Wednesday, November 15, 2006

Land Use Effects on Soil Hydrophobicity and Groundwater Recharge in Three Temperate Ecosystems.

Mario Flores1, Birl Lowery1, James G. Bockheim1, Cynthia Stiles1, and Grizelle González2. (1) Univ of Wisconsin, Dept of Soil Science, 1525 Observatory Dr, Madison, WI 53706, (2) Int'l Institute of Tropical Forestry (USDA-FS), Jardín Botánico Sur, 1201 Calle Ceiba, San Juan, PR 00926-111

Nonwetting conditions have been found to decrease water infiltration into the soil, particularly sandy soils and under certain plants. Hydrophobic conditions have been documented for potato crops grown on sands in Wisconsin.  Preliminary data suggest hydrophobicity in Sparta sand under a pine plantation in the Lower Wisconsin River Valley. At this site groundwater quantity and flow of the Wisconsin River could be negatively impacted by hydrophobicity. We are evaluating the effects of soil hydrophobicity on soil water infiltration under prairie, native forest and prairie (mixed vegetation), and pine plantations. Time domain reflectometry probes, rain gages, monitoring wells and throughfall collectors were installed to evaluate water infiltration. Soil samples were collected every 5 cm from 0-50 cm and hydrophobicity tests performed using water and ethanol drop penetration. In addition, undisturbed soil samples were collected for measuring bulk density and saturated hydraulic conductivity. The hydrophobicity tests showed more cases of water repellency for all vegetations from 0 – 15 cm compared to 15 – 50 cm. The prairie and mixed vegetation sites did not have water repellency at depths lower than 15 cm, although the pine sites had water repellency to depths of 50 cm. There was no significant difference in saturated hydraulic conductivity and bulk density. There was no difference in rain throughfall between pine and mixed vegetation, but these were both significantly lower when compared to prairie. It appears that the groundwater table is lower in the pine plantation than prairie. Preliminary data show that the prairie and mixed vegetation had greater soil water content and flux than pine plantation after rain events. We anticipate that hydrophobic soils will negatively impact groundwater recharge, however hydrophobicity might be reduced by the use of a surfactant. Land use that negatively impacts groundwater recharge should be altered given the potential impact on groundwater quantity.