How to Control the Lysimeter Bottom Boundary to Investigate the Effect of Climate Change on Soil Processes?

Abstract

A dynamic tension-controlled bottom boundary of lysimeters allows observing water and matter fluxes in lysimeters that are close to natural field conditions, as pressure heads at the lysimeter bottom are adjusted to measured pressure heads at the same depth in the surrounding field. However lysimeters are often transferred from their sampling location for practical reasons or to study, for example, the effect of climate change on soil functions. This transfer can be accompanied by a change aboveground but also in subsurface conditions that are used to control the bottom boundary and that may affect the soil water balance of lysimeters. This issue is also relevant for lysimeter stations which use a tension-controlled bottom boundary and are not directly installed near the site of excavation. The potential impact of different bottom boundary conditions on the water balance of lysimeters that were transferred in a climate impact experiment (SOILCan) was investigated exemplarily by a numerical study. Results showed that by using nonappropriate pressure heads, which were measured in soil profiles with a different texture and water table depth than the profile where the lysimeter was taken from, had partially large impacts on soil water fluxes, especially when the water table was located within a specific critical range. Different climate conditions between sampling and installation site were buffered by the soil and did not show a strong influence on the bottom boundary control of lysimeters when the groundwater table depth was assumed to remain constant. Considering a change in groundwater table depths due to changing climate tempered the effects of climate change on the soil water balance terms. In general, results demonstrate the importance of a proper control of the lysimeters bottom boundary conditions in studies that investigate the influence of climate change on soil functions and ecosystem variables by transferring lysimeter along climate gradients.

Quantification and Prediction of Nighttime Evapotranspiration for Two Distinct Grassland Ecosystems

“…The lysimeters have controlled bottom boundaries, which permit downward‐ and upward‐directed water fluxes. The water flux across the bottom boundary is controlled by field measurements of soil water potentials at the corresponding depth (1.4 m) and hence contributes to a better representation of land surface fluxes (Groh et al, ). At both sites, the lysimeters contain undisturbed soil monoliths of a Stagnic Cambisol.…”

“…The use of a dynamic tension controlled lower boundary condition based on field tension measurements enables water influx at the bottom during upward water flow conditions in the lysimeter soil. This can more realistically represent ET processes in lysimeters under conditions of upward‐directed water fluxes from shallow groundwater tables or deeper soil layers (Groh et al, ; Karimov et al, ; Schwaerzel & Bohl, ). In addition to technological improvements that enable measuring mass changes with high accuracy and temporal resolution, the data analysis has made substantial progress by developing quality checks and algorithms to reduce the impact of noise on lysimeter balance data (Küpper et al, ; Marek et al, ; Peters et al, , ; Pütz et al, ).…”

Root growth, water uptake, and sap flow of winter wheat in response to different soil water conditions

“…At the field plot scale, weighing lysimeters allow transpiration to be measured (e.g., Groh et al, 2016;Garré et al, 2011). A disadvantage of lysimeters is that they are costly and, although possible (e.g., Garré et al, 2011;Vandoorne et al, 2012), root distributions are difficult to measure in lysimeters and their spatial growth is influenced by the confined soil space, which also frequently causes undesired boundary effects (e.g., high root length densities at lysimeter walls).…”

Water flow and multicomponent solute transport in drip‐irrigated lysimeters

“…Suction lysimeters can be either active or passive. Active suction‐controlled lysimeters allow application of the pressure head, equivalent to that measured by a tensiometer under field conditions, at the bottom boundary [e.g., Hannes et al ., ; Groh et al ., ]. This type of lysimeter has high installation and maintenance costs and is difficult to repair when malfunctioning [ Bergström , ].…”