Seasonal changes in surface bulk density and saturated hydraulic conductivity of natural landscapes

Soil surface bulk density (rho(b)) and saturated hydraulic conductivity (Ks) control many land-surface processes such as water flow, chemical transport and soil erosion. The objective of this study was to examine seasonal changes in surface rho(b) and Ks in natural landscapes with few human activities. Measurements of rho(b) and Ks were made on undisturbed soil samples taken from the soil surface (0-0.05 m) five times from October 2007 to March 2009 along four natural transects in a small watershed on the Chinese Loess Plateau. The transects represented four landscapes with different vegetation and soil typical in this region. Results showed that rho(b) and Ks varied seasonally. Temporal changes in Ks generally followed the temporal patterns of rho(b). According to the mean values of all landscapes, bulk density decreased by 1.6 and 1.1% and log(10)-transformed Ks (Log(10)Ks) increased by 11.0 and 5.8% from October 2007 to March 2008 and from October 2008 to March 2009, respectively; bulk density increased by 2.1% and Log(10)Ks decreased by 4.9% from March to June in 2007; from June to October in 2007, bulk density decreased by 1.3% while a slight increase (1.4%) in Log10Ks was observed. Both landscape and time significantly influenced rho(b) and Ks, and Ks was more susceptible to temporal change than rho(b). Spatial patterns of rho(b) and Ks did not change significantly with time. Saturated hydraulic conductivity measurements taken in different seasons can affect runoff simulation results, and Ks data measured in spring may result in underestimation of runoff in a rainy season.