|Hunt, Earle - Ray|
Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/11/2004
Publication Date: 1/14/2004
Citation: Hunt, E.R., Kelly, R.D., Smith, W.K., Fahnestock, J.T., Welker, J.M., Reiners, W.A. 2004. Enviromental Management (Online) DOI:10.1007/s00267-003-9151-0, pages 1-10. Interpretive Summary: With large areas of the globe covered by rangelands and grazing lands, the potential for carbon sequestration is significant. There are two technologies which will help assess and monitor carbon sequestration, one is measurement of the net ecosystem exchange of carbon dioxide, and two is remote sensing using meteorological satellites. Remotely sensed vegetation indices such as the normalized difference vegetation index vary seasonally in rangelands in relation to the amount of carbon fixation by photosynthesis. This paper presents a method to determine the parameters necessary to estimate actual gross primary production from the normalized difference vegetation index, using the data of net ecosystem exchange. This method was tested using data at two sites, a sagebrush steppe ecosystem near Shirley Basin, Wyoming, and a northern mixed-grass prairie grassland near Chugwater, Wyoming. The sagebrush site was shown to be a net sink of atmospheric carbon dioxide, whereas the grassland site was shown to be neither a source or a sink. This method will not work for all ecosystems, particularly forests, where there is little seasonal change in normalized difference vegetation index resulting from stresses on photosynthesis. For rangelands, the seasonal changes are large so it is possible to map carbon sequestration for US rangelands if there is a sufficiently large network of sites measuring net ecosystem exchange of carbon dioxide.
Technical Abstract: With large areas of the globe covered by rangelands, the potential for carbon sequestration is significant. Aircraft eddy flux measurements of net ecosystem exchange were acquired in 1999 over two southeastern Wyoming landscapes, a mixed-grass prairie and a sagebrush steppe. A linear relationship between net ecosystem exchange (NEE) and the absorbed photosynthetically active radiation (APAR) was used to determine the efficiency of radiation use, which can be used with remotely-sensed vegetation indices to calculate gross primary production (GPP). Chamber measurements of ecosystem respiration in 1998 and 1999 were used to develop a functional relationship with daily average temperature; the Q10 of the relationship was 2.2. Using Advanced Very High Resolution Radiometer normalized difference vegetation index data (NDVI) and incident photosynthetically active radiation to determine APAR, GPP and respiration and were calculated for 1995 to 1999. The sagebrush site was a net carbon sink, whereas the grassland site was in carbon balance. The use of remotely-sensed NDVI avoids problems associated with small-scale sampling to determine areas of carbon sequestration; net ecosystem flux measurements are important data to parameterize these NDVI models.