Long-term measurements of CO2 flux and evapotranspiration in a Chihuahuan desert grassland

We measured CO2 and evapotranspiration (ET) fluxes above a Chihuahuan desert grassland from 1996 through 2001. Averaged across six years, this ecosystem was a source (positive flux) of CO2 in every month. Over that period, sustained periods of carbon uptake (negative flux) were rare. Averaged across all months, we estimated that CO2 was being released into the atmosphere at a rate of +1.5 g CO2 m−2 d−1 (+0.40 g C m−2 d−1) or +533 g CO2 m−2 yr−1 (+145.3 g C m−2 yr−1). Average ET was 299 mm yr−1 with a monthly range of 0.15 mm d−1 in December to 2.15 mm d−1 in August.