The alteration of biogeochemical cycles by anthropogenic activity has modified ecological interactions in ecosystems across the globe. In aquatic ecosystems, nutrient pollution has increased eutrophication, creating biological, chemical, and physical differences between low-nutrient (oligotrophic) and high-nutrient (eutrophic) lakes. Simultaneously, blooms of planktonic cyanobacteria are increasing in both types of lakes, with the potential to have substantial effects on ecological dynamics in them. The goal of this research is to determine the effects of cyanobacterial blooms on aquatic communities and ecosystems, and how nutrient pollution mediates the effect of cyanobacterial blooms on lake processes. Field experiments will be combined with an analysis of long-term data from the Global Lake Ecological Observatory Network to address these goals.
As cyanobacterial blooms increase in frequency and geographical range, understanding their ecological effects is increasingly critical for defining appropriate lake management strategies. Results from this research will inform lake management practices in New England, and will be disseminated to citizen scientists and schoolchildren via collaboration with a non-profit lake association in New Hampshire. The resulting global lake analyses will contribute to a limnology course for high school students and to laboratory modules for undergraduate courses.
Overview In the summer of 2010, we completed a large 40-cattle-tank experiment examining the effects of cyanobacterial blooms on aquatic food webs and nutrient cycling. Cyanobacterial blooms are a type of phytoplankton scum that form on lakes, reservoirs, and rivers, and can pose public health and ecological problems. Understanding their effects is increasingly critical because cyanobacterial blooms may be increasing in many aquatic systems due to climate change and eutrophication (increasing nutrients). The findings from this experiment have been prepared into four scientific peer-reviewed manuscripts, one Ph.D. dissertation, one undergraduate thesis, and five conference proceedings. Findings In the cyanobacterial blooms experiment, we manipulated zooplankton grazing pressure and trophic status to compare the effects of top-down and bottom-up controls on plankton food webs. In nutrient-limited mesocosms, experimental blooms of the cyanobacterium Gloeotrichia echinulata significantly increased small-sized phytoplankton in comparison to no-bloom controls, potentially due to G. echinulata’s leakage of fixed nitrogen and stored phosphorus. Surprisingly, G. echinulata’s stimulatory effect on phytoplankton was positively related to zooplankton biomass. Increased zooplankton biomass led to increased grazing of G. echinulata colonies, which may have increased the rate of G. echinulata’s nutrient leakage to other phytoplankton, thereby intensifying G. echinulata’s stimulatory effect. In contrast to G. echinulata’s positive effects on phytoplankton in the nutrient-limited ponds, G. echinulata blooms in eutrophic mesocosms had a negative effect on small-sized phytoplankton. Our findings indicate that in nutrient-limited systems, G. echinulata may subsidize plankton food webs through nutrient leakage, and thus could accelerate eutrophication. Furthermore, our data demonstrate the importance of trophic state in determining the effect of cyanobacterial blooms, thereby highlighting the context-dependency of G. echinulata’s effect on freshwater food webs. Training and Development This project provided research and teaching skills and experience to the co-PI Cayelan Carey, undergraduate thesis student Natalie Ruppertsberger (now a technician conducting biofuel research and preparing for graduate school) and technician Jennifer Brentrup (now a Ph.D. student in limnology). This project has enabled Carey to become proficient in nitrogen and phosphorus analyses, project management and mentoring undergraduates. Both Ruppertsberger and Brentrup received training in experimental design, field data collection, nutrient analyses, data management, statistical analyses and scientific writing. Outreach Activities The outreach for this project focused on five major activities: engaging the public in our research, education, mentoring, international collaboration, and conference organization. First, Carey gave five public presentations on aquatic ecology and my research to lake homeowners at the Lake Sunapee Protective Association office in 2011 and 2012. She also presented her research to homeowners and students at the University of Michigan Biological Station in Pellston, Michigan in summer 2011. Second, Carey is a collaborator on a project to develop undergraduate teaching modules in aquatic ecology and am a co-PI on a grant proposal through the NSF TUES program. Third, Carey mentored Ruppertsberger and Brentrup and directly supervised Ruppertsberger’s undergraduate thesis project. Fourth, Carey serves on the GLEON network-wide Steering Committee and GLEON Research Coordination Network Steering Committee and shared her experiences in conducting international network research in presentations at the GLEON 12 conference in Ramot, Israel and the GLEON 13 conference in Sunapee, New Hampshire. Fifth, Carey co-organized the GLEON 13 conference in Sunapee, New Hampshire in October 2011 with Kathleen Weathers. The conference’s theme was ‘Science at the Interface,’ and focused on incorporating citizen scientists into lake ecology research projects.
