Eutrophication Lab Report

The purpose of the experiment was to determine which macronutrient, nitrogen or phosphorous, had a greater influence on cultural eutrophication. It was hypothesized that nitrogen would cause a greater algal growth rate due to its higher abundance required in plant growth. Nitrogen and phosphorous were tested separately, where the concentration of each was increased while the other remained constant. The results showed a positive increase in algal growth rate in the phosphorous samples and a negative relationship with increased nitrogen levels. In this way, phosphorous acted as the more significant nutrient in algal growth and should be controlled to prevent eutrophication.
I. Introduction Several nutrients are required for plants to grow,
For the nitrogen samples the concentrations for nitrogen to phosphorous used were 0 (control), 2:1, 16:1, and 64:1. For the phosphorus samples the concentrations for nitrogen to phosphorous used were 0 (control), 32:1, 16:1, and 8:1. The liquids were measured out using micropipettes so that 4 mL total made up a sample. The tubes were labeled at the top end and capped tightly. The samples were mixed gently before undergoing readings by the spectrophotometer. The spectrophotometer measured for absorbance, which was used to calculate initial cell density. The caps on each of the samples were then loosened to allow movement of gas in and out of the tube. After a week of growth under fluorescent lighting, the tubes were inverted for mixing and measured for absorbance again. The values were used to calculated the corresponding final cell density. The calculations of initial and final density of cells were used to determine the algal growth rate of cells per milliliter per
The initial measurements of macronutrients prepared to create the samples could have been incorrect. Inaccurate ratios of nitrogen and phosphorous would create different results. The overall dilutions of the stream water could also have influenced the results. Attempting to control the amounts of nitrogen and phosphorous in the solutions resulted in also limiting the amount of stream water in each sample of only 4 mL. Controlling the solutions in this way could have actually stripped the original stream water of its already present nutrients when the water was diluted. This would be another explanation for the negative growth rate present in the nitrogen samples. The phosphorous trendline was also fairly imprecise, with an R value of .67163. Another factor that could have influenced the data was the allowance of the samples to gas exchange. If the caps of the test tubes were not equally loosened, exposure to the atmosphere would be imbalanced, leading to various effects on the overall algal