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Compost
Use In Wetland FINAL REPORT Report No. CM-96-2 TABLE OF CONTENTS
EXECUTIVE
SUMMARY.............................................................................................................
1.0 SITE
AND PROJECT HISTORY........................................................................................
1.1 SITE HISTORY...............................................................................................................
1.2 GOALS.............................................................................................................................
1.3 COMMUNITY SUPPORT AND INVOLVEMENT....................................................
1.4 STATE GUIDELINES FOR WETLAND RESTORATION........................................
2.0 SITE
DESIGN.......................................................................................................................
2.1 DESIGN GOALS............................................................................................................
3.0 EXPERIMENTAL
DESIGN................................................................................................
3.1 TARGET PARAMETERS.............................................................................................
3.2
COMPOST INCLUSION RATE...................................................................................
3.2.1 Similar
Species Nutrient Uptake...............................................................................
3.2.2 Application
Rates For Fen And Experimental Plots...................................................
4.0 EXPERIMENTAL
RESULTS..............................................................................................
4.1 PLANT GROWTH RESPONSE AND SURVIVAL RATES.......................................
4.2
SOIL ANALYSES...........................................................................................................
4.2.1 Total
and Volatile Solids Content.............................................................................
4.2.2 Particle
Size Analysis...............................................................................................
4.2.3 pH..........................................................................................................................
4.2.4 Conductivity............................................................................................................
4.2.5 Nitrogen
Dynamics..................................................................................................
4.2.6 Phosphorus
and Potassium Levels............................................................................
4.2.7 Copper...................................................................................................................
4.2.8 Other
Analyses Performed.......................................................................................
4.3 SURFACE WATER QUALITY......................................................................................
4.4 WILDLIFE OBSERVATIONS......................................................................................
5.0 GUIDELINE
FOR USE OF COMPOST IN WETLAND RESTORATION.....................
5.1 TYPE OF COMPOST.....................................................................................................
5.2 REQUIRED ANALYSES...............................................................................................
5.3 SUMMARY
WORKSHEET FOR COMPOST APPLICATION................................
6.0 INFORMATION
DISSEMINATION EFFORTS..............................................................
7.0 ACKNOWLEDGMENTS.....................................................................................................
BIBLIOGRAPHY...........................................................................................................................
APPENDICES: (Not included in
this electronic file but available upon request) APPENDIX
A
- GROWTH AND PLANT SURVIVAL RATE SPREADSHEETS......
A-1 APPENDIX
B
- LABORATORY RESULTS...................................................................
A-2 APPENDIX
C
- SITE DRAWINGS.................................................................................
A-3 APPENDIX
D
- WETLAND SPECIES SUITABLE TO WESTERN WASHINGTON
A-4 APPENDIX
E
- WORKSHEET FOR AGRONOMIC LOADING RATE.................... A-5
Table
l Experimental
Plot Design Loading................................................... ....... 8 Table
2 Plant Species and Quantities
for Experimental Plots...............................11 Table
3 Similiar Wetland Species
Nutrient Uptake.............................................14 Table
4 Estimated N Uptake and Weighted
Averages...................................
