Wetland Biogeochemistry Techniques - Wetland Techniques - page 365

larger area. Wind currents can transport leaves for a considerable distance from the
parent tree. The number of cages needed to give a relatively accurate estimate of
leaf biomass will depend on the spatial area of the target site and the number of
woody species present in the tree and shrub strata. To increase the accuracy, the
value for each cage can be weighted by the percentage of the site area shaded by
that particular tree or shrub associated with each cage.

7.4.2.8 Herbaceous Biomass

Herbaceous shoot biomass samples can be obtained by clipping at ground level all
of the plants within a delineated area. The sample area can be delineated with a
square or rectangular frame built from 2.5 cm diameter polyvinyl chloride (PVC)
pipe; each piece is connected to the next by a right angle PVC connector. The frame
is light in weight and can be easily constructed and broken down in the field. If the
site is inundated, the frame should be raised to the surface of the water. This can be
facilitated by using three-way connectors and attaching PVC 'legs' to the frame.
Another option is to mark the plot with pin flags, but that method does not provide a
continuous delineation edge. The samples should be placed in pre-weighed paper or
mesh bags and dried to a constant weight at 80 C. The bags should be pre-weighed
so that sample dry weight can be obtained without removing the sample from the
bag. Fresh harvested plant tissue will continue to respire and lose weight so samples
should be kept on ice until they can be placed in a dryer.

7.4.3 Soil Organic Matter

7.4.3.1 Loss on Ignition

Loss on ignition (LOI) is a relatively simple method of determining soil organic
matter (SOM) content as follows (Nelson and Sommers 1996 ). Pyrex beakers
(20 ml) are heated in a muffle furnace at 400 C for 2 h and then weighed to
determine tare weight of the beaker. Air-dried soil samples are ground to pass a
0.4 mm screen. One to 3 mg of dried and ground sample are placed into a tared
beaker and heated at 105 C for 24 h in a drying oven. The beaker is cooled in
a dessicator over CaCl 2 , then weighed to determine the dry mass of the sample.
The samples are ignited in a muffle furnace at 400 C for 16 h, cooled in a dessicator
over CaCl 2 , then weighed to determine weight of the beaker and the ignited sample.
All weights should be taken to within 0.1 mg. Organic matter content (%) is
calculated as 100 (Wt. 105 Wt. 400 )/Wt. 105 , where Wt. 105 is the sample weight

after heating at 105 C, and Wt. 400 is the sample weight after ignition.
The high temperatures used in this method can cause the loss of structural water
from inorganic soil constituents such as hydrated aluminosilicates resulting in
weight losses in excess of organic matter content (Nelson and Sommers 1996 ).