Abstracts

Water table fluctuations between groundwater and surface water significantly affect the biological
and geochemical functioning of soils. The pulse of oxygen introduced or removed
by cyclic draining and rewetting results in significant oxidation and reduction of redox sensitive
chemical species. Our approach to unravel the biogeochemical implications of water
table fluctuations is to conduct laboratory experiments with soil columns in which the
position of the water table can be manipulated. In this project, we used a novel automated
soil column system where the time course of the water level is imposed via a programmable
multichannel pump. Four undisturbed sand cores (10, 20, 30 and 40 cm length) were
collected from the Burlington beach site and were introduced into four columns in the lab.
The soil columns have ports that are used to install ceramic pore water samplers to characterize
the evolution of pore water chemistry (pH, major anions/cations, nutrients, DOC
and DIC) in soil columns during water table fluctuations. At the end of experiment, the
soil was extruded via the top of the column using a lifting jack and will be sliced every 2 cm
for further solid phase geochemical characterizations. The goal of this study was to better
delineate the role of water table oscillations on nutrient fate and distribution in sand from
a freshwater beach environment.
129 - Effect of freeze-thaw cycles on soil oxygen dynamics
T. Milojevic, F. Rezanezhad, & P. Van Cappellen
Ecohydrology Research Group, University of Waterloo, Waterloo, Ontario, Canada
Freeze-thaw cycles represent a major climate forcing acting on soils at middle and high
latitudes. Freezing and thawing of soils affect their physical properties, biogeochemical
processes, microbial community, and carbon and nutrient budgets, and modulate gas exchanges
between the soil and atmosphere, which, in turn, exerts a strong influence on oxygen
(O 2
) availability within soil environments. To investigate the role of freeze-thaw cycles
on soil oxygen dynamics, a highly instrumented soil column experiment was designed
to realistically simulate freeze-thaw dynamics under controlled conditions. The ability to
monitor changes in O 2
levels in both the gas and aqueous phase is key to understanding
how changes in frequency and amplitude of freeze-thaw cycles affect a soil’s geochemical
conditions and microbial activity. In this study, we perform soil column experiments in a
temperature-controlled environmental chamber. The air temperature of the chamber determines
the soil’s surface temperature, while a band-heater keeps the lower part of the column
at a constant groundwater temperature. This design allows us to reproduce realistic,
time- and depth-dependent temperature gradients in the soil column. High-resolution,
luminescence-based, Multi Fiber Optode (MuFO) microsensors are used to enable continuous
O 2
detection at a high degree of spatial flexibility in the column. High-resolution digital
images of the sensor-emitted light are recorded and light intensity is converted to O 2
concentration via signal image-processing techniques. In this presentation, we will present
preliminary results to assess the hypothesis that freeze-thaw cycles regulate the fluxes of
the greenhouse gases (GHG) not only by acting on the physical transport of gases, but also
on soil microbial respiration via the variations in O 2
availability.
IAH-CNC 2015 WATERLOO CONFERENCE
159