.....15 Table
5 Cadman Wetland Restoration
Compost Application Rates.....................17 Table
6 Everett Wetland Target Compost
Loading Rates...................................17 Table
7 C:N Ratio and Organic Content
Estimates....................................... .. ..18 Table
8 Micronutrient Analyses.........................................................................32 Table
9 Surface Water Quality Analyses
Results................................................34 Table
10 Example of Analyses
of Existing Soils and Compost........................ .....38 Table
11 Sample Plant List..................................................................................39 Table
12 Agronomic Rates
of Plant Groups.........................................................39 Table
13 Soil Parameter
Comparison...................................................................41 Table
14 Worksheet for
Agronomic Loading Rate of Compost to Wetland..........42 Table
15 Inches of Compost
to be Applied..........................................................43 Table
16 Conference Attendance
and Information Dissemination.........................44
List of Figures
Figure
l Wetland Nitrogen Cycle.......................................................................13 Figure
2 Experimental Plot
Growth Comparison................................................20 Figure
3 Survival Rate
Comparison for Experimental Plots................................21 Figure
4 Total and Volatile
Solids Content........................................................23 Figure
5 Particle Size
Analysis...........................................................................24 Figure
6 Analysis of pH
at 12 Months................................................................25 Figure
7 Conductivity Analysis..........................................................................26 Figure
8 Organic Nitrogen
Analysis...................................................................27 Figure
9 Ammonia Nitrogen
Dynamics..............................................................28 Figure
10 Nitrate Nitrogen
Dynamics..................................................................29 Figure
11 Phosphorous Levels.............................................................................29 Figure
12 Potassium Levels.................................................................................30 Figure
13 Copper Levels in
Experimental Plots....................................................31 Figure
14 Cation Exchange
Capacity...................................................................32 Executive Summary
This project was undertaken
with support from the Recycling Technology Assistance Partnership
(ReTAP), a program of the Clean Washington Center of the Washington
State Department of Community, Trade & Economic Development.
The intent was to determine if the use of compost in wetlands
had benefits which could add value to compost by decreasing the
frequency of failure of restoration efforts.
Commonly, restoration efforts fail for one of the following
reasons:
·
Hydraulic
miscalculations
·
Death
of the target wetland plant species
·
Invasive
species propagation
The last two reasons stated above may very well be
curtailed by the addition of compost.
The addition of a rich strong organic matter with some
essential plant nutrients ( i.e. nitrogen, phosphorus, and potassium)
can promote strong growth of target species and allow them to
compete with the opportunistic invaders which adapt well to adverse
soil conditions. This
report presents the findings of a year long study at a wetland
restoration site which showed excellent results in these areas. The results indicate that if a stable compost
is applied at agronomic rates, the growth and survival rate of
target wetland species can be aided.
The plots which used compost showed approximately 20% more
growth and 10 to 15% higher survival rate than the control plots,
which used no compost. The surrounding surface water quality did not
degrade as a result of the application.
This report outlines the steps necessary to design
compost applications for restoration projects.
A worksheet provides a template for the calculation of
an agronomic rate of nitrogen application from a specific compost
to a specific wetland condition.
The aim of this report is to serve as a tool for the
wetland community to responsibly use compost in restoration projects
and reduce the number of failures associated with the construction
of wetlands. The results of this study indicate that a compost
with a high organic content and a low nitrogen content will serve
this end use best by:
1.
Providing
strong organic substrate to mimic wetland soils
2.
Preventing
overloading of nitrogen and contamination of the surface water
3.
Providing
organic matter for absorption of ammonia
N to prevent transport in surface water. 1.0 Site and Project HistoryIn
early 1994, staff at the City of Everett’s Department of Public
Works , with the help of E&A Environmental Consultants, Inc.
(E&A) and Adolfson Associates, Inc., submitted a technology
validation project proposal to the Clean Washington Center’s Recycling
Technology Assistance Partnership (ReTAP). The proposed project was to determine if the
use of compost in wetlands had benefits which could add value
to compost by decreasing the frequency of failure of restoration
efforts. The City knew that such a project was of keen
interest to the Clean Washington Center (CWC) for its potential
to open the wetland restoration market to compost products and
funded the project. This report documents the findings of the study.
Ultimately, the study will lead to guidelines outlining
the best procedures for using compost to replicate wetland soils. 1.1 Site HISTORYLower Bigelow Creek in the City of Everett, which flows from the Lowell neighborhood into the Snohomish River,< consists of two large riparian wetlands connected by a 550 foot 18-inch culvert. This culvert diverts water around a two acre parcel which was filled in decades ago for the construction of a sawmill. At the outset of the project, the site was barren and all water was routed through the culvert. The fill material was very sandy, and the site was covered with Scot’s Broom, an invasive brush. This plant is generally considered a nuisance and is not native to the area.
Railroad lines run through the property
near the upper wetland. The
wetlands are home to a variety of wildlife including a relatively
large population of beavers.
