A HANDBOOK OF
CONSTRUCTED WETLANDS
a guide to creating wetlands for:
AGRICULTURAL WASTEWATER
DOMESTIC WASTEWATER
COAL MINE DRAINAGE
STORMWATER
in the Mid-Atlantic Region
Volume
GENERAL CONSIDERATIONS
-------
ACKNOWLEDGMENTS
Many people contributed to this Handbook. An interagency Core Group provided the initial impetus for the Handbook, and later provided
guidance and technical input during its preparation. The Core Group comprised:
Carl DuPoldt, USDA - NRCS. Chester, PA
Robert Edwards, Susquehanna River Basin Commission,
Harrisburg, PA
Lamonte Garber, Chesapeake Bay Foundation, Harrisburg. PA
Barry Isaacs, USDA - NRCS, Harrisburg, PA
Jeffrey Lapp. EPA, Philadelphia, PA
Timothy Murphy, USDA - NRCS, Harrisburg, PA
Glenn Rider, Pennsylvania Department of Environmental
Resources, Harrisburg. PA
Melanie Sayers, Pennsylvania Department of Agriculture, Harrisburg, PA
Fred Suffian, USDA - NRCS Philadelphia, PA
Charles Takita, Susquehanna River Basin Commission, Harrisburg, PA
Harold Webster, Penn State University, DuBois, PA.
Many experts on constructed wetlands contributed by providing information and by reviewing and commenting on the Handbook. These
Individuals included:
Robert Bastian. EPA .WashinSton, DC
William Boyd, USDA - NRCS. Lincoln, NE
Robert Brooks, Penn State University,
University Park, PA
Donald Brown, EPA, Cincinnati, OH
Dana Chapman, USDA - NRCS, Auburn, NY
Tracy Davenport, USDA -NRCS, Annapolis,
MD
Paul DuBowy, Texas A & M University,
College Station, TX
Michelle Girts, CH2M HILL, Portland, OR
Robert Hedin, Hedin Environmental,
Sewickley, PA
William Hellier. Pennsylvania Department of
Environmental Resources, Hawk Run, PA
Robert Kadlec, Wetland Management
Services, Chelsea, MI
Douglas Kepler, Damariscotta. Clarion, PA
Robert Kleinmann, US Bureau of Mines,
Pittsburgh, PA
Robert Knight, CH2M HILL, Gainesville, FL
Fran Koch, Pennsylvania Department of
Environmental Resources, Harrisburg, PA
Eric McCleary, Damariscotta, Clarion, PA
Gerald Moshiri, Center for Wetlands and
Eco-Technology Application, Gulf Breeze,
FL
John Murtha, Pennsylvania Department of
Environmental Resources, Harrisburg. PA
Robert Myers, USDA - NRCS, Syracuse, NY
Kurt Neumiller, EPA, Annapolis, MD
Richard Reaves, Purdue University, West
Lafayette, IN
William Sanville, EPA, Cincinnati, OH
Dennis Sievers, University of Missouri,
Columbia, MO
Earl Shaver, Delaware Department of
Natural Resources and Environmental
Control, Dover, DE
Daniel Seibert, USDA - NRCS, Somerset, PA
Jeffrey Skousen, West Virginia University,
Morgantown. WV
Peter Slack, Pennsylvania Department of
Environmental Resources, Harrisburg, PA
Dennis Verdi, USDA - NRCS, Amherst, MA
Thomas Walski, Wilkes University, Wilkes-
Barre, PA
Robert Wengryznek, USDA - NRCS, Orono,
ME
Alfred Whitehouse, Office of Surface
Mining. Pittsburgh, PA
Christopher Zabawa, EPA, Washington, DC.
This document was prepared by Luise Davis for the USDA-Natural Resources Conservation Service and the US Environmental Protection
Agency-Region III, in cooperation with the Pennsylvania Department of Environmental Resources. Partial funding has been provided with
nonpoint source management program funds under Section 319 of the Federal Clean Waler Act.
The findings, conclusions, and recommendations contained in the Handbook do not necessarily represent the policy of the USDA - NRCS,
EPA - Region III, the Commonwealth of Pennsylvania, or any other state in the northeastern United States concerning the use of constructed
wetlands for the treatment and control of nonpoint sources of pollutants. Each state agency should be consulted to determine specific
programs and restrictions in this regard.
-------
VOLUME 1
TABLE OF CONTENTS
CHAPTER 1. INTRODUCTION.
CHAPTER 2. CONSTRUCTED WETLANDS AS ECOSYSTEMS 7
What Are Wetlands? 7
Wetland Functions and Values.. 7
Components of Constructed Wetlands 8
Water. 8
Substrates, Sediments, and Litter 8
Vegetation 8
Microorganisms 9
Animals 9
Aesthetics and Landscape Enhancement 10
CHAPTER 3. CONSTRUCTED WETLANDS AS TREATMENT SYSTEMS 11
How Wetlands Improve Water Quality ll
Advantages of Constructed Wetlands 11
Limitations of Constructed Wetlands 11
Types of Constructed Wetlands 12
Surface Flow Wetlands 13
Subsurface Flow Wetland 13
Hybrid Systems 13
Winter and Summer Operation 13
Creation of Hazard 14
Change and Resilience 14
CHAPTER 4. GENERAL DESIGN OF CONSTRUCTED WETLANDS 17
Design Considerations 17
Planning 17
Site Selection 18
Land Use and Access.. 18
Land Availability 18
Topography 19
Environmental Resources 19
Permits and Regulations 19
Structures 20
Cells 20
Liners 20
Flow Control Structures 20
Inlets 21
Outlets 22
System Lifetimes 23
-------
Chapter 5. HYDROLOGY 25
Climate and Weather 25
Hydroperiod 25
Hydraulic Residence Time 26
Hydraulic Loading Rate 26
Groundwater Exchange 26
Evapotranspiration 26
Water Balance 26
Chapter 6. SUBSTRATES.. 29
Soil 29
Sand and Gravel 39
Organic Material 30
Chapter 7, VEGETATION 31
Selecting plants 31
Surface Flow Wetlands 31
Subsurface Flow Wetlands 34
Sources of Plants 34
Seeds 34
Wetland Soil 34
Rhizomes,Tubers. and Entire Plants 34
When To Plant. 35
Site Preparation 35
How To Plant 36
Surface Flow Wetlands 36
Subsurface Flow Wetlands 36
Establishing and Maintaining Vegetation 36
Chapter 8. CONSTRUCTION 39
Construction Plans 39
Pre-Construction Activities 39
Construction Activities 39
Inspection, Startup, and Testing 40
Chapter 9: OPERATION, MAINTENANCE, AND MONITORING 41
Operation and Maintenance 41
Operation and Maintenance Plan :. 41
Hydrology 41
Structures 41
Vegetation 42
Muskrats 42
Mosquitoes 42
Monitoring 43
Monitoring Plan 43
Monitoring for Discharge Compliance 43
Monitoring for System Performance 43
Monitoring for Wetland Health 44
-------
REFERENCES .1 45
PHOTOGRAPHS 47
LIST OF TABLES
Table 1. Emergent plants for constructed wetlands 32
LIST OF FIGURES
Figure 1. Surface flow and subsurface flow constructed wetlands 12
Figure 2. Inlet and outlet designs 21
Figure 3. Influent splitter box 22
-------
CHAPTER 1
INTRODUCTION
Natural processes have always cleansed
water as it flowed through rivers, lakes, streams,
and wetlands. In the last several decades,
systems have been constructed to use some of
these processes for water quality improvement.
Constructed wetlands are now used to improve
the quality of point and nonpoint sources of
water pollution, including stormwater runoff,
domestic wastewater, agricultural wastewater,
and coal mine drainage. Constructed wetlands
are also being used to treat petroleum refinery
wastes, compost and landfill leachates, fish
pond discharges, and pretreated industrial
wastewaters, such as those from pulp and paper
mills, textile mills, and seafood processing. For
some wastewaters, constructed wetlands are the
sole treatment; for others, they are one compo-
nent in a sequence of treatment processes.
One of the most common applications of
constructed wetlands has been the treatment of
primary or secondary domestic sewage effluent.
Constructed wetland systems modelled after
those for domestic wastewater are being used to
treat the high organic loads associated with
agriculture. A large number of wetlands have
been constructed to treat drainage from active
and abandoned coal mines and more than 500
such systems are operating in Appalachia alone.
The use of constructed wetlands to control
stormwater flows and quality is a recent applica-
tion of the technology and the number of such
systems is increasing rapidly.
The treatment of wastewater or stormwater
by constructed wetlands can be a low-cost, low-
energy process requiring minimal operational
attention. As a result of both extensive research
and practical application, insight is being gained
into the design, performance, operation, and
maintenance of constructed wetlands for water
quality improvement. Constructed wetlands can
be sturdy, effective systems. However, to be
effective, they must be carefully designed,
constructed, operated, and maintained.
This Handbook has been prepared as a
general guide to the design, construction, opera-
tion, and maintenance of constructed wetlands
for the treatment of domestic wastewater, agri-
cultural wastewater, coal mine drainage, and
stormwater runoff in the mid-Atlantic region,
The Handbook is not a design manual. The use
of constructed wetlands to improve water quality
is a developing technology. Much is not yet
understood, and questions remain regarding the
optimal design of wetland systems and their
longevity. As our experience with these systems
increases, the information offered here will be
replaced by more refined information. The
Handbook should be used with this clearly in
mind.
The Handbook is divided into five volumes.
This, the first, provides information common to
all types of constructed wetlands for wastewater
and runoff. It is to be used in conjunction with
an accompanying volume that provides informa-
tion specific to a particular type of wastewater or
runoff. The other volumes in the series are
Volume 2: Domestic Wastewater, Volume 3:
Agricultural Wastewater, Volume 4: Coal Mine
Drainage, and Volume 5: Stormwater Runoff.
While constructed wetlands are being used to
treat other kinds of wastewater, such as indus-
trial wastewaters, a discussion of these applica-
tions is beyond the scope of this Handbook.
However, the information presented here may be
useful in developing other applications.
A number of conferences on constructed
wetlands have been held recently. The proceed-
ings of these conferences include experimental
and operational data from wetland systems built
to treat a number of different kinds of wastewa-
ters and runoff, and present detailed discussions
of process kinetics and system design. Proceed-
ings from three well-known conferences are:
Moshiri, G. A. (ed.) 1993. Constructed Wetlands
for Water Quality Improvement. CRC Press, Boca
Raton, FL. 632 pp.
VOLUME 1: GENERAL CONSIDERATIONS
-------
Cooper, P. F., and B. C. Findlater (eds.) 1990.
Constructed Wetlands in Water Pollution Control.
Proceedings of the International Conference on
the Use of Constructed Wetlands in Water Pollu-
tion Control. Cambridge, UK, 24-28 September.
WRc, Swindon, Wiltshire, UK. 605 pp.
Hammer, D. A. (ed.) 1989. Constructed Wetlands
for Wastewater Treatment: Municipal, Industrial
and Agricultural. Lewis Publishers. Chelsea, MI.
831 pp.
Conferences and published' information continue
to become available as more constructed wetland
systems are built and monitored.
VOLUME 1: GENERALCONSIDERATION
-------
CHAPTER 2
CONSTRUCTED WETLANDS AS ECOSYSTEMS
Constructed wetlands for water treatment
are complex, integrated systems of water,
plants, animals, microorganisms, and the
environment. While wetlands are generally
reliable, self-adjusting systems, an understand-
ing of how natural wetlands are structured and
how they function greatly increases the likeli-
hood of successfully constructing a treatment
wetland. This chapter provides an overview of
the major components of wetland ecosystems
and of the most important processes that affect
water treatment.
WHAT ARE WETLANDS?
Wetlands are transitional areas between land
and water. The boundaries between wetlands
and uplands or deep water are therefore not
always distinct. The term "wetlands" encom-
passes a broad range of wet environments,
including marshes, bogs, swamps, wet meadows,
tidal wetlands, floodplains, and ribbon (riparian)
wetlands along stream channels.
All wetlands - natural or constructed, fresh-
water or salt - have one characteristic in com-
mon: the presence of surface or near-surface
water, at least periodically. In most wetlands,
hydrologic conditions are such that the substrate
is saturated long enough during the growing
season to create oxygen-poor conditions in the
substrate. The lack of oxygen creates reducing.
(oxygen-poor) conditions within the substrate
and limits the vegetation to those species that are
adapted to low-oxygen environments.
The hydrology of wetlands is generally one
of slow flows and either shallow waters or
saturated substrates. The slow flows and shal-
low water depths allow sediments to settle as the
water passes through the wetland. The slow
flows also provide prolonged contact times
between the water and the surfaces within the
wetland. The complex mass of organic and
inorganic materials and the diverse opportunities
for gas/water interchanges foster a diverse commu-
nity of microorganisms that break down or trans-
form a wide variety of substances.
Most wetlands support a dense growth of
vascular plants adapted to saturated conditions.
This vegetation slows the water, creates microenvi-
ronments within the water column, and provides
attachment sites for the microbial community.
The litter that accumulates as plants die back in
the fall creates additional material and exchange
sites, and provides a source of carbon, nitrogen,
and phosphorous to fuel microbial processes.
WETLAND FUNCTIONS
AND VALUES
Wetlands provide a number of functions and
values. (Wetland functions are the inherent
processes occurring in wetlands; wetland values
are the attributes of wetlands that society per-
ceives as beneficial.) While not all wetlands
provide all functions and values, most wetlands
provide several. Under appropriate circumstances.
constructed wetlands can provide:
• water quality improvement
• flood storage and the desynchronization of storm
rainfall and surface runoff
• cycling of nutrients and other materials
• habitat for fish- and wildlife
• passive recreation, such as bird watching
and photography
• active recreation, such as hunting
• education and research
• aesthetics and landscape enhancemerit.'
VOLUME 1 GENERAL CONSIDERATIONS
-------
COMPONENTS OF
CONSTRUCTED WETLANDS
A constructed wetland consists of a properly-
designed basin that contains water, a substrate, and,
most commonly, vascular plants. These components
can be manipulated in constructing a wetland. Other
important components of wetlands, such as the
communities of microbes and aquatic invertebrates,
develop naturally.
