A HANDBOOK OF

CONSTRUCTED WETLANDS

a guide to creating wetlands for:

AGRICULTURAL WASTEWATER

DOMESTIC WASTEWATER

COAL MINE DRAINAGE

STORMWATER

in the Mid-Atlantic Region

Volume1
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

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.

Timothy Murphy, USDA - NRCS, Harrisburg, PA

Glenn Rider, Pennsylvania Department of Environmental

Resources, Harrisburg. 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, WilkesBarre, 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 . . . . . . . . . . . . . . . . . . ................................................._................................................., .5

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 ........................................................................................ 11

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 Wetland s ................................................................. . ....................................... 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 .I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......................... 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
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 component 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 application 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, lowenergy 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, operation, and maintenance of constructed wetlands

for the treatment of domestic wastewater, agricultural 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 information 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 industrial wastewaters, a discussion of these applications 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 proceedings of these conferences include experimental

and operational data from wetland systems built

to treat a number of different kinds of wastewaters and runoff, and present detailed discussions

of process kinetics and system design. Proceedings from three well-known conferences are:

Moshiri, G. A. (ed.) 1993. Constructed Wetlands

for Water Quality Improvement. CRC Press, Boca

Raton, FL. 632 pp.

V OLUME 1: GENERAL C ONSIDERATIONS 5
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 Pollution 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.

V OLUME 1: GENERAL C ONSIDERATIO N
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 understanding of how natural wetlands are structured and

how they function greatly increases the likelihood 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” encompasses 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, freshwater or salt - have one characteristic in common: 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 shallow 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

VOLUME 1 G ENERAL C ONSIDERATIONS

inorganic materials and the diverse opportunities

for gas/water interchanges foster a diverse community of microorganisms that break down or transform a wide variety of substances.

Most wetlands support a dense growth of

vascular plants adapted to saturated conditions.

This vegetation slows the water, creates microenvironments 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 perceives 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.’

7
COMPONENTS OF

CONSTRUCTED WETLANDS

A constructed wetland consists of a properlydesigned 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.

W ATE R

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 landscape 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 constructed wetland. While the hydrology of constructed wetlands is not greatly different than that of

other surface and near-surface waters, it does differ in

several important respects:

l small changes in hydrology can have fairly significant effects on a wetland and its treatment effectiveness 

l 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)

l 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.

S UBSTRATE S, SEDIMENT S, AND L ITTE R

Substrates used to construct wetlands include 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:

l they support many of the living organisms in

wetlands

l substrate permeability affects the movement of

water through the wetland

l many chemical and biological (especially

microbial) transformations take place within

the substrates

l substrates provide storage for many

contaminants

l the accumulation of litter increases the amount

of organic matter in the wetland. Organic matter

provides sites for material exchange and microbial 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.

V E G ET ATIO N

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
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, redtailed hawks, and Northern harriers feed and/or

nest in wetlands.

AESTHETICS AND LANDSCAPE

E NHANCEMEN T

While wetlands are primarily treatment

systems, they provide intangible benefits by

increasing the aesthetics of the site and enhancing the landscape. Visually, wetlands are unusually 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.

V OLUME 1: GENERAL C ONSIDERATIONS
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 suspended 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 ICROORGANISM S

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:

l transforms a great number of organic and

inorganic substances into innocuous or

insoluble substances

l alters the reduction/oxidation (redox) conditions of the substrate and thus affects the

processing capacity of the wetland

l 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 facultative anaerobes, that is, they are capable of functioning under both aerobic and anaerobic conditions 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 NIMAL S

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 fragmenting 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 important predators of mosquito larvae.

Although invertebrates are the most

important animals as far as water quality improvement is concerned, constructed wetlands

also attract a variety of amphibians, turtles,

birds, and mammals.

VOLUME 1: GENERAL CONSIDERATIONS 9
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:

l settling of suspended particulate matter

l filtration and chemical precipitation through

contact of the water with the substrate and

litter

l chemical transformation

l adsorption and ion exchange on the surfaces of

plants, substrate, sediment, and litter

l breakdown and transformation of pollutants by

microorganisms and plants

l uptake and transformation of nutrients by

microorganisms and plants

l predation and natural die-off of pathogens.

The most effective treatment wetlands are

those that foster these mechanisms. The specifics 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 wastewater and runoff for several reasons:

l wetlands can be less expensive to build than

other treatment options

. operation and maintenance expenses (energy

and supplies) are low

l operation and maintenance require only

periodic, rather than continuous, on-site labor

l wetlands are able to tolerate fluctuations in

flo w

. they facilitate water reuse and recycling.

