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**Unformatted text preview: **02/20/2001 TUE 15:25 FAX 6434330 MOFFITT LIBRARY 001 ER 102 Harte/Fischer
Spring, 1997 MIDTERM EXAMINATION
March 11, l997 This exam is open books and open notes. Anything you can lug into the classroom to help you is
acceptable as long as it is: a. non-addictive, b. quiet, c. odorless, and d. inanimate. The problems are assigned points that add up to 80. By coincidence, you also have 80 minutes to
do the exam, so you would be wise to allocate your time accordingly -- roughly one minute per point. Show all your work so you can get partial credit for “right idea but wrong answer”. Ifyou need a
number that you can't ﬁnd or remember or derive, deﬁne a symbol for it and express your answer
in terms of that symbol. Then take a guess at its value -- it can’t hurt —- and substitute it in. If
you don’t have time to complete a problem but think you know how to do it, describe the steps; that way we have an excuse to give you partial credit. Circle or underline your ﬁnal numerical answer to each problem. Either write your answer in a
bluebook or, if you don’t have one, on 8.5” x 11” sheets of paper. In the latter case, be sure your
name is on every sheet not just the ﬁrst one, and staple them together. 02/20/2001 TUE 15:25 FAX 6434330 MOFFITT LIBRARY 002 1. An experiment on mountain meadow response to warmer climate (in which meadow plots are
artiﬁcially heated) reveals that the species composition of plant cover will tend under climate
warming to shift from dominance by forbs (non-woody ﬂowering plants) to dominance by
woody shrubs, but the total living biomass (sum of forbs plus shrubs) will remain constant. Forbs
differ ﬁ'om shrubs in that forb net primary productivity per unit of forb biomass exceeds that for
shrubs. In particular, the residence times for living plant biomass in forbs and shrubs are 3 months
and 24 months, respectively. Dead plant matter enters the soil organic matter compartment as
litter and is the only sizeable input to the soil organic matter pool. a. Using our simple chemical formula for the C, H, and 0 content of dry plant material, ﬁnd the
mass of carbon per unit of dry plant biomass, expressing your answer as a ﬁaction. (5 pts.) b. The experiment shows that the (living forb biomass):(living shrub biomass) ratio in the control
(i.e., unwarmed) plots is about 3 :2, whereas in the heated plots the ratio shifts to 2:3. Calculate
the ratio (the total ﬂow rate of plant material to the soil in the heated plots) : (the total ﬂow rate of plant material to the soil in the control plots). (10 pts.) c. The stock of total living plant biomass has a density of 250 g(carbon)/m2. Assume that the
only effect of warming on inputs or outputs of carbon to soil is to shift the species composition
and therefore the rate of litter input. In the control plots, soil organic matter is in steady state.
What is the rate of decomposition of soil organic matter in the unwarmed meadow? Express your answer in units of g(carbon)/m2-year. (10 pts.) d. Given the above information, at what rate will the heated plots lose carbon as a result of
warming? Express your answer in units of g(carbon)/m2-year). (10 pts.) 2. Assume that fossil ﬁlel burning in the northeastern US results in about 9.6 Mt(S)/y of SO;
emissions and 5.6 Mt(N) as NOx emissions. Assume further that 1/3 of the S and 1/2 of the N
convert to H28 04 and PIN03, respectively, and dissolve in rain or snow that falls on the
northeastern US. Assume 1.5 m of rain falls each year in the region. What will be the volume-
weighted—average pH of precipitation be in that region ﬁ'om these combined sources of acidity?
State any further assumptions clearly. (Don’t make this problem unnecessarily hard--you don’t need to solve equilibrium equations) (20 pts.) 3. Using our complete l—dimensional climate model for Earth’s average surface temperature
(Chapter 111.6 or, equivalently, Eq. 1 on p. 177 of COW, or, equivalently, the equation for T5
written on the board in class last week and two weeks ago), by how much should Earth’s surface
temperature change if deforestation simultaneously raises the albedo of earth from .30 to .32 and
lowers the globally—averaged evapotranspiration rate from 80 W/m2 to 73 W/mz? You may
assume the reduced heat of condensation is dumped into each of the two layers of the
atmosphere in the same proportions as is the unaltered heat of condensation (i.e., the 80 W/mz). (25 pts.) ...

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