Declining Acidic Deposition Begins Reversal of Forest-Soil Acidification in the Northeastern U.S. and Eastern Canada.
Decreasing trends in acidic deposition levels over the past several decades have led to partial chemical recovery of surface waters. However, depletion of soil Ca from acidic deposition has slowed surface water recovery and led to the impairment of both aquatic and terrestrial ecosystems. Nevertheless, documentation of acidic deposition effects on soils has been limited, and little is known regarding soil responses to ongoing acidic deposition decreases. In this study, resampling of soils in eastern Canada and the northeastern U.S. was done at 27 sites exposed to reductions in wet SO4(2-) deposition of 5.7-76%, over intervals of 8-24 y. Decreases of exchangeable Al in the O horizon and increases in pH in the O and B horizons were seen at most sites. Among all sites, reductions in SO4(2-) deposition were positively correlated with ratios (final sampling/initial sampling) of base saturation (P < 0.01) and negatively correlated with exchangeable Al ratios (P < 0.05) in the O horizon. However, base saturation in the B horizon decreased at one-third of the sites, with no increases. These results are unique in showing that the effects of acidic deposition on North American soils have begun to reverse.
New York Water Science Center, U.S. Geological Survey , 425 Jordan Road, Troy, New York 12180, United States.
Gregory B
GB
Lawrence
Natural Resources Canada-Canadian Forest Service , 1219 Queen Street E., Sault Ste. Marie, Ontario P6A 2E5, Canada.
Paul W
PW
Hazlett
University of Maine , School of Forest Resources, Deering Hall, Orono, Maine 04469-5722, United States.
Ivan J
IJ
Fernandez
Direction de la recherche forestière, ministère des Forêt, de la Faune et des Parcs du Québec, Complexe scientifique , 2700 Einstein Street, Quebec City, Quebec G1P 3W8, Canada.
Rock
R
Ouimet
Northern Research Station, Hubbard Brook Experimental Forest, USDA Forest Service , 234 Mirror Lake Road, North Woodstock, New Hampshire 03262, United States.
Scott W
SW
Bailey
Northern Research Station, USDA Forest Service , 271 Mast Road, Durham, New Hampshire 03824, United States.
Walter C
WC
Shortle
Northern Research Station, USDA Forest Service , 271 Mast Road, Durham, New Hampshire 03824, United States.
Kevin T
KT
Smith
New York Water Science Center, U.S. Geological Survey , 425 Jordan Road, Troy, New York 12180, United States.
Michael R
MR
Antidormi
D000143:Acids / Q000737:chemistry*; D000535:Aluminum / Q000032:analysis; D001272:Atmosphere / Q000737:chemistry; D002170:Canada; D065928:Forests; D009511:New England; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis
D000143:Acids; D012987:Soil; D012989:Soil Pollutants; D000535:Aluminum