Seminar

Abstract

The Net Ecosystem Exchange (NEE) of CO2 was examined at the Boulder Atmospheric Observatory, a 300-m tall tower in Erie, Colorado. NEE was estimated as the sum of the eddy covariance CO2 flux (Fc) and the rate of change of CO2 storage beneath eddy covariance sensor height (Fs). The turbulent flux footprint of NEE, on average, extended to 15 km for 70% of the upwind source area and was comprised of a heterogeneous landscape in a region experiencing rapid population growth. Land cover classifications in the flux footprint were determined using Landsat 5TM imagery and pixel-based classification algorithms, while an annual timeseries of the Normalized Difference Vegetation Index was constructed from MODIS imagery. Near-surface remote sensing techniques were also employed to track seasonal changes in vegetation. Both biological influences (i.e., soil temperature and moisture, incident solar radiation, and seasonal greenness estimates) and anthropogenic influences (i.e., land cover class) were examined for their effects on NEE. Biological variables were shown to have relatively little effect on NEE in comparison to anthropogenic factors. Land cover class, however, had a significant overall effect on NEE, although the impact of individual land classes on NEE could not be determined due to a well-mixed landscape and poor spatial resolution in footprint modeling. In addition, the system was a strong net annual source of CO2 to the atmosphere, suggesting a dominant influence of anthropogenic activity over biological CO2 uptake. These results may be important in elucidating the effects of land use change on CO2 exchange and predicting future alterations in climate and air quality associated with a growing global population.