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Coarse Fragments Affect Soil Properties in a Mantled-Karst Landscape of the Ozark Highlands

Al-Qinna, Mohammed, Scott, H. Don, Brye, Kristofor R., Van Brahana, John, Sauer, Thomas J., Sharpley, Andrew
Soil science 2014 v.179 no.1 pp. 42
alluvial soils, bedrock, bulk density, highlands, infiltration (hydrology), karsts, land use, landscapes, saturated hydraulic conductivity, soil depth, soil pore system, soil water movement, stony soils, water flow, Arkansas
The Ozark Highlands region of the mid-southern United States is characterized in many areas by thin stony soils overlying highly fractured and dissolution-prone carbonate bedrock that are highly susceptible to groundwater contamination. The objective of this study was to evaluate the effect of coarse fragments on soil physical and hydraulic properties within a typical mantled-karst landscape in northwest Arkansas. In 2002, three representative soil series (i.e., Clarksville, Captina, and Razort) that vary taxonomically in coarse fragment content were selected for investigation. The alluvial Razort soil had the largest coarse fragment content, ranging between 15% in the top 10 cm and 80% in the 90- to 100-cm depth, which strongly affected the soil’s hydraulic properties. With increasing coarse fragment contents with depth (P < 0.05) in all three soils, total bulk density increased with depth to approximately 1,400 kg m, whereas the soil bulk density markedly decreased to less than 500 kg m across all three soils in the 90- to 100-cm depth. Ponded infiltration measurements, which did not differ among the three soils, demonstrated that coarse fragments reduced the vertical one-dimensional volume available for water flow, increased the tortuosity, and reduced the hydraulic conductivity of the soil pore system. However, ponded intake measurements demonstrated that the soil surface properties of the alluvial soil generated greater two-dimensional water flow below the land surface once infiltration occurred. Transmissivity was roughly 35 times greater in the alluvial Razort compared with the residual Captina and Clarksville soils, resulting in greater estimated saturated hydraulic conductivity at the surface for the alluvial soil. The combination of results from this study shows that careful consideration of the coarse fragment content of the soil is necessary when managing land use in mantled-karst landscapes.