Yang Lu, Year 2 Research.
Abstract
Algae is an organism that is critical to ocean life. However, an increasingly acidic ocean due to climate change may harm important algae growth. This investigation aims to measure the possible effects of ocean acidification on algae growth. To do this, samples of algae will be grown at different pHs with increasing acidity and their growths compared with one another by cell count. The results demonstrated an inverse relationship between pH and algae growth, suggesting that an acidifying ocean could potentially have some positive effects on the growth of algae.
Introduction
Algae consist of a diverse group of aquatic, photosynthetic organisms. (Vidyasagar, 2016) The most common forms of algae include seaweed and kelp. (Vidyasagar, 2016) Algae play a critical role as the base of the ocean’s food chain. (Ecological Importance of Algae, n.d.) However, most importantly, algae’s photosynthetic properties allow it to produce an estimated 30 to 50 percent of the net global oxygen available on Earth. (Algae – Ecological and Commercial Importance, n.d.) Yet, an alarming issue present today is ocean acidification. Every year, a portion of the 50 billion tonnes of emitted greenhouse gases (Greenhouse Gas Emissions, n.d.) responsible for climate change are also dissolved into the ocean. This absorption of carbon dioxide has caused the pH of the ocean to drop by 0.1 pH units, meaning surface waters are now 30 percent more acidic than they were 200 years ago. (CO2 and Ocean Acidification, n.d.) Unfortunately, projections show that by the end of the 21st century, the ocean could potentially double in acidity. (CO2 and Ocean Acidification, n.d.)
However, algae shows promise as an important factor in the fight against climate change. Studies show that due to algae’s photosynthetic properties, large amounts of algae could be grown to absorb harmful CO2 gases, directly reducing the impacts of yearly greenhouse gas emissions. (Adeniyi, 2018, Sahoo, 2012) This grown algae also has other benefits; algae is highly reflective in comparison to water and can be added to reduce the amount of sunlight and heat absorbed from the sun. (Zhang, 2021) Algae can also be used to produce biofuels. As a form of renewable energy, these biofuels have the potential to replace pollutant-emitting fossil fuels, further reducing greenhouse gas emissions. Moreover, studies have shown that biofuels produced from algae may be the only form of biofuel capable of meeting the global demand for fuels. (Demirbas, 2010, Pires, 2017, Sahoo, 2012) There are clear potential applications of algae towards fighting climate change.However, it is still unclear as to what a lowering pH and acidifying ocean means to the growth of important organisms such as algae. Therefore, this experiment aims to investigate the impacts of pH in order to answer the question: How might ocean acidification affect the growth of algae?
Materials and Methods
Firstly, 1L of culture solution was made by mixing 1L of distilled water with 2ml of media formula f/2 and 2 bags of salt included in two algae culture kits (Algae Research and Supply). This 1L solution was then divided into one 250ml solution and five equal 150ml solutions. The pH of each of the five 150ml solutions was measured using a pH meter. Then, by adding vinegar to decrease the pH number and baking powder to increase, each solution’s pH was adjusted to one of five pH’s: 6.5, 7.0, 7.5, 8.0, or 8.5. The 8.5 pH was chosen to simulate the pH of the ocean before the industrial revolution when it sat at approximately 8.2. Currently, the ocean’s pH is close to 8.1, with the lower pHs helping to quantify the impacts of increasing acidity. A pH meter was used throughout the adjustments to ensure accuracy. 400µl of algae starter solution, also from the algae culture kits, were added to each 150ml solution. Finally, each solution was thoroughly mixed before being divided into three separate 50ml solutions. These were all poured into prepared glass flasks. In total, there were 15 solutions with 3 of each of the 5 different pH’s.
All algae samples were placed on a windowsill, under sunlight for twelve hours each day at a constant room temperature of 18 to 20 degrees. The leftover 250ml solution was stored alongside the samples. Two weeks after starting on March 15th, 15ml from the leftover 250ml solution was added to each of the fifteen samples. This was to ensure that none of the samples would dry out.
The growth period in total lasted for four weeks until April 5th. Afterwards, each solution was sampled, and a cell count was conducted using a hemocytometer and microscope. Results of the cell count were recorded by counting the number of algae cells populating a single square in one of the sets of sixteen squares. These values were multiplied by sixteen then 104 to calculate for cell density, or the number of cells per ml.
Results
Based on the growth of the algae, the experimental procedures of this investigation were successful. From the data, the sample of pH 6.5 saw the most algae growth, growing an average of 5.47 x 107 algae cells per ml, with the 8.5 sample having the least, growing an average of 4.19 x 107 algae cells per ml. The data therefore suggests an inverse relationship between pH and algae growth; an increase in pH is followed by a decrease in algae growth. The 8.0 pH and 7.5 pH solutions followed this trend. However, the 7.0 pH solution did not stay consistent with this trend.
Figure 1: Graph of Collected Data: Cell Density vs pH
Discussion
The aim of this investigation was to test the effects of acidity and lowering pH on the growth of algae.
The results of this investigation suggest that a decreasing pH and increasing acidity positively affects the growth of algae, causing the growth of more algae. There was a clear trend in the data that suggests that pH and algae growth had an inverse relationship; as pH decreased, the growth of algae increased. Additionally, it is noticeable that the solution of pH 7.0 deviated from the trend and grew less. This may have been due to procedural errors or potential contamination of the sample. However, this does not affect the overall findings of this experiment.
Similar studies conducted on the effects of pH on algae growth found that algae preferred an optimal pH within the range of approximately 4.0 pH to 7.0 pH, with decreasing rates of growth at higher pHs. However, within this range of 4.0 pH to 7.0 pH, the growth of algae did not differ much. (Gerloff-Elias, 2005, Bergstrom, n.d., Chen, 1994) The findings of this investigation are in line with the findings of past experiments, showing that the growth of algae at a pH of 6.5 is greater than the growth at higher pHs. However, the lowest pH tested was also 6.5, therefore this investigation is unable to calculate the lower bounds of optimal pH and determine whether or not lower pHs would produce even greater algae growth. This constraint should be remedied in a future experiment.
One of the limitations of this experiment was the pH adjustment of the culture solutions. The use of baking powder and vinegar to alter the pH of the solutions may have affected the growth of each algae sample differently because varying amounts of vinegar or baking powder were added to each solution. Another point of improvement is the cell count methodology itself. No dilution liquid was used in this investigation, leading to the hemocytometer squares to be crowded with algae cells. This may have caused the sizable differences in between trials.
If this investigation were to be carried out again, attention should be paid towards remedying the aforementioned limitations. Additionally, future experiments should take multiple samples throughout the four-week growth period to gauge individual growth rates more accurately. Different species of algae could also be tested. Finally, algae has had some promising results as a solution towards fighting climate change due to its ability to remove carbon dioxide from the air. Especially since the data gathered suggests that algae might benefit from ocean acidification, applications of algae toward removing CO2 from the atmosphere and fighting climate change could be explored.
References
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