River corridors are impacted by natural and anthropogenic disturbances that can interact in complex ways. Hydrologic disturbances such as drought or prolonged dry periods cause flow cessation and sediment drying in nearly all river systems, particularly within parafluvial zones that experience intermittent drying and rewetting. These variably inundated systems commonly occur in arid regions where wildfire risk is elevated, creating opportunities for interactions between hydrologic and fire disturbances. Wildfires alter river corridor processes through changes in hydrologic connectivity and pyrogenic organic matter (PyOM) inputs, yet how variable inundation and PyOM interact to influence sediment biogeochemistry remains unknown. We hypothesized that dry sediments would exhibit slower oxygen consumption rates than wet sediments, and that PyOM and organic matter additions would have greater effects on respiration in dry versus wet sediments. To test this hypothesis, we conducted a full factorial laboratory experiment using sediments from wet (continuously inundated) and dry (intermittently inundated) locations within the Columbia River parafluvial zone. Following a 7-day pre-incubation, sediments were exposed to three treatments: synthetic river water (control), unburned Douglas fir litter leachate (9 mg C/L), and high-severity burned Douglas fir litter leachate (9 mg C/L). During the incubation, we measured dissolved oxygen consumption rates continuously using optical sensors, and post-incubation we analyzed dissolved organic carbon, CO₂, and nutrients. Our results showed that wet sediments exhibited significantly faster O₂ consumption rates than dry sediments regardless of treatment, supporting our first hypothesis. However, contrary to our second hypothesis, PyOM and unburned organic matter additions did not significantly affect respiration rates in either sediment type. Dry sediments released substantially higher water-extractable organic carbon concentrations compared to wet sediments, potentially masking treatment effects. We used process-based models to distinguish biotic versus abiotic contributions to oxygen consumption. Abiotic vs biotic rate ratios ranged from 0.08-0.2, indicating predominantly biotic control of oxygen consumption. Wet sediments showed slightly higher abiotic contributions than dry sediments suggesting greater initial chemical oxygen demand from reduced species accumulated during sustained inundation. These findings suggest that inundation history impacted sediment biogeochemical responses during rewetting more strongly than PyOM additions.