Emergent Macrophyte Emergent Macrophyte Density Density In Constructed In Constructed Wetlands for Wetlands for Wastewater Wastewater Treatment Treatment Sophie Lagacé, Curtis Miller, Sophie Lagacé, Curtis Miller, and Robert Gearheart and Robert Gearheart
A little study of emergent plant density and surface area in constructed wetlands for wastewater treatment.
Why do we care? Because when free surface wetlands are used for water treatment, the volume is an important parameter and some of that volume is taken up by the emergent plants; and because these plants offer a large, fractal surface area for the growth of helpful microorganisms, just like in a trickling filter.
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leaves per stem, > 12 mm (½ leaves per stem, > 12 mm (½ in.) widein.) wide
Accumulates leaf and stem Accumulates leaf and stem litterlitter
Field Work - IField Work - I
Select a location and Select a location and
note the species note the species
(monoculture plots)(monoculture plots)
Stake and mark a 1m x Stake and mark a 1m x
1m plot1m plot
Ten plots in all: five for Ten plots in all: five for
TyphaTypha, five for , five for ScirpusScirpus
Field Work - IIField Work - II
Cut stems to about 30-Cut stems to about 30-40 cm above water 40 cm above water level in and around the level in and around the plotplot
Remove the litterRemove the litter
Field Work - IIIField Work - III
Measure water depth Measure water depth
at each corner and in at each corner and in
center of plotcenter of plot
Count every stem Count every stem
within the plotwithin the plot
As a stem is counted, As a stem is counted,
cut it just above cut it just above
water levelwater level
Field Work - IVField Work - IV For two For two ScirpusScirpus plots, measure each stem’s plots, measure each stem’s
average diameter after cutting (round stems)average diameter after cutting (round stems) For two For two Typha Typha plots, measure each stem’s plots, measure each stem’s
maximum and minimum diameters after maximum and minimum diameters after cutting (elliptical stems)cutting (elliptical stems)
Pull five randomly selected stems of Pull five randomly selected stems of Scirpus,Scirpus, whole* whole*
Measure the diameter along the Measure the diameter along the ScirpusScirpus stems stems every 50 mm (2 in.), starting at the base and every 50 mm (2 in.), starting at the base and up to 1mup to 1m
**Typha stems were too decomposed to sample
CalculationsCalculations
Mean areal stem density for each speciesMean areal stem density for each species Mean stem diameter and cross-section for Mean stem diameter and cross-section for
each specieseach species ScirpusScirpus typical taper shape equation typical taper shape equation Wet area for varying water depth and stem Wet area for varying water depth and stem
density for each speciesdensity for each species Submersed volume for varying water depth Submersed volume for varying water depth
and stem density for each speciesand stem density for each species
Areal Density: Stems per mAreal Density: Stems per m22
Stem Diameter and Cross-Stem Diameter and Cross-SectionSection
Scirpus acutus:Scirpus acutus: Maximum diameter along the stem Maximum diameter along the stem
varied between 20 and 30 mmvaried between 20 and 30 mm Typical diameter at water level: ~15 mmTypical diameter at water level: ~15 mm Typical cross-section at water level: Typical cross-section at water level:
190mm190mm22
Typha latifolia:Typha latifolia: Assumed constant cross-section along Assumed constant cross-section along
the stemthe stem Typical diameters at water level: 30mm Typical diameters at water level: 30mm
x 40mmx 40mm Typical cross-section at water level: Typical cross-section at water level:
Bulrush (Scirpus) Wet Area vs. Stem Depthby Stem Areal Density
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
0.00 0.20 0.40 0.60 0.80 1.00
Stem Depth (m)
Sp
ecifi
c S
urf
ace
Are
a (
m2/m
2)
Low 100
Medium 200
High 300
Cattail (Typha) Wet Area vs. Stem Depthby Stem Areal Density
-
1.0
2.0
3.0
4.0
5.0
6.0
0.00 0.20 0.40 0.60 0.80 1.00
Stem Depth (m)
Sp
ecifi
c S
urf
ace
Are
a (
m2/m
2)
Low 30
Medium 40
High 50
Submersed VolumeSubmersed VolumeBulrush (Scirpus) Submersed Volume vs. Stem Depth
by Stem Areal Density
0.00
0.02
0.04
0.06
0.08
0.10
0.00 0.20 0.40 0.60 0.80 1.00
Stem Depth (m)
Volu
me (
m3/m
2)
Low 100
Medium 200
High 300
Cattail (Typha) Submersed Volume vs. Stem Depthby Stem Areal Density
-
0.01
0.02
0.03
0.04
0.05
0.06
0.00 0.20 0.40 0.60 0.80 1.00
Stem Depth (m)
Volu
me (
m3/m
2)
Low 30
Medium 40
High 50
Implications for DesignImplications for Design
Emergent vegetation typically occupies 4 to Emergent vegetation typically occupies 4 to 10% of the available volume 10% of the available volume
Emergent vegetation stems typically offer 1.3 Emergent vegetation stems typically offer 1.3 to 10 mto 10 m22 of surface area for attached growth of surface area for attached growth per mper m22 of wetland (57,000 to 436,000 ft of wetland (57,000 to 436,000 ft22/acre!)/acre!)
Next question for research: Surface area and Next question for research: Surface area and volume of plant litter?volume of plant litter?