Old Midterm Exam.

 

1. (10 points) Let us assume that (1) on average one person’s body weight is a constant 50 kg; (2) approximately 60% of the body weight is from water (or there is 30 kg of water in an average body; and (3) the average residence time of the water molecules in a average person’s body is 20 days.  What is the total amount of water passing through human bodies each day in the whole world if we have a population of six billion people?

 

2. (10 points) Can you briefly discuss the similarity and difference between turnover time and residence time when used in biogeochemistry?

 

3. (20 points) Please define the following terms (4 points each):

 

(3.1) Stratosphere

 

(3.2) Aerosols

 

(3.3) Coriolis effect

 

(3.4) Soil texture

 

(3.5) Soil CEC (cation exchange capacity)

 

4. (10 points) Based on the data given in Table 4.5 in the textbook (the table is provided on the back of this page), which two elements’ cycles in the Hubbard Brook ecosystem may be considered near steady-state? Which two elements’ cycles may be regarded as farthest from steady-state?

 

5. (25 points) How do changes in atmospheric concentrations of nitrous oxide (N2O), nitric oxides (NOx), and hydroxide radicals (OH) impact ozone generation and destruction in the troposphere and in the stratosphere? If air pollution has increased the concentration of hydrocarbons in the troposphere, and assuming that photochemical reactions of these hydrocarbons are similar to that of isoprene, what has this pollution done to the ozone concentration in the polluted air during sunny days?  (Some information about several trace biogenic gases in the atmosphere is presented In Table 3.4 of the textbook. Table 3.4 is provided on the back of this page.  Please note that only gases with residence time longer than 3 years may have significant concentrations in the stratosphere.)

 

6. (25 points) Knowing that rock weathering plays a key role in the global carbon cycle at the geologic time scale as shown in Figure 1.4 in the textbook (Figure 1.4 is provided on the back of this page) and that carbon dioxide (CO2) concentration in the atmosphere are increasing at an approximate rate of 1.5 ppm per year, can you explain the interaction between the rate of rock weathering and the change of CO2 concentration in the atmosphere? (Hint: please consider both direct participation of CO2 in chemical rock weathering and indirect effect of CO2 through an enhanced “greenhouse effect” on climate.)