Tuesday, November 6, 2007
184-4

Salt Movement in a Karst Soil – First Experiences with a Transfer Function Approach.

Ole Wendroth1, Xiufu Shuai2, and Riley Jason Walton1. (1) University of Kentucky, Department of Plant & Soil Sciences, Agr. Sci. North N-122M, Lexington, KY 40546-0091, (2) University of Hawaii at Manoa, Water Resources Research Center, Manoa, HI 96822

Water and solute movement through the vadose zone of soils developed on karstic bedrock and under agricultural use, deserve special attention with respect to observing flow phenomena and quantifying transport properties. So far, most studies on karst topographies have been focused on groundwater quality and the arrival of water and solutes to ground and surface waters. This study is a first attempt in this region to evaluate and quantify vadose zone transport phenomena and transport coefficients for salt and water movement. The objectives were to test the applicability of TDR-methodology, and to derive transport coefficients for salt movement, i.e., the pore water velocity and the dispersion coefficient. These were derived from input-output response, with four cycles of salt pulses applied to the land surface as input, and the electrical conductivity (EC) monitored as output. The analysis of time series was based on auto- and crosscorrelation functions of the various input and output time series, as well as their integration in the frequency domain. The transport experiment was carried out in a sinkhole profile on the Woodford County Experiment Farm of the University of Kentucky. Water and solutes were applied continuously for approximately three days, corresponding to four application cycles. First results show the applicability of the measurement technology and analytical procedure using the transfer function concept according to Jury and Roth (1992). The following transport coefficients were derived from this experiment: The pore water velocity was estimated to be on the order of 0.013 m/hr, and the dispersion coefficient yielded a magnitude of approximately 4•10-5 m2/hr1. The analysis was based on the assumption of spatial homogeneity in soil structure. Future analyses will include site-specific estimates and an evaluation of the hierarchical pore systems with different levels of water and solute mobility.