| A study was conducted to evaluate preferential flow of water and a conservative solute in three stony soils in the mantled karst landscape of the Savoy Experimental Watershed in northwest Arkansas. A broadcast application of 2.33 kg of Br - as KBr was applied to a 100-m2 plot within the Razort gravelly silt loam and Captina cherty silt loam, while 2.33 kg of Cl- as KCl was applied to the Clarksville cherty silt loam. Soil samples were collected three times, following cumulative rainfalls of 63, 196, and 418 mm, on a 25-point grid in 10-cm increments to a depth of 1 m. Soil water movement was traced using the direct method of dye tracing with Rhodamine WT and indirect methods of water and temperature variations using time domain reflectometry (TDR) and soil thermistors, respectively. Results showed that the soils of northwest Arkansas were dominated by the presence of stones and coarse fragments resulting in preferential flow paths that accelerate water and solute movement to the groundwater. The presence of significant gravel content in the soil profile markedly affected the soil hydraulic properties by disrupting the continuity of soil pore system and providing a random distribution of large voids among coarse fragments that had no direct contact with the fine soil textural fractions. Solute transport in the three soils was dominated by convective flow that was more dominant in the Razort soil, which contained greater amounts of the coarse fragments, than in the Clarksville or Captina soils. Autocorrelation analyses and two-dimensional kriged maps revealed the dominance and patterns of preferential flow as the active solute movement mechanism in the early stages of solute transport. Direct and indirect water and solute tracing indicated that the soils exhibited unique structure where water and solute flowed rapidly through the large pores, channels, root holes, and worm holes. Mathematical modeling showed that neither the Convection-Dispersion Equation (CDE) nor the Convective Log-normal Transfer (CLT) model could adequately describe concentration distributions under the conditions of macropore flow and natural rainfall. |