In addition:

l they provide habitat for many wetland organisms

l they can be built to fit harmoniously into the

landscape

l they provide numerous benefits in addition to

water quality improvement, such as wildlife

habitat and the aesthetic enhancement of open

spaces

l they are an environmentally-sensitive

approach that is viewed with favor by the

general public.

LIMITATIONS OF

CONSTRUCTED WETLAND S

There are limitations associated with the use

of constructed wetlands:

l they generally require larger land areas than

do conventional wastewater treatment systerns. Wetland treatment may be economical

relative to other options only where land is

available and affordable.

VOLUME 1: GENERAL CONSIDERATIONS 17
they require a minimum amount of water if they

l 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 performance over the year may be acceptable, wetland

treatment cannot be relied upon if effluent

quality must meet stringent discharge standards

at all times.

l the biological components are sensitive to toxic

chemicals, such as ammonia and pesticides

l flushes of pollutants or surges in water flow may 

temporarily reduce treatment effectiveness

are to survive. While wetlands can tolerate

temporary drawdowns, they cannot withstand

Also, the use of constructed wetlands for wastewater 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

WETLAND S

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 wastewatercomplete drying. 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 Surface Flow Wetland

LINER

NATIVE SOIL

Water level is below ground; water flow is through a sand or gravel

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).

bed; roots

VOLUME 1 : GENERAL CONSIDERATIONS
S URFACE F LOW W ETLAND S

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 nearsurface 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 maintenance are straightforward. The main disadvantage

of SF systems is that they generally require a larger

land area than other systems.

S UBSURFACE F LOW W ETLAND S

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, microbial 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 concentrations 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 designed 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 YBRID S YSTEM S

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 remoral of ammonia from agricultural wastewater.

WINTER AND SUMMER

OPERATION

Wetlands continue to function during cold

weather. Physical processes, such as sedimentation. continue regardless of temperature, providing

that the water does not freeze. Many of the reactions 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.

V OLUME 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 wastewater 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 tEat 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 adequacy 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 supplemental source of water may be required to maintain 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 contaminants. Bioaccumulation and biotoxicity in

treatment wetlands is not clearly documented

nor understood.

Persistent compounds can be a concern,

depending on the constituents in the wastewater. 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-enrichment 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 inherent in all living systems and is to be expected.

The change in species composition as ecosystems mature is known as succession. In

general, species diversity increases as ecosystems 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 environment; 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

V OLUME 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.

V OLUME 1: GENERAL CONSIDERATIONS 15
CHAPTER 4

GENERAL DESIGN OF CONSTRUCTED WETLANDS

DESIGN CONSIDERATIONS

Despite a large amount of research and published information, the optimal design of constructed 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 fostering 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 rectangular basins, rigid structures and channels, and

regular morphology. Mimic natural systems.

give the system time. Wetlands do not necessarily 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 overmanage often fail.

l design the system for function, not form. For

instance, if initial plantings fail, but the overall

function of the wetland, based on initial objectives, 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 wastewater 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. Economic factors include the land area required. the

type of water containment, the control and transport of water through the system, and vegetation.

Setting and prioritizing the objectives of the

wetland system is key to the creation of a successful system. The characteristics of a local natural

wetland should be used as a model for the constructed wetland, modified to fit the needs of the

project and the specifics of the constructed wetland 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

V OLUME 1: GENERAL CONSIDERATIONS 37
Provides adeqyate space

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 performance 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 1and, 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, construction 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:

l is conveniently located to the source of the

wastewater

l is gently sloping, so that water can flow through

the system by gravity

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.

V OLUME 1: GENERAL C ONSIDERATIONS

l contains soils that can be sufficiently compacted to

minimize seepage to groundwater

l is above the water table

l is not in a floodplain

l does not contain threatened or endangered species

l does not contain archaeological or historic resources.

L AND U SE AND A CCES S

Access is an important consideration, The wetland 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 maintenance.

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 understands 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.

L AND A VAIL AB I L IT Y
T OPOG RA P H Y

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 wellsuited for a constructed wetland since the topography 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 throughout 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.

