Carbon Flux of an Urban System in México

Keywords: borderlands carbon emissions ecosystem carbon balance industrial ecology solid waste flux urban development Summary We estimated vertical and lateral fluxes of carbon for the isolated coastal city of Ensenada (Baja California, MIn 2005, the city had a resident population of about 261,000, with tourism adding about 1.5%; it occupied an area of roughly 68 square kilometers (km 2 ). Carbon (C) export was esti- mated at 400 gigagrams of carbon per year (Gg C/yr); no- table sources to the atmosphere were combustion engines (42%), cement production (38%), water heating and cook- ing (7%), and human respiration (6%). Solid waste (6%) was exported for burial, but efflux to the bay was minor (about 0.1 Gg C/yr). Local deposition was limited to sewage sludge (about 2 Gg C/yr), asphalt, and extremely low primary pro- duction. Remote fluxes driven by local demand could be es- timated only for electricity (61 Gg C/yr), but local flux from cement and other industrial production might be attributed largely to external demand. The urban system output to the atmosphere was about 6.4 kilograms of carbon per square meter per year (kg C/m 2 /yr), or roughly 23.6 kg/m 2 /yr in CO2 equivalence. By comparison, net ecosystem productivity in the surrounding watershed has been estimated at 0.04 kg C/m 2 /yr, so the city's atmospheric output of C might be balanced by productivityoverabout11,000km 2 ofthesurroundingecosys- tems. Between 2000 and 2005, C output increased faster than population growth, particularly from engine fuels.