Wind Erosion:
An International Symposium/Workshop

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Carbon, Water, and Energy Flux Monitoring Towers on Konza Prairie Research Natural Area: The Effect of Land Management and Environmental Factors on Surface-Atmosphere Exchange

Jay M. Ham and Dale J. Bremer*
Kansas State University

http://anasazi.agron.ksu.edu/envphys/research/fluxes.html

The flux of carbon between terrestrial ecosystems and the atmosphere is an important process in the global carbon cycle. Understanding the biological and geochemical factors that govern the mass flux of CO₂ and other greenhouse gases are crucial if we are to predict the complex interactions among climate change, ecosystem responses to climate and greenhouse gases, and changes in land management. Unfortunately, we do not know which terrestrial surfaces are sources or sinks of atmospheric carbon, and we know even less about how climatic variation and land management will affect the C budget. Given that almost all grasslands on the Great Plains are under extensive management for agricultural production (grazing), it is critical to determine how human decisions such as burning frequency and livestock stocking rates may affect biophysical processes and net surface-atmosphere C exchange. Long-term, continuous measurements of CO₂ flux such as those provided by flux monitoring towers on Konza Prairie Research Natural Area and adjacent rangelands will help to answer these questions.

The main objective of this research is to study the dynamics of net carbon exchange between the surface and the atmosphere in a tallgrass ecosystem. Boundary-layer fluxes of CO₂ are being continuously monitored using conditional sampling (relaxed eddy-accumulation). Carbon fluxes are monitored on land under three different burning and grazing regimes. Questions to be answered include: (1) Is the tallgrass prairie a source or sink for atmospheric CO₂, and how do seasonal and interannual variations in climate (e.g., drought) affect the carbon budget?; (2) How does prescribed burning and cattle grazing affect carbon, water, and energy fluxes between the surface and the atmosphere?; (3) Which plant and soil processes govern net carbon exchange from the prairie, and can these processes be scaled or modeled to evaluate how trace gas fluxes might be affected by changes in climate or land use?; and (4) How do carbon and water fluxes from the prairie compare to fluxes from other mid-latitude ecosystems, and can carbon storage in prairie soils help mitigate anthropogenic CO₂ emissions?

In addition to CO₂ flux, the towers on Konza Prairie also continuously measure water vapor and energy fluxes. Data are collected throughout the year to determine the effect of seasonal variations in climate, precipitation, and land management on the terrestrial carbon, water, and energy budgets. Complementary biological and soil processes are also being evaluated to determine the underlying mechanisms influencing trace gas flux. These measurements include soil-surface CO₂ flux; leaf-level gas exchange; soil water content; plant species composition; and plant biomass and leaf area.

The towers are part of the U.S. Dept. of Energy's (DOE) Ameriflux CO₂ monitoring network (See website at: http://www.esd.ornl.gov/programs/NIGEC/) and therefore contribute to global C budget studies. Carbon flux data from the grassland will be archived for comparison with other terrestrial sites. This experiment complements an ongoing 9-yr DOE study investigating the effect of elevated CO₂ on grasslands. An additional study funded by NASA began in 1999 and is monitoring carbon fluxes over encroaching cedar forests in the tallgrass prairie. These works will provide a critical foundation for determining how grasslands and their management might influence or adapt to potential climatic change.

* presenter