The Discovery of Acid Rain at the Hubbard Brook Experimental Forest: A Story of Collaboration and Long-term Research

  • Gene E. Likens
  • Scott W. BaileyEmail author


The 3,519-ha Hubbard Brook Experimental Forest (HBEF) was established in 1955 as the primary hydrological research facility in the northeastern USA. In 1963, FH Bormann, GE Likens, NM Johnson, and RS Pierce initiated the Hubbard Brook Ecosystem Study (HBES) to assess mass balance water and chemical budgets using gauged watersheds. From the study’s inception, rain and snow inputs to the HBEF were unusually acid. Using back trajectories for air masses, HBES long-term data showed clearly that sulfate deposition at HBEF was strongly related to SO2 emissions hundreds or thousands of kilometers distant. Other research showed that acid rain started in eastern North America in the 1950s. Reductions in emissions since 1970, primarily of SO2 due to federal regulations, caused ~ 60 % decline in acidity at HBEF since 1963. It required 18 years of continuous measurement to fit a significant linear regression to these data, showing the value of long-term measurements. HBEF data showed calcium depletion as a major impact of acid deposition. Other results showed slowed forest growth. In 1999, wollastonite (a calcium silicate mineral) was added experimentally to an entire watershed in an amount roughly equivalent to the amount estimated to have leached in the previous 50 years. Early results suggest positive survival and growth responses in sugar maple. The long-term data from the HBES suggest that changes in federal regulations to reduce emissions have reduced sulfate in both precipitation and stream water, demonstrating a positive link between high quality long-term research and public policy.


Hubbard Brook Ecosystem Study Acid rain Calcium depletion Clean Air Act Sulfate deposition Long-term measurements 



We thank S. Horsley, D. Jeffries, and S. Stout for thoughtful comments and suggestions on the manuscript. Financial support for long-term research and monitoring at the HBEF was provided by the NSF (including the Long-Term Research in Environmental Biology and Long-Term Ecological Research programs) and The Andrew W. Mellon Foundation. The HBEF is operated and maintained by the Northern Research Station in Newtown Square, PA. D. Buso assisted with the illustrations, and P. Likens helped with manuscript preparation.


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Copyright information

© Springer New York 2014

Authors and Affiliations

  1. 1.Cary Institute of Ecosystem StudiesMillbrookUSA
  2. 2.Department of Ecology and Environmental BiologyUniversity of ConnecticutStorrsUSA
  3. 3.Northern Research StationUSDA Forest ServiceNorth WoodstockUSA

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