Environmental Systems & Societies SL's Sample Internal Assessment
How does the decomposition of sea shells (measured in terms of mass loss over a time period of 10 days) depend on the acidity of the medium (measured in terms of pH) it is immersed in and the type of sea shell?
Table of content
Identifying the context
Environmental issue
Increased Carbon Dioxide due to human activity in the atmosphere is absorbed by the ocean; carbon dioxide molecules react with water molecules to form carbonic acid. The pH level in the ocean drops thus increasing the acidity. Carbonic Acid is a weak acid, however when it is produced in huge quantities it makes the ocean highly acidic in nature. This process is known as Ocean Acidification. It poses a threat to the marine animals and sea shells present in the ocean. The skeletons of the seashells are made up of calcium carbonate. If the ocean or seawater is acidified, less carbonic acid is available for marine animals to create sea shells. If the ocean is extremely acidified, sea shells begin to decompose which makes organisms such as Oysters, Mussels, Mollusks, and more are vulnerable to being eaten.
The impact of Ocean Acidification remains significant specifically in India, Bay of Bengal. 30 sea surface samples, 4 marine sediments, and 28 sea shells, oyster, and coral reef samples were collected.
Topic
Investigation of the effect of Ocean Acidification and type of sea shells on the decomposition of sea shells.
Another survey that was conducted along the continental shelf from Northern Washington to Southern California, depicted high levels of ocean acidity impacting pteropods.
Pteropods are marine snails that swim near the ocean's surface and are a source of food for many other organisms such as salmon, mackerel, and herring. They are vulnerable to acidity because they build shells from aragonite, which is a soluble form of CaCO3, that is highly sensitive to acidity. The research was conducted during the upwelling season in California, where Co2 levels are high. The picture on the left indicates a healthy seashell and the picture on the right indicates the after effects of the shell dissolving in corrosive waters. Almost 53% of shells in the region had dissolved sea shells.
From the results that the researchers collected they found out that the percentage of Pteropods in this region with dissolving sea shells have doubled, and they predicted that it may triple by 2050.
This topic is also significant in the ESS syllabus in chapter 7, where we learn about climate change and how human activity such as the excessive use of fossil fuels leads to ocean acidification.
Connection of research question and environmental issue
The environmental issue that will be investigated is Ocean Acidification and how it will affect the decomposition of seashells. It is related to the research question because the independent variable in my investigation is acidity. The parameter that I will be using to describe the growth of the sea shells is the mass of the sea shell which I will be measuring. Also, I will be studying how the effect of ocean acidification varies depending upon the type of sea shells.
Planning
The investigation focuses on the north - eastern part of the bay. The study recorded the average pH level of 7.75 and the lowest value was recorded at 7.47. The average amount of bicarbonate recorded was 138.940. Indicating a strong positive correlation between the pH level and bicarbonate given a value of 0.930. Indicating that the bay was highly acidic. The chemical composition of oysters and mollusks was compared to their standard composition. The study investigated that about 17% of the chemical composure of the shells were reduced in comparison to their standard composition. It also showed that the shell membrane of the mollusks were directly impacted, making the shells weaker in nature. The chemical bonding of CaCO3 was broken down as well as the amount of CaCO3 in the shell membrane was reduced.