WATER
Wetlands are likely to form where landforms
direct surface water to shallow basins and where a
relatively impermeable subsurface layer prevents the
surface water from seeping into the ground. These
conditions can be created to construct a wetland. A
wetland can be built almost anywhere in the land-
scape by shaping the land surface to collect surface
water and by sealing the basin to retain the water.
Hydrology is the most important design factor in
constructed wetlands because it links all of the
functions in a wetland and because it is often the
primary factor in the success or failure of a con-
structed wetland. While the hydrology of con-
structed wetlands is not greatly different than that of
other surface and near-surface waters, it does differ in
several important respects:
. small changes in hydrology can have fairly signifi-
cant effects on a wetland and its treatment effec-
tiveness
. because of the large surface area of the water and
its shallow depth, a wetland system interacts
strongly with the atmosphere through rainfall and
evapotranspiration (the combined loss of water by
evaporation from the water surface and loss
through transpiration by plants)
. the density of vegetation of a wetland strongly affects
its hydrology, first, by obstructing flow paths as the
water finds its sinuous way through the network of
stems, leaves, roots, and rhizomes and, second, by
blocking exposure to wind and sun.
SUBSTRATES, SEDIMENTS, AND LITTER
Substrates used to construct wetlands in-
clude soil, sand, gravel, rock, and organic
materials such as compost. Sediments and litter
then accumulate in the wetland because of the
low water velocities and high productivity
typical of wetlands. The substrates, sediments,
and litter are important for several reasons:
. they support many of the living organisms in
wetlands
. substrate permeability affects the movement of
water through the wetland
. many chemical and biological (especially
microbial) transformations take place within
the substrates
. substrates provide storage for many
contaminants
. the accumulation of litter increases the amount
of organic matter in the wetland. Organic matter
provides sites for material exchange and micro-
bial attachment, and is a source of carbon, the
energy source that drives some of the important
biological reactions in wetlands.
The physical and chemical characteristics of
soils and other substrates are altered when they
are flooded. In a saturated substrate, water
replaces the atmospheric gases in the pore
spaces and microbial metabolism consumes the
available oxygen. Since oxygen is consumed
more rapidly than it. can be replaced by diffusion
from the atmosphere, substrates become anoxic
(without oxygen). This reducing environment is
important in the removal of pollutants such as
nitrogen and metals.
VEGETATION
Both vascular plants (the higher plants) and
non-vascular plants (algae) are important in
constructed wetlands. Photosynthesis by algae
increases the dissolved oxygen content of the
water which in turn affects nutrient and metal
VOLUME 1: GENKRAI. CONSIDERATIONS
-------
Constructed wetlands attract waterfowl and
wading birds, including mallards, green-winged
teal, wood ducks, moorhens, green and great
blue herons, and bitterns. Snipe, red-winged
blackbirds, marsh wrens, bank swallows, red-
tailed hawks, and Northern harriers feed and/or
nest in wetlands.
AESTHETICS AND LANDSCAPE
ENHANCEMENT
While wetlands are primarily treatment
systems, they provide intangible benefits by
increasing the aesthetics of the site and enhanc-
ing the landscape. Visually, wetlands are unusu-
ally rich environments. By introducing the
element of water to the landscape, constructed
wetlands, as much as natural wetlands, add
diversity to the landscape. The complexity of
shape, color, size, and interspersion of plants,
and the variety in the sweep and curve of the
edges of landforms all add to the aesthetic
quality of the wetlands. Constructed wetlands
can be built with curving shapes that follow the
natural contours of the site, and some wetlands
for water treatment are' indistinguishable, at first
glance, from natural wetlands.
VOLUME!: GENERAL CONSIDERATIONS
-------
reactions. Vascular plants contribute to the
treatment of wastewater and runoff in a
number of ways:
• they stabilize substrates and limit
channelized flow
• they slow water velocities, allowing sus-
pended materials to settle
• they take up carbon, nutrients, and trace
elements and incorporate them into plant
tissues
• they transfer gases between the atmosphere
and the sediments
• leakage of oxygen from subsurface plant
structures creates oxygenated microsites
within the substrate
• their stem and root systems provide sites
for microbial attachment
• theycreate litter when they die and decay.
Constructed wetlands are usually planted
with emergent vegetation (non-woody plants
that grow with their roots in the substrate
and their stems and leaves emerging from
the water surface). Common emergents
used in constructed wetlands include
bulrushes, cattails, reeds, and a number of
broad-leaved species.
M ICROORGANISMS
A fundamental characteristic of wetlands is
that their functions are largely regulated by
microorganisms and their metabolism (Wetzel
1993). Microorganisms include bacteria, yeasts,
fungi, protozoa, rind algae. The microbial
biomass is a major sink for organic carbon and
many nutrients. Microbial activity:
. transforms a great number of organic and
inorganic substances into innocuous or
insoluble substances
. alters the reduction/oxidation (redox) condi-
tions of the substrate and thus affects the
processing capacity of the wetland
. is involved in the recycling of nutrients.
Some microbial transformations are aerobic
(that is, they require free oxygen) while others
are anaerobic (they take place in the absence of
free oxygen). Many bacterial species are faculta-
tive anaerobes, that is, they are capable of func-
tioning under both aerobic and anaerobic condi-
tions in response to changing environmental
conditions.
Microbial populations adjust to changes in
the water delivered to them. Populations of
microbes can expand quickly when presented
with suitable energy-containing materials. When
environmental conditions are no longer suitable,
many microorganisms become dormant and can
remain dormant for years (Hilton 1993).
The microbial community of a constructed
wetland can be affected by toxic substances,
such as pesticides and heavy metals, and care
must be taken to prevent such chemicals from
being introduced at damaging concentrations.
A
M
Constructed wetlands provide habitat for a
rich diversity of invertebrates and vertebrates.
Invertebrate animals, such as insects and worms.
contribute to the treatment process by fragment-
ing detritus and consuming organic matter. The
larvae of many insects are aquatic and consume
significant amounts of material during their
larval stages, which may last for several years.
Invertebrates also fill a number of ecological
roles; for instance, dragonfly nymphs are impor-
tant predators of mosquito larvae.
Although invertebrates are the most
important animals as far as water quality im-
provement is concerned, constructed wetlands
also attract a variety of amphibians, turtles,
birds, and mammals.
VOLUME 1: GENERAL CONSIDERATIONS
-------
CHAPTER 3
CONSTRUCTED WETLANDS AS TREATMENT SYSTEMS
A constructed wetland is a shallow basin
filled with some sort of substrate, usually soil or
gravel, and planted with vegetation tolerant of
saturated conditions. Water is introduced at one
end and flows over the surface or through the
substrate, and is discharged at the other end
through a weir or other structure which controls
the depth of the water in the wetland.
HOW WETLANDS IMPROVE
WATER QUALITY
A wetland is a complex assemblage of water,
substrate, plants (vascular and algae), litter
(primarily fallen plant material), invertebrates
(mostly insect larvae and worms), and an array
of microorganisms (most importantly bacteria).
The mechanisms that are available to improve
water quality are therefore numerous and often
interrelated. These mechanisms include:
. settling of suspended particulate matter
. filtration and chemical precipitation through
contact of the water with the substrate and
litter
. chemical transformation
. adsorption and ion exchange on the surfaces of
plants, substrate, sediment, and litter
. breakdown and transformation of pollutants by
microorganisms and plants
. uptake and transformation of nutrients by
microorganisms and plants
. predation and natural die-off of pathogens.
The most effective treatment wetlands are
those that foster these mechanisms. The specif-
ics for the various types of wastewater and
runoff are discussed in the wastewater-specific
volumes.
ADVANTAGES OF
CONSTRUCTED WETLANDS
Constructed wetlands are a cost-effective and
technically feasible approach to treating waste-
water and runoff for several reasons:
. wetlands can be less expensive to build than
other treatment options
. operation and maintenance expenses (energy
and supplies) are low
. operation and maintenance require only
periodic, rather than continuous, on-site labor
. wetlands are able to tolerate fluctuations in
flow
. they facilitate water reuse and recycling.
In addition:
. they provide habitat for many wetland organisms
. they can be built to fit harmoniously into the
landscape
. they provide numerous benefits in addition to
water quality improvement, such as wildlife
habitat and the aesthetic enhancement of open
spaces
. they are an environmentally-sensitive
approach that is viewed with favor by the
general public.
LIMITATIONS OF
CONSTRUCTED WETLANDS
There are limitations associated with the use
of constructed wetlands:
. they generally require larger land areas than
do conventional wastewater treatment sys-
tems. Wetland treatment may be economical
relative to other options only where land is
available and affordable.
VOLUME 1: GENERAL CONSIDERATIONS
17
-------
performance may be less consistent than in
conventional treatment. Wetland treatment
efficiencies may vary 'seasonally in response to
changing environmental conditions, including
rainfall and drought. While the average perfor-
mance over the year may be acceptable, wetland
treatment cannot be relied upon if effluent
quality must meet stringent discharge standards
at all times.
the biological components are sensitive to toxic
chemicals, such as ammonia and pesticides
flushes of pollutants or surges in water flow may
temporarily reduce treatment effectiveness
they require a minimum amount of water if they
are to survive. While wetlands can tolerate
temporary drawdowns, they cannot withstand
complete drying.
Also, the use of constructed wetlands for waste-
water treatment and stormwater control is a fairly
recent development. There is yet no consensus on
the optimal design of wetland systems nor is there
much information on their long-term performance.
TYPES OF CONSTRUCTED
WETLANDS
There are several types of constructed wetlands:
surface flow wetlands, subsurface flow wetlands,
and hybrid systems that incorporate surface and
subsurface flow wetlands. Constructed wetland
systems can also be combined with conventional
treatment technologies. The types of constructed
wetlands appropriate for domestic wastewater,
agricultural wastewater, coal mine drainage, and
stormwater runoff are discussed in the wastewater-
specific volumes.
Water level is above the ground surface; vegetation is rooted and emerges
above the water surface: waterflow is primarily above ground
WETLAND PLANTS AND WATER
SOIL
LINER
NATIVE SOIL
Surface Flow Wetland
Water level is below ground; water flow is through a sand or gravel bed; roots
penetrate to the bottom of the bed
WETLAND PLANTS
SOIL. SAND. AND GRAVEL
LINER
NATIVE SOIL
Subsurface Flow Wetland
Figure 1. Surface flow and subsurface flow constructed wetlands
(from Water Pollution Control Federation 1990).
VOLUME 1 : GENERAL CONSIDERATIONS
-------
SURFACE FLOW WETLANDS
A surface flow (SF) wetland consists of a
shallow basin, soil or other medium to support the
roots of vegetation, and a water control structure
that maintains a shallow depth of water (figure 1).
The water surface is above the substrate. SF
wetlands look much like natural marshes and can
provide wildlife habitat and aesthetic benefits as
well as water treatment. In SF wetlands, the near-
surface layer is aerobic while the deeper waters
and substrate are usually anaerobic. Stormwater
wetlands and wetlands built to treat mine drainage
and agricultural runoff are usually SF wetlands.
SF wetlands are sometimes called free water
surface wetlands or, if they are for mine drainage,
aerobic wetlands. The advantages of SF wetlands
are that their capital and operating costs are low,
and that their construction, operation, and mainte-
nance are straightforward. The main disadvantage
of SF systems is that they generally require a larger
land area than other systems.
SUBSURFACE FLOWWETLANDS
A subsurface flow (SSF) wetland consists of a
sealed basin with a porous substrate of rock or
gravel. The water level is designed to remain below
the top of the substrate. In most of the systems in the
United States, the flow path is horizontal, although
some European systems use vertical flow paths. SSF
systems are called by several names, including
vegetated submerged bed, root zone method, micro-
bial rock reed filter, and plant-rock filter systems.
Because of the hydraulic constraints imposed
by the substrate, SSF wetlands are best suited to
wastewaters with relatively low solids concentra-
tions and under relatively uniform flow conditions.
SSF wetlands have most frequently been used to
reduce 5-day biochemical oxygen demand (BOD5)
from domestic wastewaters.
The advantages cited for SSF wetlands are
greater cold tolerance, minimization of pest and
odor problems, and, possibly, greater assimilation
potential per unit of land area than in SF systems.
It has been claimed that the porous medium
provides greater surface area for treatment contact
than is found in SF wetlands, so that the treatment
responses should be faster for SSF wetlands which
can, therefore, be smaller than a SF system de-
signed for the same volume of wastewater. Since
the water surface is not exposed, public access
problems are minimal. Several SSF systems are
operating in parks, with public access encouraged.
The disadvantages of SSF wetlands are that
they are more expensive to construct, on a unit
basis, than SF wetlands. Because of cost, SSF
wetlands are often used for small flows. SSF
wetlands may be more difficult to regulate than SF
wetlands, and maintenance and repair costs are
generally higher than for SF wetlands. A number of
systems have had problems with clogging and
unintended surface flows.
H YBRIDSYSTEMS
Single stage systems require that all of the
removal processes occur in the same space. In
hybrid or multistage systems, different cells are
designed for different types of reactions. Effective
wetland treatment of mine drainage may require a
sequence of different wetland cells to promote
aerobic and anaerobic reactions, as may the re-
moral of ammonia from agricultural wastewater.
WINTER AND SUMMER
OPERATION
Wetlands continue to function during cold
weather. Physical processes, such as sedimenta-
tion, continue regardless of temperature, providing
that the water does not freeze. Many of the reac-
tions take place within the wetland substrate,
where decomposition and microbial activity
generate enough heat to keep the subsurface layers
from freezing. Water treatment will continue
under ice. To create space for under-ice flow,
water levels can be raised in anticipation of freeze,
then dropped once a cover of ice has formed.
VOLUME 1: GENERAL CONSIDERATIONS
-------
Rates of microbial decomposition slow as
temperatures drop and the wetland may need to
be made larger to accommodate the slower
reaction rates. For agricultural wetlands, which
rely on microbial activity to break down organic
wastes, it may be prudent to store the wastewa-
ter in the pretreatment unit during the cold
months for treatment during the warm months.
