We combine field and lab work with biogeochemical models to understand the control of catchment and climatic variables on headwater lake biogeochemistry. Headwater lakes are ideal study systems because they are sensitive external influence. My students and I develop and apply biogeochemical systems models with field data, new sensor-based measurements, and geospatial information to pose and answer questions about how and why lakes change. This work will ultimately lead to predictive models that can be applied to issues such as the risk of low oxygen events, harmful algal blooms (HABs), lake ‘brownification’ (due to increased dissolved organic matter from catchments) and safe provision of drinking water under different climate scenarios.