What is the Population Density
of Gloeotrichia in Samples of
Fernan Lake?
Teacher Inquiry by Cindy Rust and Rusti Kreider
Background Information:
● We were going to also look at the uptake
of CO2 of algae
● Probeware would not cooperate
● A good lesson
● Do you want to go through more work
than kids will get out of it?
● NO, so we abandoned that thought
Background Information:
We were looking for a simple and engaging
lesson to blend population density with water
quality monitoring.
Background Information:
According to wikipedia
(our students’ go to resource)
population density is a
measurement of population per unit
area or unit volume
It is a quantity of density
Background Information:
Gloeotrichia
Cell volume
2,826 µm^3 mean
Cell mass
439 pg mean
Trophic dependence
photoautotrophic
Background Information:
Classification:
Kingdom Monera
Phylum
Cyanophycota
cyanophytes
Class
Cyanophyceae
Order
Nostocales
Family
Rivulariaceae
Genus
Gloeotrichia
1886
blue-green algae,
Jg. Agardh Ex Bornet and Flah.,
Background Information:
Toxin: microcystin-LR; hepatotoxin
● Inhibitor of
certain
enzymes
● Hepatic tumor
promoter
● Chronic
exposure
increases
holes in liver
Procedure:
●
●
●
●
3 sampling sites
at surface level only
filling a 500 mL bottle each site
refrigerate sample until time of
use
● Public dock boat launch west
end, midlake, and submerged
marsh (lilypads) east end.
Quantifying Cyanobacteria
● Mark a grid using 1cm2 increments on the bottom of a plastic disposable
petri dish
● Gently invert the sample bottles to create even distribution
● Sample from surface of bottle, mid bottle, and bottom of the bottle
● Place 1 mL of sample in petri dish
● Using a dissecting scope, count total Gloeotrichia sp. in the sample,
focusing from top to bottom of water sample although most float.
● Repeat three times and record data.
● Using the average count from each sample, extrapolate to entire water
sample
Quantitative Data
West end Public Boat Launch (Sample #1) Trial 1
0
West end Public Boat Launch (Sample #1) Trial 2
1
West end Public Boat Launch (Sample #1) Trial 3
8
Quantitative Data
Midlake (#2) Trial 1
4
Midlake (#2) Trial 2
14
Midlake (#2) Trial 3
4
Quantitative Data
Lilypads East end boat launch (#3) Trial 1
2
Lilypads East end boat launch (#3) Trial 2
3
Lilypads East end boat launch (#3) Trial 3
4
Qualitative Data
When examining the sample bottles, it was easily
observed that the west end boat launch had less.
We found that sampling at the surface of the bottle
produced higher loads of organisms as they tend to
float and congregate at the surface.
Analyzed Results
sampling site Public Boat
Midlake Lily Pad Boat Launch
Launch (west
(east end of Lake)
end of Lake)
average
organisms
per mL
3
7
3
extrapolated
density per
500 mL
1500
3500
1500
New question emerged
Could disturbance such as human
traffic cause the samples to be skewed
because of forced dispersal?
Ideas for Classroom Implementation
● student data from these samplings should be shared
collectively on a class data chart.
o This would provide a more representative sampling
of the bottle and a more reasonable extrapolation to
the entire lake body.
● Small groups defined by area of the lake with each
member taking a turn counting.
o This increases student exposure but may present a
variable in counting technique so be clear in
counting technique instructions.
Resources
● http://microbiology.usgs.gov/images/Gleotrichia531x400
.jpg
● http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_
topic=TSN&search_value=1300
● http://link.springer.com/article/10.1007%2Fs10452-0129409-9#page-2
● http://www.sigmaaldrich.com/catalog/product/sigma/m2
912?lang=en&region=US