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How the Effects of Abiotic and Biotic Factors Contribute to the Stability of an Aquatic Ecosystem Abstract Aquatic ecosystems require a precise balance of abiotic and biotic factors to achieve self sufficiency. This study involves the construction of an aquatic ecosystem in a bottle with a number of abiotic and biotic components. The biotic factors were chosen by looking at how using the appropriate components can benefit the transfer of energy between trophic levels in a food web. This transfer of energy can result in an increase of biomass which can show as growth that will only happen in a stable ecosystem. The factors of stability that were visually recorded as well as measured included oxygen levels, pH, conductivity, nitrate, phosphate, temperature and organism health.

These were monitored over a period of 4 weeks and from the collected data conclusions were drawn about how all of these factors help determine the stability of an aquatic ecosystem. Through this study it was found that all of these factors strongly depend upon each other. As a result of an imbalance of both biotic and abiotic factors, the ecosystem would progressively get less stable and indicate an unsuccessful aquatic ecosystem.

Introduction The combination of non-living elements with living organisms in a single community which are affected by the physical and chemical factors of their watery environment is called an aquatic ecosystem (Nhptv.org, 2018). Aquatic ecosystems can be classified into two types, these would be freshwater and marine. When looking at freshwater ecosystems these include ponds, lakes, streams, rivers and wetlands and which only cover 0.8% of the Earth. Marine ecosystems on the other hand cover approximately 71%. Both ecosystems differ in their physical and chemical characteristics. Fresh water ecosystems contain non-saline water whereas marine ecosystems have higher salt concentrations that average 3% (Clout, 2015). Abiotic and biotic factors are necessary to create a self-sustaining stable ecosystem. These factors include oxygen availability, sunlight, pH and most importantly, tropic levels being present. Without a healthy balance of these abiotic and biotic factors this will have detrimental effects on the survival of the ecosystem (Humbert and Dorigo, 2005).

Looking at a functioning food web is essential to understanding how energy from different tropic levels can be efficiently distributed and used amongst organisms. The tropic structure involves a precise balance of producers, consumers and decomposers (Pauly et. al,1993). The primary produces gather their energy from the sun and make their food through the process of photosynthesis. These include plants and other photosynthetic organisms. Consumers such as herbivores, carnivores and omnivores are unable to create their own food and rely on the producers to provide the energy they need to survive. Decomposers which include bacteria and fungi break down dead organic matter and provide a removal of waste which gets recycled into nutrients and distributed (Society, 2018). Using this understanding, the aim of our experiment was to design and create a stable aquatic ecosystem and would continue to remain stable for a period of 4 weeks. This ecosystem was placed in a bottle and carried out in natural sunlight. This was measured weekly to investigate the different abiotic effects on the ecosystem. Biotic components were measured before they were added and after the deconstruction of the ecosystem. It was hypothesised that the ecosystem would remain stable throughout the four weeks if the variables stayed considerable well balanced.

Fresh water

“Pond Life”

Mystery Aquatic

Vallisneria

Algae

Figure 1 Predicted Food Web for the “ecosystem in a bottle”

Lemna

Materials and Methods Table 1: Biotic components used in aquatic “ecosystem in a bottle”

Name

Quantity Used

Description

Trophic level

Vallisneria gigantea or Ribbon weed

One Common pond plant and Length from root to tip 42 tolerates wide range of cm and 12 leaves. temperatures. Long leaved plant that prefers slow stream e.g. lakes or ponds however are also found in fast flowing water as well.

Producer

Lemna spp or Duck Weed

One teaspoon 20% coverage of surface No roots or flowers visible

Grown in backyard ponds Prefers stagnate or slow flowing water Reproduces rapidly

Producer

Pomacea spp or Mystery Aquatic Snails

One Weighed 2.59g Length 2.5cm

Native to South America Feed on algae or dead matter

Primary Consumer

“Pond Life”

13mL

Consists of a mixture of microinvertebrates

Primary Consumer/ Detritore

Freshwater Worm

One Length 2.5cm

Contains red respiratory pigment Decomposes dead materials

Detrivores

Table 2: Abiotic components used in aquatic “ecosystem in a bottle”

Name

Quantity Used

Description

Pebbles and sand

around 5 cm

Used as sediment to root plants. Formed base of ecosystem

Fresh Water

Up to the heigh of 15.5 cm

Manly Dam water Contains unknown microorganisms

Pebble

One large pebble

Used to help root the Vallisneria Provide shelter for organisms

Conductivity probe

One

Measures the salinity in water.

