Table 2.

Summary of critical loads information used in this study.

CL type	Pollutant	Spatial grain	Description	Source(s)
Terrestrial acidification	N and S	1 × 1 km	Modeled estimates based on the simple-mass-balance (SMB) model constrained to forested ecosystems	McNulty et al. 2007, McNulty et al. 2010
Aquatic acidification	N and S	points	Modeled estimates based on the simple-mass-balance (SMB) fluxes of cations and anions to aquatic ecosystems	Lynch et al. 2013
Forest-Tree health	N	level 1 ecoregion	Empirical estimates based on field studies that used a variety of approaches, constrained to forest land cover (2011 NLCD)	Pardo et al. 2011a, b
NO3− leaching	N	level 1 ecoregion	Empirical estimates based on field studies that used a variety of approaches, constrained to forest, shrubland, and/or herbaceous land cover (2011 NLCD)	Pardo et al. 2011a, b
Plant community composition	N	level 1 ecoregion	Empirical estimates based on field studies that used a variety of approaches, constrained to forest, shrubland, and/or herbaceous land cover (2011 NLCD)	Pardo et al. 2011a, b
Lichen	N	4 × 4 km	Empirical estimates based on comparing changes in lichen community composition along deposition gradients constrained to forest land cover (2011 NLCD)	Geiser et al. 2010; Root et al. 2015