The Effect of Nitrogen on Planktonic and Biofilm Microorganisms in a Pond Ecosystem Materials and Methods In order to prove our theory of oxygen depletion, and death of phytoplankton and consumers, we created a microcosm or a miniature representation of an aquatic ecosystem. We used 36 liters of water collected from the Cedar River, along with environmental debris such as rocks, pebbles, sticks, twigs, grass, and mud from the surrounding area. Our water sample was divided into three containers which we labeled as “Control,” our dependant variable with natural amounts of nitrogen, “Double”which we added twice the amount of existing nitrate to the solution. Our last bin was the “Quadruple,” where we combined four times the standing amount of nitrate. Weekly we collected biofilms from a scrape sample, as well as a water column sample from all three of our ecosystems. All specimens were centrifuged, stained, and refrigerated; afterward we counted the organisms found and made note. The conductivity, and nitrogen amounts within our microcosm were also collected before, during, and in the end of our experimentation. We carefully analyzed this data. Shortly into our testing our aquatic ecosystem went through anaerobiasis due to lack of oxygen. We removed the de-oxygenated water started from scratch but this time our method of carrying out our examination was different. We added mg/L to our “double,” and 9.14 mg/L to the “quadruple.” After replenishing our microcosms we once again measured nitrogen and conductivity, and this time added algae. We filtered eighteen liters of pond water and added six liters of the collected algae to each of our systems. We also aerated them to help our system survive. Through the remaining experiment we continued to collect scrape and water column samples, along with conductivity, nitrate, and dissolved oxygen levels. Our results for our second man-made aquatic ecosystem are as followed. Figure 3 A. Mean and Standard Deviation of the Quadruple Group Scrape Sample. Green filamentous algae were not present until the third week, but when compared to the control and double nitrate concentration groups this appearance was present sooner possibly showing some effect. The single celled algae and diatoms followed the dissolved oxygen curve and showed the anerobiasis well. Figure 3 B. Mean and Standard Deviation of the Quadruple Group Water Column Sample. When compared to the quadruple scrape sample the green filamentous algae in the quadruple water column were less prominent and later occurring. The single celled algae and diatoms followed the dissolved oxygen trend and both displayed the period of anerobiasis. Figure 1 B. Mean and Standard Deviation of the Control Group Water Column Sample. Green filamentous algae where not evident until week four, however, they followed the oxygen curve well. Both the single celled green algae and the diatoms directly correlated with the oxygen values, and displayed the point of anerobiasis well. Figure 1 A. Mean and Standard Deviation of the Control Group Scrape Sample. Green filamentous algae were not observed in this sample. The dissolved oxygen level directly correlated with the diatom counts. This figure shows the anerobiasis very well. However, the single celled algae appear to not be as affected by the lack of oxygen Figure 2 A. Mean and Standard Deviation of the Double Group Scrape Sample. The diatoms show slight decline when the oxygen levels dropped. The increase in organisms with the increase in oxygen is also displayed, however the anerobiasis point is not as noticeable. Green filamentous algae were not present until the fourth week. Figure 2 B. Mean and Standard Deviation of the Double group Water Column Sample. Both the single celled algae and the diatoms followed the dissolved oxygen values. The period of anerobiasis is present. Green filamentous algae were present week four but where not found again in week five. Introduction Many things can cause detrimental effects on an aquatic ecosystem. One of these negative effects is caused by nitrogen. When water is polluted by over fertilization, a process called eutrophication occurs (Eutrophication… ) The surplus of nitrogen feeds algae, which then overproduce. The algae eventually die and start to sink to the bottom of the body of water. Decomposer bacteria then break down the dead material, using the dissolved oxygen in the water, causing a depletion of oxygen. When there is such depletion that aquatic life can not survive, the body of water is known as hypoxic (Durkin 2003). The type of nitrogen that causes this is known as reactive nitrogen (Nr), which includes nitrogen compounds of ammonia, nitrogen oxide, nitric acid, and organic compounds of urea and proteins. Reactive nitrogen accumulates today unlike it did in the past. This is due to increased human output of reactive nitrogen due to combustion of fossil fuels and fertilization of crops (Galloway 2003). This group chose to see what effect nitrogen would have on the microcosm. The group was faced with many problems, including the microcosm going anaerobic, which was not an effect of the nitrogen. Even with this problem, a slight effect was seen from the nitrogen, even if not as great as would have been seen in a natural setting. Conclusions * Depletion of oxygen in aquatic ecosystems has a detrimental effect on photosynthetic life. * The loss of photosynthetic life leads to a lack of food source for consumers. * Nitrogen in high concentrations displayed the greatest influence on organisms, when compared to lower concentrations. Audra Schutte, Annette Fischels, Jerriel Berry, Aaron Timm, Sara Techau, Julie Schweinfurth