Phosphate testing kit

One

Measure amount of phosphate in the water. Plants require phosphate to grow and build.

Nitrate testing kit

One

Measure amount of nitrate in the water. Plants require nitrate to grow and build.

pH probe

One

Measure pH level. Aquatic animals can be sensitive to pH levels

Dissolved oxygen probe

one

Measures amount of dissolved oxygen in water. Oxygen is required for animal respiration.

Temperature probe

one

Measure temperature of water. Animals and plants require a balanced temperature to survive and thrive.

Construction of “ecosystem in a bottle” An aquatic ecosystem was created in a 20 cm tall plastic jar and an assortment of pebbles and sand were placed at the bottom of the jar to create a flat surface. The jar was then filled with freshwater sourced from Manly dam to the height of 15.5 cm at a temperature of 18.9ºC. This water was most likely already present with microorganisms but this could not be determined.

The chosen biotic components were examined to determine the trophic levels of the ecosystem. One rooted plant Vallisneria gigantea (producer) was firmly planted in the sediment and one large pebble was placed on top of root system to secure position. Different species were then added carefully to the jar, these include one mystery aquatic snail (primary consumer), one worm (decomposer) and 13mL of pond life (primary consumer). Using a plastic spoon, one teaspoon of Lenna spp was added last due to it’s buoyancy. Before placing the biotic components in the jar, all were weighed and measured (where possible) to compare the results from start to finish. The plastic jar was then covered with a net and labeled with group name. This was then placed in a greenhouse of which the temperature ranged between 15.0ºC and 35.2ºC.

Variables of Abiotic and Biotic components that were measured The jar was brought down from the greenhouse weekly and was first examined on the clarity and colour of the water. After this was recored, a multi-probe (rinsed beforehand with deionized water) was used to measure salinity, dissolved oxygen, water temperature and pH. Two samples of the ecosystem’s water were taken and placed in two small bottles. These were then tested using the two provided test kits which measured phosphate and nitrate concentration. By following the instructions provided in the kits, the samples produced a colour indication of the levels which were then compared to the colour charts provided. These abiotic variables were tested and recored weekly. The visual observation of any physical changes to biotic components were also recorded weekly.

The biotic components of the ecosystem which included the snail, worm and Vallisneria were all measured in length using a ruler with the snail also being weighed using an analytical scale. These measurements were only performed at the beginning and end of the experiment to reduce impact on the ecosystem. All data was gathered and discussed as a group and placed into Microsoft excel. This information was then graphed to easily interpret the results and to understand what is required to create a stable aquatic ecosystem.

Results

Phosphate/Nitrate4Concentration4(mg/L)

Abiotic Components

Phosphate4and4Nitrate4Concentration4 0.3 0.25 0.2 0.15 0.1 0.05 0 1

2

3

4

Week Nitrate4Level

Phosphate4Level

Figure 2: Phosphate and nitrate content over four weeks Figure 2 states that the initial phosphate level started at 0.25mg/L and stayed constant throughout the four weeks. The initial nitrate started at 0.0mg/L and also stayed constant throughout the four weeks. Both remained unchanged throughout the experiment.

Temperature/of/Water 25

Temperature/(ºc)

20 15 10 5 0 1

2

3

Week Figure 3: Temperature of water over 4 weeks

4

Figure 3 shows that the initial temperature of the water started at 18.9ºC and had a gradual increase until week four where it dropped from 22.8ºC to 22ºC. The ecosystem was kept in a glasshouse on a rooftop with an average temperature of 19.2ºC.

pH*Level*of*Ecosystem 12 10

pH*Level

8 6 4 2 0 1

2

3

4

Week Figure 4: pH levels over 4 weeks

Figure 4 indicates that pH had a steady increase over the four weeks. The pH level had an initial reading of 7.8 stating that the water was at a neutral level and rose to a level of 9.6 showing that over the four weeks the water in the ecosystem was gradually becoming more alkaline.

