Effects of Nutrients and Mixing on Phytoplankton Growth
EOSC 451/551, Fall 2020
Worth: 50 points (Part 1 = 10 points, Part 2 = 40 points)
Part 2: Lab Report, Due Thursday, October 8 by the start of lab
Objectives:
1. To learn about phytoplankton growth
2. To understand the effects of nutrient concentration and mixing on
phytoplankton growth rates
Part II: Report on Phytoplankton Growth Experiment
Overview: For this phytoplankton growth experiment report, you will prepare a
written report that includes the results of our phytoplankton growth experiment in
the form of graphs and tables (described below), and a discussion in which you
explain the objective of our study, interpret the results, and discuss the results in
the context of previous studies. The elements of the report and their relative point
values are described fully below. All reports must be submitted by the start of lab
on Thursday, October 8 on Blackboard; late reports will be penalized by 4 points
per day that they are late.
Results 15 points
Your results should include graphs and tables displaying all the specific analyses
described below. Each figure or table should include a caption that describes what
is being shown. Axes should be labeled correctly with accurate units and other
information. Figures and tables should be numbered based on the order they are
referred to in the text of your discussion. Although students can get feedback on
their graphs from their peers, all graphs/figures/tables included in your report must
be made by you. Presentation of results will be graded based on completeness,
accuracy, and whether the data is effectively presented in relation to the patterns
that are attempting to be conveyed. Data that should be included in an appropriate
figure or table format should include:
1. Plots of phytoplankton concentration vs. time for each of the
cultures/treatments in the two experiments with the diatom Coscinodiscus
sp. (cell size about 70 μm in diameter) carried out at USD this semester, and
for the experiment with Emiliana huxleyi (a type of coccolithophore that is
about 4 μm in diameter) that was carried out in Spring of 2015.
2. A table showing calculations of growth rate for each time point and
treatment for the two experiments carried out at USD this semester and the
experiment with E. huxleyi from 2015. Show work for just one of the
calculations above your table (the rest you can do in Excel).
3. Make a plot of growth rate vs. time for the E. huxleyi data from 2015. Label
the growth phases on that plot.
4. Now assume that the Emiliana huxleyi cultures (from the 2015 experiment)
were nitrate-limited and that the concentration of nitrate between days 2 and
3 was 5 μM and the concentration of nitrate between days 5 and 6 was 0.1
μM. Use the growth rates you calculated from the 2015 experiment for those
days to calculate the μmax and KN parameters for the Michaelis–Menten
uptake curves for both the low-nutrient non-stirring case and the low nutrient
with stirring case. Upload a picture of your work as a figure in your report.
5. Then use the calculations from #4 to plot the two Michaelis–Menten uptake
curves (nutrient concentration on the x-axis and growth rate on the y-axis)
for the stirring and non-stirring case on the same graph.
Discussion 25 points
Your report will also include a written discussion in which you briefly explain the
study and what was done, and interpret and discuss the results. This written part of
the report must be 2-3 pages (not including figures and references), single-spaced
with 12 point font. Below are descriptions of the different components that should
be included in your discussion and how they will be graded; however, the
discussion should be written cohesively and should not be divided into separate
sections. It is important for the entire report to be integrated throughout and
connect to our study objective.
• Introduction and Statement of Objective (3 points):
You should provide a concise description of our experiment and the objective of
our study. In addition provide a very brief overview of the approach. You do not
need to provide a detailed description of the methods. This section should not be
longer than 150 words or so.
• Interpretation of Results (12 points):
In your discussion, you should not only describe the patterns shown in your graphs
and tables, but also interpret these results based on concepts from biological
oceanography. Each figure or table should be referred to (making sure they are
numbered in the order that they are referred to).
Particular questions/ideas I want you to address in the interpretation of your
results are the following:
1. Describe how you expected nutrient level and stirring to affect the growth of
the Coscinodiscus cultures in our experiments and include the reasoning for
your expectations. Then describe what was observed based on the actual
experiment data and how this was similar to or different to your expectations
(referring to specific graphs/tables in your results section).
2. Reflect on your data and/or experiences tracking your phytoplankton
cultures from home. Whether you personally were able to take
phytoplankton counts or not, reflect on some of the challenges that was
associated with counting the phytoplankton from home. In particular,
consider that the ring stickers each had a volume of about 30 μL (compared
to the volume of the Sedgewick-Rafter slide counted at USD which was 1
mL). Given this, what would the expected range of cell numbers be for 2
ring stickers counted on your Foldscope? How did this relate to some of the
values that were counted How might the smaller volume affect the data
(consider variability in addition to total numbers).
3. For the phytoplankton counts that were taken by members at home in your
group, how did the patterns of that data relate to the patterns in the data
collected at USD? Also how did the cell count numbers relate to the data
collected at USD (based on your calculations of the volume of the ring
stickers above)? Explain some possible factors that might have varied
between experiments between individuals in the class and between class
members at home compared to the USD experiments that might have
affected the results.
4. Describe how stirring affected the growth of the E. huxleyi cultures from the
2015 experiments, and explain how this was similar to or different than the
experiments with Coscinodiscus from this year.
5. How did growth rate vary over the course of the experiments, and (for the E.
huxleyi cultures) how did that help you identify the different growth phases?
Were you able to identify all growth phases for E. huxleyi in your plots, or
were some not present?
6. Based on the Michaelis-Mentin curves you plotted for the E. huxleyi
treatments for low nutrients with stirring and without stirring, how did
stirring affect each of the Michaelis-Mentin curve parameters (i.e. the
maximum growth rate and the half-saturation constant) and what might that
mean for how stirring affects growth of E. huxleyi in different
environments?
• Discussion of Results in the Context of Previous Studies (7 points):
Your interpretation and discussion of our results should also be placed in the
context of previous studies from the primary scientific literature, citing at least 3
different scientific articles. One of the scientific articles you can use is the Peters et
al. (2006) study that is attached in the Blackboard assignment. Your discussion
should demonstrate a strong understanding of how our results relate to previous
findings, and should highlight similarities and differences. In addition, you should
discuss the implications for our findings and the findings of previous literature in
relation to how phytoplankton growth may be affected in different ocean
environments and in the context of climate change.
• Conclusions, Implications, and Future Directions (3 points):
Your report should also include conclusions that wrap up your discussion in
relation to your objective. There should be a clear explanation of the implications
and broader significance of our results, in addition to a description of potential
future directions that would be important to address unanswered questions. This
section should not be longer than about 150 words or so.
• References
At the end of your report, you should include a list with the full references of any
scientific articles (or other sources) that you cited in your report. Failure to include
a list of references or to properly cite sources will result in losing points towards
the final grade of your report.
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