Further measurements of carbon dioxide concentration and flux in a large agricultural region of the Great Plains of North America

Abstract

Observations of CO2 concentration and flux made from June through September 1978 are reported for an area of typical agricultural land use in the east central Great Plains of North America (Mead, Nebraska). Data are compared with earlier observations made at the same site. An increase in carbon dioxide concentration of about 0.9–1.2 ppm per year has occurred in the intervening 5 years. This increase is in agreement with other globally distributed CO2 concentration measurements in oceanic and polar regions. Flux calculations were based on measurements made at elevations sufficiently high above the ground so that they represent an integration of the carbon dioxide exchange of the region generally rather than of a single field or crop. CO2 flux rates were greatest around middle to late July. The annual minimum in carbon dioxide concentration occurs during the same period. These observations suggest a distinct peak in photosynthetic activity in the region at this time. Not all crops behave in the same way, however. Large area CO2 flux estimates based on an extrapolation of data from individual crops or fields should be avoided.