Transcript No Slide Title

Exploring the Limits of Self-Sustainable Closed Ecological Systems
Reported by Meena Padha and Luke Pinnow
Introduction to Closed
Ecological Systems
Closed Ecological Systems, like the earth's biosphere,
approach being closed to the exchange of matter, but
are open to energy exchange, receiving light for
photosynthesis and releasing heat energy. By studying
small, replicated, open and
closed microcosms, our lab
seeks to identify the
boundary conditions that will
allow plant-animal-bacterial
communities to sustain the
animal population. One of
the challenges has been to
monitor the conditions of the
animal populations without
opening the containers or
removing samples. Earlier
teams have digitally recorded
animal populations and developed computer programs
to automate counting and sizing.
Most of the previous team efforts have been in plastic
tissue culture containers because their flat surfaces
allow high quality digital recording. The degree of
closure from material exchange was one of the focus
areas of the 2003 team effort. Many of our successful
Closed Ecological Systems--some supporting animal
populations in excess of 3 years--have been in plastic
tissue culture containers.
The survival and reproduction of animals (Daphnia
magna) were compared in open and closed glass and
plastic containers. Daphnia populations were more
numerous in sealed plastic containers than in sealed
glass containers, supporting the hypothesis that plastic
may allow gases such as carbon dioxide and oxygen
to diffuse at rates that impact the community. A
mathematical model was used to explore
photosynthesis and respiration at different diffusion
rates.
Faculty Mentor: Dr. Frieda B. Taub
Methods
Results & Discussion
The experimental design consisted of 48
individual 272mL containers.
Regarding temperature, it was found that there was
no significant difference between the populations in
the open and closed plastic containers at 18 C, nor
are there significant differences between open and
closed glass at 25 C.
The data supported that there was a significant
difference in the populations in glass between the
open (average 31.7) and closed (average 15.8), with
a P-value <0.01. We think that this observed
difference could be due to the lack of diffusion in
glass.
Diffusion of carbon dioxide and oxygen could have
the largest impact on the success of the ecosystem
because of their importance to the processes of
photosynthesis and respiration. Diffusion of gas
into the system could change the success of the
system because additional carbon dioxide
introduced would be more available for
photosynthesis and would increase the amount of
carbon cycling.
Additional oxygen entering the system (possibly
through the sealed plastic containers) could be used
to sustain respiration in systems that would
otherwise be oxygen limited. Both of these should
effect the population of the algae and Daphnia
inhabiting the system.
Another factor that may determine the success of
the ecosystem is the shape the containers. The flat
sides of the plastic flasks and the round glass may
have different light transmission properties and
therefore could change the available light for
photosynthesis and could account for the difference
in algae and Daphnia populations between the
plastic and glass. The closed systems show the
same difference but it could be confused by the
differences in diffusion.
Repeated at 18 & Open Treatment
25 Deg. Celsius
Closed Treatment
Glass Container
6 Replicates
6 Replicates
Plastic Container 6 Replicates
6 Replicates
Two solutions consisting of 75% Kent and 25%
T82-LoSi mixture were added to each individual
container into which was added the following
algae: Ankistrodesmus, Scenedesmus,
Chlamydomonas, and Selenastrum grown in T82LoSi.
Next, four Daphnia magna were then placed into
each container. All systems were allowed to
remain open to the atmosphere for three days to
ensure oxidation of any organic matter that might
have created a biological oxygen demand (BOD)
and to provide the algae with a carbon source
during their initial growth. At the end of this
time, six glass and six plastic containers were
closed by tightening the lids.
All the containers were stored at a temperature of
25 C. with a photoperiod of 14 hours.
Additionally, the exact process (another 24
containers) was repeated and stored at 18 C.
with a photoperiod of 13 hours. At the time of
the final official population report, the systems
had been in place for 36 days.
It is interesting to note that as of #######, nearly
#### months later, there were still living
Daphnia magna present in #### of the glass
containers and #### present in the plastic
containers.
35
35
30
30
Plastic Open 18 Deg
Glass Open 18 Deg
Plastic Closed 18 Deg
Glass Closed 18 Deg
25
20
Plastic Open 25 Deg
Glass Open 25 Deg
Plastic Closed 25 Deg
Glass Closed 25 Deg
25
20
15
15
Average
Average
10
10
5
5
0
0
21 Days since
closure
28 Days since
closure
34 Days since
closure
#### Days
since closure
21 Days since
closure
28 Days since
closure
Light received
0
1
0
1
Available Nutrients
0
1
0
1
Dissolved Oxygen
0
0
+
0 Net production
-
+
0
-
1 Gross production 1
(green)/respiration
0
(blue)
0
Figure 1. Initial values for all variables such
that the system is at a base-line (control)
model, as defined by the author, proceeding
through a five day cycle. (12 hours of light
followed by 12 hours of dark, simulating
gradual light and dark cycles found in nature).
1
1
Light received
0
1
0
1
Available Nutrients
0
0
1
1
Dissolved Oxygen
0
+
0 Net production
1 Gross production
(green)/respiration
0
(blue)
Figure 3. Simulation of when initial
nutrients are decreased from 1.0 to 0.3.
This figure shows that when nutrients are
scarce, initially, the production of the entire
system decreases. However, after three
days, it begins to adjust and eventually
makes some net gains in production.
However, we can see that nutrients are
constantly very low compared to the
normal system.
0
+
0
1
0
Figure 4. Simulation of the diffusion
coefficient (K5) increased to 1.0.
Respiration and dissolved oxygen are
the two variables most affected by this
change. Respiration begins to decrease
during the dark periods and dissolved
oxygen levels are relatively high in
dark and light periods.
The model represents a five-day simulation showing metabolic rates
(respiration, production of oxygen via photosynthesis, net production, and
gross production), levels of dissolved oxygen, and levels of nutrients. We
can see in Figure 1. what the model results give us at the initial inputs of all
the variables. It is at a steady state, where the oxygen is produced in the
light via photosynthesis and oxygen is used in the dark via respiration.
40
40
1
1
Computer Modeling
45
45
University of Washington
34 Days since
closure
#### Days
since closure