Beaver activity in and around the 550 foot culvert has
caused constant flooding of the railroad tracks adjacent to the
upper wetland. The railroad
and the City of Everett proposed to alleviate the flooding problem
by “removing” the beavers. However,
a well organized group of neighbors opposed this plan, and as
a result, a great deal of public attention has been focused on
this project.
In response, the City proposed to
expand the upper wetland at Bigelow Creek in order to control
flooding, as mitigation for other impacted wetlands, and in order
to allow the beavers to remain in the wetland area.
The expansion of the upper wetland consisted of replacing
the old culvert with a shorter, (80 foot) fish passable culvert.
The shorter culvert would be easier to maintain and the
expanded wetland would provide better flood attenuation and increased
wildlife habitat. In addition, the City proposed to install perforated
pipes in the series of existing beaver dams in the upper wetlands
to further reduce the flooding.
All would be accomplished using compost as the restoration's
substrate. 1.2 goalsThe goals of the project included
the following:
1.
Promotion of the use of compost in wetland projects,
2.
Promotion of the beneficial re-use of locally-generated “waste”
in local applications
3.
Flood control for the area, and
4.
Generate and evaluate data for determination of success.
One of the compost materials used
was a biosolids and yard debris material from the Everett Wastewater
Treatment Plant pilot composting project (which was also conducted
by E&A). The use of this material constituted a full
cycle recycling effort, since the compost feedstocks were all
generated by the residents of the city of Everett and the product
was returned for beneficial reuse within the City limits.
Although the practice does promote responsibility for one's
own waste, the concept of using biosolids compost to construct
wetlands resulted in some concern in both the regulatory community
and the local neighborhood. First, the neighbors were concerned about the potential contaminant
levels of treated biosolids.
However, the U.S. Environmental Protection Agency maintains
strict guidelines to assure that biosolids compost from wastewater
treatment plants are “high quality” and considered safe.
Everett's material meets all guidelines and is considered
a high quality material. Second,
regulators were concerned about the potential for compost overloading
resulting in nitrate transport to the surface water, and metals
leaching. A surface water monitoring plan proposed as part of the experiment
eased concerns about unmonitored application of the compost. In fact, the results of surface water testing
during the project indicated no adverse effects from the compost
application. After extensive
collaboration with both groups, the project was able to proceed
and demonstrate the concept of full cycle recycling.
Other goals included those associated
with the marketing of compost.
This use of compost could potentially add value to compost
by opening new markets within the area of wetland restoration. If the use of compost increased the success rate of wetland restoration,
it would be viewed as a means of preventing the costly replanting
required when a site failed to promote the appropriate plant community. In addition, the wetland construction project
served to stabilize the water levels in the area. The site handled the flow of 1996’s heavy winter
rains quite well, and the railroad tracks did not flood. This is an indication that the fen area served
its purpose as a flood plain in heavy rain conditions.
In addition, there were research
and demonstration goals which were addressed during the course
of the project. The experimental plots examined the growth
and survival of the target plants as well as the invasive species
growth. The soil from each plot was analyzed for an
array of parameters in an effort to replicate the soils in the
surrounding existing wetland.
These results are presented in Section 5 of this report. 1.3 Community support AND involvementCity staff conducted a series of one-on-one meetings with neighborhood leaders and other interested persons in the neighborhood to informally discuss the project objectives and to gather input for a conceptual design. The concept of using composted products as a wetland soil substitute was introduced during these informal meetings. Collaborating with the neighborhood leaders created a positive problem-solving atmosphere which lead to the creation of a plan addressing the concerns of the City, the railroad, and the neighborhood.
Early and comprehensive involvement
of key members of the local neighborhood resulted in a project
that was not just tolerated but demanded by the neighbors. Everett's community involvement program successfully formed an alliance
with the local neighborhood that was instrumental in negotiating
the regulatory hurdles that had to be cleared.
After the consultant and Dan Thompson attended a community
meeting and briefed the citizens, over 30 letters of endorsement
requesting that the City restore the wetlands using biosolids
compost were sent to the Mayor. The neighborhood civic association voted unanimously
to endorse the use of biosolids to restore wetlands near their
homes, and the majority of the project was planted by volunteer
labor from the local neighborhood.
