This study compares carbon and energy exchanges of turf in an urban ecosystem and that of a tallgrass prairie, identifies key drivers of these exchanges, and assesses the impact of urban sprawl in a semi-arid climate on carbon, energy, and water budgets. Close links were found between vegetation development, energy fluxes, and net ecosystem exchange of CO2 (NEE). Irrigation of turf influenced energy and carbon fluxes and contributed to the differences observed between sites. In comparison to tallgrass prairie, energy partitioning at the turf site was dominated by latent heat energy, directly affecting evapotranspiration. Cumulative turf NEE exceeded that of tallgrass prairie due to a longer growing season and higher daily net CO2 uptake. However, including carbon emissions due to turf management resulted in considerable offsets. The results suggest that lawns in Denver can function as carbon sinks and vegetation may therefore contribute to the mitigation of carbon emissions in urban areas to a certain degree.