Reversal of Forest Soil Acidification in the Northeastern United States and Eastern Canada: Site and Soil Factors Contributing to Recovery

Paul Hazlett,Ivan Fernandez,Scott Bailey,Greg Lawrence,Caroline Emilson,Rock Ouimet

doi:10.3390/soilsystems4030054

Abstract

As acidic deposition has decreased across Eastern North America, forest soils at some sites are beginning to show reversal of soil acidification. However, the degree of recovery appears to vary and is not fully explained by deposition declines alone. To assess if other site and soil factors can help to explain degree of recovery from acid deposition, soil resampling chemistry data (8- to 24-year time interval) from 23 sites in the United States and Canada, located across 25° longitude from Eastern Maine to Western Ontario, were explored. Site and soil factors included recovery years, sulfate (SO42−) deposition history, SO42− reduction rate, C horizon pH and exchangeable calcium (Ca), O and B horizon pH, base saturation, and exchangeable Ca and aluminum (Al) at the time of the initial sampling. We found that O and B horizons that were initially acidified to a greater degree showed greater recovery and B horizon recovery was further associated with an increase in recovery years and lower initial SO42− deposition. Forest soils that seemingly have low buffering capacity and a reduced potential for recovery have the resilience to recover from the effects of previous high levels of acidic deposition. This suggests, that predictions of where forest soils acidification reversal will occur across the landscape should be refined to acknowledge the importance of upper soil profile horizon chemistry rather than the more traditional approach using only parent material characteristics.

Highlights

One of the initial environmental concerns expressed about acidic deposition was the potential cumulative effect of long-term pollutant loading on soil acidity and nutrient levels and the consequences of these soil changes on forest health and productivity [1,2,3]
While we found that increasing percent reduction in SO4 2− deposition over the time period between samplings led to increased levels of recovery in the O horizon, the relationships were driven by relatively few sites
Our soil resampling study identified key site and soil factors that were associated with forest soil recovery from acidification caused by atmospheric deposition in the Northeastern United States and Eastern Canada

Summary

Introduction

One of the initial environmental concerns expressed about acidic deposition was the potential cumulative effect of long-term pollutant loading on soil acidity and nutrient levels and the consequences of these soil changes on forest health and productivity [1,2,3]. 2020, 4, 54 differently to increasing or decreasing acid inputs depending on inherent site and soil conditions. Increased base cation leaching does not necessarily lead to decreases in pH and base saturation if biological cycling, atmospheric deposition or mineral weathering can counter leaching losses by providing inputs to affected soil horizons. While increased deposition of hydrogen ion (H+ ) and sulfate (SO4 2− ) can reduce pH and base saturation, site differences in inorganic SO4 2−. Berden et al [6] synthesized results from some of the earliest soil resampling studies from Northern, Central and Western Europe that were conducted to determine the impacts of acidic deposition on forests. Several studies reported 0.2 to 1.5 unit decreases in forest soil pH from the mid 19000 s up until the early 19800 s. In North America, Linzon and Temple [9] documented pH declines for A and B horizons of one soil series in central

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