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

Abstract

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.