The energy and water balance of a Phragmites australis dominated wetland in south central Nebraska was analyzed to assess consumptive water use and the potential for "water savings" as a result of vegetation eradication via herbicide treatment. Energy balance measurements were made at the field site for two growing seasons (treated and untreated), including observations of net radiation, heat storage, and sensible heat flux, which was measured using a large-aperture scintillometer. Latent heat flux was calculated as a residual of the energy balance, and comparisons were made between the two growing seasons and with model simulations to examine the relative impacts of vegetation removal and climate variability. Observed ET rates dropped by roughly 32% between the two growing seasons, from a mean of 4.4 ± 0.7 mm day-1 in 2009 (with live vegetation) to 3.0 ± 0.8 mm day-1 in 2010 (with dead P. australis). These results are corroborated by the Agro-IBIS model simulations, and the reduction in ET implies a total "water savings" of 245 mm over the course of the growing season. The significant decreases in ET were accompanied by a more-than-doubling of sensible heat flux, as well as a ~60% increase in heat storage due to decreased LAI. Removal of P. australis was also found to cause measurable changes in the local micrometeorology at the wetland. Consistent with the observed increase in sensible heat flux during 2010, warmer, drier, windier conditions were observed in the dead, P. australis section of the wetland, compared to an undisturbed section of live, native vegetation. Modeling results suggest that the elimination of transpiration in 2010 was partially offset by an increase in surface evaporation, thereby reducing the subsequent water savings by roughly 60%. Thus, the impact of vegetation removal depends on the local climate, depth to groundwater, and management decisions related to regrowth of vegetation.
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The authors would like to thank the private landowner (E. Reese) for generously providing access to the wetland so that this study could be performed. The authors also thank K. Von Buettner, S. Walters, T. Wang, B. Potter, and X. Lin for field assistance, as well as P. Snyder, A. VanLoocke, and other members of the Agro-IBIS modeling community for assistance with the model simulations. Some of the meteorological data for this study were obtained from the National Climatic Data Center (NCDC) and the High Plains Regional Climate Center (HPRCC). Funding for this study was provided by the Nebraska Environmental Trust (NET) , the University of Nebraska Water Resources Advisory Panel (WRAP) , McEntire Stennis Funds – USDA , and the University of Nebraska Rural Initiative . P. Mykleby would like to thank the Department of Earth and Atmospheric Sciences at the University of Nebraska-Lincoln for providing funding for his M.S. thesis work through a graduate research and teaching assistantship. The authors would also like to thank the anonymous reviewers for their time and energy helping to improve this manuscript for publication.
- Energy balance
- Phragmites australis
- Water balance