 ENVIRONMENTAL R ESOURCE S

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 selecting a site include the US Geological Survey Topographic Quadrangle maps, and National Aerial

Photography Program (NAPP) and and National High

Altitude Photography Program (NHAPP) photographs. 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 NW1 maps are

based on aerial photography and may not show small

wetlands or the less obvious wetlands (wet meadows, vernal pools, and some forested wetlands) and

the NW1 information should be field-checked by a

wetlands scientist. Historical aerial photography,

such as the Agricultural Stabilization and Conservation Service (ASCS) crop compliance photography 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 wetland 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 Management 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.

PERMITS AND REGULATION S

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 1 9
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 adequate 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 accommodate 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:lV and riprapped or protected

by erosion control fabric on the slopes. An emergency 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 systems 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 relatively 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. Muskrats can be excluded by installing electric fence

low to the ground or by burying muskrat-proof

wire mats in the dikes during construction.

L INER S

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

<108 ft/sec (<10-6 cm/sec). Soils that contain

more than 15% clay are generally suitable.

Bentonite, as well as other clays, provide adsorption/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 Treatment 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 punctures. 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.

F LOW C ONTROL STR UC TUR ES

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

20 V OLUME 1: GENERAL C ONSIDERTION S
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 shortcircuiting. 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 structures should be enclosed in lockable concrete

structures or manholes to avoid damage or tampering with water level settings. Structures must be

protected against damage by animals. Measures

include installing covers or wire mesh over openings, and enclosing controls, gauges and monitoring 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 imporInlet with Swiveling Tees Inlet with Gabion

Inlet with Buried

Distributor Pipe

. ‘ i

Slotted or Perforate d

 Soil. Sand or Gravel 

*

Soil. Sand or Grave

Soil Cover Over Liner

PLAN VIEW

P ROFIL E

-

r

Wat

Plan View of Outlet

Structure with

Swiveling Standpipe

Structure with

Collapsible Tubing

Structure with Swiveling

Standpipe

Figure 2. Inlet and outlet designs (modified from Watson and Hobson 1989).

V OLUME 1: GENERAL C ONSIDERATION S 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 perpendicular to the direction of flow, and simple singlepoint 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 wetland 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 protection 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 expensive 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 variableInfluent to Splitter Box (10”)

Valved Drain to Marsh ( Sampling Cinduit (6”)

Influent to

Marsh (l0”)

Influent to Splitter

Sampling Conduit (6”)

Box (l0”)

otch Weir

Influent

Valved Drain (4”)

SECTION A

toMarsh (l0”)

SECTION B

Figure 3. lnfluent splitter box

(modified from Watson and Hobson 1989).

V OLUME 1: GENERAL C ONSIDERATIONS
 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-biodegradable 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

(<l2 inch) pipes should be avoided because they

clog with litter.

At SSF wetlands, outlets include subsurface

manifold, and weir boxes or similar gated structures. 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 maximum 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

VOLUME 1

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 wetland.

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 constructed wetland systems that have provided longterm data show that treatment performance for

pollutants that are broken down in wetlands, such

as BOD5, total suspended solids (TSS), and nitrogen, 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 deposits. 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.

GENERAL CONSIDERATIONS 23
CHAPTER 5

HYDROLOGY

The hydrology of a constructed wetland is

perhaps the most important factor in its effectiveness. 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 area1 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 extremes, 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 influenced 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 resuspend 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 velocities 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

V OLUME 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 precipitation and evapotranspiration.

HYDRAULIC RESIDENCE TIME

The hydraulic residence time (HRT) of a treatment wetland is the average time that water remains 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 volume/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 contamination 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 wetlands are designed to intercept groundwater to

ensure sufficient baseflow. In this case, the wetland 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.

 WATER B ALANC E

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

2 6 V OLUME 1: GENERAL C ONSIDERATIONS
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-E T (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)

O = 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 manipulate the water budget:

l the volume of water released from the wetland

can be varied

l evapotranspiration rates can be altered by

shading, windbreaks, and the selection and

management of vegetation around the wetland

l storage capacity can be adjusted with water

control structures

l in SF wetlands, storage capacity can be increased by excavating deep pools or decreased

by adding fill.

V OLUME I : GENERAL CONSIDERATIONS 2 7
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 wetlands. 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 bonding sites for positively charged ions (cations), such

as Ca2+, Mg2+, Fe2+, A13+ 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/l00 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 contaminants 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 welldecomposed 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 amendments, such as compost, leaf litter, or sewage

sludge, must be incorporated into the substrate.

Soil texture affects root growth and the retention 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. Additions 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 hydraulic conductivities.

