Seasonal energy and water balance of a Phragmites australis-dominated wetland in the Republican River basin of south-central Nebraska (USA)

• Published in: Journal of hydrology (Amsterdam) 2011-09, Vol.408 (1), p.19-34
• Main Authors: Lenters, J.D., Cutrell, G.J., Istanbulluoglu, E., Scott, D.T., Herrman, K.S., Irmak, A., Eisenhauer, D.E.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; canopy; climate; Earth sciences; Earth, ocean, space; Energy balance; Enthalpy; equations; Evapotranspiration; Exact sciences and technology; Flux; Freshwater; Fundamental and applied biological sciences. Psychology; groundwater; growing season; Heat storage; heat transfer; hydrologic cycle; Hydrology; Hydrology. Hydrogeology; invasive species; Large Aperture Scintillometer; Mathematical analysis; phenology; Phragmites australis; quality control; seasonal variation; Seasons; soil; stream flow; surface water; Synecology; Terrestrial ecosystems; transpiration; uncertainty analysis; Vegetation; water analysis; Water balance; water temperature; water use; watersheds; Wetland; Wetlands
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2011.07.010

► The seasonal energy and water balance of a Phragmites australis wetland was analyzed. ► Evapotranspiration from the wetland averaged 4.4 mm day −1 (maximum 8.2 mm day −1). ► Net radiation and plant phenology were key drivers of ET and sensible heat flux. ► The Priestley–Taylor method performed well, except during the early growing season. ► The importance of heat storage in the canopy, water, and soil varied by timescale. Climate and vegetation strongly influence the water cycle on local to regional scales. A change in the surface energy and water balance, especially in dry climatic regions, can have a significant impact on local water availability and, therefore, water resource management. The purpose of this study is to quantify the energy and water balance of a riparian wetland in a subhumid region of the central US, as well as the role of seasonal climate variability and vegetation phenology. The site is located in the Republican River basin in south-central Nebraska, where decreases in streamflow have been observed in recent decades. In an effort to reduce consumptive water use from evapotranspiration (ET), and thereby reclaim surface water, invasive species such as Phragmites australis have been removed throughout the riparian corridor of the river basin. In this study, we used energy/water balance monitoring stations, a Large Aperture Scintillometer (LAS), and numerous water and soil temperature probes to determine the energy and water balance during the 2009 growing season (April 11−October 3). Sensible heat flux was measured using the LAS, while ET was calculated as a residual of the energy balance (i.e., net radiation minus sensible heat flux and heat storage rates in the canopy, water, and soil). Rigorous quality control and uncertainty analyses were performed, and comparisons were also made with ET rates calculated via the simpler Priestley–Taylor method. Results of the energy budget analysis indicate that the average ET rate for the wetland during the growing season was 4.4 mm day −1, with a maximum daily rate of 8.2 mm day −1 (occurring on June 29). Precipitation during the same 176-day period averaged 2.7 mm day −1. Net radiation and vegetation phenology were found to be the two largest drivers of seasonal variability in ET. Sensible heat flux was significantly larger than latent heat flux early in the season, when standing vegetation in the wetland was still dry and brown. By late May and early June, however, Bowen ratios had declined wel