The high flows that are common in winter and
spring because of snowmelt, spring rains, and
high groundwater tables can move water so
quickly through a wetland tHat there is not
enough retention time for adequate treatment.
Because removal rates are much higher during
warm weather, the agricultural wetland can
often be smaller than if the water were treated
year-round.
Wetlands lose large amounts of water in the
summer through evapotranspiration. The ade-
quacy of flow in the summer must be considered
since it will affect water levels in the wetland and
the amount of wetland effluent available for
recycling (if this is part of the design). A supple-
mental source of water may be required to main-
tain adequate moisture in the wetland.
CREATION OF HAZARD
The question of hazard arises from the fact
that, in ecological terms, everything must go
somewhere. Wetlands are able to degrade,
transform, or assimilate many contaminants,
such nitrogen, and are sinks for some materials.
For persistent materials, such as phosphorous
and metals, wetland sinks may become sources
if not properly constructed and managed. The
extent to which wetlands retain contaminants
such as phosphorous and metals is an important
unknown factor, as are the conditions under
which wetlands may release stored contami-
nants. Bioaccumulation and biotoxicity in
treatment wetlands is not clearly documented
nor understood.
Persistent compounds can be a concern,
depending on the constituents in the wastewa-
ter. For instance, mine drainage contains metals
and stormwater carries hydrocarbons deposited
on paved surfaces. Heavy metals are often
sequestered in wetland sediments that may be
washed out of wetlands during storms, thereby
providing only a lag time in pollutant dispersal.
Transport of toxic materials in this way is a
concern, as is the transport of phosphorus, an
extremely important factor in the over-enrich-
ment of surface waters. The question of hazard
underscores the importance of designing and
operating constructed wetlands properly and
monitoring them periodically.
CHANGE AND RESILIENCE
All ecosystems change over time. Wetlands for
wastewater treatment can be expected to change
more quickly than most natural wetlands because
of the rapid accumulation of sediment, litter, and
pollutants. Some natural variability is also inher-
ent in all living systems and is to be expected.
The change in species composition as eco-
systems mature is known as succession. In
general, species diversity increases as ecosys-
tems mature. Diversity (the number of species
within a habitat, such as a wetland) is often
considered a measure of ecosystem resilience
(the ability of the system to accept disturbance):
as the number of species increases, so does the
complexity of the interactions of the different
species with each other and with their environ-
ment; the greater the number of interactions, the
more resilient the system is as a whole and the
broader its capacity to adapt to change.
In wastewater treatment wetlands, the
stresses of high wastewater loadings can lead to
dominance by a few aggressive, highly tolerant
species, such as cattail and common reed, which
may eventually eliminate other species. If
wildlife habitat values are important to the
VOLUME 1 : GENERAL CONSIDERATIONS
-------
project, intervention to maintain diversity may
be necessary. If habitat values are not important,
changes can be allowed to proceed without
interference as long as the wetland continues to
treat the water to acceptable levels.
Any ecosystem, natural or constructed, has
limits to its ability to accept disturbance. The
performance of constructed wetland systems
may change over time as a consequence of
changes in the substrate and the accumulation of
pollutants in the wetland. Constructed wetlands
must be monitored periodically for evidence of
stress so that remedial action, if necessary, can
be taken.
VOLUME 1: GENERAL CONSIDERATIONS 15
-------
CHAPTER 4
GENERAL DESIGN OF CONSTRUCTED WETLANDS
DESIGN CONSIDERATIONS
Despite a large amount of research and pub-
lished information, the optimal design of con-
structed wetlands for various applications has not
yet been determined. Many constructed wetland
systems have not been adequately monitored or
have not been operating long enough to provide
sufficient data for analysis. Among the systems
that have been monitored, performance has varied
and the influences of the diverse factors that affect
performance, such as location, type of wastewater
or runoff, wetland design, climate, weather,
disturbance, and daily or seasonal variability, 'have
been difficult to quantify.
In general, wetland designs attempt to mimic
natural wetlands in overall structure while foster-
ing those wetland processes that are thought to
contribute the most to the improvement of water
quality. Mitsch (1992) suggests the following
guidelines for creating successful constructed
wetlands:
• keep the design simple. Complex technological
approaches often invite failure.
• design for minimal maintenance.
• design the system to use natural energies, such as
gravity flow.
• design for the extremes of weather and climate,
not the average. Storms, floods, and droughts are
to be expected and planned for, not feared.
• design the wetland with the landscape, not
against it. Integrate the design with the natural
topography of the site.
• avoid over-engineering the design with rectangu-
lar basins, rigid structures and channels, and
regular morphology. Mimic natural systems.
• give the system time. Wetlands do not necessar-
ily become functional overnight and several
years may elapse before performance reaches
optimal levels. Strategies that try to short-circuit
the process of system development or to over-
manage often fail.
design the system for function, not form. For
instance, if initial plantings fail, but the overall
function of the wetland, based on initial objec-
tives, is intact, then the system has not failed.
PLANNING
A conceptual planning phase is essential.
Wetlands can be designed in a variety of system
types and configurations to meet specific wastewa-
ter needs, alternative sites are often available, and
a variety of local, native plant species can be
chosen. Every site is unique and the design of a
constructed wetland system will be site-specific.
The planning phase consists of characterizing
the quantity and quality of the wastewater to be
treated, determining the discharge standards to be
met, selecting the site, selecting system type and
configuration, and specifying the design criteria to
be met by the detailed engineering plans. Eco-
nomic factors include the land area required, the
type of water containment, the control and trans-
port of water through the system, and vegetation.
Setting and prioritizing the objectives of the
wetland system is key to the creation of a success-
ful system. The characteristics of a local natural
wetland should be used as a model for the con-
structed wetland, modified to fit the needs of the
project and the specifics of the constructed wet-
land site.
A constructed wetland should be designed to
take advantage of the natural features of the site
and to minimize its disturbance. Wetland shape is
dictated by the existing topography, geology, and
land availability. The number of cells depends on
topography, hydrology, and water quality. On
level sites, cells can be created with dikes. On
sloping sites, cells can be terraced.
A site-sensitive design that incorporates
existing features of the site reduces the amount
VOLUME 1: GENERAL CONSIDERATIONS
37
-------
of earthmoving required and increases the visual
attractiveness of the site. Earth grading and
shaping can blend newly created landforms into
the existing landscape. Basins and channels can
be curved to follow the natural contours of the
site. Various types of vegetation can be planted in
and around a constructed wetland to reduce
erosion, screen views, define space, control
microclimate, and control traffic patterns.
Planning should be oriented toward the
creation of a biologically and hydrologically
functional system. Plans should include clear
goal statements and standards for success. The
possible future expansion of the operation
should be considered.
Plans should include detailed instructions
for implementing a contingency plan in case the
system does not achieve its expected perfor-
mance within a specified time. Plans should be
reviewed and approved by the appropriate
regulatory agencies.
SITE SELECTION
Selecting an appropriate location can save
significant costs. Site selection should consider
land use and access, the availability of the land,
site topography, soils, the environmental resources
of the site and adjoining land, and possible effects
on any neighbors. The site should be located as
close to the source of the wastewater as possible,
and downgradient if at all possible so that water
can move through the system by gravity. While a
wetland can be fitted to almost any site, construc-
tion costs can be prohibitively high if extensive
earthmoving or expensive liners are required.
A site that is well suited for a constructed
wetland is one that:
. is conveniently located to the source of the
wastewater
• provides adequate space
. is gently sloping, so that water can flow through
the system by gravity
. contains soils that can be sufficiently compacted to
minimize seepage to groundwater
. is above the water table
. is not in a floodplain
. does not contain threatened or endangered species
. does not contain archaeological or historic resources.
LAND U S E AND ACCESS
Access is an important consideration, The wet-
land should be placed so that the water can flow by
gravity. If the odors or insects could be a problem, as
with some agricultural wastewaters, the wetland
should be placed as far from dwellings as possible.
The site should be accessible to personnel, delivery
vehicles, and equipment for construction and mainte-
nance.
For agricultural and some domestic wastewaters,
the wetland may be installed on private land. The
landowner must be carefully chosen. It is essential
that the landowner is cooperative and fully under-
stands the limitations and uncertainties associated
with a developing technology such as constructed
wetland treatment.
The current and future use and values of adjoining
land also will affect the suitability of a site for a
constructed wetland. The opinions of area residents
and those of environmental and public interest groups
should be considered. A large buffer zone should be
placed between the wetland and neighboring property.
The wetland should not be placed next to the edge of
the property.
LAND AVAILABILITY
The effectiveness of a constructed wetland in
treating wastewater or stormwater is related to the
retention time of the water in the wetland. The
usefulness of a constructed wetland may therefore be
limited by the size of the wetland needed for adequate
retention time. The site selected should be large
enough to accommodate present requirements and any
future expansion.
VOLUME 1: GENERAL CONSIDERATIONS
-------
TOPOGRAPHY
Landform considerations include shape, size,
and orientation to the prevailing winds. While a
constructed wetland can be built almost anywhere,
selecting a site with gradual slopes that can be easily
altered to collect and hold water simplifies design
and construction, and minimizes costs.
Previously drained wetland areas, including
prior converted (PC) agricultural sites, may be well-
suited for a constructed wetland since the topogra-
phy is usually conducive to gravity flow. The
appropriate regulatory agencies must be contacted
before disturbing any PC site.
Since the best location for a constructed wetland is
a low, flat area where water flows by gravity, it is
important to ensure that the area is not already a
wetland: not all wetlands have standing water through-
out the year. The Natural Resources Conservation
Service (NRCS), the US Fish and Wildlife Service, or
state regulatory personnel should be contacted to
determine whether or not a site contains jurisdictional
wetlands.
such as the Agricultural Stabilization and Conser-
vation Service (ASCS) crop compliance photogra-
phy and county soil survey information, can be
useful in identifying hydric soils and drained
wetlands that may be difficult to detect otherwise.
Surface and groundwater considerations
include possible flooding and drainage problems,
location and depth of aquifers, and the location,
extent, and classification of receiving waters such
as streams and groundwater. A constructed wet-
land should not be sited on a floodplain unless
special measures can be taken to limit its impact
on the floodway. Floodplain elevations can often
be determined from sources such as Federal Flood
Insurance maps or from the Federal Land Manage-
ment Agency. Landuser input may be the best
source of information for assessing previous
hydrologic conditions.
US Fish and Wildlife Service and state natural
resource agencies should be contacted regarding
the potential for significant habitat, or habitat for
rare or endangered species. The possible presence
of archaeological resources should be verified.
ENVIRONMENTAL RESOURCES
To avoid damaging important resources
on the site, the presence or absence of significant
environmental resources must be determined.
Sources of information that can be helpful in select-
ing a site include the US Geological Survey Topo-
graphic Quadrangle maps, and National Aerial
Photography Program (NAPP) and and National High
Altitude Photography Program (NHAPP) photo-
graphs. Geographical information system (GIS) maps
are also available.
The National Wetlands Inventory (NWI) maps
and the County Soil Survey with the list of county
hydric soils should be checked for possible locations
of existing wetlands. However, the NWI maps are
based on aerial photography and may not show small
wetlands or the less obvious wetlands (wet mead-
ows, vernal pools, and some forested wetlands) and
the NWI information should be field-checked by a
wetlands scientist. Historical aerial photography,
PERMITS AND REGULATIONS
The appropriate agency(ies) must be contacted
to determine the regulatory requirements for a
proposed constructed wetland and its discharge.
Work in a waterway or natural wetland requires a
permit. Discharges to natural waters also require a
permit. In some zoned communities, zoning
approval may be required.
Any stormwater plan must meet local and state
stormwater regulations. Some local ordinances
have incorporated stormwater provisions which
must be complied with. Stormwater regulations
vary from place to place and should be consulted
before developing a stormwater management plan.
The regulatory status of a proposed stormwater
wetland, and its relationship to streams and any
nearby natural wetlands, must be discussed with
the state and/or federal wetland permitting agency
before site plans are decided upon.
VOLUME 1: GENERAL CONSIDERATIONS
-------
STRUCTURES
CELLS
Wetlands can be constructed by excavating
basins, by building up earth embankments (dikes),
or by a combination of the two.
Dikes must be constructed of soils with ad-
equate fine-grained material that will compact into
arelatively stable and impervious embankment.
The dikes should be high enough to contain the
expected volume plus ample freeboard to accom-
modate occasional high flows as well as the
buildup of litter and sediment over time. To
ensure long-term stability, dikes should be sloped
no steeper than 2H:1V and riprapped or protected
by erosion control fabric on the slopes. An emer-
gency spillway should be provided.
If multiple cells are used, divider dikes can be
used to separate cells and to produce the desired
length-to-width ratios. On steep sites, they can be
used to terrace cells. Dikes can also be used to
control flow paths and minimize short-circuiting.
Finger dikes are often used to create serpentine
flow paths and can be added to operational sys-
tems to mitigate short-circuiting. Finger dikes can
be constructed of soils, sandbags, straw bales, or
treated lumber.
Bottom slopes are generally not critical. An
exception may be mine drainage wetlands that use
subsurface flow through deep beds of compost to
induce sulfate reduction; these cells should slope
about 1 - 3% upstream. Bottoms should be rela-
tively level from side to side.
Muskrats can damage dikes by burrowing into
them. Although muskrats generally prefer to start
their burrows in water than is more than 3 ft deep,
they can be a problem in shallower waters. Musk-
rats can be excluded by installing electric fence
low to the ground or by burying muskrat-proof
wire mats in the dikes during construction.
LINERS
Constructed wetlands must be sealed to avoid
possible contamination of groundwater and also to
prevent groundwater from infiltrating into the
wetland. Where on-site soils or clay provide an
adequate seal, compaction of these materials may
be sufficient to line the wetland. Sites underlain
by karst, fractured bedrock, or gravelly or sandy
soils will have to be sealed by some other method.
