Interannual variability seasonal dynamics of evapotranspiration of Arundo donax L. and populations of its biological control agent.

Authors: RACELIS, ALEX - University Of Texas Rio Grande Valley; Wagle, Pradeep; ESCAMILLA, JOSE - University Of Texas Rio Grande Valley; Goolsby, John; Gowda, Prasanna

Submitted to: Ecohydrology & Hydrobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2021
Publication Date: 8/10/2021
Citation: Racelis, A., Wagle, P., Escamilla, J., Goolsby, J., Gowda, P.H. 2022. Interannual variability seasonal dynamics of evapotranspiration of Arundo donax L. and populations of its biological control agent.. Ecohydrology & Hydrobiology. 22(1):178-187.

Interpretive Summary: Gaining a better understanding of the water budget in riparian areas is crucial, especially in water-limited. There is a growing body of evidence on the effects of invasive and non-native plants on the hydrology of water-limited rivers. Giant reed, woody grass native to the Mediterranean, is adversely affecting riparian ecosystems in southwestern United States by aggressively displacing their native flora and fauna. This study quantified evapotranspiration (ET), using the eddy covariance method, of giant reed stands along the Rio Grande River in Eagle Pass, Texas during the 2014 and 2015 growing seasons. A biological control program targeting giant reed was concurrently implemented by the USDA-ARS. Although the 2015 growing season was wetter, we observed larger daily magnitudes (7.7 vs. 6.07 mm) and seasonal budgets (842 mm vs 625 mm) of ET in 2014 than in 2015. Daily ET rates were strongly associated with the phenology of giant reed. Our study suggests that the reduction in ET in 2015 may be attributed to the presence of stem-galling specialist insect biological control agents at relatively higher density in 2015 than in 2014. The results of this study suggest that management of invasive plants, such as giant reed, can lead to significant conservation of water resources in arid regions like south Texas.

Technical Abstract: Giant reed (Arundo donax L.), a woody grass native to the Mediterranean, adversely impacts riparian ecosystems in southwestern United States by aggressively displacing their native flora and fauna. Giant reed has become a cause of concern for national water security, especially in water-limited areas of the arid southwestern United States, Australia, New Zealand, and South Africa. The main objective of this study was to provide the first, landscape-level estimates of water use by giant reed in the United States. The study utilized the eddy covariance method to quantify evapotranspiration (ET) throughout the 2014 and 2015 growing seasons along the Rio Grande River in Eagle Pass, Texas. We monitored ET concurrently with the implementation of a biological control program targeting giant reed by the United States Department of Agriculture-Agricultural Research Service (USDA-ARS). Daily magnitudes of ET reached 7.7 and 6.07 mm in 2014 and 2015, respectively. Daily ET rates were strongly associated with the phenology of giant reed, as estimated by degree day accumulation. Seasonal (DOY 121-304) ET was significantly higher in 2014 (842 mm) than in 2015 (625 mm) although the 2015 growing season was wetter. Our study suggests that this reduction in ET may be attributed to the presence of stem-galling specialist insect biological control agents at relatively higher density in 2015 than in 2014. Additional studies are needed to quantify the long-term water conservation and economic benefits of the biological control program in the Rio Grande Basin.