Global Change, Fall 2010
A. Biogeochem #1: Carbon Cycle Basics
1. What are the three main processes/timescales that control the atmospheric composition of CO2?
What are the corresponding reservoirs of carbon for each of these three processes/timescales?
2. At the multi-million year timescale, the balance of what two processes determines the amount of
CO2 in the atmosphere?
3. 400 Million years ago, atmospheric CO2 was 10-15 times higher than today. By 350 Mya, it was
within factors of 2-3 of present day. What is believed to have caused the big draw down, and
how?
4. Define these terms: pedosphere, lithosphere, hydrosphere, biosphere
5. Why does atmospheric CO2 not increase by the same amount as the CO2 being added by fossil
fuel combustion?
6. What is ecosystem ecology? What is biogeochemistry?
7. What is the simplified net chemical reaction known as photosynthesis? What is the net chemical
reaction known as respiration? What is the difference between the two?
8. Define the following terms, and be able to relate them to each other mathematically:
a. Gross Primary Production (GPP)
b. Autotrophic respiration (Rauto)
c. Net Primary Production (NPP)
d. Heterotrophic respiration (Rhet)
e. Net Ecosystem Production (NEP)
f. Ecosystem respiration (Reco)
9. What are some of the most important controls on NPP?
10. What does it mean for NPP to be “limited” by factor X (for example, nitrogen)?
11. NPP is the fundamental biological process by which CO2 enters terrestrial ecosystems and is
stored as organic carbon. What is the basic loss process by which organic matter leaves
terrestrial ecosystems, returning to CO2?
B. Biogeochem 2: Ecosystem development and Nitrogen cycling
1. What are the basic ingredients for building an ecosystem?
a) in particular, after C, H, and O, which are the most predominant elemental constituents of
organic matter, what are the next two most common elements needed to build plants?
b) For each of the 5 elements listed in part a, what is their ultimate source (where do
plants/ecosystems get these elements?)
2. Describe the simple conceptual model of soil/ecosystem development presented in class and in
the Chadwick et al. reading. What nutrients are expected to be limiting early in ecosystem
development, and which ones later?
3. What is stoichiometry?
4. What general difference is observed between the C:N:P stoichiometry of marine organisms
(called the “Redfield ratio”), and that of terrestrial plants? What is the reason for the difference?
5. What general difference is observed globally between the C:N:P stoichiometry of terrestrial plant
litter and that of the comparable foliage from which it derives? What is the reason for the
difference?
Be prepared to think about how stoichiometric relations constrain biogeochemical cycling.
SAMPLE PROBLEM: Consider the figure from Hungate et al. 2003 (discussed in lecture):
Fig. The amount of Nitrogen required to
support a given amount of model-predicted
terrestrial carbon uptake for 6 models
(summed from the present to the year
2100). Model runs project terrestrial
ecosystem response to elevated
atmospheric CO2 by itself (in blue), and to
the combined effects of elevated CO2 and
climate change (red).
Consider the elevated CO2-only model runs (blue markers), and for the time being, don't worry
about additional constraints that might limit carbon storage: (a) which 4 models project the most
carbon storage? (b) Which 4 are expected to require the most nitrogen to store their carbon?
(c) Now, let's consider the nitrogen constraint that limits plausibility of some of the projections
shown in the figure. According to this figure's depiction, which models project plausible
amounts of carbon storage when only CO2 changes are taken into account, and which are
implausible? Which models project plausible carbon storage under scenarios in which the
combined effects of CO2 and climate are included? What rules out the other scenarios as
implausible?
(d)What is the highest amount of Carbon storage that is plausible, according to the above
figure? Which model, and how much carbon? Compare your answer to the pre-industrial
carbon stock of the atmosphere, which was about 550 PgC.
6. What are some reasons why N is an essential nutrient for plants?
7. In what forms do plants typically take up N?
8. What is N–fixation? What is N mineralization? What is denitrification? (alternative formulation:
draw a diagram of a simple Nitrogen cycle that includes the above terms)
9. What are some of the requirements biological nitrogen fixation?
10. What are three activities engaged in by humans that alter the amount of Nitrogen that is fixed
globally?
