HJ Andrews Airshed Project:
The Andrews Airshed Project utilizes the skills of a multidisciplinary team to improve the understanding of ecosystem processes in mountainous systems as well as develop a completely new approach for monitoring these processes. A primary goal of this project is to answer questions and test hypotheses about sources of variation in ecosystem-respired CO2 (d13CR) and airflow patterns in cold-air drainage, with the eventual aim of "inverting" this understanding so that we can use d13CR CO2 measurements to monitor intra- and inter-annual variations in ecosystem metabolism on a basin-wide scale.
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(Photo-animation by Eva LaMar)
Although we focus on a single watershed, we believe the principles learned will be applicable to many other mountainous systems. Interactions between vegetation and the physical environment are often very different in mountains than on flat land. Few studies address these unique interactions, and many of the tools currently being used to measure and monitor ecosystem metabolism are difficult or impossible to implement in complex, mountainous terrain.
Our premise is that when energy exchanges between the earth and the atmosphere cause cooling of the surface (occurring most frequently on cloudless nights), air adjacent to the surface cools by conduction, and the cool dense air tends to flow "downhill" along the gravity-driven pathways, creating "airsheds". We learned from a pilot study that very deep (> 30 m) and well-mixed drainage systems occur almost every night, and we were able measure pronounced seasonal variation in d13CR CO2 from air samples collected in the drainage system. We focused on d13CR because recent studies have shown that it is strongly influenced by conditions affecting recent photosynthesis.
In this study, we are initiating a long-term monitoring program of weekly measurements of d13CR CO2 in watershed 01 of HJ Andrews Experimental Forest. Long-term data, in coordination with pulse sampling, will help us explore the physiological health of the vegetation and estimate ecosystem respiration. The long-term monitoring of d13CR will be a valuable addition to the continuous measurements of stream flow and stream chemistry already being collected in this watershed.