Impacts of urbanization on land-atmosphere carbon exchange within a metropolitan area in the USA

Abstract

Urbanization can cause changes in carbon fluxes, which, in turn, impacts atmospheric carbon dioxide (CO 2 ) concentrations and possibly global surface temperatures. Using the Atlanta, Georgia, region as a case study, this paper explores the impact of urban expansion from 1973 to 2002 on land -atmosphere carbon exchange. The major objectives were to estimate net ecosystem production (NEP) values for multiple land-cover classes and to link urbanization-induced changes in land-cover to changes in NEP and overall carbon fluxes. The principal data were daily climatic data, year-specific land-cover data, annual net ecosystem exchange (NEE) values, and annual anthropogenic carbon emissions estimates. The principal methods were testing for climatic trends, determining the composition of the land-cover classes, estimating annual NEP values for the land-cover classes, and estimating the overall carbon exchange. The major findings: (1) there were no significant trends for any of the climatic variables; (2) the region was only ~16% urbanized in 1973; however, by 2002, the region was ~38% urbanized; (3) the NEP in 1978-1980 of 443 g C m -2 yr -1 may have continued until 1996-1998, despite the substantial loss of forest land; and (4) net carbon emissions increased from ~150 g in 1978-1980 to ~940 g C m -2 yr -1 in 1996-1998. Therefore, urban expansion greatly increased the carbon emissions of the Atlanta region; however, it is possible that, through increasing the growing-season length as well as increasing nitrogen and CO 2 fertilization, urban expansion may not decrease the region-wide NEP.