It may be necessary to have a laboratory analyze
the construction material before choosing a
sealing method. On-site soils can be used if
they can be compacted to permeability of
<108ft/sec (<10"6 cm/sec). Soils that contain
more than 15% clay are generally suitable.
Bentonite, as well as other clays, provide adsorp-
tion/reaction sites and contribute alkalinity. The
SCS (now the NRCS) South National Technical
Center (SNTC) Technical Note 716, "Design and
Construction Guidelines for Considering Seepage
from Agricultural Waste Storage Ponds and Treat-
ment Lagoons" (1993) and its companion SNTC
Technical Note 717, "Measurement and Estimation
of Permeability of Soils for Animal Waste Storage
Facilities:' (1991) provide guidance in determining
when in-situ soils will adequately meet seepage
control needs.
Synthetic liners include asphalt, synthetic butyl
rubber, and plastic membranes (for example, 0.5 to
10.0 mil high density polyethylene). The liner
must be strong, thick, and smooth to prevent root
attachment or penetration. If the site soils contain
angular stones, sand bedding or geotextile cushions
should be placed under the liner to prevent punc-
tures. The liner should be covered with 3-4 inches
of soil to prevent the roots of the vegetation from
penetrating the liner. If the wetland is to be used
for mine drainage, the reaction of the clay or
synthetic liner should be tested before it is used
since some clays and synthetics are affected by
some acid mine drainages.
FLOW CONTROL SxRuC TuREs
Water levels are controlled by flow control
structures. Flow control structures should be
simple and easy to adjust. They should allow
flexibility so that processes can be optimized
VOLUME 1: GENERAL CONSIDERATIONS
-------
initially and adjusted later in response to system
changes. 'Multiple inlets must be fully and
independently adjustable to ensure an even
distribution of flow. Structures should be sized
to handle maximum design flows and should be
located for easy access and to minimize short-
circuiting. Boardwalks and piers make access
easy and reduce disturbance of the wetland.
PVC pipe is recommended.
If the wetland will be accessible to the public,
or located in an isolated area where it will be
vulnerable to vandalism, inlet and outlet struc-
tures should be enclosed in lockable concrete
structures or manholes to avoid damage or tamper-
ing with water level settings. Structures must be
protected against damage by animals. Measures
include installing covers or wire mesh over open-
ings, and enclosing controls, gauges and monitor-
ing devices in pipes or boxes.
Inlets
Inlets at SF wetlands are usually simple: an
open-end pipe, channel, or gated pipe which
releases water into the wetland (figure 2). The
smaller the length-to-width ratio, the more impor-
Inlet with Buried
Inlet with Swiveling Tees Inlet with Gabion Distributor Pipe
; ' JpT*" 3" Stone
I ' •£& Soil. Sand or Gravel
• ' *%f Distribulor Pipe with Tees
1 . '.' (Joints must contain
J , y^T elastometiic gaskets: insert a
^ " ».*.** lever in each tee to ro ate: pipe ; ;
; ' ji" between tees should be
j( • iJ.'« anchored.)
..<:• *
-•?•;> s
p •" Soil. Sand or Grave
/ ,
V- N"
:: a
A}« V-
ry* '£>t5~*~ 3"- 4" Stone
r.^-'i ;>j ••<
•V< . „ fiSlotted or Perforated
Jn Inlet Pipe ""«>'•-?• Distributor Cap
I'.v ^Jvi ^.
r«i ^, 5^» s
y2' Soil Sand or GraveLx •STt Soil. Sand or Gravel
5fl/ .•!•*•*
r /
PLAN VIEW
Soil Cover Over Liner
.£_ x Swiveling Tee ~v. , , "~~x. , .
^^X / , B , > Level X 3 feet Level
~~^ ,,.1'r » ,' Level V ' Surface \r*-H Surface
vjag, i_2 feel ~ Stirlace
^igf..^
\ PSK >*S<
xea*- — — "=s»».
\ Liner Liner Liner^^"^
PROFILE
/ v-
> 'AS o Adjust Chain /
3-4" Stone ;ig> , ,0 obtain lhe fc
igj a Desired Water =
Slotted or *& ( Level =
Perforated -*® j =
Collector 1^ jl o —
Stt Ljj i i— rlll^OlMl^
\
1_
TOO
. .^-"~ ~" Rotate Standpipe
U — 3 feel «1 .f and Elbow to the
1 '/ Desired Water
s^,,n
Plan View of Outlet Structure with Standpipe
Structure with Collapsible Tubing
Swiveling Standpipe
Figure 2. Inlet and outlet designs (modified from Watson and Hobson 1989).
VOLUME!: GENERAL CONSIDERATIONS
2 1
-------
tant equal flow distribution becomes. Accessible
and easily adjustable inlets are mandatory for
systems with small length-to-width ratios.
Inlet structures at SSF systems include surface
and subsurface manifolds, open trenches perpen-
dicular to the direction of flow, and simple single-
point weir boxes. A subsurface manifold avoids
the buildup of algal slimes and the consequent
clogging that can occur next to surface manifolds,
but is difficult to adjust and maintain. A surface
manifold, with adjustable outlets provides the
maximum flexibility for future adjustments and
maintenance, and is recommended. A surface
manifold also avoids back-pressure problems.
The distance above the water surface of the wet-
land is typically 12 - 24 inches. The use of coarse
rock (3-6 inches, 8-16 cm) in the entry zone
ensures rapid infiltration and prevents ponding
and algal growth. To discourage the growth of
algae, open water areas near the outlet should be
avoided. Shading with either vegetation or a
structure in the summer and some thermal protec-
tion in the winter will probably be necessary.
A flow splitter will be needed for parallel
cells. A typical design consists of a pipe, flume,
or weir with parallel orifices of equal size at the
same elevation (figure 31. Valves are impractical
because they require daily adjustment. Weirs are
relatively inexpensive and can be easily replaced
or modified. Flumes minimize clogging in
applications with high solids but are more expen-
sive than weirs.
Outlets
At SF wetlands, the water level is controlled
by the outlet structure, which can be a weir,
spillway, or adjustable riser pipe. A variable-
«—®
Influent to Splitter Box (10")
Valved Drain to Marsh (.4")
Influent to
Marsh (10"
Sampling Cinduit (6")
Influent to
Marsh (10")
Sampling Conduit (6"),
Influent to Splitter Box (10") — > O
V-Notch Weir
Influent toMarsh (10")
Valved Drain (4")
SECTION A
Figure 3. Influent splitter box
(modified from Watson and Hobson 1989).
SECTION B
VOLUME 1: GENERAL CONSIDERATIONS
-------
height weir, such as a box with removable
stoplogs., allows the water levels to be adjusted
easily. Spillways are simple to construct but are
not adjustable; incorrect water levels can lead to
wetland failure and correcting spillway height can
be difficult.
Weirs and spillways must be designed to pass
the maximum probable flow. Spillways should
consist of wide cuts in the dike with side slopes
no steeper than 2H:1V and lined with non-biode-
gradable erosion control fabric. If high flows are
expected, coarse riprap should be used. Vegetated
spillways overlying erosion control fabric provide
the most natural-looking and stable spillways.
Weirs or spillways should be used for mine
drainage wetlands since pipes tend to clog with
deposits of iron precipitates.
Adjustable riser pipes or flexible hoses offer
simple water level control (figure 2). A PVC
elbow attached to a swivel offers easy control of
the water level. If pipes are used, small diameter
(<12 inch) pipes should be avoided because they
clog with litter.
At SSF wetlands, outlets include subsurface
manifold, and weir boxes or similar gated struc-
tures. The manifold should be located just above
the bottom of the bed to provide for complete
water level control, including draining. The use
of an adjustable outlet, which is recommended to
maintain an adequate hydraulic gradient in the
bed, can also have significant benefits in operating
and maintaining the wetland. The surface of the
bed can be flooded to encourage the development
of newly planted vegetation and to suppress
undesirable weeds, and the water level can be
lowered in anticipation of major storms and to
provide additional thermal protection against
freezing in the winter. The design of SSF beds
should allow controlled flooding to 6 inches
(15 cm) to foster desirable plant growth and to
control weeds. A perforated subsurface manifold
connected to an adjustable outlet offers the maxi-
mum flexibility and reliability as the outlet device
for SSF systems. Since the manifold is buried and
inaccessible after construction, careful grading
and subbase compaction are required during
construction, and clean-out risers in the line must
be provided.
The final discharge point from the wetland
system should be placed high enough above the
receiving water that a rise in the water level in the
receiving water, for instance after a storm, will not
interfere with the flow of water through the wet-
land.
SYSTEM LIFETIMES
A constructed wetland used for wastewater
treatment may have a finite lifetime which will be
determined by wastewater loadings, the capacity of
the wetland to remove and store contaminants, and
the buildup of litter. A number of systems have
been operating for more than 20 years with little, if
any, loss of effectiveness. Long-term data on the
performance of constructed wetlands are being
acquired as more systems are being monitored for
longer periods of time. Data from the few con-
structed wetland systems that have provided long-
term data show that treatment performance for
pollutants that are broken down in wetlands, such
as BOD5, total suspended solids (TSS), and nitro-
gen, does not decrease as long as loadings are
reasonable, and the wetland system is designed'.,
built, and maintained with care.
For pollutants that are retained within a
wetland, such as phosphorous and metals, the
capacity of the wetland to remove and store the
pollutants may decrease over time. The buildup of
these substances must be monitored periodically to
assess the wetland's performance. Wetlands can be
sized to accommodate the accumulation of depos-
its. It is generally assumed that deposition of
contaminants in sediments and litter constitutes a
relatively long-term sink for contaminants. If
necessary, wetland sediments and litter can be
removed periodically and the wetland rebuilt with
fresh substrate.
VOLUME 1 GENERAL CONSIDERATIONS
23
-------
CHAPTER 5
HYDROLOGY
The hydrology of a constructed wetland is
perhaps the most important factor in its effec-
tiveness. However, the design of constructed
wetland treatment systems is still in a state of
flux and there remain a number of uncertainties
that will not be answered until the results of
longer and more numerous operational studies
become available. Many wetland designs have
been based on the design used for conventiona)
ponds and land treatment systems. While the
design of conventional systems is usually based
on hydraulic residence time (and therefore water
volume), some wetland treatment systems show
a more consistent correlation with area and
hydraulic loading rate than with hydraulic
residence time (R. Kadlec, pers. comm.). This
seems reasonable since a wetland is a shallow
water system with large surface area in relation
to its volume, and receives energy inputs (sun,
rain, propagules, gases) on an areal basis that is
not related to volume. Also, because of the
depth limits of wetland plants, the biomass of
microbes attached to plants and sediments does
not increase proportionally to depth except in a
narrow range. The design guidelines presented
in this Handbook are thus tentative.
Hydrologic factors in wetland design pertain
to the volume of water, its reliability and ex-
tremes, and its movement through the site.
Hydrologic considerations include climate and
weather, hydroperiod, hydraulic residence time,
hydraulic loading rate, groundwater exchanges
(infiltration and exfiltration), losses to the
atmosphere (evapotranspiration), and overall
water balance.
CLIMATE AND WEATHER
Because wetlands are shallow water bodies
open to the atmosphere, they are strongly influ-
enced by climate and weather. Rainfall, snowmelt,
spring runoff, drought, freeze, and temperature can
all affect wetland treatment.
The high flows caused by heavy rains and
rapid snowmelt shorten residence times. The
efficiency of a wetland may therefore decrease
during rainfall and snowmelt because of increased
flow velocities and shortened contact times. High
flows may dilute some dissolved pollutants while
increasing the amount of suspended material as
sediments in the wetland are resuspended and
additional sediments are carried into the wetland
by runoff. The first flush of runoff from a storm,
often carries much higher pollutant concentrations
than flows later in the storm. Taylor et al. (1993)
found that intense storms during summer, when
conditions were generally dry, often had greater
impacts on treatment than storms during other
times of the year, when conditions were generally
wetter. Snowmelt and spring runoff can resus-
pend and export stored pollutants. Jacobson
(1994) found that runoff during spring may carry
more than half the annual nitrate and phosphorus
exported during the year and suggests that wetland
management should focus on this time of the year.
Runoff in excess of maximum design flows should
be diverted around the wetland to avoid excessive
flows through the wetland.
Minimum temperatures limit the ability of
wetlands to treat some, but not all, pollutants..
Wetlands continue to treat water during cold
weather. However, freezing temperatures in
winter and early spring can reduce treatment if the
wetland either freezes solid or a cover of ice
prevents the water from entering the wetland. If
under-ice water becomes confined, water veloci-
ties may increase, thereby reducing contact times.
HYDROPERIOD
Hydroperiod is the seasonal pattern of water
level fluctuations and is described by the timing,
duration, frequency, and depth of inundation. The
hydroperiod of a wetland results from the balance
of inflow, outflow, and storage. Hydroperiod
determines the availability of water throughout the
VOLUME 1: GENERAL CONSIDERATIONS
25
-------
year, the extreme wet and dry conditions that can be
expected, the extent of storage and drainage that may
be required, and the criteria to be used in designing
the water control facilities. While hydroperiod can
be engineered to control surface flow and to reduce
its variability, the hydroperiod of a wetland will be
strongly affected by seasonal differences in precipita-
tion and evapotranspiration.
HYDRAULIC RESIDENCE TIME
The hydraulic residence time (HRT) of a treat-
ment wetland is the average time that water re-
mains in the wetland, expressed as mean volume
divided by mean outflow rate. If short-circuiting
develops, effective residence time may differ
significantly from the calculated residence time.
HYDRAULIC LOADING RATE
Hydraulic loading rate (HLR) refers to the
loading on a water volume per unit area basis.
[loading = (parameter concentration)(water vol-
ume/area)].
GROUNDWATER EXCHANGE
The movement of water between a 'wetland add
groundwater will affect the hydrology of the
wetland. Constructed wetlands for domestic
wastewater, agricultural wastewater, and mine
drainage are usually lined to avoid-possible con-
tamination of groundwater. If the wetland is
properly sealed, infiltration can be considered
negligible.
