Variation of surficial soil hydraulic properties across land uses in the southern Blue Ridge Mountains, North Carolina, USA

Abstract

summary A full understanding of hydrologic response to human impact requires assessment of land-use impacts on key soil physical properties such as saturated hydraulic conductivity, bulk density, and moisture retention. Such properties have been shown to affect watershed hydrology by influencing pathways and transmission rates of precipitation to stream networks. Human land use has been shown to influence these soil physical properties as a result of erosion, compaction, and pore structure evolution. Our objective was to characterize soil physical properties under three land-use classes (forest, pasture, and managed lawn) in the southern Blue Ridge Mountains of southwestern North Carolina. A total of 90 points were sampled (30 in each land-use class) throughout a 983 km 2 study area. Saprolitic and alluvial soils were emphasized, and sites were selected that showed consistent land-use history over a period of at least 30 years. Particle size distribution, in situ saturated hydraulic conductivity (measured using an Amoozemeter compact constant head permeameter), bulk density, and volumetric moisture content at field capacity were measured at each point. Forest soils demonstrated markedly lower bulk densities and higher infiltration rates, and water holding capacities, than lawn and pasture soils. No soil property significantly differed between pasture and lawn. Mean values for each property were as follows (forest = F, lawn = L, pasture = P): saturated hydraulic conductivity (mm h 1 )– F = 63, L =7 , P = 8; bulk density (g cm 3 )– F = 0.8, L = 1.2, P = 1.2; volumetric moisture content (%) – F = 72%, L = 42%, P = 39%. Particle size distributions did not significantly differ among land-use classes or parent materials, and the differences between the hydraulic properties of forest vs. nonforest soils were attributed to compaction associated with land management practices. The magnitudes of differences between forest and nonforest infiltration rates suggest that widespread conversion of forest to other land uses in this region will be accompanied by decreased infiltration and increased overland flow, potentially significantly altering water budgets and leading to reduced baseflows and impaired water quality. Published by Elsevier B.V.