do mineral soils (Mitsch and Gosselink 1993). The results discussed from Figures 5.19-
5.22 clearly show that the organic hummocks have much higher average volumetric
water content meaning more available pore water. Sand has fewer pore spaces than
organic and overburden soils and contains the least amount of soil water. Overburden,
with its composition of sand, clay, and organic material, holds water better than sand,
making more available for plant uptake.

 Organic hummocks show greater available pore water and in this case likely have
 greater nutrient availability of nutrient (indicated by higher percent cover). Figures 5.11-
 5.14 show that organic soils also have a wider range of micro-sites for plant growth. The
 organic hummocks show lower species diversity and evenness. A few fast growing
 species colonizing these hummocks likely are better able to uptake nutrients and out
 compete other slower growing species. Overburden hummocks show greater ability to
 hold soil water at higher elevation than do sand hummocks creating more available
 micro-sites for plant growth. Overburden and sand hummocks show higher diversity than
 organic hummocks. The same fast growing plants that can uptake readily available
 nutrients are likely out competed in the lower nutrient situation by plants better able to
 access nutrients.

 Tree growth and survivorship is also related to soil moisture and nutrient
availability. The results of the tree study show that the growth of understory vegetation
may also have a large impact. Figure 5.9 shows that trees growing on organic hummocks
do not survive nearly as well as those on the sand and overburden hummocks. The
growth of understory vegetation on organic hummocks may have choked the trees by
using all available nutrient, water, and blocked most of the sunlight from the small tree
seedlings. The trees growing on the other hummocks showed an increase in basal
diameter and small increases in height. With lower nutrients and pore water, the likely
difference in survivorship and growth can be linked to the lack of competing understory
vegetation.


CARGILL

 Overburden and muck were used to construct the hummocks in the Cargill
wetland. Figure 5.7 shows the muck hummocks fared slightly better than the overburden
hummocks in terms of soil erosion. The change was only seen between two sampling
periods, thus it is hard to see any trends developing. Both hummock types had relatively
high percent covers of vegetation (Table 5.1) whose root structure helps hold soil in
place. In contrast to the Agrifos wetland, the Cargill wetland was flooded by water from
other mining sites. Flooding the wetland had the added effect of surface water erosion on
the hummocks. Surface water movement caused by wind has the potential to carry away
soil particles causing undercutting along the sides of the hummocks. The wetland was not
flooded immediately, but gradually. Thus, the effect of surface water erosion was not
seen over the entire sampling period.


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