TEMPORAL PERSISTENCE IN VERTICAL DISTRIBUTIONS OF SOIL MOISTURE CONTENTS

Authors: Pachepsky, Yakov; GUBER, ANDREY - ARS VISITING SCIENTIST; JACQUES, DIEDERIK - SCK-CEN, BELGIUM

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2004
Publication Date: 1/3/2005
Citation: Pachepsky, Y.A., Guber, A.K., Jacques, D. 2005. Temporal persistence in vertical distributions of soil moisture contents. Soil Science Society of America Journal. 69:348-352.

Interpretive Summary: When a field or a small watershed is repeatedly surveyed for soil water content, sites often can be spotted where soil is consistently wetter or consistently dryer than average across the study area. The phenomenon has been called time stability, temporal stability, or temporal persistence in spatial patterns of soil water contents. Knowing the persistence patterns is important for soil management. It is also critical for establishing an efficient soil water monitoring network. Relatively little is known about temporal persistence of water content at various depths. The objective of this work is to demonstrate the temporal persistence in soil water contents measured on a vertical two-dimensional grid with TDR probes, and to propose a technique to utilize this persistence to remedy the effect of probe malfunctioning on the estimates of the average water content in the layer. Sixty two-rod TDR probes were installed along the trench in loamy soil at 12 locations with 50-cm horizontal spacing at 5 depths. The individual probes from the same depth generated time series of water contents that clearly demonstrated the temporal persistence in water contents. To quantify the persistence, we converted individual-probe water contents into water contents relative to their average from the same depth, and proposed and successfully tested a technique to use the relative water contents in estimating the average water content accounting for the missing data. The correction for temporal persistence can be useful in estimating average water contents and their uncertainty.

Technical Abstract: Temporal persistence in spatial patterns of soil water contents is important for soil management. Knowing it is critical for establishing an efficient soil water monitoring network. Relatively little is known about temporal persistence of water content at various depths. The objective of this work is to demonstrate the temporal persistence in soil water contents measured on a vertical two-dimensional grid, and to propose a technique to utilize this persistence to remedy the effect of probe malfunctioning on the estimates of the average water content in the layer. Sixty two-rod TDR probes were installed along the trench of 5.5 meter in loamy soil at 12 locations with 50-cm horizontal spacing at 5 depths (15, 35, 55, 75, and 95 cm). The water content data were incomplete due to malfunctioning of the probes. When all probes worked, the individual probes from the same depth generated time series of water contents that clearly demonstrated the temporal persistence in water contents. To quantify the persistence, we converted individual-probe water contents into water contents relative to their average from the same depth. Those relative water contents had narrow distribution functions. Many of them did not include the value of one corresponding to the average water content. We proposed and tested a technique to use the relative water contents in estimating the average water content accounting for the missing data. The maximum corrections constituted 18% to 50% of the water content ranges at different depths. The correction for temporal persistence can be useful in estimating average water contents and their uncertainty.