Congratulations to Jenny Bowen who successfully defended her thesis on Wednesday July 21st, 2021.
Advisor: Rose Cory
Freshwaters currently emit comparable amounts of carbon dioxide (CO2) to the atmosphere as the net amount taken up by all land on Earth, making it a critical component of the global carbon cycle. The amount of CO2 emitted from freshwaters depends largely on the sunlight-driven and bacterial degradation of dissolved organic matter that is derived from decaying plant biomass and gets flushed from land to freshwaters. Yet, it remains poorly understood when and where the sunlight-driven degradation pathway impacts freshwater CO2 emissions.
This dissertation investigated the importance of the sunlight-driven degradation of dissolved organic matter in arctic and temperate freshwaters by (1) evaluating whether sunlight-driven degradation is an important pathway for the conversion of old permafrost carbon to CO2 in the future as permafrost soils thaw, (2) quantifying the impacts of sunlight-driven degradation on the amount of CO2 produced in periodically shaded freshwaters, and (3) testing whether the sunlight-driven degradation of dissolved organic matter can provide an important source of inorganic nitrogen to freshwaters. The importance of the sunlight-driven pathway was tested using radiocarbon measurements, by scaling laboratory measures of dissolved organic matter degradation to rates in the water column, and by comparing those sunlight-driven degradation rates to other pathways. Together, the results from this dissertation demonstrate that the sunlight-driven degradation of dissolved organic matter can substantially impact freshwater CO2 emissions by degrading millennia-aged permafrost to CO2, making large organic compounds more susceptible to bacterial degradation, and converting organic nitrogen to an inorganic nitrogen source that supports primary production.