VIDEO
2110 Environmental Science Predictions
Science, Matter, and Energy
Carrying Out a Controlled Scientific Experiment
One way in which scientists learn about how nature works is to conduct a controlled experiment.
To begin, scientists isolate variables, or factors that can change within a system or situation being studied. An experiment involving single-variable analysis is designed to isolate and study the effects of one variable at a time.
To do such an experiment, scientists set up two groups. One is an experimental group in which a chosen variable is changed in a known way and the other is a control group in which the chosen variable is not changed. With proper experimental design, any difference between the two groups should result from the variable that was changed in the experimental group.
In the 1960s, botanist Frank H. Bormann, forest ecologist Gene Likens, and their colleagues began carrying out a classic controlled experiment. The goal was to compare the loss of water and nutrients from an uncut forest ecosystem (the control site) with one that was stripped of its trees (the experimental site).
They built V-shaped concrete dams across the creeks at the bottoms of several forested valleys in the Hubbard Brook Experimental Forest in New Hampshire. The dams were anchored on impenetrable bedrock so all surface water leaving each forested valley had to flow across a dam, where scientists could measure its volume and dissolved nutrient content.
The first experiment measured the amounts of water and dissolved plant nutrients that entered and left an undisturbed forested area. These baseline data showed that an undisturbed mature forest is very efficient at storing water and retaining chemical nutrients in its soils.
The next experiment involved disturbing the system and observing any changes that occurred. One winter, the investigators cut down all trees and shrubs in one valley (the experimental site), left them where they fell, and sprayed with herbicides to prevent the regrowth of vegetation. Then they compared the inflow and outflow of water and nutrients in this modified experimental site with those in the control site for 3 years.
With no plants to help absorb and retain water, runoff of water in the deforested valley increased by 30-40%. As this excess water ran rapidly over the surface of the ground, it eroded soil and carried dissolved nutrients out of the deforested site.
Overall, the loss of key nutrients from the experimental forest was six to eight times that in the nearby undisturbed forest
Key Questions and Concepts
2-1 What is science?
Concept 2-1 Scientists collect data and develop theories, models, and laws about how nature works.
2-2 What is matter?
Concept 2-2 Matter consists of elements and compounds, which are in turn made up of atoms, ions, or molecules.
2-3 How can matter change?
Concept 2-3 When matter undergoes a physical or chemical change, no atoms are created or destroyed (the law of conservation of matter).
2-4 What is energy and how can it change its form?
Concept 2-4A When energy is converted from one form to another in a physical or chemical change, no energy is created or destroyed (first law of thermodynamics).
Concept 2-4B Whenever energy is changed from one form to another, we end up with lower quality or less usable energy than we started with (second law of thermodynamics).
2-5 How can we use matter and energy more sustainably?
Concept 2-5A The processes of life must conform to the law of conservation of matter and the two laws of thermodynamics.
Concept 2-5B We can live more sustainably by using and wasting less matter and energy, recycling and reusing most matter resources, and controlling human population growth.
