1. pH DO DIP TDP Bethany Remeniuk, Department of Biology, York College of Pennsylvania Is Microcystis aeruginosa an Initiator in a Positive Feedback Cycle Promoting Self-Growth? Introduction Microcystis aeruginosa is a cyanobacteria that inhabits the freshwater tributaries of the Chesapeake Bay. In recent years, it has been most noted for its role in Harmful Algal Blooms (HAB). A HAB is the rapid growth of phytoplankton that adversely affects other marine life. M. aeruginosa blooms often deplete oxygen from the environment thus killing off mass quantities of fish. Some strains of M. aeruginosa also produce toxins that can make people sick if consumed or swum in. The study conducted was done to determine if there was a possible positive feedback cycle involving the rapid growth of M. aeruginosa during a HAB. Conceptual Model By lowering the CO 2 concentration in the water, M. aeruginosa alters the pH from a normal range (7-8) to a very basic level (>9.5) while dissolved oxygen (DO) levels increase due to photosynthesis The lower pH induces a release of two types phosphorus from the sediments: dissolved organic phosphorus (DOP) and dissolved inorganic phosphorus (DIP) The phosphorus is taken up by M. aeruginosa, which the cyanobacteria require for growth and promotion of the bloom Because photosynthesis occurs only during the daylight hours, the reduction of photosynthesis at night creates a lag effect that is felt in a series of steps. As photosynthesis slows down, CO 2 is no longer being removed from the water, resulting in a decrease in DO and pH. Without a high pH to interact with the sediments, there is no release of phosphorus into the water. When sunlight is introduced to M. aeruginosa, the cycle begins anew. I would like to thank Dr. Jon Anderson and all the interns and staff at the Estuarine Research Center for all their help with this experiment A huge thank you to Dr. Nolan for all her guidance and input with both the poster and paper References Microcystis CO 2 pHpH PO 4 Acknowledgements Boers, P.C.M., 1991. The influence of pH on phosphate release from lake sediments. Water Research 25, 309-311. Seitzinger, S.Y., 1991. The effect of pH on the release of phosphorus from Potomac Estuary Sediments: implications for blue-green algal blooms. Estuarine, Coastal and Shelf Sciences 33, 409-418. Xie, L.Q. and Tang, H.J., 2003. Enhancement of dissolved phosphorus release from sediment to lake water by Microcystis blooms – an enclosure experiment in a hyper-eutrophic, subtropical Chinese lake. Environmental Pollution 122, 391-399. Figure 1. Experiment 1 and Experiment 2 average pH with error bars representing the standard error mean. Shading represents dark period from 9pm to 6am. 2-way ANOVA on Experiment 1 showed that M+S and +S was significantly different than +M. For both experiments, there was a significant change in pH over time. Results Conclusion M. aeruginosa in Experiment 1 had little photosynthesis occurring. Because CO 2 was not being removed from the water, DO levels were relatively low and the pH did not go above 9. Without a high pH to react with the sediments, no phosphorus was released into the water. M. aeruginosa in Experiment 2 had high levels of photosynthesis. CO 2 was removed from the water as shown by the high DO. pH levels increased above 9, resulting in the interaction with sediment and the subsequent release of phosphorus into the water. The lack of significance in Experiment 2 for pH can be attributed to the possibility of phytoplankton or algae that may have resided in the sediment core during the experiment. While the data follows the hypothesized trend of a positive feedback cycle, the lack of significance in the data observed means that the positive feedback cycle cannot be supported at this time. ResultsMethods Control Group 1: M. aeruginosa Control Group 2: Sediment Experimental Group: M. aeruginosa + Sediment Determine Possible Positive Feedback Cycle 24-hour acclimation of samples in a 28° C ± 1° C constant temperature room Collection of M. aeruginosa samples and sediment cores 1st experiment: Potomac River (death phase) 2nd experiment: Sassafras River (logarithmic growth) Control/ Treatment Groups used in 24-hour experiment A: M. aeruginosa B: Sediment C: M. aeruginosa + Sediments AB C M. aeruginosa 100x magnificationMicrocystis bloom in the Sassafras River Table 1. Change in TDP over 24-hour Experiment Experiment 12 DIP a 0.002 ± 0.0130.004 ± 0.06 DOP a -0.0070.058 TDP a -0.011 ± 0.0070.071 ± 0.022 Figure 2. Experiment 1 and 2 average dissolved oxygen with standard error mean bars. Dark period starts at the 9-hour point and ends at the 18-hour point. For Experiment 1 and 2, a 2-way ANOVA revealed that there was a significant change in DO over time. In Experiment 1, +M was significantly different from M+S and +S while in Experiment 2, +S was different from M+S and +M. a – mg of Phosphorus/ L (M+S) – (+M) – (+S) Figure 3. Total Dissolved Phosphorus for Experiment 1 and 2 with standard error mean bars. Total gain and loss of phosphorus every 3 hours over the 24-hour cycle based on combination of DIP + DOP. An ANOVA showed no significant change over time in phosphorus levels. Measure 24-hour experiment and observation period 15 hours light – 9 hours dark 2 replicates per treatment Objectives of Research 1. Measure pH and DO levels in the water 2. Collect phosphorus from water samples and analyze the total dissolved phosphorus (TDP), DIP, and DOP results 3. Determine if these factors play a role in a positive feedback cycle promoting M. aeruginosa blooms Future Research Have more replicates per treatment. Find a way to remove other phytoplankton from sediments without killing M. aeruginosa or releasing the phosphorus from the sediments prematurely.