Q9
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McGill University *
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215
Subject
Geography
Date
Dec 6, 2023
Type
docx
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2
Uploaded by ChancellorDuck3776
Ecologists are concerned about the effects of global warming on ecosystem properties. The
following results were obtained in experiments designed to simulate the impact of a global increase
in mean temperature on aquatic ecosystems. At each site (#1-7), a replicated set of small lakes was
warmed by 2-5 degrees (red bars) and compared to non-heated controls (black bars). Measurements
of total ecosystem respiration (respiration of all organisms) and gross primary production were
made throughout the year and their ratio (Total ecosystem respiration/GPP) is plotted on the y-axis.
The overall mean of the data is shown on the extreme right.
a) (3 marks) Do these lakes naturally take up or release CO2 to the atmospheric reservoir? Explain
the evidence.
I believe that these lakes naturally take up CO2 from the atmospheric reservoir because as the
temperature increased, their uptake decreased. Since it is a ratio, if GPP was greater than total
ecosystem respiration, then the red bars would actually be lower than the black bars but since that is
not the case, I believe that these lakes take up CO2.
b) (2 marks) What is the overall effect of warming on CO2 uptake by these ecosystems? What is the
evidence?
In order for the red bars to be greater than the black bars, the GPP value has to be smaller. Since
GPP is the total energy/carbon that is fixed by plants per unit area per unit time in photosynthesis,
the overall effect of warming has reduced the uptake of CO2 by the ecosystems.
c) (2 marks) How does the size of the C reservoir change annually in the unheated lakes and the
heated lakes?
I believe that the size of the C reservoir actually decreased in the heated lakes over time as we see a
steady increase in the red bars whereas the C reservoir in the unheated lakes increased slightly.
d) (4 marks) The experiment described here only varied ecosystem temperature, but what other
environmental variable(s) should be considered if ecologists want to study how ecosystem
respiration and GPP may respond to future warming? Explain why and how changes in these
variables this might affect the results.
Factors such as soil fertility and precipitation level should also be considered if ecologists want to
study how ecosystem respiration and GPP may respond to future warming. With increasing levels of
warming, it is predicted that the level of precipitation would also increase due to increase in level of
evaporation. When Rosenzweig tried to understand the factors that regulate primary production at
the global scale, he discovered that along with temperature, precipitation and moisture level could
explain a lot of variation in primary production. Level of precipitation and moisture directly correlate
with the process of decomposition which contributes to the energy spent on respiration. Therefore
changes in these variables might affect the results.
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