The overwhelming support of the neighborhood overcame the
initial skepticism of the regulators.
All necessary permits were negotiated in less than four
months. 1.4 state guidelines for wetland restorationThe Washington State Department of Ecology published
a report entitled Restoring
Wetlands in Washington - A Guidebook for Wetland Restoration,
Planning and Implementation. The guidebook is a strong reference for such
projects in the state, and offers suggestions on suitable substrates. The report states that restoration sites with
suitable soil types are often limited.
Organic amendments are recommended in order to boost organic
content of wetland soils. Suggested
materials are processed peat, straw, or hay which can be mixed
with mineral soils to provide preliminary levels of organic matter.
It is also suggested that importing hydric soils can be
a benefit, since roots and microbes will aid in the success of
a restoration project. The guidebook states that these measures are
necessary to promote moisture retention, add organic materials,
and add nutrients and micronutrients.
The use of compost is not specifically outlined, although
compost would add to all of the above stated criteria.
This report will be forwarded to the state DOE and an amendment
recommended.
2.0 Site Design2.1 DESIGN GOALSThe site restoration plan was designed to allow for
flow through the fen area, which served as a flood plain during
heavy flow periods. The
excavation plan also called for the gradual sloping of the experimental
plots down to the water surface, which allowed for the planting
of a wide variety of wetland species throughout the water regime.
These excavation plans are shown in Appendix C.
In addition to the excavation plans, Appendix C contains
the plot plans for the planting design. The fen area is shown, with the prescribed plant arrangements.
The planting schemes for each of the experimental plots
shows that the target species were placed in the same areas of
each plot. An effort was
made to ensure that each of the plots had similar slope, sun,
and water conditions. This
was accomplished for all but plot one, which was flooded after
the original drainage culvert was plugged.
The remainder of the plots all had similar conditions,
and therefore represent identical plots aside from the compost
application rate.
The application rates of the compost were designed
to bracket the agronomic needs of the plant community chosen for
each plot. Two plots were
established for each of three application rates for two types
of compost (greenwaste and biosolids/greenwaste) and a control
(no compost) for a total of 14 plots. One of the three application rates was designed
to closely match the agronomic rate, and the other two were designed
to be higher and lower than the agronomic rate. Table 1 describes the application rates and compost type for each
of the 14 plots.
Table 1: Experimental Plot Design Loading
gw = greenwaste, bio = biosolids 3.0 Experimental Design3.1 TARGET PARAMETERSThree application rates of two different composts were applied in an effort to simulate the existing wetland soil conditions. Analysis of the surrounding wetland soils defined the desired target ranges of the chosen soil parameters to be achieved in the restoration effort. These ranges were met through the introduction of a compost and sand mixture as a substrate in the newly constructed area. Parameters studied included organic content, C:N ratio, pH, conductivity, water holding capacity, soil oxygen levels, cation exchange capacity, and trace nutrients. In addition to the lab analyses, plant populations and dynamics (survival rate and plant height) were recorded to study the effect of compost use on promoting the growth and survival of target species as well as suppressing invasive species. 3.2 COMPOST INCLUSION RATECompost inclusion rates were based on creating optimum
conditions for wetland plant growth while minimizing environmental
impacts. A table was developed
that summarizes literature information on nutrient uptake of wetland
plants. Nitrogen (N) uptake will usually be the limiting
factor for the application of the compost, since over-application
of nitrogen can cause water quality degradation.
The nutrient uptake shown in Table 3 follows the list of
plants (Table 2) which were used in the experimental plots.
The plants were grouped into similar categories (trees, shrubs,
herbs, etc.). Each experimental
plot contained a predetermined number of plants from each grouping. By assigning an average nitrogen uptake for each of the groups of
plants, a weighted average of uptake can be estimated according
to the number of each type of plant in each plot.
This estimate can then be presented in pounds of nitrogen
per acre. Table 2: Plant Species and Quantities for Experimental
Plots
Table
3: Similar Wetland Species
Nutrient Uptake
Next, the nitrogen content of the compost was examined.
