Labs - Environmental Science - page 359

ic heats, which affects the amount of solar radiation needed to heat a particular substance. In this lab, the heat-
holding capacity of various substances is tested.
The principle of specific heat also applies to the atmosphere and climate. This particular lab compares the spe-
cific heat of soil to that of water and then relates the results to effects on climate.
Tragedy of the Commons
The commons is any resource that is shared by a group. This includes the air we breathe, water we drink, and
fish taken from the oceans. It also refers to city parks and many other things that are shared by a group or are
used by the public.
In this activity, students "fish" from a common ocean of fish (goldfish crackers, M&M's, or other similar
products may be used) and usually all the "fish" are taken on the first round. In subsequent games, students
learn to cooperate to avoid depleting the ocean.
Transects
Frequently, instead of studying entire areas, scientists sample small sections and then extrapolate the data to
represent likely conditions in the area as a whole. One method of sampling is to run a 100m tape transect line.
At every 10m interval, a 1-square-meter area is placed, first on the left side of the tape and then on the right
side, alternating sides every 10m. In each square-meter area, the percentage of ground cover is estimated. Then
the plant species are identified and the percentage of each is determined. Next, any animal present in the square
or evidence of animals in the square is recorded. Finally, the information is tallied and compared to other tran-
sects in the study area. This is an excellent activity to repeat on a regular basis to examine seasonal variation.
Water Quality
A variety of tests can be conducted to test water quality. A brief description of each is noted below:
• pH: Measures the concentration of either free H + or OH - ions. Normal pH for freshwater is between 6.5
and 8. The pH of saltwater is 8.2.
• Temperature: Measures the heat content of the water usually in °C (sometimes °F).
• Dissolved oxygen (DO): A measure of the amount of oxygen dissolved in the water. The concentration
of DO is temperature-influenced, with higher temperatures able to hold less DO. Other factors that can
influence the concentration of DO in water include the amount of organic waste, the plant and animal
communities present, the water depth, and the flow rate of rivers and streams. Average needed DO con-
centration is 4 ppm for freshwater fish, 5 ppm for saltwater fish.
• Percent saturation: Measures the amount of oxygen dissolved in the sample water compared to the max-
imum that could be present at that temperature. One hundred percent saturation is the maximum amount
of DO that the water can hold at that temperature. DO percent saturations between 80 percent and 120
percent are considered excellent.
• Turbidity: Measures the clarity of the water. The test can be conducted using a Secchi disk, usually di-
vided into quarters with opposite black and white quadrants. A colored disk also can be used in areas
where the water is very clear, usually in the open ocean water. A turbidity test is a measurement of the
dissolved solids in the water. High turbidity means much suspended solid material in the water, which
results in the water being less clear. This reduces the penetration of sunlight and reduces photosynthesis
in the water, which, in turn, can affect the food chain.