Many stormwater wetlands are sealed so that
that water needed to support the wetland will be
retained between storms. Other stormwater wet-
lands are designed to intercept groundwater to
ensure sufficient baseflow. In this case, the wet-
land will receive groundwater when the water
table is high and may discharge to groundwater
when the water table is low.
EVAPOTRANSPIRATION
Evapotranspiration (ET) is the combined water
loss through plant transpiration and evaporation
from the water surface. In wetlands, the amount of
surface area is large relative to the volume of water
and ET is an important factor. Also, many wetland
plants do not conserve water during hot, dry
weather as most terrestrial plants do, and can
transfer considerable amounts of water from a
wetland to the atmosphere in summer. If ET losses
exceed water inflows, supplemental water will be
required to keep the wetland wet and to avoid
concentrating pollutants to toxic levels.
Estimates of ET values vary widely. The Water
Pollution Control Federation (1990) suggests that,
for wetlands that are continuously flooded, ET can
generally be estimated as being equal to lake
evaporation, or approximately 70% to 80% of pan
evaporation values. (Rainfall and pan evaporation
data can be obtained from National Oceanic and
Atmospheric Administration in Asheville, NC, or
from local weather stations.) Kadlec (1993) found
that dense stands of emergent vegetation reduced
the total water loss from prairie potholes and
concluded that the vegetation removed less water
through transpiration than would have evaporated
from open surface water. Other data indicate that
most wetlands show ET to be equal to or slightly
less than pan evaporation and that experiments
that show higher ET rates have been conducted on
too small a scale to compensate for edge effects.
WA TERBALANCE
The overall water balance for a constructed
wetland is an account of the inflow, storage, and
outflow of water. Water inflow to the wetland
includes surface water (the wastewater or
stormwater), groundwater infiltration (in unlined
wetlands), and precipitation: Storage is the
surface water plus that in the pore spaces of the
substrate. Outflow comprises evaporation from
the water surface, transpiration by plants, effluent
discharge, and exfiltration to groundwater. During
26
VOLUME 1: GENERAL CONSIDERATIONS
-------
design and operation, the wetland water balance is
important for determining conformance with
desired limits for HLR, hydroperiod range, HRT,
and mass balances. A simple water balance
equation for a constructed wetland is expressed as:
S = Q + R + I-O-ET (5.1)
Where: S = net change in storage
Q = surface flow, including wastewater
or stormwater inflow,
R = contribution from rainfall
I = net infiltration (infiltration less
exfiltration)
0 = surface outflow
ET= loss due to evapotranspiration.
Equation 5.1 can be used to calculate water
budgets for daily, monthly, or yearly intervals.
Detailed water balances can be prepared with
site-specific monitoring data collected during
pilot- or full-scale operation of the wetland. If
large seasonal variation is expected, monthly
data are essential.
A number of factors can be used to manipu-
late the water budget:
. the volume of water released from the wetland
can be varied
. evapotranspiration rates can be altered by
shading, windbreaks, and the selection and
management of vegetation around the wetland
. storage capacity can be adjusted with water
control structures
. in SF wetlands, storage capacity can be in-
creased by excavating deep pools or decreased
by adding fill.
VOLUME i : GENERAL CONSIDERATIONS 27
-------
CHAPTER 6
SUBSTRATES
Wetland substrates support the wetland
vegetation, provide sites for biochemical and
chemical transformations, and provide sites for
storage of removed pollutants. Substrates include
soil, sand, gravel, and organic materials.
SOIL
Many soils are suitable for constructed wet-
lands. Soil properties that should be considered in
selecting soils include cation exchange capacity
(CEC), pH, electrical conductivity (EC), texture, and
soil organic matter.
The pH of the soil affects the availability and
retention of heavy metals and nutrients. Soil pH
should be between 6.5 and 8.5. The EC of a soil
affects the ability of plants and microbes to process
the waste material flowing into a constructed
wetland. Soils with an EC of less than 4 mmho/cm
are best as a growth medium.
The surface area of the soil particles and
'the electrical charge on the surfaces of the soil
particles account for much of a soil's activity., In the
northeastern United States, most soils carry a net
negative charge, thus providing electrostatic bond-
ing sites for positively charged ions (cations), such
as Ca2+, Mg2+, Fe2+, Al3+and Mn2. These cations on
the soil surface can exchange with other cations in
the soil solution, hence the term cation exchange.
CEC measures a soil's capacity to hold positively
charged ions and varies widely among different
soils. The CEC of a soil that will be used as
a planting medium should be greater than
15 meq/100 g of soil.
The redox potential of the soil is an important
factor in the removal of nitrogen and phosphorus.
A reducing substrate must be provided to promote
the removal of nitrate and ammonia. The removal
of iron and manganese from mine water also
requires a reducing environment.
A soil's capacity to remove and retain contami-
nants is a function of soil-water contact. Sandy or
gravely soils have high K (porosity) values and
water moves quickly through the soil. In contrast,
the finer textures of silty or loamy soils promote
longer soil-water contact. Flow through well-
decomposed organic soils and most clays is slow.
The soil must provide enough organic matter.
to fuel plant growth and mocrobial activity,
particularly during startup. Wetlands are often
built with infertile site soils, and organic amend-
ments, such as compost, leaf litter, or sewage
sludge, must be incorporated into the substrate.
Soil texture affects root growth and the reten-
tion of pollutants. Sandy, coarse-textured soils
have a low potential for pollutant retention but
little or no restriction on root growth. Thesesoils
hold plants well but are low in nutrients. Addi-
tions of organic matter to coarse textured soils
have been shown to improve plant survival and
growth during the first several years while the
organic litter is beginning to build up within the
wetland. Medium textured or loamy soils are a
good choice, as these soils have high retention of
pollutants and little restriction on plant growth.
Loamy soils are especially good because they are
soft and friable, allowing for easy rhizome and root
penetration. Dense soils, such as clays and shales,
should be avoided because they may inhibit root
penetration, lack nutrients, and have low hydrau-
lic conductivities.
Soils with a high clay content aid in phospho-
rous retention but their low nutrient content may
limit growth and development, although such soils
may be suitable for wetlands used for nutrient-rich
wastewaters, such as agricultural and domestic
wastewaters. Organic admendments will be
required. Soils with greater extractable aluminum
have greater potential for phosphorous assimila-
tion than do organic soils, making them well
suited for domestic wastewater treatment. Highly
organic soils enhance sulfate reduction and ionic
adsorption and are well suited for mine drainage
wetlands.
Although peats are common in natural wet-
lands, they are not the preferred soil for establish-
ing constructed wetlands. Peats can release
VOLUME 1: GENERAL C ONSIDERATIONS
29
-------
organic acids, which contribute to low pH.
Also, when flooded, peats have a soft, loose
texture that may not provide adequate support
for plants.
The county soils maps, which are available
through libraries or through the county NRCS
offices, show the major soil types present and
their relationship to site topography. The soils
maps include a general description of the soil
characteristics. However, the NRCS soils maps
cannot be relied upon for detailed, site-specific
information for several reasons:
. the NRCS data are averages and estimates
tallied over many acres of ground
. most soils units include inclusions that may
differ in significant ways from nearby soils
. soils vary with depth, that is, they are stratified.
If the wetland is to be excavated, it is important
to know the characteristics of the soil at the
excavated depth.
Soils should 'be analyzed before they are used
in the wetland. Site-specific information on the
hydraulic conductivity and permeability of the site
soils must be made through field data collection.
Laboratory soil analyses should include clay
content and type of clay, percent organic matter,
and mineral content.
ORGANIC MATERIAL
Stabilized organic material, such as spent
mushroom compost, sawdust, hay or straw bales,
and chicken litter, have been used as organic
substrates. Organic material provides a source of
carbon to support microbial activity. Organic
material also consumes oxygen and creates the
anoxic environments that are required for some
treatment processes, such as nitrate reduction and
the neutralization of acidic mine drainage.
SAND AND GRAVEL
Constructed wetlands receiving with water
high in nutrients, such as domestic and agricul-
tural wastewaters. can be built with sand or gravel.
Sand is an inexpensive alternative to soil and
provides an ideal texture for hand planting.
Gravel can also be used. Many domestic sewage
SSF wetlands in the United States have used
media ranging from medium gravel to coarse rock.
Sands and gravels dry out quickly and may need
to be irrigated to maintain water levels while the
vegetation is becoming established.
30
VOLUME 1 : GENERAL CONSIDERATIONS
-------
CHAPTER 7
VEGETATION
The function of plants in constructed wetlands
is largely to grow and die: plant growth provides a
vegetative mass that deflects flows and provides
attachment sites for microbial development; death
creates litter and releases organic carbon to fuel
microbial metabolism. In addition, plants stabilize
substrates while enhancing its permeability, and
plants add greatly to the aesthetic value of the
wetland. A dense stand of vegetation appears to
moderate the effects of storms.
SELECTING PLANTS
The plants that are most often used in con-
structed wetlands are persistent emergent plants,
such as bulrushes (Scirpus), spikerush
(Efeocharis), other sedges (Cyperus). rushes
(Juncus), common reed (Phragrnites), and cattails
(Typha). Not all wetland species are suitable for
wastewater treatment since plants for treatment
wetlands must be able to tolerate the combination
of continuous flooding and exposure to wastewa-
ter or stormwater containing relatively high and
often variable concentrations of pollutants. A
number of species that have been used success-
fully in the northeastern United States are listed in
table 1.
For wastewater treatment wetlands, the par-
ticular species selected are less important than
establishing a dense stand of vegetation. Any
species that will grow well can be chosen. For
stormwater wetlands, species should be chosen to
mimic the communities of emergent plants of
nearby natural wetlands. For both wastewater and
stormwater wetlands, native, local species should
be used because they are adapted to the local
climate, soils, and surrounding plant and animal
communities, and are likely to do well.
NRCS conservation agents and state personnel
can recommend species for constructed wetlands.
SURFACE FLOW WETLANDS
In wetlands constructed to treat domestic
sewage, agricultural wastewaters, and other
wastewaters relatively high in organic matter,
bulrushes (either softstem or common three-
square) are often used because they are tolerant of
high nutrient levels and because they establish
readily but are not invasive. Arrowhead and
pickerelweed have also been used successfully in
agricultural wetlands. Blueflag iris can be planted
along wetland edges to provide color. Cattails and
common reed have been used frequently because
of their high tolerances for many types of wastewa-
ter, but both have disadvantages. Cattails are
invasive. Since cattail tubers are a favorite food of
muskrats, cattails are susceptible to damage by
muskrats. Also, Surrency (1963) found that
cattails were subject to attack by insects similar to
army worms and suggests that cattails may not be
the best choice for agricultural wetlands. Common
reed is a highly aggressive species that can elimi-
nate other species once it is introduced. It pro-
duces abundant windborne seed and spreads
readily to natural wetlands. It is becoming a
problem in the Northeast and should not be used
without approval from the regulatory agency.
For agricultural wastewater wetlands, the
ammonia tolerances of the species must be consid-
ered. Wetland species vary in their ability to
tolerate ammonia. Plants may be able to tolerate
higher concentrations of ammonia if the plants are
slowly acclimated to it.
For stormwater wetlands, the goal should be a
diverse assemblage of plants. A diverse vegetation
is aesthetically pleasing and may be more likely to
resist invasive species, to recover from distur-
bance, and to resist pests than a less diverse stand.
The numbers of wildlife attracted to a wetland
generally increases as vegetation diversity in-
creases. ' The State of Maryland guidelines for
stormwater wetlands suggest planting two primary
species (some combination of arrowhead, common
three-square, or softstem bulrush) and three other
VOLUME 1 : GENERAL CONSIDERATIONS
31
-------
Table 1. Emergent plants for constructed wetlands
(adapted from Schueler 1992 and Thunhorst 1993).
Recommended Species
Arrow arum
Peltandra virginica
Arrowhead/duck potato
Saggitaria latifolia
Common three-square
bulrush
Scirpus pungens
Softstem bulrush
Scirpus validus
Blue flag iris
Iris versicolor
Broad-leaved cattail**
Typha latifolia
Narrow-leaved cattail**
Typha angustifolio
Reed canary grass
Phalaris arundinocea
Lizard's tail
Saururus cernuus
Pickerelweed
Pontedaria cordata
Common reed**
Phragmites australis
Maximum Notes
Water Depth*
12 inches Full sun to partial shade. High wildlife value.
Foliage and rootstocks are not eaten by geese
or muskrats. Slow grower. pH: 5.0-6.5.
12 inches Aggressive colonizer. Mallards and muskrats
can rapidly consume tubers. Loses much water
through transpiration.
6 inches Fast colonizer. Can tolerate periods of dryness.
High metal removal. High waterfowl and
songbird value.
12 inches Aggressive colonizer. Full sun. High pollutant
removal. Provides food and cover for many
species, of birds. pH: 6.5-8.5.
3-6 inches Attractive flowers. Can tolerate partial shade
but requires full sun to flower. Prefers acidic
soil. Tolerant of high nutrient levels.
12-18 inches Aggressive. Tubers eaten by muskrat and
beaver. High pollutant treatment, pH: 3.0-8.5.
12 inches Aggressive. Tubers eaten by muskrat and
beaver. Tolerates brackish water. pH : 3.7-8.5.
6 inches Grows on exposed areas and in shallow
water. Good ground cover for berms.
6 inches Rapid grower. Shade tolerant. Low wildlife
value except for wood ducks.
12 inches Full sun to partial shade. Moderate wildlife
value. Nectar for butterflies. pH: 6.0-8.0.
3 inches Highly invasive; considered a pest species in
many states. Poor wildlife value. pH: 3.7-8.0.
VOLUME 1: GENERAL CONSIDERATIONS
-------
Recommended Species
Maximum
Water Denth*
Notes
Soft rush
Juncus effusus
Spikerush
Eleocharis palustris
Sedges
Carex spp.
Spatterdock
Nuphar luteum
Sweet flag
Acorus calamus
3 inches Tolerates wet or dry conditions. Food for birds.
Often grows in tussocks or hummocks.
3 inches Tolerates partial shade.
3 inches Many wetland and several upland species.
