Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2011
Publication Date: 4/25/2011
Citation: Gowda, P., Goolsby, J., Yang, C., Basu, S., Racelis, A.E., Howell, T.A. 2011. Estimating water use by giant reed along the Rio Grande River using a large aperture scintillometer. Subtropical Plant Science. 63:1-6. Interpretive Summary: Giant reed is an invasive weed from Eurasia. It is presenting a severe threat to native species in riparian areas in the southeastern United States. Giant reed is also known to consume excessive amounts of water. Very limited information is available on its water usage in the United States. In this study, we conducted a three day experiment along the Rio Grande River near Laredo, Texas, to measure water use by giant reed. Water use by giant reed was measured using a Large Aperture Scintillometer (LAS). On a day with clear skies in March 2009, the water use by giant reed was about 5.2 mm. The LAS is proved to be an invaluable instrument to measure water consumption by giant reed in riparian ecosystems. A long term monitoring of the giant reed is required to quantify seasonal and annual water demand.
Technical Abstract: Giant reed (Arundo donax L.) is a bamboo-like perennial invasive weed from Eurasia presenting a severe threat to agroecosystems and riparian areas in Texas and Mexican portions of the Rio Grande River Basin. It is known to consume excessive amounts of water to support its rapid vegetative growth rate. However, very limited information is available on its water usage in the United States. The objective of this study was to evaluate the use of Large Aperture Scintillometer (LAS) to estimate evapotranspiration (ET) rates by the giant reed in a riparian ecosystem. A three-day field experiment was conducted for this purpose during March 18-20, 2009 along the Rio Grande River near Laredo, Texas. A LAS was deployed at 1-m above the giant reed canopy (5.3 m above the ground level) for estimating sensible heat flux (H). Scintillometer measurements were made at 1-min interval and averaged to 15-min, synchronized with weather station measurements. In addition, net radiation (Rn) and soil heat fluxes (G) were measured. Latent heat fluxes (LE) and ET rates were derived as a residual, using LAS-estimated H in the energy balance equation (LE=Rn-G-H) and hourly ET values, computed from the hourly mean LE values and the latent heat of vaporization, were summed to obtain daily ET values. Analysis of the data for a day with clear skies (March 20, 2009) indicated that the daily water demand for giant reed was 5.2 mm. A long term monitoring of the giant reed canopy is required to accurately quantify the variations in water demand at different growth stages and meteorological conditions. Considering the capability to measure ET over heterogeneous landscape and relatively easy instrumentation setup, the LAS proved to be an invaluable instrument to estimate ET rates of giant reed in the riparian ecosystem. Scintillometer-based estimated water use data has the potential to be used as a ground truth to validate remote sensing based regional scale daily/monthly/seasonal water use maps covering giant reed areas in the Rio Grande River Basin and elsewhere.