Toward understanding the behavior of carbon dioxide and surface energy fluxes in the urbanized semi-arid Salt Lake Valley, Utah, USA

摘要

This paper describes the Salt Lake Valley urban flux study that was designed to understand the role of vegetation and urbanization on CO_2 and surface energy fluxes over surfaces typical of urbanized and pre-urbanized land cover in the semi-arid Salt Lake Valley. The eddy covariance technique was applied at two different sites with distinct land forms within an urbanizing mountain basin. One site was located in a suburban neighborhood with substantial mature vegetative cover (urban forest), prototypical of many residential neighborhoods in the valley, and the other site was in a pre-urban area. Results indicate that the suburban site was a net sink of CO_2 during the midday period in the summer due to photosynthetic activity and was a source of CO_2 during the evening and nighttime periods. The pre-urban site was a net source of CO_2 with positive fluxes throughout the day. Even though the vegetation at the suburban site sequestered carbon dioxide during the daytime in the summer months, the daily net CO_2 flux remained positive (i.e. a net source). In addition, the net CO_2 emission at the suburban site was found to be three times greater in the fall than during summer. The vegetative cover around the suburban site also had a significant impact on the partitioning of the surface energy fluxes. During the summer months, the contribution of the latent heat flux was substantially higher at the suburban site, while the sensible heat flux was much larger at the pre-urban site. The general behavior of the energy and CO_2 fluxes are consistent with typical climate modification due to urbanization in semi-arid climates (i.e. introduction of an urban forest), but quite different from changes reported in more mesic climates where highly vegetated regions are replaced with urban surfaces.