Environmental Engineering Reference
In-Depth Information
Procedures
Overview
: There are several options with this exercise with respect to the type of
organic materials used and the location of bag deployment in the field. In the
procedures below, we suggest collecting fallen leaves from one deciduous tree
species. This is the simplest approach and promotes uniformity in the samples.
However, the exercise can be modified to compare multiple species or even root
samples. With respect to deployment location, we suggest two sites, a wetland and
an adjacent upland. The main point to this exercise is that wet conditions slow down
decomposition rates. To further illustrate this point, the class may choose to place
some litter bags in inundated areas. We suggest avoiding permanently inundated
areas as it may be difficult to retrieve the bags.
9.
Litter bag construction
. Ten litter bags will be needed for each team of students.
For each litter bag cut a 20 cm
40 cm section of screen. Double the screen
section over and staple the sides together at 5 cm intervals. You should now have
a screen pouch open at one end. The open end will be stapled shut after the bag is
filled with leaf litter. Each bag should be numbered with a permanent marker for
future identification. Weigh each bag with three additional staples. Record the
weight. The weight of the additional staples is needed to account for the staples
used to close the open end of the bag after the leaf sample is added.
10.
Leaf litter sample collection
. Collect fallen leaves from the chosen field site. To
promote uniformity in the samples; collect all samples from the adjacent
upland, sample only the top layers of the litter, and sample only one deciduous
tree species.
11.
Sample preparation
. Chop the leaves into 2-5 cm lengths. Randomly collect
five sub-samples of the chopped leaves. Determine fresh weight of the
sub-samples, then dry them (70
C, 48-72 h) and re-weigh to obtain their
water content.
12.
Bag filling
. Fill the bags with the prepared samples. Try to place a similar
amount of material in each bag (It does not need to be exactly the same). The
material should be relatively loose in the bag to allow for air movement. Staple
the open end closed with three staples. Weigh each bag and record. Sample
fresh weight is calculated as the difference between the filled bag weight and
the empty bag weight.
13.
Litter bag deployment
. Place five bags in the upland and five bags in the
wetland. For placement in the wetland, choose deployment points with similar
hydrologic conditions as soil moisture will impact decomposition rates. For
example, if the site has pit and mound topography, do not place 1 bag on top of
a mound and another bag in a pit. Avoid permanently inundated areas. Clear
away any duff and place the bags directly on top of the mineral soil surface.
Mark the location of each bag with a pin flag.
14.
Litter bag retrieval and analysis
. Retrieve the bags after 2-3 months. Dry the
retrieved bags (70
C, 48-72 h) and weigh. Calculate sample dry weight.
