Impact of Vegetation on the Energy and Water Balance of a Temperate Wetland

Climate and vegetation can dramatically alter the water cycle on local to regional scales. A change in the surface water balance, especially in an arid region, can have significant impacts on the local water availability and therefore water resource management. The focus of this study is to understand the role of climate and vegetation in the energy and water balance of a riparian wetland in the central Great Plains. The site is located near the Republican River in southwestern Nebraska, where decreases in streamflow have been observed in recent decades. In an effort to reduce evapotranspiration and reclaim surface water, Phragmites australis is being removed throughout the riparian corridor of the river basin. In this study, we have installed meteorological instruments to conduct an energy and water balance of the wetland, before and after P. australis removal, using the Bowen ratio energy budget approach. This includes the deployment of a Large Aperture Scintillometer (LAS) to measure the flux of sensible heat between the wetland and the atmosphere. Together with measurements of net radiation and heat storage at two locations in the wetland, one area dominated by P. australis and another area dominated by native cattail and rush species, the energy balance is used to calculate the amount of water lost through evapotranspiration. Preliminary results indicate that relatively high sensible heat fluxes early in the season are soon displaced by strong latent heat fluxes during the remainder of the growing season. We also observe that the native and invasive plant species exhibit prominent differences in albedo and vegetation height early in the season, which dissipate as the season progresses. Lastly, we examine changes in the energy and water balance after herbicide treatment of P. australis late in the season.