| Approximately one half of terrestrial carbon runoff is processed by inland waters and released into the atmosphere as carbon dioxide (CO2) prior to reaching the oceans, and bacterial consumption of dissolved organic carbon (DOC) comprises a dominant proportion of this carbon loss. Though peatlands export more DOC per area than most other ecosystems, the sources and biodegradability of peatland DOC and their effects on downstream DOC loads and fluxes are poorly understood. Moreover, photochemical degradation plays an important role in the loss of carbon from aquatic ecosystems, especially in peatlands with high DOC concentrations rich in photochemically reactive humic and phenolic compounds, but its contribution to global CO2 evasion from inland waters has not been quantified. This dissertation focuses on predictors of biodegradable DOC (BDOC) in aquatic ecosystems, the sources and biodegradability of DOC in peatland watersheds, and the contribution of photochemical degradation of DOC to global CO2 evasion from peatlands and fluvial ecosystems. Key findings from these studies were that SUVA, a measurement broadly used in ecology and environmental engineering and fairly simple to obtain, is an excellent predictor of the amount of long-term BDOC concentrations in Minnesota lake ecosystems. The peatland bog may be the most important source of BDOC exported from peatlands annually, rather than the upland. And, photochemical enhancement of bacterial respiration in peatland and fluvial ecosystems contributes approximately 0.11--0.22 Pg C yr-1 to the total global CO2 evasion from inland waters (∼1.4 Pg C yr-1), or 9--18% of all inland water CO2 evasion. The results from this dissertation will lend insight into how future changes in hydrology and surface water DOC concentrations will alter the sources, biodegradability, and photochemical enhancement of DOC in aquatic ecosystems in the northern hemisphere, especially peatlands. |
