Environmental Science Lab
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Lab8CarbonSequestrationandtheLithosphere.docx( ENVIRONMENTAL SCIENCE LAB 110L New Mexico State University Plant and Environmental Science Department )
Lab 8: Carbon Sequestration and the Lithosphere
The Lithosphere and global warming
Goals The main goal of this lab is to understand how carbon sequestration by the lithosphere can help reduce greenhouse gasses in the atmosphere, and help to lessen the affects of global warming.
Key Words Soil organic carbon, soil inorganic carbon, carbon sequestration and global warming
Introduction
As we all know, soils do not photosynthesize, thus they do not directly remove CO2 from the atmosphere as plants do. Rather, they accumulate carbon through more indirect means. There are two major forms of carbon in soils; organic carbon and inorganic carbon. Soil organic carbon (SOC) is the carbon in the soil from living organism such as animals, plants and microbes. These living organisms produce wastes, drop leaves and eventually die in the soil. Thus, SOC is the carbon in the soil from things that lived and died in it. Soil inorganic carbon (SIC) is the carbon in the soil not in organic form. While the dark soils of the mid-west are high in organic carbon, our light colored desert soils are often high in carbonates, a form of inorganic carbon.
Soil organic and inorganic carbon are by far the largest terrestrial carbon pools, storing more than double the quantity of carbon found in vegetation or the atmosphere. For this reason soils can serve as a carbon source (putting carbon into the atmosphere) or sink (sequestering carbon from the atmosphere). Part of what determines if the soil is a carbon source or sink is our land use practices.
In this lab we will estimate the amounts of organic and inorganic carbon in three diverse soils. We will use these measurements to answer the questions: Do all soils sequester carbon equally well? How much carbon can an acre of soil sequester? In a pecan orchard, which sequesters more carbon, the trees or the soil below them?
Lab Activity
Objectives
1. Understand the difference in SOC and SIC.
2. Explore the role of soils in carbon sequestration.
3. Test for the amounts of organic and inorganic carbon in various soils.
4. Calculate the total amount of carbon in an acre-foot of these soils and compare to the amount of carbon stored aboveground.
Procedure
In this lab you will work in small groups to complete one section of the lab procedure. Then you will combine your results with those of the rest of the class to collect all of the data needed to complete the calculations.
Group assignments
Carbonate Calibration:
1: Carbonate calibration 500 mg (1 tablet)
2: Carbonate calibration 1000 mg (2 tablets)
3: Carbonate calibration 1500 mg (3 tablets)
4: Carbonate calibration 2000 mg (4 tablets)
Carbonate determination
Soil A carbonate determination
Soil B carbonate determination
Soil C carbonate determination
Organic Carbon
Soil A organic carbon determination Soil B organic carbon determination
Soil C organic carbon determination
( Carbonate calibration procedure )
1. On an zip-close plastic sandwich bag, measure and mark in increments of 5 mm along both edges symmetrically (see Figure 1).
Figure 1: Labeled sandwich bag
( Zip Closure Volume of vinegar )
2. Add 150 mL of vinegar to the bag and mark the upper level of the vinegar. It should be near 60mm.
3. Carefully evacuate all of the air in the bag by laying it flat and leaving a small section of the seal open. Gently press out as much air as possible without losing any vinegar. Seal the bag.
4. Laying the bag flat and folding it at the top of the vinegar, carefully add the appropriate number of antacid tablets to the bag without letting in air or allowing the tablets to touch the vinegar.
5. Quickly reseal the bag.
6. Press the tablets down into the vinegar and allow them to react for 30 minutes, mixing as needed to insure complete reaction.
7. Role the bag up from the top as far as possible and mark on the sandwich bag the amount of gas produced.
8. Record the value in mm. Remember to subtract the volume of vinegar.
( Soil carbonate determination procedure )
Follow steps 1 – 7 in the carbonate calibration procedure, except in step 4 put 1 level teaspoon of your assigned soil rather than the antacid tablets. In step 7 record the amount of gas produce by the soil. It may be very little.
( Organic carbon determination procedure )
1. As a group mix equal volumes of NaOH and EDTA to prepare the “Basic EDTA” solution. 100 mL of each solution should be enough to test all soils.