Dissolved0Oxygen0Levels Dissolved0Oxygen0(mg/L)

16 14 12 10 8 6 4 2 0 1

2

3

4

Weeks Figure 5: Dissolved oxygen levels over 4 weeks Figure 5 reveals that the dissolved oxygen started at 10.19mg/L, increasing in week 2 to 13.28mg/L. However, this remained relatively unchanged for the last two weeks, ending on a reading at 13.25mg/L.

Salinity.Levels. 350

Salinity.(µs/cm)

300 250 200 150 100 50 0 1

2

3

4

Week Figure 6: Salinity levels over 4 weeks Figure 6 shows an initial reading 220.5µs/cm and had a spike increase in week 2. Over week 3 and 4 there was a gradual increase in salinity of approximately 10%, with a final result of 300µs/cm.

Biotic Components Table 3: Biotic components start and end results Name

Starting Measurements

Ending Measurements

Status

Vallisneria gigantea or Ribbon weed

Length from root to tip 42cm 12 leaves One

Length from root to tip 52cm 18 Leaves 2 new shoots

Alive

Lemna spp or Duck Weed

Coverage 20% of surface No roots or flowers visible

Coverage 60% of surface Roots 2cm long Flower growth

Alive

Pomacea spp or Mystery Aquatic Snails

One Alive Weight at 2.59 g Length 2.5cm

One Weight at 1.72 g Length 2cm

Dead

“Pond Life”

13mL added

Could not tell if increased amount

Alive

Freshwater Worm

One Length 2.5cm

Two Alive Worm one length 5.5cm Worm two length 1.5cm

  Week 1

Week 4

Figure 6: Increased Lemna spp coverage

Table 3 shows that for the Vallisneria gigantea, Lemna spp and freshwater worm the conditions in the aquatic ecosystem were ideal for growth and reproducing. All three components doubled in size and reproduced themselves. Vallisneria gigantea was observed in week 3 with an extra shoot and week 4 had produced another one. The Lemna spp was observed to have the development of flowers in week 2 however did not increase coverage until week 4 as shown in figure 5. The mystery snail was alive and moving around until week 4 where it was discovered that it had died. Due to the pond life being not being visible this was not measurable in the experiment.

Other Observations

  

Week 1 Week 2 Week 3 Figure 7: Colour and Clarity of ecosystem over 4 weeks

 Week 4

The most noticeable change was the clarity and colour of the water as seen in figure 7. The ecosystem began transparent with a slight yellow colour to it and no visible green algae. Over the weeks this progressively changed and by the end of week four there was a noticeable cloudiness to the water and green algae appeared on the walls, pebbles and Vallisneria gigantea. The colour had also changed to a slight green colour, this colour change would be due to the green algae growth on the plants and jar sides.

Discussion At the end of the experiment it was clear the aquatic ecosystem was partially functioning as there was plentiful plant life and the freshwater worm had reproduced and increased it’s biomass. Due to the mystery snail dying however, it shows that is was not as stable as hypothesised and progressively got less healthy. The predicted food web presented in figure one was not successful due to this outcome.

Algae has an important role as an energy source in producing oxygen for other organisms. Green algae was not present at the start of the experiment but continued to build throughout the weeks. Green algae need nutrients such as nitrate and phosphate to thrive. In figure 2 shows in this experiment this was not the case and could be due to the abiotic factors of warm temperature, shallow stagnate water and increase in pH (Trochine et al., 2010). The mystery snail was observed eating the green algae through weeks 2 and 3 but unfortunately died by week 4. The ideal temperature for these snails is 18-28ºC which was relatively maintained throughout the four weeks. However, there was a spike in higher temperatures at the end of week 3 reaching 35ºC. This is a result of an unusually sunny winter which could have contributed to the death of the snail. Food source was plentiful with green algae starting to grow from week 2. However the steady rise in pH levels as shown in figure 3 could be the reason for the death as these mystery snails prefer a neutral pH level of 7-7.5 (Bernatis et al., 2016).

