DOES SOIL HYDROGEOCHEMISTRY MATTER? COMPARING ERODING AND NON-ERODING TERRA ROSSA IN EAST TENNESSEE

Carbonate (limestone and dolostone) derived terra rossa soils comprise approximately 20%, of the total land area of the contiguous United States (including Tennessee, Georgia, Montana, and Florida). Generally distributed on slopes of undulating karst landforms, terra rossa support agriculture and pasture land uses, and they are encountered as earth materials in both land reclamation and civil engineering projects. Soil erosion, relating to improper land management, is a serious land degradation problem in terra rossa, and results in rill and gully erosion. Erosion in terra rossa depends on external factors such as slope, precipitation intensity, and vegetation in addition to internal factors which include soil physical, mineralogical and chemical properties. The aim of this research is to examine the physical, chemical and hydrological properties of terra rossa with respect to gullying potential of the soil. The 0.58 square km (144 acre) study area is located at the East Tennessee State University Valleybrook research facility in Washington County, Tennessee. One-meter cores were extracted from two eroding and two non-eroding sites, and each core was partitioned into thirteen samples, a total of fifty-two samples. Clay mineralogy of each sample was determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) methods. Soil pH, grain size distribution (GSD), Atterburg limits, bulk density, moisture content, porosity, saturated hydraulic conductivity (Ksat), and swelling potential were also determined. The soils were classified as sandy loam, loam to clay loam and silty clay loam. Significant differences (p<0.05) existed between eroding and non-eroding soils for the following factors: clay and silt content, porosity, moisture content, K_sat, Atterberg limits, and swelling potential. Statistically significant correlations were established between clay content and Atterberg limits, bulk density, K_sat, and swelling potential. Variability in K_sat and swelling potential with depth observed in the eroding soils has been linked to soil erosion. Overall results indicate that selected physical and hydrological properties can be used as an indicator of gully erosion in southern Appalachian terra rossa.