Canadian Forest Service Publications

Declining acidic deposition begins reversal of forest-soil acidification in the Northeastern U.S. and Eastern Canada. 2015. Lawrence, G.B.; Hazlett, P.W.; Fernandez, I.J.; Ouimet, R.;Bailey, S.W.; Shortle, W.C.; Smith, K.T.; Antidormi, M.R. Environmental Science and Technology 49:13103-13111.

Year: 2015

Issued by: Great Lakes Forestry Centre

Catalog ID: 36378

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1021/acs.est5b02904

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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 SO42– 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 SO42– 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

Plain Language Summary

There has been limited data published on changes in soil chemical properties in North America due to the effects of acid rain. A few studies have linked acidic deposition to increased soil acidity and exchangeable aluminum and decreased exchangeable calcium. Soil calcium depletion has been linked to reductions in forest health and growth. The objective of this study was to assess whether soils in recent decades have 1) continued to acidify, 2) stabilized, or 3) begun to recover as acidic deposition levels have declined. Forest soils were resampled at 27 sites across northeastern U.S and eastern Canada to determine the response to declining acidic deposition. Sites represented the most common forest and soil types of the region. Soil chemical property response was varied across sites. For surface organic horizons calcium and base saturation increased and aluminum decreased to a greater extent at sites were sulphate deposition reductions were greatest. The response of deeper mineral soil horizons was less clear and not consistent with the model that assumes base cation replenishment by weathering. Results suggest a link between reduction of sulphate deposition and a reversal of acidification of soils within the study region