Spatially explicit estimates of critical loads of nitrogen (N) deposition (CL(Ndep)) for nutrient enrichment in aquatic ecosystems were developed for the Rocky Mountains, USA, using a geostatistical approach. The lowest CL(Ndep) estimates (<1.5 ± 1 kg N ha(-1) yr(-1)) occurred in high-elevation basins with steep slopes, sparse vegetation, and abundance of exposed bedrock and talus. These areas often correspond with areas of high N deposition (>3 kg N ha(-1) yr(-1)), resulting in CL(Ndep) exceedances ≥ 1.5 ± 1 kg N ha(-1) yr(-1). CL(Ndep) and CL(Ndep) exceedances exhibit substantial spatial variability related to basin characteristics and are highly sensitive to the NO(3)(-) threshold at which ecological effects are thought to occur. Based on an NO(3)(-) threshold of 0.5 μmol L(-1), N deposition exceeds CL(Ndep) in 21 ± 8% of the study area; thus, broad areas of the Rocky Mountains may be impacted by excess N deposition, with greatest impacts at high elevations.
Copyright © 2012 Elsevier Ltd. All rights reserved.