustees. All rights reserved. This document is a product of the Illinois State Water Survey, and has been selected and made available by the Illinois State Water Survey and the University Library, University of Illinois at Urbana-Champaign. It is intended for research and educational use, and proper attribution is requested.
Date Available in IDEALS:2019-05-03


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