The present study aimed to study the role of pore contact of
micro-lysimeters in the soil column on tracer transport in relation to the
structure, as assessed by X-ray CT under different initial conditions and
irrigation. As it is not possible to carry out these investigations under field
conditions, non-destructive CT data were used, making it possible for 3-D
reconstruction of the structure of the investigated soil columns. Quantitative
relationships between soil structure (especially macropore characteristics,
namely their size, number, type, distribution and continuity) and soil
hydraulic properties are essential for improving our ability to model flow and
transport in structured soils. Ten undisturbed soil monoliths of clayey Pelosol
at Gottingen, Germany covering the horizons Ah and P were collected. Some
columns were left at natural humidity, some were oven-dried to simulate drought
situations in forest soils in consequence of climate change. In seven columns,
four micro-lysimeters, each, were installed at half height in order to obtain
data for analysis of single solute pathways. A fixed amount of KBr tracer was
applied to the humus layer. The columns were irrigated with CaCl2. Column
output and lysimeter output were collected and analyzed to record breakthrough
curves. Bimodal analytical convection dispersion equation (CDE) solutions were
fitted for the column outputs using a non-linear least square fit. A simple CDE
solution did not fit well. This supports the model of two overlaying transport
phenomena. After breakthrough recording was complete, all columns were scanned
using X-ray computed tomography (CT). From the CT data 3-D reconstructions of
the porous system were created for visual inspection, and the exact pathways
for macropores along the micro-lysimeters were determined. Additionally, indices
of the pore structure were computed to compare with the slow and fast
dispersivity values from the bimodal CDE fit.
The three-dimensional reconstruction could be used to explain the
difference in micro-lysimeter performance. Following the conclusion of irrigation,
no statistically significant variations were found in the pore structure of the
wet and dried columns. In general, there is a positive linear relationship
between the pore index and slow dispersivity and a negative linear relationship
with rapid dispersivity. In topsoil, these relationships are more robust. The
CT images and 3-D reconstructions offer a fascinating look into the soil pore
system and could be useful in understanding drought issues caused by climate
change that are caused by humans.
Author(s) Details:
A. Spangenberg,
University of Göttingen, Institute for Soil Science and Forest
Nutrition, Büsgenweg 2, 37077 Göttingen, Germany.
Y.
Nagarajarao,
University
of Göttingen, Institute for Soil Science and Forest Nutrition, Büsgenweg 2, 37077
Göttingen, Germany.
C. Hinz,
University of Göttingen, Institute for Soil Science and Forest
Nutrition, Büsgenweg 2, 37077 Göttingen, Germany.
Please see the link here: https://stm.bookpi.org/RACAS-V7/article/view/14270
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