Soils with a high clay content aid in phosphorous 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 assimilation 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 wetlands, they are not the preferred soil for establishing constructed wetlands. Peats can release

V OLUME 1: GENERAL C ONSIDERATION S 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:

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.

l the NRCS data are averages and estimates

tallied over many acres of ground

l most soils units include inclusions that may

differ in significant ways from nearby soils

l 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.

SAND AND GRAVEL

Constructed wetlands receiving with water

high in nutrients, such as domestic and agricultural 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.

3 0 V OLUME 1 : GENERAL C ONSIDERATIONS
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 constructed 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 wastewater or stormwater containing relatively high and

often variable concentrations of pollutants. A

number of species that have been used successfully in the northeastern United States are listed

table 1.

in

For wastewater treatment wetlands, the particular 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.

S URFACE F LOW W ETLAND S

In wetlands constructed to treat domestic

sewage, agricultural wastewaters, and other

wastewaters relatively high in organic matter,

bulrushes (either softstem or common threesquare) 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 wastewater, 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 eliminate other species once it is introduced. It produces 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 considered. 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 disturbance, and to resist pests than a less diverse stand.

The numbers of wildlife attracted to a wetland

generally increases as vegetation diversity increases.’ 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

V OLUME 1 : GENERAL C ONSIDERATIONS 31
Table 1. Emergent plants for constructed wetlands

(adapted from Schueler 1992 and Thunhorst 1993).

Recommended Species Maximum Note s

Water Depth*

Arrow arum

Peltandra virginica

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.

Arrowhead/duck potato

Saggitaria latifolia

12 inches Aggressive colonizer. Mallards and muskrats

can rapidly consume tubers. Loses much water

through transpiration.

Common three-square

bulrush

Scirpus pungens

Softstem bulrush

Scirpus validus

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.

Blue flag iris

Iris versicolor

3 - 6 inches Attractive flowers. Can tolerate partial shade

but requires full sun to flower. Prefers acidic

soil. Tolerant of high nutrient levels.

Broad-leaved cattail**

Typha latifolia

Narrow-leaved cattail**

Typha angustifolio

12-18 inches

12 inches

Aggressive. Tubers eaten by muskrat and

beaver. High pollutant treatment, pH: 3.0-8.5.

Aggressive. Tubers eaten by muskrat and

beaver. Tolerates brackish water. pH : 3.7-8.5.

Reed canary grass

Phalaris arundinocea

Lizard’s tail

Saururus cernuus

6 inches

6 inches

Grows on exposed areas and in shallow

water. Good ground cover for berms.

Rapid grower. Shade tolerant. Low wildlife

value except for wood ducks.

Pickerelweed

Pontedaria cordata

Common reed** 

Phragmites australis

12 inches

3 inches

Full sun to partial shade. Moderate wildlife

value. Nectar for butterflies. pH: 6.0-8.0.

Highly invasive; considered a pest species in

many states. Poor wildlife value. pH: 3.7-8.0.

V OLUME 1: GENERAL C ONSIDERATIONS
ommended Species Maximum

Water Depth*

Notes

Soft rush

Juncus effusus

3 inches Tolerates wet or dry conditions. Food for birds.

Often grows in tussocks or hummocks.

Spikerush

Eleocharis palustris

3 inches Tolerates partial shade.

Sedges

Carex spp.

3 inches Many wetland and several upland species.

High wildlife value for waterfowl

and songbirds.

Spatterdock 5 ft,

Nuphar luteum 2 ft minimum

Tolerant of fluctuating water levels. Moderate

food value for wildlife, high cover value.

Tolerates acidic water (to pH 5.0).

Sweet flag

Acorus calamus

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.

l These depths can be tolerated, but plant growth and survival may decline under permanent inundation at these

depths.

l **Not recommended for stormwater wetlands because they are highly invasive, but can be used in treatment

wetlands if approved by regulatory agencies

V OLUME 1: GENERAL CONSIDERATIONS 3 3
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).

S U B SU RFACE F LOW W ETLAND S

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 generally will not sprout under water. Many emergents

have rhizomes, rootstocks, or tubers which, although

they are primarily food storage organs, can generate

new plants.

S EEDS 

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 germinate. 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.

W ETLAND SO IL

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 transplanted to the constructed wetland. Cores are

excellent sources of seeds, shoots, and roots of

various wetland plants and will promote the development 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 E NTIRE PLANTS

Plant materials include entire plants and plant

parts, such as rhizomes and tubers. These materi3 4 V OLUME 1: GENERAL C ONSIDERATIONS
als are generally obtained from commercial

nurseries or donor wetland sites (on-site nurseries or nearby constructed wetlands).

