| Summary: | Climate change is dramatically altering the global carbon cycle. The warming caused by climate change is approximately twice the global average in Arctic and contiguous northern high-latitude regions, which are thus especially susceptible to ecosystem shifts (e.g. permafrost thaw, wetland drying/wetting cycle exacerbation). Rivers process and transport organic matter (OM) from land where warming is destabilizing previously stabilized carbon stocks to the ocean. This dissertation examines how fluvial OM in northern high latitudes responds to climate change, and how the fate of such OM may influence the global carbon cycle. Specifically, it focuses on how the source and processing of dissolved and particulate organic matter (DOM and POM) interact to dictate OM fate. To do so, Fourier-transform ion cyclotron resonance mass spectrometry, carbon isotopes (Δ14C, δ13C), and data on OM concentrations and carbon to nitrogen (C:N) ratios are used. Across the pan-Arctic (Chapters 2 and 3) and northeast Pacific coastal temperate rainforest (NPCTR; Chapters 4 and 5), sources appear to influence the fate of DOM (Chapters 2, 4, and 5) and POM (Chapter 3). Both landscape-scale factors like permafrost or agricultural extent (Chapters 2 and 3) and watershed slope and wetland extent (Chapters 3, 4, and 5), as well as specific source types like tree canopy or bark and soil layer (Chapters 4 and 5) impact OM molecular, isotopic, and elemental compositions and thus processing. Further, seasonality varies between the pan-Arctic watershed (Chapters 2 and 3) and the NPCTR (Chapters 4 and 5), leading to differential timing of the strongest terrestrial carbon source impacts on the system.In large pan-Arctic rivers, spring freshet contains DOM primarily sourced from terrestrial material but also includes a latent high-energy subsidy that explains the historical paradox of freshet DOM's bulk terrestrial composition but apparent high biolability. Winter riverine DOM is mostly sourced from old, microbially degraded groundwater DOM. This work ...
|
|---|