2. Place a few spoonfuls of your assigned soil sample into a mortar, pulverize thoroughly and mix well.
3. Place 0.5 g of soil in labeled vial.
4. Add 20 ml of basic EDTA to container.
5. Stopper and shake vigorously for 30 seconds.
6. Transfer to funnel lined with filter paper; catch clear filtrate in test tube.
7. Compare color of your sample to the color of standards to estimate SOC percent (see Figure 2).
Figure 2: SOC standards
Calculations and Data Presentation
Before leaving lab, be sure to collect the data from all other groups, so that you will have the information needed to complete all calculations.
Carbonate Data table
Hint: If the gas and vinegar in the sandwich bag is 110 mm and the vinegar line is at 60, then the mm of gas is 110 – 60 = 50 mm
Use a spreadsheet program such as Excel to make a scatter plot of the carbonate calibration data, putting g of carbonate on the x axis and mm of gas evolved on the y axis. Fit a straight line to this set of data and use the equation of the straight line to calculate the g of carbonate in each soil. See the example below.
SAMPLE DATA
This is only a sample. DO NOT USE THIS DATA.
|
Experiment |
mm of gas (measure from the vinegar line) |
|
1 tablet 0.5g CaCO3 |
15 |
|
2 tablets 1.0 g CaCO3 |
25 |
|
3 tablets 1.5 g CaCO3 |
32 |
|
4 tablets 2.0 g CaCO3 |
41 |
|
Soil A ? g CaCO3 |
8 |
|
Soil B ? g CaCO3 |
11 |
|
Soil C ? g CaCO3 |
33 |
For this example the equation of the line is: y=17x + 7
Where y is the mm of gas evolved, and x is the g of CaCO3. For our soils A, B and C we know the mm of gas evolved (y) and want to find the grams of CaCO3. So the equation can be rearranged to:
x = (y-7)/17
Now we can find the g of CaCO3 in soils A, B and C by substituting the mm of gas evolved values for y.
Soil A
x = (8-7)/17 = 0.06 g of CaCO3
Soil C
x = (33 - 7)/17 = 1.53 g of CaCO3
Of course your equation will differ from the one above depending on your carbonate calibration data.
To find the percent carbonate (% C) in the soil, assume that the weight of the 1 teaspoon of soil you added to the sandwich bag was 6 g.
%C = g of CaCO3 / g of soil * 100 For our example soil A:
%C = 0.06 / 6 * 100 = 10%
Soil C
%C = 1.53 /6 * 100 = 25.5 %C
Note: it is possible that a soil has such a little amount of carbonates that you will get a zero or even a negative number for g of carbonate. If this happens, simply record that no carbonates were detected in that soil.
Total carbon data table
|
|
% SIC |
% SOC |
Total % Carbon |
|
Soil A |
|
1.0% |
|
|
Soil B |
|
2.5% |
|
|
Soil C |
|
3.5% |
|
Discussion
Last week you calculated the amount of carbon sequestered in an acre of pecan trees. Using the
% carbon values above calculate the amount of carbon in an acre of soil A, B and C. To do this you will need to know the approximate density of the soil. For this lab use 100 pounds per cubic foot. Another important fact is that an acre is a measure of area, but we want to calculate the amount of carbon in a volume of soil. For this lab use an acre-foot of soil, which is 1 acre of soil to a depth of 1 foot and is equal to 43,560 cubic feet. To calculate the pounds of carbon in an acre-foot of soil use the equation:
WC = 43,560ft3 * 100 lb/ft3 * TC
Where WC is the weight of carbon in pounds for 1 acre-foot, and TC is the total carbon from the total carbon data table above. NOTE: In the table you recorded % total carbon, but in the equation the decimal form is required, so remember to divide %TC by 100.
Compare the pounds of carbon sequestered above ground by 1 acre of pecan trees to that sequestered in the top foot of 1 acre of each of the soils tested in this lab. Discuss the fact that the carbon sequestered by the trees in on a yearly basis, and what would happen to the trees carbon upon the death of the tree. Also discuss the fact that we calculated soil carbon for an acre- foot of soil. What if the soil was 2 or 10 feet deep?
Important information
Do not forget to submit your FULL lab report by the time and date given by your TA.
Pre-lab Questions and Resources
· Can lawns serve as a sink for atmospheric carbon?
ASA-CSSA-SSSA 2009 International Annual Meetings
http://a-c-s.confex.com/crops/2009am/webprogram/Paper52288.html
· What are some agricultural practices that can increase carbon sequestration?
Extension Service http://www.extension.org/pages/Agricultural,_Forestry_Practices_Can_Increase_Carbon_Sequest ration
