Send to

Choose Destination
Proc Natl Acad Sci U S A. 2016 Jul 5;113(27):7580-3. doi: 10.1073/pnas.1607287113. Epub 2016 Jun 22.

Acid rain mitigation experiment shifts a forested watershed from a net sink to a net source of nitrogen.

Author information

Cary Institute of Ecosystem Studies, Millbrook, NY 12545;
Department of Biology, Duke University, Durham, NC 27708;
Cary Institute of Ecosystem Studies, Millbrook, NY 12545;
Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY 13244;
Cary Institute of Ecosystem Studies, Millbrook, NY 12545; Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06268


Decades of acid rain have acidified forest soils and freshwaters throughout montane forests of the northeastern United States; the resulting loss of soil base cations is hypothesized to be responsible for limiting rates of forest growth throughout the region. In 1999, an experiment was conducted that reversed the long-term trend of soil base cation depletion and tested the hypothesis that calcium limits forest growth in acidified soils. Researchers added 1,189 kg Ca(2+) ha(-1) as the pelletized mineral wollastonite (CaSiO3) to a 12-ha forested watershed within the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire. Significant increases in the pH and acid-neutralizing capacity of soils and streamwater resulted, and the predicted increase in forest growth occurred. An unanticipated consequence of this acidification mitigation experiment began to emerge a decade later, with marked increases in dissolved inorganic nitrogen (DIN) exports in streamwater from the treated watershed. By 2013, 30-times greater DIN was exported from this base-treated watershed than from adjacent reference watersheds, and DIN exports resulting from this experiment match or exceed earlier reports of inorganic N losses after severe ice-storm damage within the study watershed. The discovery that CaSiO3 enrichment can convert a watershed from a sink to a source of N suggests that numerous potential mechanisms drive watershed N dynamics and provides new insights into the influence of acid deposition mitigation strategies for both carbon cycling and watershed N export.


acid deposition; calcium; nitrate

[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center