High wildlife value for waterfowl
and songbirds.
5 ft; Tolerant of fluctuating water levels. Moderate
2 ft minimum food value for wildlife, high cover value.
Tolerates acidic water (to pH 5.0).
3 inches Produces distinctive flowers. Not a rapid
colonizer. Tolerates acidic conditions.
Tolerant of dry periods and partial shade.
Low wildlife value.
Wild rice
Zizania aquatica
12 inches
Requires full sun. High wildlife value (seeds,
plant parts, and rootstocks are food for birds).
Eaten by muskrats. Annual, nonpersistent.
Does not reproduce vegetatively.
. These depths can be tolerated, but plant growth and survival may decline under permanent inundation at these
depths.
. **Not recommended for stormwater wetlands because they are highly invasive, but can be used in treatment
wetlands if approved by regulatory agencies
VOLUME 1: GENERAL CONSIDERATIONS
-------
secondary species (see table 1) to enhance short- and
long-term development and to reduce the invasion by
undesirable plants such as common reed (Livingston
1989).
SUBSURFACE FLOW WETLANDS
Many of the SSF constructed wetlands in the
United States have used bulrush, common reed,
cattail, or some combination of the three. About
40% of the operational SSF systems use only
bulrush. Common reed has been widely used in
British and European systems; however, it is a
highly invasive species that can be very difficult to
eradicate once started and a number of states now
prohibit its use. Some SSF systems have been
planted with a diverse vegetation similar to that of a
natural marsh.
SOURCES OF PLANTS
Seeds, seedlings, entire plants, or parts of plants
(rootstocks, rhizomes, tubers, or cuttings) can be used
to establish wetland vegetation. While many wetland
plants produce wind-borne seeds, vegetative spread
by stolons and runners is common since seeds gener-
ally will not sprout under water. Many emergents
have rhizomes, rootstocks, or tubers which, although
they are primarily food storage organs, can generate
new plants.
SEEDS
Seeds are the least expensive but also the least
reliable approach to planting. Seeds are generally
broadcast on the saturated surface of the wetland.
Seeds can also be scattered by shaking ripe spikes of
plants over the wetland surface. Germination is
unpredictable. Propagation by seeds requires an
exposed, wet surface on which the seeds can germi-
nate. Water levels can be raised as the plants grow,
but the leaves must remain above water since the
plants must be able to photosynthesize and transpire
if they are to grow.
Seed stands are typically difficult to establish
because scarification (abrasion of seed coat) and
stratification (exposure to cold) requirements are
largely unknown and because seeds are easily
moved about by rain. However, many wetland
species produce abundant wind-borne seed and
will appear quickly on newly exposed surfaces if
there is another wetland in the area to act as a
source of seed.
WETLAND SOIL
The seeds of many wetland species remain
viable for many years buried in sediments. Soil
from a nearby wetland can be used as a source of
plants since this soil will contain seeds of a number
of native species that are well-adapted to local
conditions. Approval must be obtained from the
appropriate agency before removing wetland soil.
Soil must not be taken from natural wetlands
without a permit.
Cores (3-4 inch, or 8 - 10 cm, in diameter) of
wetland soil from the donor marsh can be trans-
planted to the constructed wetland. Cores are
excellent sources of seeds, shoots, and roots of
various wetland plants and will promote the devel-
opment of diverse wetlands. The disadvantages of
soil cores are the time and cost associated with
collecting, transporting, and planting the soil mass.
Also, the soil is likely to contain propagules of
undesirable, as well as desirable, species. If the
cores are taken from a wetland dominated by a
species that spreads by rhizomes (such as cattails),
the resulting wetland will probably be dominated by
that species since earthmoving cuts the rhizomes
into pieces, each of which can produce a new plant.
Once in place, the soil should be kept moist, but
not flooded, until the seeds germinate.
RHIZOMES, TUBERS,
AND ENTIRE PLANTS
Plant materials include entire plants and plant
parts, such as rhizomes and tubers. These materi-
34
VOLUME 1: GENERAL CONSIDERATIONS
-------
als are generally obtained from commercial
nurseries or donor wetland sites (on-site nurser-
ies or nearby constructed wetlands).
Plants should be obtained from local
sources. The US Army Corps of Engineers
(1993) recommends that plants should be trans-
ferred from areas within 100 miles latitude, 200
miles longitude, and 1,000 feet in elevation but
notes that ecologists are expressing concern
about the unknown consequences of relocating
genetic stock to new areas. For example, plants
become adapted to local pathogens, as well as
beneficial mutualistic species, and their survival
and growth are diminished when they are
transplanted to different areas. The State of
Florida now recommends a 50-mile radius for
obtaining plants.
Locally-grown nursery stock is generally the
most reliable and ecologically appropriate way
to obtain plants. The NRCS Plant Materials
Centers test and develop plants for various
'applications and can provide plants. On-site
nurseries established to provide plants for the
project offer convenience, reliability, and low
cost. Outdoor beds can be constructed at the-
site of the construction project. The beds usu-
ally consist of pits 12 - 20 inches (30 - 50 cm)
deep dug into the soil, lined with plastic film to
prevent water loss, and partially filled with 8 - 12
inches (20 - 30 cm) of soil. Water inlets and
outlets for the beds should be adjustable so that
water levels can be varied to accommodate the
different stages of germination and growth.
Rhizomes and tubers are usually collected
in the late fall after growth has stopped or in
early spring before new growth begins. The
entire root system should be taken along with
some soil, including the soil helps to inoculate
the constructed wetland with microbes from
the donor wetland.
Rhizomes generally are cut into lengths of
two to three nodes, placed in moist peat or sand,
and stored at cool temperatures (40°F, 4-5°C)
until planting. Storage at cool temperatures
stratifies the tubers and rhizomes (prepares them
for growth) and enhances growth after spring
planting. A common pitfall is to store plants
under conditions that are too dry or too warm.
Collecting plants in the spring and planting
them immediately at the new site may reduce
the mortality of rhizomes and rootstocks, but
collection is more difficult because of the high
water levels in most wetlands in the spring.
Manual collection is more common than
machine collection, which is not practical unless
large quantities of plants are needed or the project
is a long-term one. Manual harvesting equipment
includes modified garden tools, bags, buckets, and
boats or canoes. Vegetative propagules are usually
obtained by hand-digging whole plants and cutting
apart roots, rhizomes, and tubers. At sites where
water levels can be controlled, machinery can be
used to dig underground parts.
Private wetland nurseries are becoming more
widespread and can custom-propagate stock for
wetlands if given enough advance notice. Some
commercial nurseries will recommend species and
will do the planting.
WHEN TO PLANT
In the Northeast, the planting period typically
begins after dormancy has begun in the fall and
ends after the first third of the summer growing
period has passed. Fall dormant planting is
recommended for tubers and rootstock and is very
successful for bulrushes, rushes, and arrowhead.
Sedges and cattails are grown more successfully in
the spring after dormancy has been broken. Plant-
ing early in the spring growing season is generally
successful. The NRCS Field Office Technical
Guide (FOTG) or local nurseries can be consulted
about planting times.
SITE PREPARATION
For SF wetlands, the site should be disked or
harrowed to break up compacted soil once the
wetland has been shaped and graded. The bed
should then be shallowly flooded to settle the soil
VOLUME 1 GENERAL CONSIDERATIONS
35
-------
and level the bed. An extended settling period
(a year or to the next growing season) should be
provided, if possible. Constructed wetlands are
often built in the fall and left flooded over the
winter. The bed is then dewatered (but not com-
pletely dried) shortly before planting to produce a
soft, moist soil.
will improve coverage and reduce channeling
while the vegetation is filling in. When the plants
have been placed, enough clean water should be
added to maintain good saturation of the substrate,
but not flood it. After new growth has reached
4-5 inches (10 - 12 cm), the water level can be
raised. The water must not overtop the plants for
extended periods or the plants will die.
HOW TO PLANT
Planting is usually done by hand. Few sophis-
ticated planting techniques have been applied to
wetland planting.
SURFACE FLOW WETLANDS
Dormant propagules, such as tubers and
rhizomes, are planted by simply placing them
deep enough in the substrate to prevent them from
floating out of the medium. Approximately
1-2 inches (2-5 cm) of stem should be left on the
tubers so the plants can obtain oxygen through the
stem when the wetland is flooded. Tubers of
arrowhead and softstem bulrush are often planted
in this way.
For bareroot plants and tubers, a tree planting
bar (dibble) or tile spade is a good tool. A slit is
made in the substrate, the propagule inserted, and
the slit sealed. The propagule must be planted
deep enough to prevent it from floating out of the
planting hole. For tall plants such as cattails, the
stems should be broken over or cut back to 1 ft to
prevent windthrow. Wetland cores and potted
plants are placed in small holes dug with a shovel.
Temporary anchoring may be needed if the sub-
strate is' soft, the plants are buoyant, or erosion
could disturb the existing system.
Vegetative propagules are usually spaced at
1 - 3 ft (0.3 - 1 m) intervals, depending on how
rapidly the project must be completed. Clustered
rather than ,uniform arrangements provide species
and spatial diversity and better simulate a natural
wetland. If the plants are planted in rows, running
the rows perpendicular to the direction of flow
SUBSURFACEFLOWWETLANDS
Most SSF wetlands are planted by hand. The
use of individual root/rhizome material with
growing shoots at least 8 inches (0.2 m) long is
recommended. If mature, locally available
plants are used, they can be separated into
individual root/rhizome/shoot units containing
root, rhizome, and shoot, with the mature stem
cut back to <1 ft (<0.3 m) before planting.
The root/rhizome should be placed in the
medium at a depth equal to the expected opera-
tional water level. The growing shoot should
project above the surface of the media. To
encourage deeper root penetration, some Euro-
pean systems lower the water level in the bed in
the fall. In Europe, three years is necessary for
the roots of common reed to reach their 2 ft
potential depth. An alternative to lowering the
water level in the entire wetland is to divide the
system into two or more parallel cells and to
alternate drawdown between the cells to encour-
age root penetration in the dormant cell.
ESTABLISHING AND
MAINTAINING VEGETATION
In SF wetlands, water level is the most critical
aspect of plant survival during the first year after
planting. A common mistake is to assume that
because the plant is a wetland plant, it can tolerate
deep water. Frequently, too much water creates
more problems for wetlands plants during the first
growing season than too little because the plants
do not receive adequate oxygen at their roots. For
VOLUME 1: GENERAL CONSIDERATIONS
-------
best survival and growth of small stalks
(1-2 inches) during the first growing season,
the substrate should only be saturated, not
flooded. As the plants become well-established
(2-3 months), water levels can be raised.
Mechanical protection may be needed to
prevent animals from damaging newly established
plants. Canada geese cause significant depredation
by grazing on young shoots and seedlings and by
uprooting rhizomes and tubers. Deer and black-
birds can also damage newly established seedlings.
Muskrats feed on the fleshy tubers of plants such as
cattails and can quickly demolish a cattail wetland.
Preventive methods include planting through
chicken wire fence fastened over the surface of the
substrate to prevent animals from excavating tubers
and rhizomes.
Plantings should be allowed to become well
established before the wastewater is introduced into
the system since the plants need an opportunity to
overcome the stress of planting before other stresses
are introduced. The water must supply enough
nutrients to support plant growth. If not, a solution
of commercial nutrient supplement should be
added. Satisfactory establishment may take from
several months to one or two full growing seasons.
The plants may not begin to reach maturity and
equilibrium until late in the second growing season.
A gradual rather than sudden increase in the
concentration of the wastewater applied reduces
shock to the vegetation. Alternatively, if plants are
readily available and inexpensive, some die-off and
replanting can be planned for in order to apply the
wastewater sooner.
Water level management is key to maintaining
wetland vegetation. Despite relatively broad depth
tolerances, freshwater plants often sort by small
variations in water depth, producing the apparent
zonation of vegetation along the shores of marshes.
Most wetland species are adapted to daily or
seasonal fluctuations in water level but most
wetland plants can tolerate neither extended
periods of flooding nor drying of their roots.
Water quality also affects the health and
survival of wetland plants. High nutrient loads,
high or low pHs, high dissolved solids concentra-
tions, and buildup of heavy metals and other
toxics can affect the vegetation in wetlands.
Constant pollutant loads work against species
diversity and favor pollution-tolerant species such
as cattails. In wetlands constructed to treat
domestic wastewater and mine drainage, Kadlec
(1989) and Webster et al. (1994) found that plant
diversity declined and dominance by cattails
increased as the wetlands aged.
Harvesting or winter burning of above-ground.
biomass is sometimes used as a means of removing
nitrogen and carbon and maintaining the wetland
vegetation in a log (growth) phase of high physi-
ological activity to enhance removal, but may
disrupt the wetland and the maturation of the
plant community. Decisions as to whether or not
to harvest will depend on the objectives of the
project and will be site-specific.
VOLUME 1: GENERAL CONSIDERATIONS
37
-------
CHAPTER 8
CONSTRUCTION
Wetlands should be designed and constructed
to provide reliability and 'safety. Standard engi-
neering techniques should be used. It is impor-
tant to use a skilled contractor since elevations
must be accurate to assure proper hydraulic
regimes, and compaction requirements must be
met to control infiltration and exfiltration and to
ensure berm stability. It is also important to have
someone on site who is familiar with the plans,
tolerances, and overall wetland objectives to
answer the questions that always arise during
construction.
CONSTRUCTION PLANS
Construction plans and specifications
developed from treatment area requirements
and siting investigations should be carefully
reviewed. The level of detail depends on
the size and complexity of the wetland, the
physical characteristics of the site, and the
requirements of the regulatory agencies. At
a minimum, construction plans must have suffi-
cient detail for accurate bid preparation
and for construction.
A pre-bid conference with potential contrac-
tors is recommended to explain the concept,
goals, and requirements of the project. This
meeting can be effective in soliciting accurate
bids from qualified contractors.
