Episodic Rainwater Movement in a Hydrophobic Sparta Sand under Three Ecosystems in Lower Wisconsin River Valley

Vegetation can directly affect soil water dynamics through rainfall interception and evapotranspiration. Vegetation type probably is one factor that causes soil hydrophobicity, and hydrophobicity can influence water infiltration and groundwater recharge. Surfactants can be used to alleviate non-wetting conditions. The objectives of this study were to determine the effects of vegetation type on soil water content and groundwater recharge and to explore if a soil-applied surfactant can increase both conditions. The research was located in the Lower Wisconsin River Valley (LWRV), on Sparta sand with three different vegetation ecosystems: prairie, pine plantation, and mixed prairie and forest (mixed vegetation); hydrophobicity has been found to be pronounced under pine plantations in the LWRV. Soil water content was monitored at three depths (5, 25, and 70 cm) with time domain reflectometry. Groundwater recharge was assessed by monitoring wells equipped with pressure transducers. Rain gauges and weather stations were installed to measure precipitation and air temperature. Soil core samples were collected for tests of saturated hydraulic conductivity (Kₛ) and bulk density (Db). Surfactant was applied on half of the plots after collecting several years of background data. There was significantly less soil water under the pine plantation than the prairie and mixed vegetation. Groundwater recharge did not vary among vegetation types, probably because differences were obliterated due to high aquifer transmissivity. The pine plantation had less profile drainage; however, the surfactant did not increase profile drainage. There were no differences in Kₛ and Db. The conversion from prairie to pine plantation resulted in reduced soil water content and drainage.