With data on moisture content, bulk density, and nitrogen
content of the compost, an estimate was made of cubic yards of compost
per acre. Assumptions were
made concerning the availability of nitrogen in a wetland environment,
and are presented later in this chapter. An assumption was made for the nitrogen uptake
of shrubs which was based on the numbers for similar groundcover
and trees. This estimate
was used for the design of the experimental plots.
The evidence from the Monroe Cadman wetland restoration
site was also examined to aid in determining compost inclusion rates.
The Monroe Cadman project was a demonstration project sponsored
by the Clean Washington Center completed prior to this project. The Clean Washington Center report was published
in 1993. Its purpose was
to complete a cursory demonstration of the use of compost in a wetland
restoration project. This
project is the follow up, and builds upon the previous work by examining
soil parameters much more closely.
There was strong evidence that varying levels of nitrogen
loading gave varying degrees of success for plant survival and invasive
species suppression. This
evidence was noted and taken into consideration, but was eventually
superseded by the nitrogen needs of the plants in each experimental
plot. 3.2.1 Similar Species Nutrient Uptake
In order to estimate the nutrient uptake of each plot,
an investigation into the nutrient needs of wetland species was
conducted. Nitrogen uptake
is of special significance as it will usually be the limiting factor
affecting application rate. Application
rates that exceed the plants uptake rate will likely result in nitrate
leaching and runoff. As
a result, the experimental plots were designed to use no more nitrogen
than was needed by the plants to be grown in each plot.
For agricultural soils, there is a tremendous amount
of information regarding the transformation of organic N to inorganic
N after an organic amendment is incorporated.
Likewise, there is considerable information regarding plant
nitrogen requirements. The
research behind this data was prompted by the need to optimize fertilizer
use for low cost and high crop yield.
There is less information about this pertaining to wetland
soils. However, some research
has been done from the standpoint of using artificial wetlands for
wastewater treatment. As
a result, a small amount of data has been generated concerning the
nutrient uptake of wetland species.
Nitrogen exists in three forms - inorganic, organic, and gaseous. Organic N consists of carbon based compounds such as protein and is not available to plants. Soil microbes convert organic N to inorganic N (mineralization). Plants use inorganic N for nutrition in the form of nitrate (NO3-) and ammonia (NH4+) ions, which are the plant available forms. Ammonia, which can be absorbed by clay and organic matter preventing transportation by water, is converted to nitrate by soil microbes (nitrification). Nitrate is very mobile in water. Microbes and plants convert inorganic N back to organic N (immobilization). N2 gas comprises about 80% of the soil atmosphere, and can be used as a source of N for legumes but is not used by other plants. N2 is the end product of denitrification, which occurs under anaerobic conditions when microorganisms convert nitrate to N2 and N2O gases which escape to the atmosphere. N2 that does not escape to the atmosphere is rapidly converted to ammonia in the soil. Figure 1 describes the nitrogen cycle in a wetland setting. Figure
1 Wetland Nitrogen Cycle
I=imobilization, M=mineralization, N=nitrification,
D=denitrification It is suspected that organic N nitrification rates
in the wetland environment are considerably less than in the agricultural
environment. Reducing conditions
are seen under anaerobic conditions when inorganic compounds (such
as nitrate) are used for electron exchange instead of oxygen.
Reducing conditions not only inhibit nitrification, but also
promote denitrification. For
compost application in agricultural soils it is assumed 10 to 30
percent of the organic N becomes available in the first year, depending
on soil type, temperature, moisture and other factors.
It is also believed that the lack of oxygen in the wetland
setting will inhibit the mineralization of nitrogen into plant available
forms. Some oxygen will
be introduced into the soil through the root zones of the plants,
so mineralization will occur at some small level. Also, an unstable compost with high available
carbon content will have a very low mineralization rate. The compost used in this project was very stable.
This project used a conservative estimate of 10% mineralization
for the compost. Levels of nitrogen were monitored throughout
the project so as to form a better understanding of the dynamics
of the soil.
The data for the trees and the data for the undergrowth
(shrubs and herbs) assumed that the individual plant type was planted
uniformly across the entire acreage.