The deceased snail provided food for the plants as well as the freshwater worm. It is unable to determine when the freshwater worm reproduced itself, for it was too small to see within the settlement. The ecosystem also had the ideal temperatures and pH levels as shown in figures 2 and 3, for the fresh water worm to thrive. As a decomposer, the worm had plentiful plant growth and decay which provided them with a large food source and helped recycle the nutrients back to the plants. The Lemna spp coverage also increased which was not noticeable until week 4. This could be due to the ecosystem not reaching optimal growing temperatures of between 20 to 31ºC until week 4. This plant has a very fast reproduction at these temperatures (Lasfar et al. 2007). It did however produce roots at 2.5 cm and also started to what is believed to be flowers. Due to the slow reproduction of the Lemna spp sunlight was

not blocked. This helped the Vallisneria gigantea to be the most successful biotic component in the ecosystem. The availability of nutrients increased the Vallisneria gigantea metabolic activity and allowed new roots and shoots to grow. As shown in table 3 it increased in length and leaves as well as new shoots (Bai et al., 2014).The new leaves increased the amount of sunlight captured therefore provided a high rate of photosynthesis which in turn lead to the increase in dissolved oxygen in week 2 shown in figure 5.

The experiment did have limitations as to the size and duration of the “ecosystem in a bottle”. A typical aquatic freshwater ecosystem is normally much larger in size and experiences a high amount of environmental factors such as pollution, depth of water, water flow and so on. The size of the ecosystem might have had limited nutrients aquatic ecosystem There were also limitations to the measurements taken as the nitrate and phosphate kits were not detailed enough to test slight changes and using equipment such as nitrate electrode, dissolved carbon dioxide sensor and phosphate electrode would provide an increase in reliability of these measurements. Abiotic measurements were only taken once a week, this decreases the reliability of the results. The experiment could also be improved by prolonging the length of time the experiment is observed for as well as recording the abiotic components measurements daily or even hourly. Improving these aspects will help understand the relationship between abiotic and biotic components.

The increase of biomass in the plants and freshwater worm show that conditions were stable until week 4. The death of the snail as well as the increased coverage of Lemna sp indicated the system might progressively become less healthy as there were no primary consumers left and sunlight would become increasingly scarce, putting a strain on the production of photosynthesis. The overall stability of the ecosystem during the study was only partially optimal and due to having a change of biodiversity this can cause sudden an imbalance of the ecosystem (Boero and Bonsdorff, 2007). The proposed hypothesis was not supported as some biotic and abiotic components became unstable, causing only some organisms to thrive.

References Bai, X., Chen, K., Zhao, H. and Chen, X. (2014). Impact of water depth and sediment type on root morphology of the submerged plant Vallisneria natans. Journal of Freshwater Ecology, 30(1), 75-84.

Bernatis, J., Mcgaw, I. and Cross, C. (2016). Abiotic Tolerances in Different Life Stages of Apple Snails Pomacea canaliculata and Pomacea maculata and the Implications for Distribution. Journal of Shellfish Research, 35(4),1013-1025.

Boero, F. and Bonsdorff, E. (2007). A conceptual framework for marine biodiversity and ecosystem functioning. Marine Ecology, 28,134-145.

Christensen, V and Pauly, D. (1993). Flow characteristics of aquatic ecosystems. In: ‘Trophic Models of Aquatic Ecosystem’. (Eds D. Pauly and V. Christensen, ed.) pp. 338-352. (International Center for Living Aquatic Resources Management: Manila)

Clout, M. (2015). An Introduction to Ecology and the Biosphere. In ‘Campbell Biology’. (Eds Reece, J., Meyers, N., Urry, L., Cain, M., Wasserman, S., Minorsky, P., Jackson, R. & Cooke, B.) pp. 1200. (Pearson Australia Group: Australia.)

Nhptv.org. (2018). Ecosystems - NatureWorks. [online] Available at: http://www.nhptv.org/natureworks/ nwepecosystems.htm [Accessed 24 Sep. 2018].

Hao, Z., Li, Y., Cai, W., Wu, P., Liu, Y. and Wang, G. (2012). Possible nutrient limiting factor in long term operation of closed aquatic ecosystem. Advances in Space Research, 49(5), 841-849.

Humbert, J. and Dorigo, U. (2005). Biodiversity and aquatic ecosystem functioning: A mini-review. Aquatic Ecosystem Health & Management, 8(4),.367-374.

Lasfar, S., Monette, F., Millette, L., Illette, L., and Azzouz, A. (2007). Intrinsic growth rate: A...