Agriculture Reference
In-Depth Information
airport chemicals, as well as the increase of rates caused by optimizing the C:N:P ratio are
reported in French et al. (2002). Although degradability of de-icing chemicals in general is
positive for the environment, negative consequences can be anaerobic conditions. Field
experiments (French et al., 2001) showed an increase in manganese concentration when
propylene glycol and Potassium acetate was supplied to the ground surface even in the
unsaturated zone, indicating oxygen limitation. On-going research (French et al., 2009)
suggests that nitrate could increase remediation and improve redox conditions in local soils.
3. Non-invasive versus destructive methods for soil characterisation
The theoretical considerations concerning spatial variability, described in the next section
requires that we have some knowledge about 1) the geostatistics of the hydrogeological
properties, and 2) the scale of the contaminant source or plume relative to this variability.
3.1 Non-uniform infiltration
The boundary conditions influencing the flow and transport during snowmelt are
characterized by ground frost and the formation of impermeable ice on the ground surface
which redistributes melt water during the snowmelt period (Fig. 1). The ice-cover often
inhibits infiltration in sediments with otherwise high infiltration capacity (sandy aquifers).
As a result, a large amount of melt water collects in depressions or becomes surface runoff.
According to Baker & Spaans (1997); Derby & Knighton (1997); Johnsson & Lundin (1991),
infiltration during snowmelt often occurs as focused recharge in local depressions on the
surface.
Monitoring water accumulation in snow and also the infiltration below the snow cover is a
challenge. The traditional but laboursome way of collecting information about snow cover is
to measure snow depths along a transect and estimate the snow water equivalent (SWE) by
weighing the snow column. The advantage is that one gets a spatial coverage, but only for
single times, also the method is destructive. Snow pillow measurements involves placing a
logged scale beneath the snow cover, hence direct measurement of SWE above the snow
pillow, this method prevents infiltration and is only representative of one location, also it
may give wrong values when ice crusts are formed in the snow which reduces the weight
load on the scale. Remote sensing using natural emissions of gamma rays and micro waves
has become a common method for mapping snow storage over larger areas (Glynn et al.,
1988; Durand et al., 2008; Schaffhauser et al., 2008), but also local measurements can be
conducted using this principle (Campbell scientific; Bland et al., 1997).
A snow lysimeter is a method where meltwater is collected via drain pipes from trays below
the snow cover, and volumes and quality measured. Hence destructive in the way that
water is prevented from infiltrating the ground. Variations in release of water from a
melting snowpack was documented by French & van der Zee (1999) by collecting meltwater
from snow lysimeters placed beneath a melting snow cover. Despite a fairly uniform snow
depth over the monitored area (a few square meters), the total melt volumes varied from
nearly 0 to 200% of expected values based on the snow water equivalents measured prior to
snowmelt. To further characterise the infiltration pattern in the soil, French & Binley (2004)
installed electrodes near the surface and monitored changes in electrical resistivity of the
soil volume, which indirectly reflected changes in water contents during snowmelt. Figure
2, shows the spatio-temporal variability of electrical resistivity observed in a horizontal
plane during this experiment. This may cause higher velocities through the unsaturated