Plants should be obtained from local

sources. The US Army Corps of Engineers

(1993) recommends that plants should be transferred 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 thesite of the construction project. The beds usually 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 (40oF, 4 - 5

o C)

until planting. Storage at cool temperatures

stratifies the tubers and rhizomes (prepares them

V OLUME 1

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. Planting 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

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 completely dried) shortly before planting to produce a

soft, moist soil.

HOW TO PLANT

Planting is usually done by hand. Few sophisticated planting techniques have been applied to

wetland planting.

S URFACE F LOW W ETLAND S

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 substrate 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

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.

S UBSU RF ACE F LOW W ETLAND S

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 operational water level. The growing shoot should

project above the surface of the media. To

encourage deeper root penetration, some European 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 encourage 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

V OLUME 1: GENERAL C ONSIDERATIONS
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 blackbirds 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 concentrations, 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 physiological 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.

V OLUME 1: GENERAL C ONSIDERATIONS 3 7
CHAPTER 8

CONSTRUCTION

Wetlands should be designed and constructed

to provide reliability and ‘safety. Standard engineering techniques should be used. It is important 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 sufficient detail for accurate bid preparation

and for construction. 

A pre-bid conference with potential contractors 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 contractors who are experienced with other kinds of

construction may have had little experience in

building wetlands. Construction plans, specifications, 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 construction.

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 Restoration, 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 engineering 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 specifications must be followed carefully to prevent

leakage into or out of wastewater wetlands, if this

is part of project specifications. If synthetic liners

V OLUME 1: GENERAL C ONSIDERATIONS 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 compaction 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 constructed because of the heavy traffic involved in

placing the rock or sand medium. In several

cases, carefully graded beds were seriously disrupted 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.

INSPECTION, STARTUP,

AND TESTING

Before accepting the final product, the wetland should be flooded to design depth and all

components, such as pumps and water control

structures, should be thoroughly tested to ensure

that they are operating properly and to check that

water levels and flow distributions meet expectations.

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 stabilization 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 recovered 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.

40 V OLUME 1: GENERAL C ONSIDERATIONS
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 performance:

l providing ample opportunity for contact of the

water with the microbial community and with

the litter and sediment

l assuring that flows reach all parts of the wetland

l 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:

l setting of water depth control structures

l schedule for cleaning and maintaining inlet

and outlet structures, valving, and monitoring

devices

l schedule for inspecting embankments and

structures for damage

l depth of sediment accumulation before removal is required

l operating range of water levels, including

acceptable ranges of fluctuation

the supplemental water source to be used to

ensure adequate water levels during establishment 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 discharges 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 periodically 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 decreases 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.

S TRUCTURE S

Dikes, spillways, and water control structures

should be inspected on a regular basis and immediately 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 catastrophic failure and expensive repairs.

VOLUME 1: GENERAL CONSIDERIATIONS 41
V EGETATION

Water level management is the key to determining 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 established. 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 circumstances, 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 burrowing. 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 development. 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 minimize mosquito development.

Control methods include unblocking flows to

eliminate stagnant backwaters, shading the water

surface (females avoid shaded water for egglaying). 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 aggressive 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 insecticides adsorb onto the organic matter and because

they are rapidly diluted or degraded by the water

traveling through the wetland. Chemical treatment should be used with caution because it is

poorly understood and runs the risk of contaminating both the wetland and the receiving stream.

Before beginning any involved control procedures,

every aspect of the wetland system and the surrounding area should be carefully inspected,

perhaps with the aid of a good vector control

specialist. The inspection should include such

42 V OLUME S: GENERAL C ONSIDERATIONS
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.

the specific objectives of monitoring

organizational and technical responsibilities

tasks and methods

data analysis and quality assurance procedures

schedules

MONITORING

Monitoring is an important operational tool that:

l provides data for improving treatment performance

reporting requirements

resource requirements

budget.

l identifies problems M ONITORING FO R

D ISCHARGE C OMPLIANC E

l documents the accumulation of potentially toxic

substances before they bioaccumulate

• determines compliance with regulatory requirements.

Monitoring is needed to measure whether the

wetland is meeting the objectives of the wetland

system and to indicate its biological integrity. Monitoring the wetland can identify problems early on,

when intervention is most effective. Photographs can

be invaluable in documenting conditions. Photographs should be taken each time at the same locations and viewing angles.

