Lakes around the world are experiencing the excessive growth of algae and cyanobacteria. The causes for these changes are not fully known. In many lakes, the cyanobacteria are capable of producing toxins (cyanotoxins), which can negatively affect lake organisms and human health. While monitoring programs and laboratory experiments have increased in recent years, very little is known about the cyanotoxin ecology and the history of cyanotoxin production prior to human disturbances. This CAREER award will analyze sediment cores collected from over 25 lakes throughout the SE USA and Mexico and used to reconstruct cyanotoxin production and other lake important ecological factors through time. Three timescales will be investigated including modern human disturbance (past ~100 years), pre-modern disturbance (500 to 5000 years), and ancient human disturbance during Maya occupation around lakes in Mexico. This award will also provide educational materials, mentoring, and training to students from high school through graduate school with a focus on students from rural areas. <br/><br/>This CAREER award will test fundamental theories about state changes in lake ecosystems and the potential for early warning signs termed flickering by using paleolimnology to establish baseline conditions and past trajectories of cyanotoxin production in lake ecosystems throughout the Holocene. Unique experiments will be conducted using sediment-recorded historic disturbances of humans, nutrients, temperature and combinations of each to determine historic drivers of cyanotoxin production. A better understanding of cyanotoxin ecology during cultural and natural ecosystem change will improve the ability of forecasting models to predict how future climate, land use change, and lake management will influence cyanotoxin production as well as establish paleo-histories of cyanotoxin production. The establishment of cyanotoxins as a sedimentary tool could improve global paleolimnological investigations focusing on eutrophication as well as the monitoring of sediments for cyanotoxins. Finally, the measurement of cyanotoxins on Maya-occupied lakes could provide new understanding to the relationship between ancient societies and water quality as an analog to modern cultural eutrophication. A tier-mentoring system will be implemented to train high school, undergraduate and graduate students that will integrate various aspects of the project into educational curriculum including a study abroad trip to lake sites in Mexico, an undergraduate lab course on sediment analysis, and connections with high school students through classroom exercises. Results from this research will aid in the understanding, prediction, and impact of cyanotoxins linked to humans and lake eutrophication.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.