Aboveground Biomass and Soil Organic Matter as a

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Aboveground Biomass and Soil Organic Matter as
a Function of Planting Strategy and Water Depth
in Six Experimental Wetland Cells After One Year
of Planting Rachel Cohn, Gavin M. Platt, H.
Siv Tang Systems Ecology (ENVS316) Research
Project, Fall 04
Background

• Soil Organic Matter Although SOM was greater
  overall in deep areas, the differences among
  depths are not statistically significant. We
  found no statistically significant effects of
  either depth or planting strategy on SOM.

Wetlands are crucial ecosystems that serve many
purposes, including wildlife habitat, flood
abatement, and nutrient filtration. Despite their
importance, increased land-use in the U.S. has
led to enormous reductions in wetland cover, with
97 lost in Ohio alone. Recent efforts to reverse
this trend have left ecologists to the challenge
of recreating wetlands with similar structure and
function as natural wetlands. Ecologists have
observed that restored wetlands often fall short
of natural wetlands biotic structure,
functioning, and stability (Zedler 2003). In
collaboration with Oberlin College and Ohio State
University, the Ecological Design Innovation
Center (EDIC) has created an experimental wetland
facility to study the effects of different
planting strategies on wetland restoration. Its
long-term goal to develop improved restoration
management practices in order to maximize
desirable structural attributes such as species
diversity and functional aspects such as carbon
accumulation and nutrient retention. Two main
factors that contribute to and reflect wetland
function are aboveground biomass and soil organic
matter (SOM). Aboveground biomass provides a
direct measurement of net ecosystem productivity.
SOM content reflects long-term storage of organic
carbon and associated nutrients, and contributes
to water holding capacity and cation exchange
capacity (CEC). The results of previous studies
suggest that biomass and SOM are thought to be
controlled in part by water depth and species
diversity (Callaway 2003, Weiher 2004).
Effects of Planting Strategy and Depth on Soil
Organic Matter
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Picture 1. Harvesting biomass at the site.
4.0
A permanent grid was established in each cell for
research purposes (Fig. 2). Aboveground biomass
was harvested using cutters and a 1m x 1m square
sampling device, constructed of PVC pipe (Pic.
1), within each of the six wetland cells at rows
7 (shallow) and 5 (deep). Soil cores were taken
from each corner of the sampling unit, and water
depth was assessed at the center.
Shallow
SOM
Deep
2.0
Figure 2. Sampling protocol in wetland cells. Row
1 is the deep end, row 8 the shallow end. The six
locations where samples (and subsamples) were
taken are located as indicated in the diagram.
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Selective
Natural
Combined
Planting
Recruitment
Treatment Type
Figure 4. SOM (ash-free dry
weight)/(oven-dried weight)100. Y-error bars
represent standard error of the mean among
replicates.
Conclusions
We used standard laboratory techniques to
estimate the dry-weight of aboveground plant
biomass and to determine soil organic matter. We
used analysis of variance to determine whether
there were differences as an effect of either
planting treatment or depth.
Even just one year after these wetlands were
initiated, we found that plant biomass is already
a function of depth (P.04). However, we found no
significant effect of planting with a high
species diversity on biomass or SOM. Because the
wetlands are only two years old, and the last
planting and seeding occurred only one year ago,
we are not able to make concrete conclusions
about whether this pattern will remain true in
the future. We anticipate that, as the wetland
matures, SOM will increase because of an
accumulation of dead plant matter due to slow
decomposition. We also anticipate a significant
difference between naturally recruited and
planted cells as community composition in the
planted cells stabilizes. Further research will
be necessary to determine the longer term effects
of planting strategy on ecosystem structure and
function.
Purpose

• Our two primary goals were
• To determine whether restored wetlands initiated
  with high species diversity (both seeding and
  planting) differ from those allowed to naturally
  recruit.
• 2) To determine whether biomass and SOM differ as
  a function of depth within the wetland cells.

Picture 2. Incinerating soil to determine SOM.
Findings

• Plant Biomass Our analyses indicate that depth
  had a significant effect on plant biomass in the
  planted cells and among all treatments, but not
  in the cells subject to natural recruitment
  P.01 (planted), P.04 (combined). We did not
  find significant overall differences in biomass
  between planted and natural recruitment
  treatments (Fig. 3).

Experimental System Methods
The wetland facility consists of six
hydrologically isolated 1/2 acre cells which were
constructed to have nearly identical dimensions,
soil properties, and hydrological conditions.
Cells were graded from a shallow, seasonally
inundated south side to a permanently aquatic
north side. Four of the cells were seeded and
planted in fall of 03 with species native to
northeast Ohio to achieve a high level of species
diversity. Two of the cells were not planted and
were subjected to natural recruitment (Fig. 1).
Effects of Planting Strategy and Depth on Plant
Biomass
References
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Callaway, J.C., Sullivan G., and Zedler J.B.
(2003). Species-rich plantings increase biomass
and nitrogen accumulation in a wetland
restoration experiment. Ecological Applications,
13 (6), 1626-1639. Weiher, E., Forbes S.,
Schauwecker, T., Grace, J.B. (2004). Multivariate
control of plant species richness and community
biomass in blackland prairie. Oikos, 106,
151-157. Zedler, J.B. (2003). Wetlands at your
service Reducing impacts of agriculture at the
watershed scale. Frontiers in Ecology and the
Environment, 1 (2), 65-72.
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Shallow
Biomass (kg/m2)
Deep
0.2
0.0
Selective
Natural
Combined
Planting
Recruitment
Treatment Type
Figure 3. Biomass oven-dried weight in kg/m2.
Y-error bars represent standard error of the mean.
Figure 1. Diagram of planting regime of the
experimental system at EDIC.