Monitoring for compliance with the limitations of the discharge permit represents the minimum 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 FO R

S Y ST EM P ERFORMANC E

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 detailed monitoring.

Wetland system performance is usually assessed by determining:

l hydraulic loading rates

l inflow and outflow volumes

l water quality changes between inflow and

outflow

M ONITORING P L A N

V OLUME 1: GENERAL CONSIDERATIONS

A written monitoring plan is essential if continuity is to be maintained throughout the life of the

project, which may span many decades. The monitoring plan should include:

l excursions from normal operating conditions.

The effectiveness of contaminant removal can

be determined from the difference between influent loads (inflow volume x contaminant concentration) and effluent loads (discharge volume x

contaminant concentration). The parameters of

concern may include:

l clearly and precisely stated goals of the project

l domestic wastewater: BOD,, nitrogen, phosphorus, total suspended solids, heavy metals,

bacteria (total or fecal coliform)

43
l agricultural wastewater: BOD,, nitrogen, phosphorus, total suspended solids, pesticides,

bacteria (total or fecal coliform)

l mine drainage: pH, iron, manganese, aluminum,

total suspended solids, sulfate

l stormwater: total suspended solids, nitrogen,

phosphorus. heavy metals, vehicle emission

residue s

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.

M ONITORING F O R

W ETLAND H EALT H

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 quantitative and qualitative observations of the site will

usually suffice. Large systems and those that are

heavily loaded will require more frequent, quantitative 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

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 recordkeeping becomes essential. 

The buildup of accumulated sediment and

litter decreases the available water storage capacity, affecting the depth of the water in the wetland

and possibly altering flow paths. Sediment, litter,

and water depths should be checked occasionally.

44 V OLUME 1: GENERAL C ONSIDERATIONS
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 Pollution 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 Improvement, 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 Pennsylvania, 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 Constructed 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. Ecological Engineering l(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. Measurement 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. Engineering Field Handbook, Chapter 13: Wetland restoration, enhancement, or creation. 210-EFH, l/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 Wetland 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 Constructed Wetlands for Water Quality Improvement, 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. Environmental 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.

V OLUME I: GENERLAL C ONSIDERATION S 45
4 6

Water Pollution Control Federation. 1990.

Natural Systems for Wastewater Treatment.

Manual of Practice FD-16, Chapter 9. Alexandria, 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 Wetlands 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 Volume 3, Proceedings International Land Reclamation and Mine Drainage Conference and

Third International Conference on the Abatement 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.
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.

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.

7. Perforated inlet pipes are a simple way to

distribute wastewater across the width of the

cell.

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 butdoes 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

V OLUME 1: GENERAL C ONSIDERATIONS 5 1
NOTES

5 2 V OLUME 1: GENERAL C ONSIDERATION S
GLOSSAR Y

abiotic ......................... not involving biological processes

aerobic ........................ requiring free oxygen

algae .......................... primitive green plants that live in wet environments

ALD.... . ...................... anoxic limestone drain

........................... 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 (BOD5); the consumption 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 elements 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

NPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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

tube r . . . . . . . . . . . . . . . . . . . . . . . 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

O

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

lb, pound

lb/ac, pound per acre

m, meter

m

2

, square meter

m

3

, cubic meter

m

3

, cubic meter

m

3

/ha/day, cubic meter per hectare per day

mm, millimeter

mi, mile

BY

0.4047

440.831

2.8317 x l0-2

0.3937

3.28 x 10-2

5/9 (0F - 32)

0.305

9.29 x 10-2

2.83 x l0-2

0.1895

18.29

8.92

3.785

3.765 x 10-3

6.308 x l0-2

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 l0-2

1.609

TO OBTAIN

ha, hectare

gpm, gallon per minute

m

3

/s, cubic meter per second

inch

fps, foot per second

oC, degree Celsius

m, meter

m

2, square meter

m

3

, cubic meter

m/km, meter per kilometer

m/min, meter per minute

lb/ac/day, pound per acre per day

L, liter

m

3

, cubic meter

L/s. liter per second

ac, acre

cm, centimeter

lb, pound

lb/ac/day, pound per acre per day

lb/ft 2, pound per square foot

ft3, cubic foot

gal, gallon

kg, kilogram

kg/ha, kilogram per hectare

ft, foot

ft2, square foot

y d

3

, 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 o-16-052999-9

9000 0

9 780160 529993