emerged. Figure 7.12 shows site means for bulk density, soil water content and organic
matter graphed against each other. Figures 7.13, 7.14 and 7.15 show these relationships
for each site.

 Some assumptions can be made concerning the condition of wetland soil in
constructed wetlands that could make any changes in these relationships within a site
useful for assessment. These include:

 Upon completion of construction, the initial conditions of bulk density and
 organic matter content are reasonably uniform throughout the wetland.
 Wetlands are often constructed from either overburden or sand tailing with
 perhaps a layer of mulch.

 Any changes in soil bulk density or organic matter content result from self-
 organizational processes being driven primarily by soil water content and site
 productivity. Increased soil water content often creates in anaerobic
 conditions within the soils, resulting in decreased organic matter
 decomposition rates and provided there ib sufficient productivity with the site
 storage of organic matter in the soil will increase.


 While the relationships in Figure 7.31a and 7.31c are often represented with
organic matter and bulk density as the independent variable, the reverse is done here.
Throughout this research the assumption was made that data collected from a
chronosequence of similar wetlands would resemble data collected from an individual
site over time. With this in mind, the initial soil organic matter and bulk density of a site
have the potential to decrease throughout the site differentially dependent upon the
variation of soil moisture content throughout the site.

 First, as was done in this study, soil samples within a given wetland must be taken
across the moisture gradient from the edge of the wetland inward. The sampling of the
moisture gradient within the wetland is essential if this method is to work.

 If the assumptions are true, then initial graphs of bulk density vs. soil water
content of newly constructed wetlands would result in a straight horizontal line at some
initial value. Very little change in bulk density of primarily mineral soils is expected
from increased soil water content, since water should be filling empty space and
contributing very little to increasing volume. In addition, the initial graphs of organic
matter vs. soil water content should result in a straight horizontal line. (The first graph in
Figures 7.13, 7.14 and 7.15 shows the graphs of these relationships in LP2 Phase 1.)

 With time, there should be differential increases in organic matter and a decrease
in bulk density across the moisture gradient, with greater changes occurring with greater
soil water content. The graph of bulk density vs. soil water content should begin to show
exponential decreases in bulk density with increasing soil water content. In addition, the
points representing individual soil samples should shift to the right as decreasing bulk


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