Water, Energy and Carbon Dioxide Exchange of a Riparian Mesquite Woodland

• Main Author: Edwards, Eric Alan.
• Other Authors: Shuttleworth, William James
• Language: en
• Published: The University of Arizona. 2002
• Online Access: http://hdl.handle.net/10150/191339

Fluxes of water, energy and carbon dioxide were measured above a riparian mesquite woodland for an entire growing season using the eddy covariance method. Measurements of water vapor and carbon dioxide concentration were contaminated by erroneous measurements caused by sunlight incident on the bottom window of the Infrared Gas Analyzer, although a procedure was developed to remove this influence from the calculated fluxes. Data analysis suggests that daytime fluxes were underestimated by approximately 10%, while nighttime fluxes are difficult to measure accurately as a result of atmospheric stability. The growing season appears approximately bounded by freeze events in the spring and fall. Within the growing season there are two distinct periods characterized by different precipitation regimes. During the early summer months there is little rainfall, and high vapor pressure deficits appear to cause partial stomata' closure in the afternoon, resulting in reduced fluxes of water vapor and carbon dioxide. Later in the year, during the summer monsoons, this closure no longer occurs and the fluxes remain high throughout the afternoon. Annual water vapor flux is approximately 60% of the atmospheric demand, indicating the mesquite trees limit transpiration despite having access to groundwater. Nighttime respiration appears to increase with soil moisture during the summer months, while there is little or no effect of temperature during this time.