PRE-CONSTRUCTION ACTIVITIES
A preconstruction conference should always be
held to interpret and explain the intent of the plans
to the operator and the contractor. Many contrac-
tors who are experienced with other kinds of
construction may have had little experience in
building wetlands. Construction plans, specifica-
tions, and field layout must portray to the operator
and the contractor the desired work. Because of
wide variations in conditions and experience, plans
may vary from very simple plans and a few
stakes in the ground to complicated plans with
detailed specifications and extensive staking.
Pre-construction activities should be consistent
with the size and complexity of the site and
adequate to assure orderly and effective con-
struction.
CONSTRUCTION ACTIVITIES
Construction includes building access roads;
clearing; constructing basins and dikes; piping and
valving; planting; and seeding, liming, fertilizing,
and mulching dikes and disturbed areas. A
valuable reference document for constructed
wetlands is the Engineering Field Handbook (SCS
1992), especially Chapter 13: "Wetland Restora-
tion, Enhancement, or Creation". EPA's 1993
publication Wetland Creation and Restoration:
Status of the Science, Chapters 2, 3, 4, 13, and 17,
is also recommended. Both are available through
the National Technical Information Service (NTIS),
US Department of Commerce, 5285 Royal Road,
Springfield, VA, 22161; telephone (703) 487 4650.
Use of the correct type and size of heavy
equipment is crucial for proper and cost-effective
construction. Under- and over-sized equipment
can result in time and cost overruns. It is a good
practice to show the equipment operator(s) the site
during the planning stages to obtain his or her
opinion on equipment, time requirements, and
potential problems.
Construction must precisely follow the engi-
neering plan 'if the system is to perform properly.
If shallow sheet flow is desired, lateral bed slope
should not vary by more than 0.1 ft from high spot
to low spot since large slope or surface variations
can cause channeling, especially in systems with
high length-to-width ratios. Permeability specifi-
cations must be followed carefully to prevent
leakage into or out of wastewater wetlands, if this
is part of project specifications. If synthetic liners
VOLUME 1: GENERAL CONSIDERATIONS
39
-------
are required, installation should follow precisely
the manufacturer's instructions for bedding
material, sealing (liner-to-liner and liner-to-piping
and control structures), and material placement on
top of the liner.
SSF systems depend on high hydraulic
conductivities in the substrate, and special
provisions must be taken to avoid compacting
and rutting of the substrate during construction.
The importance of using low-ground-pressure
equipment in the wetland and of controlling
small machine or foot traffic to reduce compac-
tion must be made clear to the contractor. Walk
boards should be placed on the substrate during
hand planting:
The hydraulic performance of both SF and
SSF systems can be significantly influenced by
improper construction, and short-circuiting of
flow can often be traced to improper construction.
In particular, SSF beds must be carefully con-
structed because of the heavy traffic involved in
placing the rock or sand medium. In several
cases, carefully graded beds were seriously dis-
rupted when the trucks delivering the rock were
allowed access to the beds during wet weather.
One solution is to prohibit trucks from driving on
the medium. Trucks should back in to unload at
the edge of the area already covered. Subgrades
can also be stabilized with geotextiles.
Muskrats and beavers can burrow into dikes or
obstruct discharge pipes. Muskrat damage can be
minimized or prevented by installing hardware
cloth (metal screen) vertically in the dikes or by
riprapping both upstream and downstream slopes.
The initial cost is small compared to replacing the
dike. If beavers are likely to be a problem, state
wildlife personnel should be consulted to develop
a plan to prevent their unwanted damming.
structures, should be thoroughly tested to ensure
that they are operating properly and to check that
water levels and flow distributions meet expecta-
tions.
During the initial operation, any erosion and
channeling that develops should be eliminated by
raking the substrate and filling by hand. Rills on
the dike slopes and spillways should be filled with
suitable material and thoroughly compacted.
These areas should be reseeded or resodded and
fertilized as needed. If there is seepage under or
through a dike, an engineer should be consulted to
determine the proper corrective measures. Startup
of a new wetland system is a critical time. System
startup comprises the filling and planting of the
wetland and a period in which the soil/media,
plants, and microbes adjust to the hydrologic
conditions in the wetland. Like all living systems.
wetlands are better able to tolerate change if they
have been allowed time to stabilize initially.
After the initial stabilization period, a gradual
increase in wastewater flow to allow the system to
adjust to the new water chemistry is often wiser
than immediately operating at the ultimate flow.
In Europe, a full growing season is often allowed
before wastewater is added. Much shorter stabili-
zation periods (several weeks to several months)
are typical in the United States. Wastewater
should not be added until the plants have shown
new growth, indicating that the roots have recov-
ered from transplanting. Highly concentrated
wastewaters, such as some agricultural wastes.
will require a more gradual introduction than will
less concentrated waters, such as stormwater or
pre-treated sewage effluent.
INSPECTION, STARTUP,
AND TESTING
Before accepting the final product, the wet-
land should be flooded to design depth and all
components, such as pumps and water control
40
VOLUME!: GENERAL CONSIDERATIONS
-------
CHAPTER 9
OPERATION, MAINTENANCE, AND MONITORING
OPERATION AND
MAINTENANCE
Wetlands must be managed if they are to
perform well. Wetland management should focus
on the most important factors in treatment perfor-
mance:
. providing ample opportunity for contact of the
water with the microbial community and with
the litter and sediment
. assuring that flows reach all parts of the wetland
• maintaining a healthy environment for microbes
• maintaining a vigorous growth of vegetation.
OPERATION AND
MAINTENANCE PLAN
Operation and maintenance (O&M) should be
described in an O&M plan written during the
design of the constructed wetland system. The
plan can be updated to reflect specific system
characteristics learned during actual operation.
The plan should provide a schedule for routine
cleaning of distribution systems and weirs, dike
mowing and inspection, and system monitoring.
The plan should specify those individuals
responsible for performing and paying for
maintenance. The plan should address:
. setting of water depth control structures
. schedule for cleaning and maintaining inlet
and outlet structures, valving, and monitoring
devices
. schedule for inspecting embankments and
structures for damage
. depth of sediment accumulation before re-
moval is required
. operating range of water levels, including
acceptable ranges of fluctuation
the supplemental water source to be used to
ensure adequate water levels during establish-
ment and operation
wastewater application schedule, if this is part
of the system design. An application schedule
should be selected that is both convenient and
relatively continuous. Short, high-flow dis-
charges to a wetland are more likely to erode or
damage established vegetation than lower
velocity, more continuous flows.
scheduling discharges to or from the wetland,
recycling/redirecting flows, or rotating between
cells, if such are part of the design.
HYDROLOGY
In SF wetlands, water should reach all parts of
the wetland surface. The wetland should be peri-
odically checked to ensure that water is moving
through all parts of the wetland, that buildup of
debris, has not blocked flow paths, and that stagnant
areas have not developed. The importance of
assuring adequate water depth and movement
cannot be over-emphasized. Stagnant water de-
creases removal and increases the likelihood of
mosquitoes and unsightly conditions. Flows and
water levels should be checked regularly.
SSF wetlands should be checked to see that
surface flow is not developing.
STRUCTURES
Dikes, spillways, and water control structures
should be inspected on a regular basis and immedi-
ately after any unusual flow event. Wetlands
should be checked after high flows or after rapid ice
break-up; both can scour substrates, particularly at
outlets. Any damage, erosion, or blockage should
be corrected as soon as possible to prevent cata-
strophic failure and expensive repairs.
VOLUME 1: GENERAL CONSIDERATIONS
41
-------
VEGETATION
Water level management is the key to deter-
mining the success of vegetation. While wetland
plants can tolerate temporary changes in water
depth, care should be taken not to exceed the
tolerance limits of desired species for extended
periods of time. Water depth can be increased
during the cold months to increase retention time
and to protect against freezing. Alternating flows
and drawdown may help to oxidize organic matter
and to encourage the recruitment of new plants
into the wetland. Vegetative cover on dikes should
be maintained by mowing, and fertilizing or
liming, as needed. Frequent mowing encourages
grasses to develop a good ground cover with
extensive root systems that resist erosion, and
prevents shrubs and trees from becoming estab-
lished. The roots of shrubs and trees can create
channels and subsequent leakage through the
berm.
Vegetation should de inspected regularly and.
invasive species should be removed. Herbicides
should not be used except in extreme circum-
stances, and then only with extreme care, since
they can severely damage emergent vegetation.
MUSKRATS.
Muskrats and other burrowing animals can
damage dikes and liners. If wire screening was not
installed in the dikes, a thick layer of gravel, rock,
or bentonite over trouble spots may inhibit bur-
rowing. If damage continues, the animals may
have to be trapped and removed for temporary
relief until wire screen can be installed. Burrows
can also be sealed by placing bentonite clay in the
entryway and adding water to the bentonite to seal
the opening.
MOSQUITOES
Mosquitoes are common in natural wetlands
and can be expected in constructed wetlands.
However, in the mid- atlantic states, mosquitoes
are usually not a major problem in constructed
wetlands.
The best approach to avoiding mosquito
problems in constructed wetlands is to create
conditions in the wetland that are not attractive to
mosquitoes or are not conducive to larval develop-
ment. Open, stagnant water creates excellent
mosquito breeding habitat, and stagnant, high
nutrient water is ideal for larval development.
Flowing water and a covered water surface mini-
mize mosquito development.
Control methods include unblocking flows to
eliminate stagnant backwaters, shading the water
surface (females avoid shaded water for egg-
laying), and dispersing floating mats of duckweed
or other floating plants.
Purple martins, swallows, and bats can eat
thousands of adult mosquitoes every day, so
providing purple martin houses, swallow
perches, and bat boxes will reduce the number
of mosquitoes.
Mosquitofish (Gambusia) can be introduced to
prey on mosquito larvae. The green sunfish
(Lepornis cyanellus), a native, hardy, and aggres-
sive mosquito-eating fish, can be used in areas that
are too cold for mosquitofish. Some control is
provided by the larvae of insects, such as dragon-.
flies, which prey on mosquito larvae.
The control of mosquitoes with insecticides,
oils, and bacterial agents such as Bti (Bacillus
thuringiensis isroelensis) is often difficult in
constructed wetlands. The use of insecticides in
constructed wetlands with large amounts of
organic matter is ineffective because the insecti-
cides adsorb onto the organic matter and because
they are rapidly diluted or degraded by the water
traveling through the wetland. Chemical treat-
ment should be used with caution because it is
poorly understood and runs the risk of contami-
nating both the wetland and the receiving stream.
Before beginning any involved control procedures,
every aspect of the wetland system and the sur-
rounding area should be carefully inspected,
perhaps with the aid of a good vector control
specialist. The inspection should include such
42
VOLUMES: GENERAL CONSIDERATIONS
-------
minor components as old cans, discarded tires,
undrainable depressions in wooded areas, hollow
stumps, water control structures, open piping, and
anywhere else that standing water can accumulate.
Mosquito problems often originate from some small
and frequently overlooked pocket of standing water
rather than from the wetland as a whole.
MONITORING
Monitoring is an important operational tool that:
. provides data for improving treatment performance
. identifies problems
. documents the accumulation of potentially toxic
substances before they bioaccumulate
• determines compliance with regulatory require-
ments.
Monitoring is needed to measure whether the
wetland is meeting the objectives of the wetland
system and to indicate its biological integrity. Moni-
toring the wetland can identify problems early on,
when intervention is most effective. Photographs can
be invaluable in documenting conditions. Photo-
graphs should be taken each time at the same loca-
tions and viewing angles.
The level of detail of the monitoring will depend
on the size and complexity of the wetland system and
may change as the system matures and its perfor-
mance becomes more well known. As a minimum.
lightly-loaded systems that have been operating
satisfactorily may only need to be checked every
month and after every major storm. Those that are
heavily loaded will require more frequent and de-
tailed monitoring.
M ONITORING PLAN
A written monitoring plan is essential if continu-
ity is to be maintained throughout the life of the
project, which may span many decades. The moni-
toring plan should include:
. clearly and precisely stated goals of the project
the specific objectives of monitoring
organizational and technical responsibilities
tasks and methods
data analysis and quality assurance procedures
schedules
reporting requirements
resource requirements
budget.
M ONITORING FOR
DISCHARGE COMPLIANCE
Monitoring for compliance with the limita-
tions of the discharge permit represents the mini-
mum of sampling and analysis a requirements. A
fixed weir at the outlet provides a simple means
of measuring flow and collecting water samples.
The parameters to be monitored and the frequency
of data collection will be set by the terms of the
permit.
M ONITORING FOR
SvsTEM PERFORMANCE
Wetland system performance is usually as-
sessed by determining:
. hydraulic loading rates
. inflow and outflow volumes
. water quality changes between inflow and
outflow
. excursions from normal operating conditions.
The effectiveness of contaminant removal can
be determined from the difference between influ-
ent loads (inflow volume x contaminant concen-
tration) and effluent loads (discharge volume x
contaminant concentration). The parameters of
concern may include:
. domestic wastewater: BOD,, nitrogen, phospho-
rus, total suspended solids, heavy metals,
bacteria (total or fecal coliform)
VOLUME 1: GENERAL CONSIDERATIONS
43
-------
. agricultural wastewater: BOD,, nitrogen, phos-
phorus, total suspended solids, pesticides,
bacteria (total or fecal coliform)
• mine drainage: pH, iron, manganese, aluminum,
total suspended solids, sulfate
. stormwater: total suspended solids, nitrogen,
phosphorus, heavy metals, vehicle emission
residues
Surface water sampling stations should be
located at accessible points at the inlet and outlet,
and, depending on the size and complexity of the
system, at points along the flow path within the
wetland. Surface water quality stations should be
permanently marked. Boardwalks can be installed
to avoid disturbing sediment and vegetation while
sampling. If the wastewater could contain toxic
pollutants, such as pesticides or heavy metals,
sediments should be sampled once or twice a year
to monitor the potential buildup of contaminants
in the wetland sediments. The effluent should be
sampled during high storms and high spring
runoff flows to assure that sediments are being
retained in the wetland. Groundwater should also
be monitored once or twice a year to ensure that
the wetland is not contaminating groundwater.
plots, usually 3 ft x 3 ft) within the wetland at
selected locations. A lightweight, open frame of
wood or PVC pipe is laid on the wetland and the
number of stems of each species present within
the frame is counted. Changes of concern include
an increase in the numbers of aggressive nuisance
species, a decrease in the density of the vegetative
cover, or signs of disease.
