Ecocolumn Lab

Background Information

An ecocolumn is a model ecosystem used to observe ecological processes on a smaller scale. These models typically have different layers which correspond to layers of a true ecosystem. These typically begin at the top with a terrestrial layer, consisting primarily of soil and grasses with the potential of a few bugs. Underneath the terrestrial layer is a decomposition layer. This includes decomposers, compost, and soil. This layer has the function of decomposing matter to cycle nutrients, as they would be in the natural world. The third and final layer is an aquatic layer. This layer includes a water plant, some marine life such as fish or snails, and water. The layers in the ecocolumn work together to create a sustainable, living environment as they would in an ecosystem.

The ecocolumn is also used to determine the relationship between abiotic and biotic factors in an ecosystem such as nutrient cycles, pH, and temperature. The nutrients being observed in the aquatic chamber are nitrates and dissolved oxygen. Nitrates are released as a result of the nitrification of ammonia from fish waste and is used by the plant as a nitrogen source. Dissolved oxygen is the content of oxygen in the water which is necessary for the survival of both the fish and the plant. The nutrients being observed in the terrestrial layer are nitrogen, potassium, and phosphorus. All of these nutrients are crucial to the growth of the grass, and therefore, to the survival of the terrestrial layer. Along with these specific nutrients, pH and temperature are tested in both the aquatic and terrestrial layer.

Purpose

The purpose of this lab is to create a model ecosystem so different nutrient cycles and interactions could be observed and recorded. These included the observation of nitrogen, phosphorus, and potassium cycles in the terrestrial layer, the observation of nitrates and dissolved oxygen in the aquatic layer, as well as pH and temperature in both these layers of the ecocolumn. This 'mini-ecosystem' allowed the intricacies of an ecosystem to be demonstrated in an easily testable environment that provided the opportunity to progress the knowledge of ecosystems as a whole. The analysis of these nutrients also allowed conclusions to be drawn in regards to how biotic and abiotic factors influence each other to sustain life.

The goal of the ecocolumn was to evaluate and analyze a small-scale, self-sustaining ecosystem. There were three layers to this ecocolumn: the terrestrial layer, which represents the land habitat; the decomposition layer, which represents the decomposition of materials typically done in soil; and the aquatic layer, which represents a freshwater habitat. Two small fish were placed into the aquatic chamber, with an aquatic pant to serve as a food source and keep dissolved oxygen levels sustainable. In the decomposition layer, worms and insects were introduced to function as decomposers and cycle nutrients. The terrestrial chamber started with grass seeds and was placed on top so nutrients could flow into the decomposition layer below it, eventually bringing nutrients to the aquatic layer at the base.

The first week consisted of water testing, which included pH, temperature, dissolved oxygen, and nitrate testing. This level of water testing continued weekly for the duration of the ecocolumn (four weeks) and new data was recorded with each test. Every other week the soil testing would be conducted. Soil testing included pH, temperature, nitrogen, phosphorous, and potassium testing.

The pH testing was done using pH strips, which simply required a small amount of a sample, water or damp soil, to be applied to them. The strips then changed color based on the acidity of the sample. The pH was determined by the correspondence of the color to a pH chart. Temperature testing was done using a wireless thermometer connected to a computer, which was then placed into the sample (water or soil). Dissolved oxygen and nitrate testing was done using CHEMets kits, simple do it yourself water testing kits. These kits provide quick and reliable feedback for each different test. Finally, the nitrogen, phosphorous, and potassium tests were done using Rapitest, an at home soil test kit. These tests required a sample of the soil to be mixed with water and left to settle, then the solution was mixed with a given capsule and the solution changed color based on the level of chemical present in the water.

All of these factors were important to test for because they all directly impacted the health of the ecosystem. As limiting factors, too much or too little of any of these elements could not only kill some of the organisms in the ecosystem, but cause a collapse to the ecosystem as a whole.

1. In creating the ecocolumn, there was some human error that had to be resolved. When the hole was cut as an access point for a pipette to water test, it was cut too low. This meant that when the aquatic layer was filled with water some of it began to spill out. This was fixed by taping the hole and creating a new one higher up. No replacement of any organisms was necessary throughout the duration of the experiment.

2. Starting with the first habitat, the terrestrial layer's purpose was to mimic regular terrain and ground surface with grass growing in it. From there, water, which carried nutrients from the soil, was poured into the terrestrial layer, which trickled down to the decomposition layer. In the decomposition layer, the water and nutrients from the terrestrial layer above helped to nourish the worms that were placed in as decomposers to break down nutrients. As the water travels from the terrestrial layer, down to the decomposition layer, and into the aquatic layer, nutrients are carried and absorbed by living things to sustain life. Which was shown by the survival of the fish and growth of plants. All three layers of the ecocolumn worked together to sustain the life of organisms and contributed to nutrient cycling.

3. While watering the ecocolumn, precipitation was being mimicked. There was a soda bottle cap placed in between layers with small holes cut in them so that water filtered through to create the pattern of rainfall seen in real-world ecosystems. Additionally, after the grass in the terrestrial layer was watered, it evaporated. This released water vapor into the air through transpiration, adding additional moisture to the layer.

4. One way that the carbon cycle is demonstrated in the ecocolumn is through the release of carbon dioxide from biotic factors in the ecosystem. Through respiration, the living organisms released carbon dioxide into the air, which affected the terrestrial layer by aiding in grass growth. In the decomposition layer, carbon was released back into the soil to encourage plant growth. Carbon was also produced by the consumers in the ecocolumn through waste production and used by producers for photosynthesis.

