Higher-order closure turbulence modeling of long term carbon exchange in an old-growth temperate forest: implications for land-use and climate changes

Carbon dioxide concentration [CO2] and net ecosystem exchange of carbon (NEE) at the Wind River Canopy Crane Research Facility (WRCCRF) have been modeled for the period June, 1998 through December, 2003 (every ½ hour)using the University of California, Davis Advanced Canopy-Atmosphere Soil Algorithm (ACASA). The main goal of this work is to increase understanding of NEE between the old growth ecosystem at WRCCRF and the atmosphere in an unprecedented, sophisticated fashion, as well as providing a means to fill gaps in the observed records. Such gap-filling is useful in long-term assessments of NEE, as there exist vast uncertainties in how the terrestrial biosphere acts as sources or sinks of carbon, how these sources and sinks evolve over time, and how such exchanges will vary due to changing land use patterns and increases in [CO2]. Preliminary results suggest that ACASA is able to capture main features of the diurnal cycle of NEE and intracanopy [CO2], as well as seasonal and interannual variations in accumulated NEE at WRCCRF within observational uncertainty. Results also show that cumulative NEE estimates are sensitive to whether data gaps are filled or not, stressing the importance of developing adequate gap-filling strategies for NEE.