Abstract
The purpose of this experiment is to determine the effect of organic pollution, with regards to nitrogen and phosphorus, and ocean acidification on algal growth. Nitrogen and phosphorus and limiting nutrients necessary for increased algal growth, which is also known as eutrophication. The experiment was performed by placing culturing green algae into seven test tubes containing different concentrations of pollutants. The absorbance was then used to quantitate the effect of the pollutants on algal growth. The results of the experiment supported the hypothesis, that algal growth increased with increasing nitrogen and phosphorus concentration. However, it decreased with increasing acid rain concentration.
Introduction
Surface water pollution is among the primary issues affecting the environment. There are two types of surface water pollution, and they include organic pollution, which results in high organic content in aquatic ecosystems, hence eutrophication, and ocean acidification that lowers the pH of water bodies (Flynn et al., 2015). Both organic pollution and ocean acidification occur due to human activities, for instance, eutrophication occurs due to the improper use of nitrogenous and phosphoric fertilizers. On the other hand, ocean acidification is attributed to an increase in the amount of atmospheric carbon (IV) oxide, a by-product of burnt fossil fuels. It is known that pollution reduces water quality; thus, interfering with the aquatic ecosystem. This is because pollution and ocean acidification affect the availability of nutrients and the pH of water bodies thus impacting the growth of green algae. Algae are the primary producers in marine ecosystems, and they are involved in water pollution in several ways (Yothi et al., 2016). First and foremost, the increase of algal nutrients in water via organic effluents selectively stimulates the growth of algal species, therefore, resulting in massive surface growths that consequentially affect the water quality and restrict its use (Yothi et al., 2016). Moreover, certain algae that flourish in polluted water are toxic to fish, human beings, and animals (Yothi et al., 2016). Overall, since algae play a major role in the food chain of aquatic life, whatever elements that alter its population and species growth significantly affect all other succeeding organisms in the chain. Therefore, this suggests that algae can be regarded as a suitable bioindicator organism (Barinova et al., 2015). It can be used in identifying and qualifying the effects of pollutants on the ecosystem.
In this experiment, different solutions, nitrogenous solution, phosphorus solutions, acidic rain, stream water, and algae stock solution, were used to evaluate the effect of organic pollution and acidification on algal growth. This was achieved by measuring the absorbance. Therefore, based on the above discussions, the following hypotheses were formulated:
- Algal growth will increase with increasing nitrogen concentration.
- Algal growth will increase with increasing phosphorus concentration.
- Algal growth will decrease with increasing acid rain concentration.
Methods
Seven test tubes were filled with different concentrations of pollutants: control, low and high nitrogen solution, low and high phosphorus solution, and low and high acid rain solution. Equal amounts of green algae cultures were added to each test tube and inoculated for two weeks. After that, the degree of turbidity, which is indicative of algal growth, was measured using a spectrophotometer at an absorbance of 450nm and the results were recorded. A total of six trials were performed and the absorbance for each trial in distinct pollutants was summed up and averaged.
Results
Figure 1 shows an increase in algal growth inoculated in both the nitrogen and phosphorus solution as compared to the control. However, the rate of growth in the phosphorus solution was higher than the former. On the other hand, overall, in both the low and high concentrated acid rain, the algal growth was less than that in the control. In addition, with regards to concentration, solutions with high concentrations of nitrogen and phosphorus exhibited greater algal growth as compared to the lowly concentrated solutions. Conversely, in acid rain, the highly concentrated solution was characterized with a lesser algae population in comparison to the lowly concentrated solution.
Discussion
This experiment was based on the principle that organic pollution and ocean acidification alter algal growth, which in turn affects the turbidity of the final solutions, hence, the absorbance. As predicted, algal growth was observed to increase with increasing nitrogen and phosphorus concentration and decrease with increasing acid rain concentration. These results are reflected in Flynn et al. (2015), which showed that organic pollution and ocean acidification had an effect on algal growth. The development and proliferation of algal blooms are a result of a multitude of environmental factors comprising nutrients, temperature, and pH, among others. With regards to the first and second hypotheses, the primary nutrients contributing to eutrophication are phosphorus and nitrogen, and their availability can limit algal growth. Therefore, an increase in their concentration will lead to an increase in algal growth. However, Liebig’s Law of the Minimum states that only a single resource is capable of limiting the growth and reproduction of a particular species at a given time (Dolman & Wiedner, 2015). Therefore, with phosphorus and nitrogen being the most common limiting nutrients in aquatic environments, three resultant scenarios are probable for nutrient limitation. Most often, phosphorus is acknowledged to be the primary limiting nutrient, hence, it is most likely to limit algal biomass. Therefore, this explains the reason for greater algal growth in phosphorus solutions as compared to the nitrogen solutions.
On the other hand, the results supported the third hypothesis, algal growth decreased with the increase in the concentration of acid rain. This result is similar to a study conducted by Roleda et al. (2015) that illustrated a reduction in algal growth under high pH. Algae thrive in a specific range of 7-9; therefore, any deviation, for instance, lowering of the pH due to acidic rain will result in the disruption of cellular processes (Roleda et al., 2015). As a result, this will discourage the growth of green algae. This is explained by the reduction in the ability of algae to photosynthesize in basic water. When carbon (IV) oxide dissolves in water, it can exist in the form of either of its tree species depending on water pH. Only the ineffective species, bicarbonate, and carbonate ions are made available at neutral and high pH, respectively. Therefore, since the main species, carbon (IV) oxide, is unavailable, the ability of the algae to photosynthesize is impaired. This experiment had one major limitation, which was, it did not consider the species of green algae used. There are several species of green algae and each has its ideal environment for growth. Hence, it is possible that there might have been different species of green algae used in the experiment and this would interfere with the results. It is recommended that future experiments first identify the species of the green algae before proceeding. This will enable the collection of accurate results.
In conclusion, this experiment established that the combined effect of eutrophication and ocean acidification has an impact on algal growth, a bioindicator of water quality. Therefore, since green algae are the primary producers in the aquatic ecosystem, it is essential to keep their population in control. Furthermore, nonconformity in their growth has implications for water quality issues, for instance, harmful algal blooms, and other ecosystems.
References
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