In situ characterization of hydrologic properties of Sparta sand: relation to solute movement

Hydrologic characteristics of soils are of general significance for many land use activities because of their relationship to water and solute flow. Water plays important roles in soil genesis, agricultural productivity, and transport of potential contaminants to groundwater. Sandy soils in portions of the Lower Wisconsin River Valley (LWRV), dominated by Sparta sand (uncoated, mesic Typic Quartzipsamments), have been under intense scrutiny recently because of extensive atrazine (2-chloro-(4-ethylamino)-6-(isopropylamino)-s-triazine) contamination of groundwater. However, groundwater beneath broadly similar sandy soils elsewhere in Wisconsin, with similar land-use (crop) management and production potentials, does not show such contamination. The purpose of this study was to determine particular hydrological properties of Sparta sand of the LWRV for use in modeling solute flux, and whether these properties might be distinct from those of a dominant soil of another major intensively farmed agricultural area in Wisconsin. In situ measurements of hydraulic conductivity and pore water pressure of the Sparta sand were made with an automated time-domain reflectometry system and pressure transducer-equipped tensiometers, respectively. Hydraulic conductivity of unsaturated Sparta sand was significantly different (P<0.01) between monitored depths in the profile. The differences observed in hydraulic conductivity were correlated with morphologically and physically described soil profile features. Hydraulic conductivity values for Sparta sand ranged from approximately 1 × 10^-4 to 2 × 10⁸ ms^-1. This is about one order of magnitude greater than values reported for Plainfield sand (mixed, mesic Typic Udipsamments), a similar sandy soil, at comparable water content and profile depth. Water redistribution data for Sparta sand were fitted to a non-linear model of the form θ_v(ag)=0.261 (t+2.3)^-0.1475, where θ_v(avg) is the mean profile water content (m³ m^-3) and t is time (minutes).