Organism Viability in a Closed Ecosystem

This study focused on the carrying capacity of a closed-system aquatic microcosm. Four microcosms of varying size were constructed and sealed. Temperature and observational quality of the microcosms were measured weekly (three week period,) while the system’s overall stability was examined at the end of the experiment. Probes measuring pH, dissolved oxygen, and water turbidity were utilized to assess the viability of each biosphere.

Samantha Barrus1, Lisa Briggs2

Abstract

Jar & Capacity

Soil/Water Plants Other

4: 1 gallon 1 cup: 1 liter 5 Elodea, 8 Azolla

1 tsp. limestone,

shells

3: ½ gallon ½ cup: 500 mL 3 Elodea, 4 Azolla

½ tsp. limestone,

shells

2: ½ gallon ½ cup: 500 mL 3 Elodea, 4 Azolla

½ tsp. limestone,

shells

1: 1 liter ¼ cup: 200 mL 3 Elodea, 4 Azolla

¼ tsp. limestone,

shells

Methods and Materials

Tabletop aquatic microcosms were created in glass jars and sealed for the duration of the experiment. Soil and water samples were collected from Ninigret Wildlife Refuge in Charlestown, RI; soil to water ratios are present in the below figure. The remainder of the jar was filled with non-chlorinated well water. Limestone and coarsely crushed shells were added to act as a buffer. Elodea and Azolla were garnered from professors in the Plant Sciences Department and distributed depending on container volume. Organisms were purchased from a local pet supply shop; the organism’s biomass was to be proportional to the volume of each container, with larger organisms inhabiting the larger microcosms. Temperature measurements were taken from a thermometer (intended for use in personal aquaria) affixed inside each container. Probes used for pH, dissolved oxygen, and water turbidity were provided by Jay Fogleman. The experiment relied heavily on qualitative observation, weekly temperature measurements, and a final examination of ecosystem viability in terms of data collected using the provided probes.

1,2University of Rhode Island—Secondary Education and Biology Departments

Fish Type Jar NumberGoldfish 4

Goldfish minnow 3Platy 2

Relevant Literature

Published by the University of Washington1, this article focuses on an experiment introducing the concept of building and maintaining a self-sustaining biosphere, with the goal being to apply the findings to the advancement of space travel. Tabletop microcosms were constructed to examine each ecosystem in terms of viability of the introduced organisms. One copepod (Tigriopus californicus) and one zooplankton (Daphnia magna) species were added to each set up. The relevant variables being examined included light intensity, nutrient concentration, temperature and airspace gas composition. Results showed population growth increased and maintained the best at a moderate level for both light intensity and nutrient concentration; a higher temperature also yielded the best growth. Not allowing any air space in the microcosm lead to quick system failure. Letting the system balance before the addition of organisms is key.

This article2 written by members of the European Space Research and Technology Center of The European Space Agency. They discuss three large scale artificial closed ecological systems (CES) and their manner of control. The closed ecosystems that were focused on were the Russian “Bios-3” set up in the early 1970’s and designed as 4 separate chambers, 3 for biomass and one for living and the control machinery. CES 2 was America’s Biosphere 2 with it’s seven different ecosystems. The third discussed CES is the MELISSA Project (Micro Ecological Life Support System Alternative) that is a European joint effort of five different organizations. All of the CES are designed to find biological solutions to life support for long distance manned space flight. Control systems discussed are the holistic approach: endogenous control, where the system balances itself due to massively redundant systems i.e. earth and the way our ecosystem balance. The other control system discussed was the deterministic approach: exogenous control, with this approach all biological processes are controlled by man. Currently a mixed approach is used in most CES.

1Armentrout, B., Kappes, H. Studies in Closed Ecological Systems: Biosphere in a Bottle. http://www.lpi.usra.edu/publications/reports/CB-1063/UWash.pdf

2Closed ecological systems. By: Tamponnet, Christian, Savage, Christopher, Journal of Biological Education (Society of Biology), 00219266, Autumn94, Vol. 28, Issue 3

High School Level: use microscopy to view microinvertebrate species, focus on soil/water chemistry (pH, dissolved oxygen) or energy transfer, ecology (populations, trophic levels, growth and decay rates, growth curves and charting data)

Middle School Level: use project to visualize the concepts behind the water/carbon/nitrogen cycles, open and closed ecosystems

In the Classroom…

Jar Temperature (degrees Fahrenheit)

Probe Measurements Observations

4 70 pH: 7.46D.O: 4.9 mg/L

Turbidity: 1.4 NTU

Plant quality 8/10, plant quality maintained but no noticeable

growth or new plants, minimal decay, one snail

3 73 pH: 6.91D.O: 4.8 mg/L

Turbidity: 0 NTU

Plant quality 9/10, original quality maintained, new Azolla

taking root in sediment, no adult snails, baby snails present on Elodea and decaying material,

water slightly cloudy

2 70 pH: 6.65D.O: 3.8 mg/L

Turbidity: 0.7 NTU

Plant quality 8/10, saw some copepods/amphipods,

discoloration of 1 Elodea strand, minimal decay, baby snails (3/4)

1 73 pH: 7.13D.O: 3.1 mg/L

Turbidity: 0.2 NTU

Plant quality 6/10, 1 strand of Elodea is brown, at least 3 large snails, may be white mold above

water line

Plant Ranking Scale: 0-2 (bad) 3-4 (ok) 5-6 (good) 7-8 (very good) 9-10 (excellent)

References