11. What are some ecosystem impacts of Nitrogen cycle alterations caused by human activities?
C. Biogeochem #3: Water Cycle & Climate interactions with Ecosystems
1. How big is global average precipitation? Is average precipitation on land greater or less than
this global average?
2. Only about 2/3 of the water that falls as precipitation on the land surface is returned to the
atmosphere via evapotranspiration. What happens to the rest of the water?
3. What is the residence time of water vapor in the atmosphere, and how does it compare to the
residence time of other greenhouse gases, such as CO2, CH4, and N2O?
4. What effect is global climate change expected to have on precipitation for: (a) the globe on
average? (b) tropical regions? (c) sub-tropical regions, and (d) high latitudes?
5. How can changes in the water cycle affect the temperature of the land surface?
6. How do plants regulate their water loss?
7. What are some of the most important direct controls on evapotranspiration, and what are some of
the indirect controls?
8. What is the definition of Water Use Efficiency? What is increased atmospheric CO2 expected to
do to Water Use Efficiency, on average? All else being equal, what consequence for the global
water cycle is this likely to have?
9. What is potential evapotranspiration?
10. What is a basic indicator of water limitation at the ecosystem-scale?
11. Changes in water cycling may cause droughts and increases in water limitation of vegetation in
some ecosystems. Drawing on the homework reading (Adams et al., 2009), what are two main
mechanisms by which droughts can cause plant mortality.
12. What is NDVI? How is it defined? What does it measure?
13. Summarize the Zhao and Running (2010) paper assigned in class.
D. Land Use Change
1. What are the stages of land-use change as human societies evolve? (as discussed in lecture and
in Foley et al., 2005)
2. Name three mechanisms by which land use changes can affect climate, and indicate the scales
on which these mechanisms operate.
3. What important general trend in land-use has occurred in temperate zones over the last
century? (e.g., what has happened to the farms on the marginal farmland in many areas of the
northeast U.S.? )
4. What important general trend in land-use has occurred in the last few decades in the tropics?
5. What are some possible causes of a northern hemisphere carbon sink? (remember Thoreau!)
6. What are the potential impacts of large-scale deforestation on climate (temperature and
precip), and how might you expect these to differ between high latitudes (e.g. boreal forests)
and low latitudes (e.g. tropical forests)? Why?
E. Microbes in terrestrial and marine biogeochemical cycling
1. What are 3 "big picture" points of how microbes are important to biogeochemical cycling?
2. What % (roughly) of net primary production occurs on land versus in the oceans?
3. At sea, what are the two major groups responsible for photosynthesis?
4. What process causes the largest flux of CO2 to the atmosphere from both land and sea?
5. What imbalance defines NEP?
6. Which two types of organisms are responsible for the majority of soil respiration
(note respiration, not decomposition), and in what approximate ratio?
7. Decomposition is controlled both directly and indirectly at a variety of time scales, which
were summarized in a figure (from Chapin, Matson and Mooney) that we examined in
lecture. List 3 of the controls and specify whether they are long or short time-scale.
8. Soil respiration correlates linearly with what ecosystem property? (hint: you saw a graph of
this relationship in class). What are some reasons for this relationship?
9. What 3 reasons did we discuss that microbial decomposition is important for
biogeochemical cycling? (hint: 1 general, 1 terrestrial, 1 marine)
10. Describe 2 ways in which climate change may effect decomposition.
Extra credit Q: Although we did not emphasize memorizing definitions of various trophic groups
in lecture, we did spend several slides discussing chemoautotrophs as a possible missing
component of primary production. (1) what are chemoautrophs, (2) what is an example of one
habitat where such chemoautrophs might be thriving, and (3) how might they be surviving there
(in one-to-several WORDs)?
Carbon cycle summary numbers
Know these figures about the carbon cycle (very rough numbers sufficient): (rough answers given here)
a) About how much CO2 is in the present-day atmosphere (~750 GtC ≈ 380 ppm)
b) How much carbon is in living organic matter (biomass) (~600 GtC)
c) How much carbon is in soils (1500-2000 GtC)
d) How much CO2 is emitted from fossil fuel burning (7-8 GtC) and deforestation (1-2 GtC)
9
NOTE: know this: 1 Gt (gigaton) = 10 metric tons = 1 Pg (petagram) = 10
6
(implying, of course that 1 metric ton = 10 grams = 1000 kg)
15
gram