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 (CO2), 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. CO2 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 CO2 concentrations led to high emissions on a per area basis during low flow times, but whole‐channel stream CO2 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 CO2 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.

Demystifying the particulate black carbon conundrum in aquatic systems

“…Bowring et al [25] highlighted the challenges of constraining the impact of fire derived carbon offsets on the terrestrial C balance due to lack of understanding of the mineralisation of BC in aquatic systems. In riverine systems, the transport and transformation of C are controlled by the residence time, which is indirectly governed by the flow regime of the river system [26,27]. The effect of modulations of river channels on the BC cycling is still unknown.…”