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

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 airwhich 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 RecoveryI. 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.


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).


SO4 and NO3 concentrations in precipitation

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

1960 1970 1980 1990 2000 2010

Year

Co

nc

en

tra

tio

n (

mg

/L)

SO4 NO3

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


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?


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.



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 ExperimentII. Calcium Experiment


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.


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:


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


Wollastonite, a calcium-rich mineral, was pulverized…

Photos courtesy of T. Siccama


…and made into pellets.


The wollastonite pellets were were loaded into sacks.


A backhoe then put a sack into a hopper


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


Can you spot the pellets on the forest floor?


After eight years, some pellets are still there, under layers of organic matter.

wollastonite pelletsPhoto courtesy of T. Siccama


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.


• 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 SoilsIII. Introduction to Soils


Cd

OAE

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 ResultsIV. Calcium Experiment Results


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)


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)


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

4.4 4.4 0

Soil horizons O 3.5 4.5 1.0W 1 is 10 times less

acidic than W6*

Bh 4.0 4.0 0

Bs 4.5 4.5 0

C 5.0 5.0 0

Stream 5.1 5.4 0.3W1 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.


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.


To find out how ecosystem recovery happens, see…

The Hubbard Brook Acid Rain StoryPart III: Ecosystem Recovery

32

For more detailed information on ecosystem recovery:

Acid Rain Revisited

a Science Links publication by the Hubbard Brook

Research Foundation

http://www.hubbardbrookfoundation.org

http://www.hubbardbrookfoundation.org/

Documents

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