Simulating the Effects of Water Pollution on Daphnia Magna

By: Joselyn G.
Year: 2022
School: Westminster High School
Grade: 10
Science Teacher: Huy Pham

The goal of the project is to determine at what concentration will Daphnia Magna (aquatic invertebrates) react to water pollution, specifically ammonium nitrate. We raised the daphnia in clear containers until they were able to reproduce. The negative control group was the optimal habitat for the daphnia, and the positive control group was a nonoptimal habitat (consisting of extreme temperatures, pH, and salinity).

To alter the temperature of the containers storing the daphnia, we used aquarium temperature controllers, and to alter the pH, we used acids and bases. The experimental control group will be the optimal habitat for the daphnia, but we gradually added in small concentrations of the pollutants (separately) into each container over a certain length of time.

Water pollution is a serious issue and we wanted to simulate the effects of water pollution (using ammonium nitrate) on Daphnia magna. We measured the heart rate of the Daphnia magna over time with different concentrations, from 0.00005 to 0.05 mol/L of ammonium nitrate, in 600 mL of purified water to determine Daphnia magna’s ability as an indicator of water quality. We observed the Daphnia magna had faster heart rates at higher concentrations, from 0.00005 to 0.005 mol/L, and died at a concentration of 0.05 mol/L because of their high sensitivity to toxins. In conclusion, our hypothesis that heart rate would have a negative correlation with concentration was false as the data proposed a positive correlation.

Water pollution is a major concern in our society with some drinking water containing unsafe levels of contaminants like lead (ex. Flint, Michigan). One contaminant in water is ammonium nitrate, found in fertilizer. Health concerns arise when nitrate levels exceed 10 mg/L, possibly causing increased heart rate, nausea, headaches, and abdominal pain. Ammonium nitrate causes algal blooms, an overgrowth of vegetation in water bodies (i.e. lakes, ponds, etc) from excess of nutrients.
As concerns for water pollution continue, some propose to monitor chemical contamination levels using Daphnia magna, because they are sensitive to toxins and can indicate water pollution. We hypothesized that Daphnia magna’s heart rate would have a negative correlation with concentrations of ammonium nitrate, as they usually die from toxin exposure. Using ammonium nitrate as an example pollutant for its common occurrence in water pollution, we explored the limits of Daphnia magna.

Overall, our study showed heart rate positively correlates with ammonium nitrate concentration, thus the data does not support our hypothesis. As concentration increases, heart rate increases, but high concentrations overwhelm and kill the Daphnia. Our results may not be accurate because of biased heart rates, colder temperatures while experimenting (Daphnia magna thrive at 18-22C), and long culture time (should’ve been tested after arrival).
We chose Daphnia magna because they are easy to examine (transparent bodies). Ammonium nitrate was used for its widespread use and effect on water pollution. For future experiments, we want to test mobility (how they move a certain distance) and other contaminants in water pollution to see their effect on Daphnia magna.