Spatio-temporal patterns of soil moisture status highly affect the heterogeneity of soil water and solute transport and leaching of chemicals to the groundwater. In order to quantify and describe spatial variability of ecologically highly relevant spatial and temporal processes linked to soil moisture at the land surface, the spatio-temporal covariance structure and the reasons for its change in time need to he identified. Therefore, soil water pressure head was monitored in two surface horizons between April and November 1995 at two field sites with a shallow ground water table, a sandy loam and a heavy clay soil in north-east Germany. For the 10- and the 30-cm depth of the sandy loam soil and for the 30-cm depth of the heavy clay soil the variance of soil water pressure head h (on log basis) was large under wet conditions. With decreasing soil water pressure head the variance of log10(- h) decreased to a critical value, for which a spatial correlation structure disappeared. With further drying, the variance of log10(- h) increased again, and a spatial range of correlation existed. During drying, temporally stable variation patterns developed at both field sites. The change of variance of log10(- h) which is probably associated with changing degree of heterogeneity of flow conditions validates the findings of Roth (1995) obtained from stochastic flow model calculations. In general, the temporal correlation length was better defined than that of spatial correlation. At both depths, correlation lengths of the sandy loam were larger than those of the heavy clay soil. Random spatial variation of log10(- h) occurred under conditions when the hydraulic gradient was close to zero. With our experimental design we could identify (i) temporal persistence of spatial patterns and correlation ranges of soil water status that can be used for representativity studies, (ii) the within-site variation of land surface moisture status, and (iii) a basis for description of spatial processes of effective soil properties that are linked to soil water status at the land surface.
|Number of pages||21|
|Journal||Journal of Hydrology|
|State||Published - Feb 1999|
Bibliographical noteFunding Information:
The authors are indebted to an anomnymous reviewer for his helpful suggestions on an earlier version of this manuscript. The technical assistance of N. Wypler, K. Seidel, I. Onasch, A. Griegoleit, M. Scholz, R. Hypscher, and J. Biese is gratefully acknowledged. This study was funded by the European Commission in the program ‘Analysis and improvement of existing models of field-scale solute transport through the vadose zone of differently textured soils with special reference to preferential flow’.
- Nested sampling
- Soil water pressure head
- Spatio-temporal pattern
- Variogram analysis
ASJC Scopus subject areas
- Water Science and Technology