However, the trees and the undergrowth coexist on the same
plot of land. Therefore,
the weighted averages of the shrub and herb data were added to the
weighted average of the tree data.
This accounts for total potential nitrogen uptake.
Table 4: Estimated N Uptake and Weighted Averages
Tables 5 and 6 show the data for the recently completed
Monroe Cadman wetland restoration project in Monroe, as well as
the target loading rates of nitrogen and corresponding volumes needed
for the Everett restoration project.
Consideration for the loading rates was based first on the
success of the plots at the Cadman site and their corresponding
loading rates. After looking at these numbers, the loading
rates were adjusted according to the nutrient needs of the plants
going into the experimental plots.
Compost for the experimental plots was obtained from the
Everett pilot compost project (biosolids/greenwaste) and from Phoenix
Composting (greenwaste). 3.2.2 Application Rates For Fen And Experimental Plots
After determining allowable nitrogen loading has been
made, it is necessary to calculate whether the organic content and
the C:N ratio of the final mix is within the range of average wetland
soils. Studies show that there is a wide range of
data for certain parameters in what are considered wetland soils
due to varying plant life, hydrology, and climate.
Since wetland soils can vary greatly, there is a benefit
in sampling the soil from an adjacent area with hydrology similar
to the final design of the restoration area, if such an area exists.
This will serve as a reference for determining the desired
final mix ratios of compost and fill.
The substrate from the down stream wetland was sampled along
with the fill to be mixed with the compost.
These samples were sent for analysis, and the results were
used to calculate the target contents and final mix estimates contained
in Table 7. The calculations
assume that 55% of the organic matter consists of organic carbon. Table 5:
Cadman Wetland Restoration Compost Application Rates
Table 6:
Everett Wetland Target Compost Loading Rates
Table 7:
C:N Ratio and Organic Content Estimates
The other parameters are probably not extremely critical
and it is unlikely the addition of compost at reasonable rates would
create a suboptimal growing environment for wetland species. 4.0 Experimental Results
The experimental plots were designed to generate data
in order to determine which application rate and compost type
would best mimic the parameters of the surrounding wetlands. The results indicate that if a stable compost is applied at agronomic
rates, the growth and survival rate of target wetland species
can be aided. The plots
which used compost showed approximately 20% more growth and 10
to 15% higher survival rate than the control plots, which used
no compost. The surrounding
surface water quality did not degrade as a result of the application.
Details of experimental results are provided in the following
sections. 4.1 PLANT GROWTH RESPONSE AND SURVIVAL RATESIn order to study the effects of the use of compost
on wetland species growth and survival, this report presents and
analyzes data on both of these items for each of the experimental
and control plots. These items are of importance to the restoration
of a wetland since they are indicators used to judge the success
of a project. A regulatory
agency can deem a project a success or failure based on plant
survival and invasive species propagation.
Other definitions of success include improvement of wetland
functions such as hydrologic (flood peak reduction, shoreline
stabilization, groundwater exchange), water quality improvement
(sediment, nutrient), and food chain support (species diversity).
If compost could be shown to promote better target species
survival, it might prevent some regulatory failures, and therefore
prevent costly replanting.
The average growth rate (height of plant) of the target
plant species is an indication of their ability to take hold and
out compete invasive species.
Invasive species are highly adaptable and, therefore, can
often out-compete a target plant when substandard substrate is
used. The use of a good
organic substrate offers the target species a good chance to survive
against the opportunistic invaders. Figure 2 on the following page shows the average percent of grow
rate for each of the application rates. The first two bars indicate the first and second plots,
and the third, the average of the two.
As can be seen, nearly all of the application rates had
considerably higher growth rates than the control plots.
The one exception is the 200 lb/acre N greenwaste plots. This is likely due to high water in the first
plot, which led to low growth and high mortality. The second plot did considerably better.
Figure 2
Experimental Plot Growth Comparison
Figure 3 shows the survival rate of the target species
in each application and in the control. Again, each plot is shown along with the average of the two. Similar to what was seen in the growth data,
nearly all of the application rates had higher survival rates,
on average, than the control plot.