The vegetation in constructed wetlands is
subject to gradual year-to-year change, just as in
natural wetlands. There may be tendency for
some species to die out and be replaced by others.
Temporary changes, such as the appearance of
duckweed or algae, can occur in response to
random or seasonal climatic changes. Because
vegetative changes are often slow, they may not be
obvious in the short-term, and good record-
keeping becomes essential.
The buildup of accumulated sediment and
litter decreases the available water storage capac-
ity, affecting the depth of the water in the wetland
and possibly altering flow paths. Sediment, litter,
and water depths should be checked occasionally.
M ONITORING FOR
WETLAND HEALTH
The wetland should be checked periodically to
observe general site conditions and to detect major
adverse changes, such as erosion or growth of
undesirable vegetation. Vegetation should be
monitored periodically to assess its health and
abundance. For wetlands that are not heavily
loaded, vegetation monitoring need not be quanti-
tative and qualitative observations of the site will
usually suffice. Large systems and those that are
heavily loaded will require more frequent, quanti-
tative monitoring. In general, more frequent
monitoring also is required during the first five
years after the wetland is installed.
Species composition and plant density are
easily determined, by inspecting quadrats (square
44
VOLUME!: GENERAL CONSIDERATIONS
-------
REFERENCES
Cooper, P. F., and B.C. Findlater (eds.). 1990.
Constructed Wetlands in Water Pollution Control.
Proceedings of the International Conference on
the Use of Constructed Wetlands in Water Pollu-
tion Control, Cambridge, UK, 24-28 September.
WRc, Swindon, Wiltshire, UK. 605 pp.
EPA (Environmental Protection Agency). 1993.
Wetland Creation and Restoration: Status of the
Science. Washington, DC.
Hammer, D. A. (ed.). 1989. Constructed Wetlands
for Wastewater Treatment: Municipal, Industrial
and Agricultural. Lewis Publishers, Chelsea, MI.
831 pp.
Hilton, B. L. 1993. Performance evaluation of a
closed ecological life support system (CELSS)
employing constructed wetlands, pp 117-125 in
Constructed Wetlands for Water Quality Improve-
ment, G. A. Moshiri (ed.). CRC Press, Boca Raton,
FL.
Jacobson, M. A. 1994. Prairie Wetland Restoration
and Water Quality Concerns. Master's thesis,
University of Minnesota, MN. 101 pp.
Kadlec, J. A. 1993. Effect of depth of flooding on
_ summer water budgets for small diked marshes.
Wetlands 13:1-9.
Kadlec, R. H. 1989. Wetlands for treatment of
municipal wastewater. pp 300-314 in Wetlands
Ecology and Conservation:, Emphasis in Pennsyl-
vania, S. K. Majumdar, R. P. Brooks, F. J. Brenner,
and R. W. Tiner, Jr. (eds.). The Pennsylvania
Academy of Science, Philadelphia, PA.
Livingston, E. 1989. Use of wetlands for urban
stormwater management, pp 253-262 in Con-
structed Wetlands for Wastewater Treatment, D.
A. Hammer (ed.). Lewis Publishers, Chelsea, MI.
Mitsch, W. J. 1992. Landscape design and the role
of created, restored and natural riparian wetlands
in controlling nonpoint source pollution. Eco-
logical Engineering 1(1992): 27-47.
Moshiri, G. A. (ed.). 1993. Constructed Wetlands
for Water Quality Improvement. CRC Press, Boca
Raton, FL. 632 pp.
SCS (Soil Conservation Service). 1991. Measure-
ment and Estimation of Permeability of Soils for
Animal Waste Storage Facilities. Technical Note
717, South National Technical Center (SNTC),
Ft. Worth, TX. 35 pp.
SCS (Soil Conservation Service). 1992. Engineer-
ing Field Handbook, Chapter 13: Wetland restora-
tion, enhancement, or creation. 210-EFH, 1/92.
SCS (Soil Conservation Service). 1993. Design and
Construction Guidelines for Considering Seepage
from Agricultural Waste Storage Ponds and
Treatment Lagoons. Technical Note 716, South
National Technical Center (SNTC), Ft. Worth, TX.
unpaged.
Schueler, T. R. 1992. Design of Stormwater Wet-
land Systems: Guidelines for Creating Diverse
and Effective Stormwater Wetland Systems in the
Mid-Atlantic Region. Metropolitan Council of
Governments, Washington, D.C. 127 pp.
Surrency D. S. 1993. Evaluation of aquatic plants
for constructed wetlands, pp 349-357 in Con-
structed Wetlands for Water Quality Improve-
ment, G. A. Moshiri (ed.). CRC Press, Boca Raton,
FL.
Taylor, H. N., K. D. Choate, and G. A. Brodie. 1993.
Storm event effects on constructed wetland
discharges, pp 139-145 in Constructed Wetlands
for Water Quality Improvement, G. A. Moshiri
(ed.). CRC Press, Boca Raton, FL.
Thunhorst, G. A. 1993. Wetland Planting Guide
for the Northeastern United States. Environmen-
tal Concern, Inc. St. Michaels, MD.
US Army Corps of Engineers. 1993. Selection
and acquisition of wetland plant species for
wetland management projects. WRP Tech. Note
VN-EM-2.1. US Army Engineer Waterways
Experiment Station, Vicksburg, MS. 5 pp.
VOLUME i: GENERLAL C ONSIDERATIONS
45
-------
Water Pollution Control Federation. 1990.
Natural Systems for Wastewater Treatment.
Manual of Practice FD-16, Chapter 9. Alexan-
dria, VA.
Watson, J. T., and J. A Hobson. 1989. Hydraulic
design considerations and control structures
for constructed wetlands for wastewater
treatment, pp 379-391 in Constructed Wet-
lands for Wastewater Treatment, D. A. Hammer
(ed.). Lewis Publishers, Chelsea, MI.
Webster, H. J., M. J. Lacki, and J. W. Hummer.
1994. Biotic development comparisons of a
wetland constructed to treat mine water with a
natural wetland system, pp 102-110 in Vol-
ume 3, Proceedings International Land Recla-
mation and Mine Drainage Conference and
Third International Conference on the Abate-
ment of Acidic Drainage, Pittsburgh, PA. April
24-29, 1994. Bureau of Mines Spec. Publ.
SP 06C-94.
Wetzel, R. G., 1993. Constructed wetlands:
scientific foundations are critical, pp 3-7 in
Constructed Wetlands for Water Quality
Improvement, G.-A. Moshiri (ed.). CRC Press,
Boca Raton, FL.
46 VOI.UME 1: GENERAL CONSIDERATIONS
-------
1. Constructed wetlands, such as this stormwater
wetland, provide aesthetics and wildlife habitat as
well as water quality improvement and stormwater
control.
2. Constructed wetlands are a cost-effective
means of removing metals from mine
drainage. The black deposits are
manganese precipitates.
3. Site surveys are necessary for proper
design and construction.
4. Including a deeper, open water area
increases the wildlife value of the
wetland and may increase ammonia
removal.
-------
5. An organic substrate is often used for wetlands
that will treat coal mine drainage.
7. Perforated inlet pipes are a simple way to
distribute wastewater across the width of the
cell.
6. This anoxic limestone drain, which is being built
with the help of the National Guard, will add
alkalinity to acidic drainage from an abandoned
coal mine before wetland treatment.
8. Construction usually requires heavy
equipment.
-------
9. Straw bales can be used to create long flow paths
as part of the initial design, as here, or they can
be added later to correct short-circuiting.
10. A V-notch weir is simple to construct but-
does not allow water levels to be adjusted
easily.
12. After excavation, grading, and compaction.
a newly-constructed wetland is ready for
planting.
11. Structures may need to be protected from
vandals and animals.
-------
13. After flooding the wetland to settle the
substrate, the wetland should be drained
for planting.
15. A cattail rhizome.
14. Water levels can be raised gradually as the
plants grow.
16. Dense vegetation promotes sedimentation
and pollutant removal.
-------
NOTES
VOLUME 1: GENERAL CONSIDERATIONS 51
-------
NOTES
52 VOLUME 1: GENERAL C ONSIDERATIONS
-------
GLOSSARY
abiotic not involving biological processes
aerobic requiring free oxygen
algae primitive green plants that live in wet environments
ALD anoxic limestone drain
AMD acidic mine drainage
AML abandoned mine lands
anaerobic a situation in which molecular oxygen is absent; lacking oxygen
anoxic without free oxygen
aquifer a permeable material through which groundwater moves
aspect the ratio of length to width
AWMS animal waste management system
baseflow the portion of surface flow arising from groundwater; the between-storm Bow
biomass the mass comprising the biological components of a system
biotic the living parts of a system; biological
BMP Best Management Practice
BOD biochemical oxygen demand, often measured as 5-day biochemical oxygen demand (BOD,); the consump-
tion of oxygen by biological and chemical reactions
CEC cation exchange capacity
community (plant) the assemblage of plants that occurs in an area at the same time
denitrification the conversion of nitrate to nitrogen gas, through the removal of oxygen
detritus loose, dead material; in wetlands, largely the leaves and stems of plants
emergent wetland a wetland dominated by emergent plants, also called a marsh
EC electrical conductivity
effluent the surface water flowing out of a system
emergent plant a non-woody plant rooted in shallow water with most of the plant above the water surface
ET evapotranspiration
evapotranspiration loss of water to the atmosphere by evaporation from the water surface and by transpiration by plants
exfiltration the movement of water from a surface water body to the ground
exotic species not native; introduced
HLR hydraulic loading rate: loading on a unit area basis
HRT hydraulic residence time; average time that moving water remains in a system
hydric soil a soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic
conditions in the upper part of the soil
hydrolysis chemical decomposition by which a compound is resolved into other compounds by taking up the ele-
ments of water
bydroperiod the seasonal pattern of changes in water level
infiltration the movement of water from the ground into a surface water body
influent the surface water flowing into a system
karst irregular, pitted topography characterized by caves, sinkholes, and disappearing streams and springs, and
caused by dissolution of underlying limestone, dolomite, and marble
marsh an emergent wetland
microbe microscopic organism; includes protozoa, bacteria, yeasts, molds, and viruses
-------
microorganism term often used interchangeably with microbe
native species one found naturally in an area; an indigenous species
nitrification the conversion of ammonia to nitrate through the addition of oxygen
non-persistent plant... a plant that breaks down readily after the growing season
non-vascular plant a plant without differentiated tissue for the transport of fluids; for instance, algae
NFS nonpoint source
organic matter matter containing carbon
oxidation the process of changing an element from a lower to a higher oxidation state by the removal of an
electron(s) or the addition of oxygen
pathogen a disease-producing microorganism
peat partially decomposed plant material, chiefly mosses
perennial plant a plant that lives for many years
permeability the capacity of a porous medium to conduct fluid
persistent plant a plant whose stems remain standing from one growing season to the beginning of the next
redox reduction/oxidation
reduction the process of changing an element from a higher to a lower oxidation state, by the addition of an
election(s)
rhizome a root-like stem that produces roots from the lower surface and leaves, and stems from the upper surface
riparian pertaining to the bank of a stream, river, or wetland
SAPS successive alkalinity-producing system
SF surface flow
SSF subsurface flow
stolon a runner that roots at the nodes
scarification abrasion of the seed coat
stratification treatment of seed by exposure to cold temperatures
succession the orderly and predictable progression of plant communities as they mature
transpiration the process by in which plants lose water
tussock a hummock bound together by plant roots, especially those of grasses and sedges
tuber a short thickened underground stem having numerous buds or "eyes"
TSS total suspended solids
vascular plant a plant that possesses a well-developed system of conducting tissue to transport water, mineral salts, and
foods within the plant
wrack plant debris carried by water
-------
ABBREVIATIONS AND CONVERSION FACTORS
MULTIPLY
ac, acre
cfs, cubic foot per second
cfs, cubic foot per second
cm, centimeter
cm/sec, centimeter per second
°F, degree Fahrenheit
ft, foot
ft2, square foot
ft3, cubic foot
ft/mi, foot per mile
fps, foot per second
g/m2/day, gram per square meter per day
gal, gallon
gal, gallon
gpm, gallon per minute
ha, hectare
inch
kg, kilogram
kg/ha/day, kilogram per hectare per day
kg/m2, kilogram per square meter
L, liter
L, liter
Ib, pound
Ib/ac, pound per acre
m, meter
m2, square meter
m3, cubic meter
m3, cubic meter
m3/ha/day, cubic meter per hectare per day
mm, millimeter
mi, mile
BY
0.4047
440.831
2.8317 x 10J
0.3937
3.28 x lO'2
5/9 (°F - 32)
0.305
9.29 x 10'2
2.83 x 10'2
0.1895
18.29
8.92
3.785
3.765 x 10J
6.308 x 10-2
2.47
2.54
2.205
0.892
0.2
3.531 x 10'2
0.2642
0.4536
1.121
3.28
10.76
1.31
264.2
106.9
3.94 x 10J
1.609
TO OBTAIN
ha, hectare
gpm, gallon per minute
m3/s, cubic meter per second
inch
fps, foot per second
°C, degree Celsius
m, meter
m2' square meter
m3, cubic meter
m/km, meter per kilometer
m/min, meter per minute
Ib/ac/day, pound per acre per day
L, liter
m3, cubic meter
L/s. liter per second
ac, acre
cm, centimeter
Ib, pound
Ib/ac/day, pound per acre per day
lb/ft2, pound per square foot
ft3, cubic foot
gal, gallon
kg, kilogram
kg/ha, kilogram per hectare
ft, foot
ft2, square foot
yd3, cubic yard
gallon, gal
gallon per day per acre, gpd/ac
inch
kilometer, km
-------
For sale by the U.S. Goverment Printing Office
Superintendent of Document Mail stop: SSOP. Washington DC 20402-9328
ISBN 0-16-052999-9
ISBN 0-16-052999-9
9' 780160 529993
------- |