Effects of evapotranspiration partitioning, plant water stress response and topsoil removal on the soil moisture regime of a floodplain wetland: implications for restoration

Understanding how the soil moisture regime changes following hydrological restoration activities in wetlands is essential for managers interested in establishing targeted wetland vegetation species. Based on observations from two floodplain sites in southwestern Wisconsin, a variably saturated hydrological model was developed and used to illustrate the importance of changing evapotranspiration (ET) partitioning [through changes in leaf-area index (LAI)], the plant water stress function, and the thickness of a surficial silt-loam alluvial deposit on the soil moisture regime. Floodplain restoration activities at these sites consisted of removing a layer of post-settlement alluvium, which is a part of this deposit. Field observations following restoration of the pre-settlement floodplain surface at one of the sites show a drier soil moisture regime at 10 and 25 cm depths at the restored (RES) site than at the unrestored site even though the potentiometric surface in a shallow monitoring piezometer was closer to the surface at the RES site. Simulations show that four factors may have contributed to this observation of relatively drier soils at the RES site: (1) lower LAI increases soil evaporation, (2) anaerobiosis limits transpiration near saturation, (3) a confining unit inhibits upward flow of water, and (4) removal of a 0.5-m silt-loam layer decreases the reservoir of soil moisture available to plant roots. Our work suggests the importance of effectively characterizing parameters that affect ET partitioning (i.e. LAI), determining the appropriate plant water stress function, and considering the effect of floodplain deposits that act as confining units when simulating the hydrology of floodplain wetland ecosystems. Copyright (c) 2010 John Wiley & Sons, Ltd.