The one exception, again, is the 200 lb/acre N greenwaste
plots. This is likely
also due to the flooding in the first plot. The second plot did considerably better than
the first.
Figure 3 Survival Rate Comparison for Experimental
Plots
The data presented in the graphs above is available
in a spreadsheet in Appendix A - Growth and Plant Survival Rate
Spreadsheets. 4.2 SOIL ANALYSESSeveral mesh bags of each soil/compost mixture were
buried in each plot in order to track the nutrient dynamics and
other parameters. At three
points during the first year (0, 6, and 12 months) after construction,
one bag was removed from each plot and sent for lab analysis.
The purpose of these analyses was to determine how the
different mixes would respond over time.
Two experimental plots were established for each compost
application (type and loading rate) and control (no compost applied)
for a total of 14 plots. In
addition, soil samples were taken from the upstream wetland and
analyzed for comparison. The
graphics which follow for each of the target parameters show the
results for the surrounding wetland as well as the averages for
each of the experimental plots.
The following information describes the results of
the analysis of the soils sampled from each of the experimental
plots at 0, 6, and 12 months after the construction of the wetland. The target parameters studied included the following:
·
Total
solids content
·
Volatile
solids content
·
Particle
size
·
pH
·
Conductivity
·
Nitrogen
dynamics
·
Phosphorus
and potassium dynamics
·
Copper
Each of these parameters is tracked and compared to
the existing wetland substrate in the bar charts which follow. Along with the data is a description of each
parameter and its importance within the soil ecosystem. Where appropriate, average wetland soil content
of each parameter is described.
In addition, the section includes information on additional
parameters which were tracked, beyond those originally described
in the proposal. These include:
·
Cation
exchange capacity
·
Magnesium
·
Calcium
·
Sodium
·
Boron
·
Sulfur
·
Zinc
·
Manganese All data for each plot is included in a spread sheet
in Appendix B in addition to the bar charts included in each of
the following sections. At
the end of the section is a matrix of all parameters and best
matches to the existing substrate. 4.2.1 Total and Volatile Solids ContentTotal solids are the total amount of suspended (or
filterable) solids in the compost.
Volatile solids are the organic fraction (anything that
can be decomposed) of the total solids content.
Their measure is important in determining biological stability. Total and volatile solids content at the end
of the 12 month period for each application are shown in Figure
4. All of the plots, with the exception of the
controls, had a solids content similar to that of the existing
wetland. The volatile solids content (organic matter)
for each of the applications was less than that of the existing
substrate, but grew over the 12 month period.
The control plot did not see this increase in organic content. The increase in the volatile solids might be
explained by the favorable conditions for plant growth afforded
by the addition of the compost.
The growth of plants in these plots would result in increased
root growth. The mesh bags may have allowed some root growth through the sides,
which should account for the increased volatile solids.
Figure 4
Total and Volatile Solids Content
4.2.2 Particle Size AnalysisAnalyses of the particle size for each of the plots
allowed for a comparison of soil composition.
This comparison is shown in Figure 5.
The mixes used for this project were designed so as not
to over load the nitrogen. The
composts chosen for use had average levels of nitrogen.
As a result, large amounts of sand substrate had to be
mixed with the compost in order not to overload the nitrogen on
the wetland plots. The results are soils with 10 to 20% more sand
content than the surrounding wetland soils. In hind sight, a compost with a high organic content and a lower
nitrogen content should have been used to provide for a higher
organic content and lower nitrogen content in the final application
mix.
Figure 5
Particle Size Analysis
4.2.3 pHThe pH scale is defined as a measure of acidity or
alkalinity. The range
is from 0 to 14, with seven representing neutrality.
Numbers lower than 7 represent acidity, and numbers greater
than 7 represent alkalinity.
Wetland soils are normally organic and slightly acidic.
All of the pH measurements from the experimental plots
were within one-half a point of the soils in the surrounding wetland. All were slightly acidic, and no dramatic patterns
were seen from the data collected for each plot. The data can be seen in Figure 6.
Figure 6
Analysis of pH at 12 Months
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