Soil moisture gradients and controls on a southern Appalachian hillslope from drought through recharge

Abstract

Abstract. Soil moisture gradients along hillslopes in humid watersheds, although indicated by vegetation gradients and by studies using models, have been difficult to confirm empirically. While soil properties and topographic features are the two general physio-graphic factors controlling soil moisture on hillslopes, studies have shown conflicting results regarding which factor is more important. The relative importance of topographic and soil property controls was examined in an upland forested watershed at the Coweeta Hydrologic Laboratory in the southern Appalachian mountains. Soil moisture was measured along a hillslope transect with a mesic-to-xeric forest vegetation gradient over a period spanning precipitation extremes. The hillslope was transect instrumented with a time domain reflectometry (TDR) network at two depths. Soil moisture was measured during a severe autumn drought and subsequent winter precipitation recharge. In the upper soil depth (0-30 cm), moisture gradients persisted throughout the measurement period, and topography exerted dominant control. For the entire root zone (0-90 cm), soil moisture gradients were found only during drought. Control on soil moisture was due to both topography and storage before drought. During and after recharge, variations in soil texture and horizon distribution exerted dominant control on soil moisture content in the root zone (0-90 cm). These results indicate that topographic factors assert more control over hillslope soil moisture during drier periods as drainage progresses, while variations in soil water storage properties are more important during wetter periods. Hillslope soil moisture gradients in southern Appalachian watersheds appear to be restricted to upper soil layers, with deeper hillslope soil moisture gradients occurring only with sufficient drought.

Topography may mitigate drought effects on vegetation along a hillslope gradient

“…Notwithstanding differences in soil texture, this manifests as lower θ d compared to downslope positions. This variation in soil moisture distribution with topographic gradients has been observed in other studies (Helvey et al, ; Pacific et al, ; Tromp‐van Meerveld and McDonnell, ; Yeakley et al, ). In southern Appalachians watersheds, hillslope soil moisture gradients were observed in the root zone (0–90 cm) during drier periods, indicating that topography exerted a more dominant control than soil properties in those periods (Yeakley et al, ).…”

Effects of rainwater harvesting on herbage diversity and productivity in degraded Aravalli hills in western India

“…Interestingly, increase in the difference in SWCs between USP and MSP in September indicated that soil texture is more important in controlling hillslope soil water during wet periods i.e., in September, while topographic features (slope gradient) showed more control on soil water in hillslope during drier period. This finding was similar to the observations (Yeakley et al 1998). Differences in soil water, SOM, total N, available N, P, K and the soil particle fractions of size <0.002 mm between different slope segments were also observed in other studies (Ge et al 2007).…”

Changing controls of soil moisture spatial organization in the Shale Hills Catchment

“…Soil properties, such as texture, rock fragment, and organic matter content also exert a first-order control on the ability of a soil to store and transmit water (Henninger et al, 1976;Maeda et al, 2006;Yeakley et al, 1998). Additionally, depth to bedrock and bedrock topography have been increasingly recognized as important controls on hillslope and catchment water movement (Buttle et al, 2004;Lin and Zhou, 2008;Tromp van Meerveld and McDonnell, 2005).…”