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In order for a freshwater ecosystem to sustain life it must be under optimal and balanced conditions. The experiment involved the construction of an aquatic ecosystem in a plastic bottle. A careful balance of biotic and abiotic factors was maintained to ensure the ecosystem is sustainable. The biotic components of the ecosystem included a food web of pomacea spp, paratya australiensis, freshwater worm, vallisneria gigantea and lemna spp. The abiotic aspects included water level, dissolved oxygen, PH, temperature, electrical conductivity as well as nitrate/phosphate concentrations.
Measurements and observations were taken over a 4-week period to ensure consistency and reliability. The ecosystem must be under optimal abiotic conditions so that the biotic components can thrive and reproduce.
An aquatic freshwater ecosystem is a complex system that consists of living biota interacting with the surrounding abiotic environment. In order to maintain a sustainable and healthy ecosystem the biotic and abiotic aspects of the experiment as well as their symbiotic relationship together must be delicately balanced.
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For example the food web of the variation of the biotic components must be chosen according to the different trophic levels required for a functioning ecosystem. Whereas the abiotic environment such as the freshwater, oxygen, pH, conductivity, nitrate and phosphate levels must be under optimal conditions to assist the survival of the biota.
The different trophic levels in an ecosystem illustrate the flow of energy and recycling of nutrients. Producers also known as autotrophs make up the first level of the food chain, as they are photosynthetic which means they produce their own food.
These include of vallisneria gigantea (ribbon weed,) lemna spp (duckweed,) as well as Nitella spp (algae.) Primary consumers also known as heterotrophs include organisms that are unable to produce their own food thus consume other individuals for energy such as pomacea spp (mystery snails) and paratya australiensis (glass shrimp.) Moreover detritivores such as freshwater worms decompose dead organic matter. The different trophic levels are essential to the survival of an ecosystem as ‘’trophic position represents the number of feeding links separating an organism from the base of production”.
Conducting an ‘ecosystem in a bottle’ experiment enables the investigation of whether or not “the sustainability of a freshwater ecosystem is dependent upon the symbiotic relationship between the abiotic and biotic environment.” It was hypothesized that the ecosystem constructed ‘will self-sustain itself if the abiotic and biotic components symbiotically interacted together while maintaining a state of equilibrium.
To form the benthic zone of the ecosystem the container was prefilled with a 4 cm layer of aquatic sediment consisting of gravel/sand. To form the limnetic and littoral zones of the ecosystem, 1500 ml of water from the Manly dam river was poured into a 2L plastic container. A line was drawn on the bottle to mark the water level so that signs of evaporation can be noted in the following weeks. Before adding the water, 3 ribbon weed plants (Vallisneria gigantean) were measured and added into the bottle. The organisms used were also measured and placed into the jar. These included of 1 worm, 2 snails and 2 shrimp. Between each practical, the jar was covered by a wire mesh and taken to the glasshouse during the four-week period.
During each week the same measurements were taken to ensure consistency. In the final week the ecosystem in a bottle was dismantled and all final results were taken.
The organisms were chosen based upon the hypothesized idea that they would interdependently create a sustainable and balanced ecosystem. The bio-components added included of 2 snails, 1 worm, 2 shrimp, 1 bunch of ribbon weed and 16.03 g of duckweed. The colors of each organism were observed and noted before being added into the jar. The length of the plants and aquatic snails were measured using a ruler. The length of the worms and snails were estimated due to impracticality. All the organisms were weighed using a digital scale. All measurements and observations were recorded weekly in the lab.
The abiotic components measured included conductivity, dissolved oxygen, PH, nitrate and phosphate levels. The water level, odor and color were also measured and observed. Electrical conductivity, oxygen and pH levels were measured using probes rinsed with de-ionized water to remove residue from other ecosystems. The nitrate and phosphate concentrations were measured using test kits that required the observation of color change in accordance to a given chart. All measurements and observations were recorded weekly in the lab.
The sustainability of an ecosystem is affected by the abiotic components and the amount of fluctuation from the optimal conditions. The biotic components in the experiment were balanced according to an expected food web to ensure an effective flow of nutrients and energy. Most of the observations noted over the 4-week period can be explained through a change in abiotic and/or a biotic component of the ecosystem. This is because both aspects work interdependently to create a functioning network that thrives, reproduces and has a high survival rate. Over the experiments course, the pH level experienced a gradual increase from 7.2 in week 1 to 8.8 in the fourth week, changing from neutral conditions to slightly basic. This can be explained in accordance to the increase of plant shoots and duckweed, as an increase in plants results in an increase of photosynthetic activities. With an increase of photosynthesis, more carbon dioxide is removed and more oxygen is released. This is because carbon dioxide reacts with water to form carbonic acid, which will decrease the ph. Hence, the varying level of carbon dioxide results in the fluctuation of pH concentration. Therefore with a decrease in carbon dioxide and carbonic acid there will be an increase in pH.
