Cold air drainage flows subsidize montane valley ecosystem productivity

Area of Science:

• Ecology
• Climate Science
• Biogeochemistry

Background:

• Cold air drainage significantly impacts local temperatures in mountainous regions.
• Temperature is a critical factor influencing ecosystem processes like carbon uptake and storage.
• Understanding these microclimate effects is crucial for accurate ecosystem modeling.

Purpose of the Study:

• To quantify the relationship between macroclimate, cold air drainage, microclimate, and ecosystem carbon cycling in a Southern Appalachian valley.
• To assess how cold air drainage influences local temperature and ecosystem respiration.
• To determine the impact of drainage flows on net carbon uptake.

Main Methods:

• Utilized new methods for interpreting ecosystem carbon flux data in complex terrain.
• Combined data from long-term climate stations and eddy covariance flux towers.
• Employed simple models for ecosystem carbon fluxes and chamber-based respiration estimates.

Main Results:

• Cold air drainage suppressed local temperatures by several degrees, reducing growing season respiration by ~8%.
• Drainage flows increased growing season and annual net carbon uptake by >10% and >15%, respectively.
• Reductions in aboveground biomass respiration were the primary driver of decreased ecosystem respiration.
• Enhanced carbon uptake was greatest under clear, dry conditions, a counterintuitive finding.

Conclusions:

• Cold air drainage plays a significant role in enhancing carbon uptake in valley microclimates.
• Current regional and global terrestrial ecosystem models may not adequately represent these topographic effects.
• Topographic flows could buffer ecosystem processes against macroscale climate change impacts.
• Further research into topographic influences on eco-physiological processes is warranted.