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Dr. Johansen demonstrating how to collect
phytoplankton |
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| Fig. 1 - a plankton tow net |
During this lab, Horseshoe Lake, Lower Lake
and Doan Brook were visited in order to collect samples of algae. Horseshoe
Lake is located in Cleveland near the intersection of South Park Boulevard and
Park Drive. Lower Lake is also located at Shaker Lakes along with Horseshoe
Lake. Doan Brook is located on South Park Boulevard as well.
The
method of obtaining the algae is called plankton tow. With this method, the
algae is obtained by throwing whats called a plankton net (figure 1), into the
water. The net that is used is very fine and allows the net to catch the
microorganisms, but lets the water pass through easily. In order to
successfully execute this procedure, the net must first be thrown into the
water. Once the net is in the water, it should be kept there for a few minutes
so the water and microorganisms can go into the net. Moving the net around in
the water is also a good idea in order to ensure that different types of
organisms are brought into the net. After leaving the net in the water for a few
minutes, the net should be pulled out and held in a vertical position to allow
all the water to drain through the net. The samples will be present in the
collection vessel that is located at the bottom of the net. In addition to using the plankton tow, we were able to grab larger samples of algae off the walls and from the surface of the water. At Horseshoe Lake there were floating mats on the water which we were able to grab. Once we were able to look at the sample closely, it was determined that it was Hydrodictyon. When we went to Lower Lake we found some more Hydrodictyon and then we were able to scrape off some samples of periphyton from the walls. At Doan Brook, we used the plankton tow, and also tried to get some algae off of the rocks, but we didn’t have much success because there wasn’t a lot of algae to collect due to the pessimal environment.
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Collecting phytoplankton from
Horseshoe Lake |
Upon
returning to the lab, we prepared wet mounts from all samples. In total, we recorded 17 genera: 4 genera of phylum Bacillariophyta, 2 genera of Chlorphytes, 2 Charophytes, 3 Cyanobacteria genera, 2 Syrophytes, and 3 genera of Euglenophyta. Out of the three
sites sampled, Horseshoe Lake had
the highest diversity; we recorded 10 genera from 5 phyla.
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| Fig. 2 - Synura, Euglena, and Lepocinclis |
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| Fig. 3 - Pediastrum |
Plankton
tow samples from Horseshoe Lake were dominated by Mallomonas and Synura
(Synurophyta) as well as eutrophication indicators Euglena and Lepocinclis (Euglenophyta,
figure 2) and some Chlorophytes including Pediastrum
(figure 3).
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| Fig. 4 - Melosira, Chroococcusand Gloeothece |
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| Fig. 5 - Gomphonema, Chroococcus and Gloeothece |
We
recorded 3 genera of diatoms from wet wall samples at Horseshoe Lake; Melosira (figure 4) formed long, brown
chains. Rhopalodia and Gomphonema species were also abundant in
these samples (figure 5). Two dominant genera of cyanobacteria were recorded as
well: Chroococcus and Gloeothece (figures 4 and 5), which
look very similar, however Chroococcus
differs from Gloeothece by cell
division in 3 planes instead of 2.
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| Fig. 6a - Hydrodictyon |
Horseshoe
Lake was covered in thick mats along the littoral zone, which consisted of
mostly the “water net” Hydrodictyon (figure
6a, 6b). This alga was identified in the field when stretched apart.
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| Fig 6b - Hydrodictyon |
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| Fig. 7 - Spirogyra |
Lower
Lake was dominated by green algae (Chlorophyta and Charophyta), with three
genera recorded. Spirogyra (figure 7)
was quickly identified due to its spiral-shaped chloroplasts and formed large
mats in the lake. Oedogonium and Scenedesmus (Charophyta, Chlorophyta, respectively) were also found in these
samples. Doan
Brook appeared to be quite disturbed; few rocks in the stream had mucilaginous
diatom colonies but were covered in Platyhelminthes, indicating a degraded
water body. The algae collected from this site confirmed this; Pleurosira (Bacillariophyta) were
abundant and formed chains connecting at alternating polar nodules (figure 8); Pleurosira is an indicator of elevated
conductivity.
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| Fig. 8 - Pleurosira |
Dolichospermum
(Cyanobacteria, figure 10) was also present. This planktonic alga is
potentially toxin producing and capable of living in poorer water quality due
to its ability to fix nitrogen via its heterocytes. Ankistrodesmus, another green alga, was found in some of these
samples. Trachelomonas (Euglenophyta) was also present. This alga is easily
identified because of its hard, loricate shell.
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| Fig. 9 - Dolichospermum |
Because the lab period was shortened, we
looked at the same samples on Tuesday, September 17th, however most
of the algae had died and were difficult to identify. No other genera were
recorded during this time. This lab was a great introduction to using algae as
indicators of water quality; we were able to determine that our sites were
somewhat subject to disturbance and eutrophication by identifying important
algal bioindicators.
