Carbon Biogeochemistry and Export Governed by Flow in a Non‐Perennial Stream

Abstract Non‐perennial headwaters experience extremes in flow conditions that likely influence carbon fate. As surface waters contract through dry periods, reconnect during storms, and re‐expand or dry again, there is a great deal of variability in carbon emissions and export. We measured discharge, dissolved oxygen, carbon dioxide (CO 2 ), and dissolved organic carbon (DOC) continuously in a persistent pool at the base of a non‐perennial, forested headwater stream in the southeastern United States to characterize how flow changes affect carbon emissions and export as the stream expands and shrinks. We also compared carbon concentrations and export during different stream flow categories before and after fall wet‐up. CO 2 concentrations were high when discharge was lowest (median = 10.2 mg L −1 ) and low during high flows (3.2 mg L −1 ) and storms (1.1 mg L −1 ). High CO 2 concentrations led to high emissions on a per area basis during low flow times, but whole‐channel stream CO 2 emissions were limited by the small surface area of the stream during periods of surface water disconnection. DOC concentration varied by season (range = 0.1–16.2 mg L −1 ) with large pulses during smaller summer storms. We found that CO 2 and DOC concentrations differed among binned stages of stream flow. As non‐perennial streams become more prevalent across the southeastern United States due to shifts in climate, the relationships between flow and carbon movement into and out of stream networks will become increasingly critical to understanding stream carbon biogeochemistry.