Fact Sheet 2012–3134
Gross primary production (GPP) and ecosystem respiration (Re) are the fundamental environmental characteristics that promote carbon exchanges with the atmosphere, although other exchanges of carbon, such as direct oxidation can modify net ecosystem production (NEP). The accumulation of carbon in terrestrial ecosystems results in systems in which soil organic matter (SOM) carbon often exceeds biomass carbon. This SOM pool exists at a steady state between GPP and Re in ecosystems unless drivers change or the ecosystem endures environmental perturbations (for example, climatic). Conversion of grasslands to agriculture and cultivation can result in reduced soil carbon, with the release of carbon dioxide (CO2) to the atmosphere by stimulated oxidation and higher Re; therefore, land-use and land management practices have clear effects on NEP, with potential repercussions on ecosystems. The recent demand for biofuels has changed land-use and cropping patterns, especially in Midwestern United States. It is important to ensure the sustainability of these and other land uses and to assess the effects on NEP.
Flux tower networks, such as AmeriFlux and FLUXNET, consist of a growing number of eddy covariance flux tower sites that provide a synoptic record of the exchange of carbon, water, and energy between the ecosystem and atmosphere at various temporal frequencies. These towers also detect and measure certain site characteristics, such as wind, temperature, precipitation, humidity, atmospheric pressure, soil features, and phenological progressions. Efforts are continuous to combine flux tower network data with remote sensing data to upscale the conditions observed at specific sites to a regional and, ultimately, worldwide scale. Data-driven regression tree models have the ability to incorporate flux tower records and remote sensing data to quantify exchanges of carbon with the atmosphere. Previous study results demonstrated the dramatic effect weather has on NEP and revealed specific ecoregions and times acting as carbon sinks or sources. As of 2012, more than 100 site-years of flux tower measurements, represented by more than 50 individual cropland or grassland sites throughout the Great Plains and surrounding area, have been acquired, quality controlled, and partitioned into gross photosynthesis (Pg) and ecosystem Re using detailed light-response, soil temperature, and vapor pressure deficit (VPD) based analysis.
First posted December 6, 2012
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Howard, D.M., Gilmanov, T.G., Gu, Yingxin, Wylie, B.K., and Zhang, Li, 2012, Net Ecosystem Production (NEP) of the Great Plains, United States: U.S. Geological Survey Fact Sheet 2012–3134, 6 p.
Grassland NEP in the Great Plains
NEP Uncertainty Assessment and Site Selection and Development of Future Flux Towers
Crop Type Mapping and Cropland NEP in the Great Plains