5. The nitrogen cycle begins in the decomposition layer, as matter, such as the worms, decayed and released nitrogen into the air. The nitrogen then traveled into all of the layers, promoting the growth and survival of the ecocolumn. In the aquatic layer, ammonia is present as a result of fish urination, which can be toxic to fish. However, the ammonia goes through nitrification, resulting in nitrites, and subsequently nitrates. As a result of this, as time progressed and fish waste increased, so did the nitrate levels. The nitrates were then used by plants to aid in growth.

6. Phosphorus was found in the soil while doing testing. This phosphorous was absorbed by the plants in the terrestrial layer, but could also be found in the decomposition layer. This is supported by the fact that as the ecocolumn was watered, the water would filter through the gravel that separated the layers and carried some of the phosphorous found in the gravel and rocks into the next layer.

7. As the matter in the decomposition layer broke down and decomposed, it released nutrients that would be brought down through the compost and into the aquatic layer. The decomposition layer must have been working to some proper extent because both of the fish lived and did not die or become lethargic. The worms were among the first to die in the ecocolumn, and because they were in the decomposing layer, they set the ecocolumn up for success by giving it plentiful nutrients from the beginning.

The lab was conducted with the purpose of creating a mock ecosystem to observe how different cycles and layers interact with each other. The goal was to create a sustainable environment without interfering with the natural processes. Some of these processes include the nitrogen cycle, decomposition, and the hydrologic cycle. Tests were conducted for pH and temperature in both chambers, dissolved oxygen and nitrates in the aquatic chamber, and nitrogen, phosphorus, and potassium in the terrestrial chamber. These were tracked over a four week time span in order to determine the successes and shortcomings of the ecocolumn. The tests also demonstrated many of Earth's natural processes and helped enhance understanding the roles played by biotic and abiotic factors in ecosystems.

Overall, the ecosystem was successful in sustaining the life of the fish, however the snail did die within the first couple of days. The ecosystem was also successful in stimulating plant growth which was observed through an overall grass growth of ten inches. Lower levels of dissolved oxygen resulted in higher amounts of nitrates in the aquatic layer. In the soil, phosphorus levels stayed consistent, whereas potassium and nitrogen levels decreased. This makes sense because the plants require nitrates and potassium in order to grow, therefore the grasses used some of the nutrients from the soil to grow in the terrestrial layer. The changing levels of these three components represents the cycles that are seen in real world ecosystems. For example, nitrogen undergoes nitrogen fixation, which leads to the formation of nitrates that are essential for plant growth. This explains the decrease of nitrogen in the soil and is part of the nitrogen cycle in real ecosystems. The temperature and pH of the soil and water stayed fairly consistent with temperatures around 20 degrees Celsius and with pH between six and seven. The pH of the soil and water stay within a healthy range for both environments which allowed the survival of the organisms in the ecocolumn. The turbidity increased slightly over the four weeks, however this is not surprising as the fish created waste which would result in murkier water. The increase in dissolved oxygen is not surprising either as more plants grew in the ecocolumn, so photosynthesis was occurring at a faster rate. The most surprising result was the sharp decrease in nitrates between weeks two and three. A possible explanation for this is the plant started using nitrates for growth at a more rapid pace since the nitrates were so readily available. This led to a quick decrease in nitrates as the plant's rate of growth increased. This explanation is supported by the displayed growth of the plant in the days following the observed nitrate levels. Through the data collected from the ecocolumn, real world processes, such as photosynthesis and transpiration, are evident and the requirements of an ecosystem to sustain life are exemplified.

One human error made from the start was that there was a leak in the ecocolumn. This was combatted by saran wrap initially and then the hole was covered by duct tape, which was more efficient in preventing leakage. A second human error occurred when initially watering the ecocolumn, as the same water was supposed to be used to filter through the column twice. However, when conducting the experiment, the water was only filtered through once.

One of the major processes exemplified by this experiment was nitrogen cycle. It was found that nitrate levels decreased over the weeks as the plant started to absorb nutrients. In the textbook, there is a section on the nitrogen cycle which explains that "nitrate ions... are easily taken up by the roots of plants" (pg 66, paragraph 5). This supports why nitrate levels would drop throughout the weeks as the plant absorbed them in order to sustain life and grow. The concept of limiting factors was also demonstrated in the ecocolumn. A limiting factor, "can limit or prevent the growth of a population, even if all other factors are at or near the optimal range of tolerance" (pg 112, paragraph 6). Grass growth plateaued at about ten in after the first two weeks as soil became potassium deficient and nitrogen levels decreased. Although the temperature and pH didn't fluctuate much, the nutrients were not as readily available. Therefore, grass growth was regulated by the limiting factor, the nutrients. In the experiment, the dissolved oxygen levels experienced a sharp increase as nitrate levels fell. In an analysis of the Gulf of Mexico, it was determined that "the level of nitrates discharged from the Mississippi River into the northern Gulf of Mexico... nearly tripled" which resulted in "severe oxygen depletion" with levels below two parts per million, "low enough to kill bottom-dwelling shellfish" (pg 551, paragraph 8). In this real life example, it is evident that a sharp increase in nitrates causes oxygen depletion. The vice versa of this concept is exemplified in the ecocolumn.

The ecocolumn was successful as the plants and fish were able to survive and thrive in the conditions. The conditions stayed within the range of tolerance and the plant performed it's role as producer effectively, as shown by the survival of the fish. The consistency of pH and temperature aided in fish survival and an increase in nitrates led to an effective aquatic plant. All organisms were able to use the resources and nutrient cycling occurred which ultimately led to the success of the ecosystem. The ecocolumn showcased the processes, such as the nitrogen cycle demonstrated through the correlation between nitrates and dissolved oxygen, that occur in real-world ecosystems.

Miller, Tyler, and Spoolman, Scott. Living in the Environment. Eighteenth Edition, AP Edition. Cengage Learning, 2015.