Contents I.Ecosystem Recovery II.Calcium Experiment III.Introduction to Soils IV.Calcium Experiment Results

Hubbard Brook Acid Rain Story: Part II The Clean Air Act and Amendments have decreased emissions of sulfur dioxide in air which has increased the pH of precipitation in the Northeast… … but ecosystems are responding more slowly. Both pH and the ability to buffer acidity in soil, lakes and streams remain low in acid sensitive areas. I. Ecosystem Recovery

Why is there a delay in ecosystem recovery? 1.Acid rain continues to fall in the Northeast 2.The effects of acid rain on acid-sensitive soils, and thus ecosystems, is complex and long-lasting. I. Ecosystem Recovery There are several reasons …

7 Acid rain still falls in the Northeast: 1.The Clean Air Act(s) reduced sulfur dioxide, but another emission, nitrogen oxide, has not been substantially reduced and still contributes to acid rain. 2. Sulfur dioxide has been reduced, but not eliminated (see following graph). I. Ecosystem Recovery

Data provided by G.E. Likens through funding from the National Science Foundation and the A.W. Mellon Foundation. I. Ecosystem Recovery

1. Acid rain causes increased loss of base cations from soil Decrease in acid neutralizing capacity (ANC) of soils (reduced ability to buffer the incoming acids) Lower fertility of soils (base cations are nutrients necessary for tree growth). this causes Why is ecosystem recovery delayed? I. Ecosystem Recovery

Why is ecosystem recovery delayed? At high concentrations, this form of aluminum is toxic to plants and animals. 2. Acid rain has increased dissolved inorganic aluminum in soil waters. I. Ecosystem Recovery Hubbard Brook Acid Rain Story: Part II

If calcium is replaced across a whole forested watershed, recovery from acidification will accelerate. This response will allow us to better understand the role acid rain plays as a forest stressor To further investigate the effects of acid rain on an ecosystem, HBES scientists developed a hypothesis: II. Calcium Experiment Hubbard Brook Acid Rain Story: Part II

HBES scientists received a 5-year grant from the National Science Foundation in 1999 to conduct an experiment to replace the calcium lost from one entire, 29-acre watershed (Watershed 1), and monitor the forest response. II. Calcium Experiment

Chemical and biological characteristics of Watershed 1 (calcium-treated watershed) compared with the same characteristics of Watershed 6 (“reference” watershed that is not treated in any way) They monitored: II. Calcium Experiment A “reference” in ecosystem science is similar to a “control” in an experiment.

Some of the characteristics they monitored included: Chemical: –Soil and stream pH –Soil and streamwater chemistry Biological: –Nutrient content of plant foliage –Tree seedling regeneration –Canopy tree health –Soil arthropod density and diversity –Snail densities II. Calcium Experiment

Wollastonite, a calcium-rich mineral, was pulverized… Photos courtesy of T. Siccama II. Calcium Experiment

…and made into pellets. II. Calcium Experiment

The wollastonite pellets were were loaded into sacks. II. Calcium Experiment

A backhoe then put a sack into a hopper II. Calcium Experiment

Then a helicopter picked up the hopper and spread the pellets evenly across Watershed 1. II. Calcium Experiment

Can you spot the pellets on the forest floor? II. Calcium Experiment

After eight years, some pellets are still there, under layers of organic matter. wollastonite pellets Photo courtesy of T. Siccama II. Calcium Experiment

These remaining pellets represent a “bank” of calcium in Watershed 1. They continue to contribute to the acid neutralizing capacity of the soil and stream water. II. Calcium Experiment

Soils have layers. You can see these layers if you dig a pit to expose a soil profile. Each layer has a different composition, which can be seen in terms of color, texture, chemistry, etc. The next slide shows layers of a soil profile. III. Introduction to Soils Hubbard Brook Acid Rain Story: Part II

Cd O A E Bhs Bs BC O “Humus”or “organic layer”: contains leaf litter and decomposed organic matter A “Topsoil”: contains humus and mineral particles E “Eluviation layer”; contains sand and silt. Minerals and clay have leached away as water drips down through soil. B “Subsoil”: contains minerals and silt received from layers above C “Regolith”: contains broken up bedrock and very little organic matter Photo courtesy of S. Bailey III. Introduction to Soils

Here are some soil pH and stream pH results for Watershed 6 (reference) and Watershed 1 (calcium treated) IV. Calcium Experiment Results Hubbard Brook Acid Rain Story: Part II

Bedrock Precipitation Soil Stream Stream pH at Weir  5.1 pH  4.4 Soil pH: O  3.5 Bh  4.0 Bs  4.5 C  5.0 General pH today in the Reference Watershed (W 6: no treatment) Hubbard Brook Acid Rain Story: Part II

Bedrock Precipitation Soil Stream Stream pH at Weir  5.4 pH  4.4 Soil pH: O  4.5 Bh  4.0 Bs  4.5 C  5.0 Mean pH in treated watershed (WS 1) General pH today in the Treated Watershed (W 1: calcium added) Hubbard Brook Acid Rain Story: Part II

pH Comparison of W 6 and W 1 * The pH scale is logarithmic; every increase of 1 on the pH scale means that acidity decreases by a factor of 10. Watershed 6 typical pH (reference) Watershed 1 typical pH (Ca treated) Differences in pH Notes Average Precipitation Soil horizonsO W 1 is 10 times less acidic than W6* Bh4.0 0 Bs4.5 0 C5.0 0 Stream W1 is 3 times less acidic than W6*

Watershed 1 is showing signs of chemical recovery: higher pH of stream water more soil base cations as compared to Watershed 6, the reference (no treatment) watershed. IV. Calcium Experiment Results

Watershed 1 is showing signs of biological recovery: better growth of sugar maples sugar maple seedlings show higher densities and survival as compared to Watershed 6, the reference (no treatment) watershed. IV. Calcium Experiment Results

To find out how ecosystem recovery happens, see… The Hubbard Brook Acid Rain Story Part III: Ecosystem Recovery

32 For more detailed information on ecosystem recovery: Acid Rain Revisited a Science Links  publication by the Hubbard Brook Research Foundation