Variables
| Independent Variable | Justification |
|---|---|
| Acidity of the medium | The investigation will study the effect of acidity on the mass decomposition of sea shells, hence the acidity of the medium will be varied with different concentrations of vinegar (10%, 20%. 30%, 40%, 50%). As the concentration of vinegar increases, the acidity of the medium will also increase. It will be expressed in terms of percentage concentration. Where percentage concentration means that the volume of the acid is present within 100cm, if 10cc vinegar is taken, it will be expressed as 10% of vinegar. Vinegar will be used to replace carbonic acid since Vinegar is also a weak acid like carbonic acid. |
| Types of Seashells | The investigation will probe if the effect of Ocean Acidification is the same with all the biological varieties taken, or it depends upon the variety of the Sea Shells chosen for the investigation. Hence, different types of Seashells
|
Figure 6 - Table On Variables
| Dependent Variable | Justification |
|---|---|
| Decrease in mass of Seashells | The investigation will study how the acidity and the types of sea shells can impact the growth of the sea shells. The growth can be determined by its biomass, since the sea shells are composed of calcium carbonate which will undergo decomposition in the acidic medium releasing Co2 and water, so the mass of the sea shells will be measured over a definite period of time of 10 days and it will give a clear idea of the rate of decomposition. |
Figure 7 - Table On Dependent Variable
| Controlled Variable | Significance of control | Method of control |
|---|---|---|
| Volume of Acid added | If the volume differs, the rate at which the decomposition takes place will also be impacted and will differ. Hence, the total volume of the solution should be constant. | The exact value of a volume of 100cc will be added and measured with a measuring cylinder. |
| Type of Acid | The type should be kept constant, because if they are changed they may not have the same effect vinegar will have on the sea shells. Some acids may be stronger or weaker, hence the strength and nature of the acid will also impact how fast the rate of decomposition takes place. | The acid used for the investigation will be vinegar because it is a weak acid just like carbonic acid, however since carbonic acid cannot be obtained, vinegar will be used as a replacement. |
| Time period | The time period should remain constant for all sea shells to obtain accurate values. If more time is taken for certain sea shells kept in the acid, more they decompose and greater the loss of mass resulting in accurate data. | The time period for the investigation will be conducted over a span of 10 days. |
Figure 8 - Table On Controlled Variable
Materials and method
Procedure
- Type A sea shell was chosen.
- 25 plastic cups were placed on a flat surface and all of them were numbered.
- A digital mass balance was switched on, the sea shell was placed on the balance, and its initial mass was recorded.
- The mass of the petri dish was kept to 0.00 before placing the seashell on the balance.
- After recording the initial mass of the sea shells, it was placed inside each of the plastic cups.
- For the first 5 cups (1 - 5), 10cc of vinegar was transferred using a graduated measuring cylinder.
- Next, 90cc of water was added to all the 5 cups.
- This process was repeated with different variations of vinegar for the remaining 20 cups.
- 20cc vinegar, 80cc water (6 - 10)
- 30cc vinegar, 70cc water (11 - 15)
- 40cc vinegar, 60cc water (16 - 20)
- 50cc vinegar, 50cc water (21 - 25)
- The cups were kept for a time period of 10 days and then the new mass of the sea shells were recorded.
- The same procedure was repeated for type B and C sea shells.
Materials required
- Plastic cups - 100 cups
- Sea shells - 3 types
- Moonshell
- Turitella
- Lucine
- Vinegar - 5 L
- Digital mass balance
- Graduated measuring cylinder
- Tap water
All Seashells were purchased from the market and the equipment was provided from the school laboratory.
Data collection and processing
In Figure 25, Turitella and Lucine, change in the mass of both these sea shells is increasing as the percentage concentration is increasing. If there is more vinegar, or if the medium becomes more acidic, there is a higher loss of mass in the seashell. Hence, both Turitella and Lucine have been proven that an acidic environment is not favourable. Comparing the trend of Turitella and Lucine, Lucine has a steeper trend than Turitella. This means that the decrease in mass because of increasing the acidity of the medium is more impactful with Lucine in comparison to Turitella. Acidity is a harmful factor for seashells, more specifically Lucine, than Turitella. The findings for Moonshell are different. The trend line for Moonshell indicates that the change in mass is decreasing as the percentage concentration is increasing. There may be a few reasons why this could occur. It could be that the data collected was inaccurate or there was a random error in the experiment, or the seashell has certain biological features that allows it to produce more calcium carbonate as the acidity of the medium increases.
When the percentage concentration of vinegar is increased, from 10.00 to 20.00%, the change in mass is decreasing from 0.60g to 0.22g. From 30.00 to 40.00%, it is decreasing again, from 0.72g to 0.62g. Lastly from 40.00 to 50.00%, the concentration is increasing from 0.62g to 0.75g. Overall, there is no trend or correlation witnessed from the data obtained. However, the hypothesis states that higher the concentration of vinegar, there will be a higher loss of mass. The pattern obtained for Turitella and Lucine from Figure 25 is different from the pattern obtained from Moonshell. When a cumulative representation of all values is taken and if the data collected for Moonshell is inaccurate, it will affect the overall result of the data. Hence, this could be the reason why there is no proper correlation obtained for Figure 25.