The Effect of Phosphate on Biofilm Algal Numbers
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The Effect of Phosphate on Biofilm Algal Numbers By Riley Lehman, Ryan Martin, Adriana McMullan, Shelly Meyer, Jacob Phillips & Josiah Polito. Abstract

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The effect of phosphate on biofilm algal numbers

The Effect of Phosphate on Biofilm Algal Numbers

By Riley Lehman, Ryan Martin, Adriana McMullan, Shelly Meyer, Jacob Phillips & Josiah Polito


After hypothesizing that doubling the phosphate concentration will double the algae numbers, we filled two containers full of water from the Avenue of the Saints pond. For four weeks we sampled the microcosms, centrifuged, and then counted the algae. We also doubled the amount of phosphate in the experimental container each week.


Phosphate is a very important nutrient that limits the productivity of many algae in freshwater and marine environments. In fact, it is important to have a large supply of phosphorus because the phytoplanktons, kinds of algae, form the base of the food web. These species are responsible for half the photosynthesis on earth, they remove almost as much carbon dioxide from the atmosphere as all land plants, and supply half the oxygen we breathe. We tested our microcosm to see if the added concentration of phosphate was helping the algae grow.

Materials and Methods

Our microcosms consisted of two seventeen liter plastic containers each filled with 15 L of water taken from the samples of water in the 45-gallon garbage cans using a one liter graduated cylinder. One container was labeled “Experimental” and the other “Control.” The two containers were stored in the Biology lab’s greenhouse. After placing the two containers in the greenhouse, eight tiles were first cleaned and then four were placed into each container, one along each side of the container. We used the HACH DR/700 Calorimeter with PhosVer 3 Phosphate Reagent Powder Pillow for a 10 mL sample to determine the level of phosphate in the experimental container. The stock solution of phosphate used in the microcosms was NaPO4. Along with testing the phosphate level in the microcosms, we also tested the pH level and the conductivity. The HACH sensION5 conductivity tester was used to calculate the conductivity by placing it in the two containers and waiting for the display to stabilize and show a number. After calculating the levels of phosphate, pH, and conductivity, samples from each microcosm were taken and viewed using microscopes. Before adding new levels of phosphate to the experimental microcosm, a tile from each microcosm was removed in order to obtain samples to view. Ten different fields were viewed and the number of each organism was counted.


From our results, the group derived the general idea that the algae increased with the phosphate level because the algae thrived on the higher phosphate levels. Over the period of five weeks we increased the level of phosphate from 0.03 mg/L the first week to 2.09 mg/L the last week. Specific types of algae increased to different levels while other specific types of algae decreased. We have shown below the results of our control and experimental environments. We could not show all of the figures, but we put in the first sample, the middle sample, and the final sample.


Our findings proved our hypothesis that doubling the phosphate concentration will double the algae numbers. We experienced an increase in the total amount of algae found in the experimental environment. Not all of the specialized types of algae increased in number, but that was made up for by the excessive increase found in the other types of algae. Our experiment is very important because high/low levels of phosphate concentration can either hinder or benefit an ecosystem. Elevated levels of phosphate are some of the causes for trouble in the river runoff from fertilizers. Paddy fields and golf courses are a source of contamination after rainfall washes away the fertilizer. People need to know this because it greatly affects the ecosystem. Our experiment helps to discover the rate at which the algae increases and the types of algae that do or do not increase in number. Researchers need to study the water quality so people and other organisms do not get hurt. Water quality and periphyton structure differs significantly between sites upstream and downstream of the discharge. Typha latifolia, a type of periphyton, is a useful indicator of the impact of waste waters on the biota and can also be used to evaluate water body recovery. This is a type of algae that might be useful to study if we were to do our experiment again. Our experiment can benefit other people and the environment by helping future studies.