Net CO2 emissions from dry inland waters persist in the presence of vegetation

Many inland waters are shrinking due to shifts in climate and water diversion for human uses. As they dry out, their exposed sediments emit large amounts of carbon dioxide (CO₂) to the atmosphere. However, current global estimates of CO₂ emissions from dry inland waters are derived exclusively from bare sediment dark-chamber measurements that do not account for the colonization of desiccated areas by vegetation. To understand the impact of vegetation on CO₂ emissions from dry sediments, we analyzed 164 dry inland water bodies across five climatic regions and five inland water body types (lakes, ponds, reservoirs, streams and wetlands). On average, within vegetated zones, vegetation occupied 47 ± 35% in measured biomass quadrants. Light-induced decreases in instantaneous CO₂ emissions in vegetated dry sediments were lower (mean ± SD = −3.7 ± 12.9 mmol CO₂ m⁻² hr⁻¹) than increases during dark conditions (14.7 ± 20.1 mmol CO₂ m⁻² hr⁻¹). Diel (24-hr) CO₂ emissions from dry, vegetated sediments (mean ± SD = 100 ± 261 mmol CO₂ m⁻² d⁻¹) were 25% lower than in bare sediments (133 ± 245 mmol CO₂ m⁻² d⁻¹). These results indicate that vegetation can partially off-set sediment respiration, although the magnitude of this effect is insufficient to switch dry beds from net sources to net sinks of carbon.