An overall increase in pH was beneficial to the ecosystem as it lies within the ph range of 6.5-8.5, which is the optimum level for aquatic organisms. A high concentration of dissolved oxygen is essential for cellular respiration in aquatic animals. An overall increase in oxygen concentration was observed during the course of the experiment, increasing 11.28%. This can be explained through the reproduction of new plant shoots, increased duckweed biomass as well as the formation of algae, which collectively increase photosynthetic activity. The reproduction of plants suggests that the conditions of the ecosystem were optimal and balanced as cellular respiration was effectively taking place. For example new plant shoots formed in the second week, which corresponds to a slight increase of nitrate, and phosphate levels in week 2 suggesting that there was a sufficient flow of energy and nutrients for plant reproduction. Even though overall the oxygen concentration has increased, in week 2 the concentration of oxygen was lower than week 1, changing from 10.22 mg/L to 9.38 mg/L. This may be due to sunlight not adequately penetrating the plants, thus resulting in decreased photosynthesis. However, the overall increase in oxygen levels from week 1 to week 4 can also be due to there being no deaths of aquatic animals, hence decomposition of organic matter, which requires the uptake of oxygen was low. Thus, an increased oxygen concentration suggests that abiotic and biotic components of the aquatic ecosystem were interdependently functioning to sustain life.
Electrical conductivity is used to measure inorganic materials including calcium, bicarbonate, sulphur and other ions dissolved in a water body. According to the water quality standards of Australia, freshwater usually has conductivity between 0 and 1,500 uS/cm. Where “low levels of salts are important for plants and animals to grow” as high levels of salts can be detrimental to an aquatic ecosystem. According to figure 2 there was a fluctuation of water conductivity in week 2 from 277 µS to 287 µS but a gradual decrease in the following weeks (3 and 4) from 274 µS to 266 µS. According to figure 2 and figure 8 there is a “direct correlation” between EC and plant growth performance. Nitrate and Phosphate concentrations were measured weekly to determine the nutrient levels within the ecosystem. Phosphate and nitrate ions are the two main sources of nutrients within an aquatic ecosystem. Nitrate ions assist in protein synthesis, which is crucial for plants and animals to acquire. Phosphate is an important nutrient for plants as it catalyzes photosynthesis in plants by assisting photo pigments to convert light into an energy source.
However a high level of both nitrate and phosphate is detrimental to an aquatic ecosystem as it assists the growth of unrequired plants such as algae, which can reduce water quality and increase the competition of nutrients among the animals and plants.
Throughout the experiment there was a slight fluctuation of nitrate and phosphate levels (figure 5,) with both nutrients increasing in week 2. However the average nitrate and phosphate levels were 0.13 ppm, and 0.25 ppm respectively, which is a small amount that is crucial for plant growth and metabolic reactions. This can further be explained in accordance to the growth of ribbon weed in weeks 3 and 4, suggesting that there was an assimilation of nitrates and phosphates, which was used for growth. The observation in figure 9, suggest that the biotic organisms interact with the abiotic environment, as there was a growth in the shrimp, worm, and snails. This directly relates to the levels of nitrate and phosphate, as well as dissolved oxygen levels and pH. The shrimp grew in length by an average of 22.5%. The worm increased in size by an estimate of 7.9%, while the snails grew by an average of 21.9%. The percentage rates suggest that the abiotic factors, including high oxygen levels, low nitrate and phosphate levels as well as optimal pH levels were a large factor that contributed to the growth rates in the primary consumers. This is further substantiated in the worm that only showed a growth rate of 7.9%, suggesting that decomposition of dead organic matter was low, a conclusion which also substantiated the high oxygen levels. This explanation if further exemplified in the decrease of oxygen levels in week 2 and the death of one of the 2 snails which was observed in week 3. Thus it is evident that abiotic and biotic components of an aquatic ecosystem are equally as important as both aspects work together to sustain life.
Overall, the experiment conveyed a high survival rate of approximately 90%. This is due to the efficient and effective flow of nutrients and energy across the food web (figure 1), as well as the effective balance of abiotic aspects of the ecosystem. A limitation encountered during the experiment was the impractability of measuring the worm and shrimp using a ruler, hence it was often estimated and not highly accurate. Another limitation that was noted was the lack of temperature measured of the ecosystem. This was crucial to identifying and substantiating the strong symbiotic relationship between abiotic and biotic aspects of an ecosystem. Moreover, due to the small scale of the experiment and small time frame not all abiotic and biotic factors were examined, thus future studies is highly recommended to further understand the extent of the relationship between abiotic and biotic components and there interdependent role in sustaining a healthy and thriving aquatic ecosystem.
Experiment Report: The Construction Of an Aquatic Ecosystem in a Plastic Bottle. (2024, Feb 29). Retrieved from https://studymoose.com/experiment-report-the-construction-of-an-aquatic-ecosystem-in-a-plastic-bottle-essay
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