Soil water balance in a boreal forest

Abstract

Measurements of root zone soil water content and soil hydraulic properties at the flux tower sites were conducted during the course of the Boreal Ecosystem‐Atmosphere Study (BOREAS) experiment. Instrumentation included neutron probe, time domain reflectometry (TDR), and tension infiltrometer. Several methods of data visualization were employed to demonstrate fluctuations in soil water content with depth and time during the intensive field campaigns (IFCs). These methods started with two‐dimensional plots of soil water content as a function of time and depth and evolved into the construction of three‐dimensional soil water prisms. The prisms were constructed by using cubic‐spline (vertical z‐direction) and linear (horizontal x‐direction) interpolations for soil water content and linear interpolations along the time (y direction) axis. The prisms allow for animation along any plane or combination of planes to demonstrate the evolution of soil water conditions due to evapotranspiration, drainage, and precipitation. Soil hydraulic properties were determined at the flux tower sites based on analysis of in situ tension infiltrometer tests and soil water retention data from laboratory analysis of soil cores. Results from this analysis are saturated hydraulic conductivity and fitting parameters for the van Genuchten soil water retention function and Mualem hydraulic conductivity function at each flux tower site. These functions are required for physically based simulation models of soil water dynamics, soil water balance, and the interaction of the soil profile with the atmospheric boundary layer. Examples of cumulative evapotranspiration and drainage calculated from the soil water balance are presented and compared with flux tower measurements.