Long-Term Research Page 1


How can long-term research help us understand trends in precipitation acidity? This and the next two pages will show you a quick glimpse of some of the acid rain research that has been conducted at the HBEF over the past 40 years. You will learn more about acid rain later, on page 13 of this Introduction.


A few basic facts about acidity...

The measure of the acidity of a liquid sample is referred to as "pH." Acidic substances (like lemon juice) have low pH values, while basic substances (like ammonia) have high pH values.

The pH scale runs from 0 (acid) to 14 (basic), with 7 being neutral. Natural rainfall that has not been affected by humans is slightly acidic, and would have a pH of ~ 5.6 at the HBEF.

"Acid Rain" refers to rain that has a pH lower than 5.6 because of human influences such as the burning of coal and petroleum products.


Precipitation Acidity at the Hubbard Brook Experimental Forest

HBEF scientists have measured the pH of precipitation - rain, snow, sleet, etc. - in Watershed 6 since 1965. Watershed 6, as you have learned, is the chemical reference watershed.

Examine the graph below.

  • Can you make any conclusions?

  • Is there an apparent trend in precipitation acidity over time?

  • Are data from six years enough to make long-term predictions?

  • What would you expect to happen from 1970 - 1975? Will precipitation become more or less acidic?

Go to the next page to look at another short-term precipitation data set.


The data used to produce this and the next two graphs were provided by Gene E. Likens with funding from the National Science Foundation and The Andrew W. Mellon Foundation.

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