Understanding the Benefits & Design of Constructed Wetlands

Understanding the Benefits & Design of Constructed Wetlands

In a previous discussion titled “What is a wetland?“, we explore the multifaceted roles of natural wetlands. They are crucial for supporting diverse plant and animal species, controlling floods by absorbing surplus water, enhancing water quality through the removal of pollutants, and preserving biodiversity. Recognizing these benefits, constructed wetlands are specially engineered to treat various types of waste- and stormwater. They remove nutrients, sediments, heavy metals, and other contaminants, offering a sustainable and cost-effective alternative to traditional water treatment methods.

A cattail wetland in the foreground and large grain silos in the background.
A stormwater constructed wetland at the CHS grain transfer facility in Belle Chase, LA.

Constructed wetlands are a cost-effective alternative to conventional treatment facilities, with lower construction and maintenance costs and adaptability to fluctuating water levels. Additionally, the vegetation in these wetlands not only beautifies the landscape but also reduces unpleasant odors typically associated with wastewater treatment facilities.

A row of sprayers releasing wastewater into a constructed wetland.
A constructed treatment wetland at the Mandeville, LA wastewater treatment facility.

Key Components of Constructed Wetlands

Core components of constructed wetlands are similar to their natural counterparts, comprising of soils or other growth-supporting media, a defined path for water to flow evenly through the system, and water tolerant wetland vegetation. However, the specific design can vary widely depending on the intended purpose of the wetland.

Point Source Pollution Treatment:

Constructed wetlands for municipal wastewater treatment have meticulously controlled water flow through the wetlands with predefined inlets and outlets. The area is lined with impermeable materials to prevent leakage, layered with growth media such as rock or graded gravel, and planted with specific species of wetland vegetation.

Non-Point Source Pollution Treatment:

Constructed wetlands for stormwater treatment typically utilize soils already present at the site, and allow vegetation to establish naturally once wet. This approach manages runoff and improves water quality more passively than constructed wetlands for municipal wastewater treatment.

Construction and Placement

Constructed wetlands are generally positioned on uplands to minimize disruption to natural wetlands and aquatic ecosystems. The construction process includes:

  • Excavation of the area where the wetland will be established;
  • Backfilling with suitable growth media and shaping it for proper water flow;
  • Creation of dikes to contain water during high water levels;
  • Installation of water control structures to manage water flow effectively.

Benefits of Constructed Wetlands

When designed and maintained properly, constructed wetlands not only significantly improve water quality but also create additional wildlife habitat, provide spaces for public recreation, and offer opportunities for water reuse. These engineered ecosystems represent a harmonious blend of functionality and sustainability, offering a natural solution to modern environmental challenges.


Lower construction and maintenance costs compared to conventional treatment facilities.

Improved Water Quality

Effective removal of nutrients, sediments, heavy metals, and other contaminants.

Wildlife Habitat

Creation of new habitats, enhancing biodiversity.

Aesthetic and Recreational Value

Attractive spaces for public recreation and education.

Water Reuse

Treated water can be reused for various purposes, reducing the demand on freshwater resources.

Comite Resources has experience designing and maintaining constructed wetlands.  Please contact us to discuss your project.

Why rSETs are Important for Wetland Monitoring

Wetland elevation dynamics hinge on the intricate interplay between subsidence and accretion processes. Subsidence includes several local factors that contribute to the gradual lowering of wetland elevation such as compaction and consolidation of sediments, occurring both in shallow and deep layers, tectonic activity influencing the geological framework, and human-induced impacts like the withdrawal of oil and gas. These various elements collectively shape the subsidence profile of a wetland, highlighting the dynamic nature of the landscape.

Shows profile of rSET benchmark with instrument mounted on top and pins lowered to the wetland surface. Accretion markers are shown with accumulated soil material on top.
The combined Surface Elevation Table – Marker Horizon technique enables estimates of both above and below-ground process contributions leading to wetland elevation change (from Lynch et al. 2015).

Accretion, Subsidence and Sea Level Rise

Conversely, accretion denotes the vertical buildup of soil on the wetland surface, a measurable phenomenon often tracked using markers like feldspar. This accumulation process plays a pivotal role in maintaining wetland elevation and countering the effects of subsidence. The combination of eustatic sea-level rise and subsidence is encapsulated in the concept of Relative Sea-Level Rise (RSLR), a critical metric for understanding the overall changes in wetland elevation over time.

The Surface Elevation Table-Marker Horizon Method

Achieving long-term stability in wetland ecosystems necessitates that the gain in wetland surface elevation equals or surpasses RSLR. This equilibrium is crucial for preserving the intricate balance of these ecosystems in the face of environmental challenges. The Surface Elevation Table-Marker Horizon (SET-MH) method (i.e., rSET) emerges as a valuable tool in this context. This method allows for the simultaneous measurement of both wetland surface elevation change and surface accretion, offering a comprehensive understanding of the factors influencing the wetland elevation dynamics.

Utilizing the SET-MH method provides insights into the local estimates of relative sea-level rise (RSLR) and submergence potential. By quantifying elevation change and shallow subsidence through this method, researchers and environmental practitioners can better comprehend the nuanced interactions shaping wetland landscapes. This knowledge becomes instrumental in formulating effective conservation and management strategies to safeguard these critical ecosystems against the backdrop of ongoing environmental changes.

Further Reading:



Wetland Delineations

What is a Wetland Delineation?

A wetland delineation determines the boundary between uplands and wetlands on a property following guidelines established by the United States Army Corps of Engineers (USACE). It involves identifying, characterizing, and mapping wetlands based on soil, vegetation and hydrologic characteristics. The process of delineation involves a combination of fieldwork, data analysis, and consultation with regulatory agencies. In the field, a skilled wetland scientist evaluates the site’s characteristics for key indicators such as wetland hydrology, hydric soils and hydrophytic vegetation, which define wetland ecosystems (See “What is a Wetland?”). These findings are then meticulously mapped and documented to delineate the precise boundaries of the wetlands on the property.

Why Do I Need a Wetland Delineation?

Because of their benefits (e.g., habitat, water quality improvement, stormwater storage, carbon sequestration), wetlands are important and regulated ecosystems in the United States. The U.S. Environmental Protection Agency (EPA) generates and enforces policies that avoide or minimize adverse impacts to wetlands when possible. A wetland delineation is needed whenever there is a potential impact on wetland areas due to land development projects. By identifying and mapping wetland boundaries accurately, stakeholders can make informed decisions that prioritize the conservation and sustainable use of these vital ecosystems.

A wetland delineation is also necessary if an activity negatively impacts a wetland to determine the amount of “compensatory mitigation” needed.  Compensatory mitigation could mean several things:

    • Restoration: Re-establishing or rehabilitating a degraded wetland.
    • Establishment: Creating a new wetland where one did not previously exist;
    • Enhancement: Improving existing one or more wetland functions; or
    • Preservation: Using legal and physical mechanisms to protect or enhance an existing, ecologically important wetland.

As a developer or project decision-maker, wetland delineation and its potential findings may appear daunting. Here are some common concerns and why they might be causing unnecessary worry:

  1. Limited Expertise: Wetland delineation demands specialized knowledge and skills. Collaborating with an experienced consultant can help alleviate uncertainties and ensure precise determination of wetland boundaries.
  2. Regulatory Complexity: The rules governing wetland delineation and permitting can be intricate and difficult to decipher. Partnering with a consultant well-versed in regulatory compliance and environmental permitting is essential for success.
  3. Time Constraints: Tight project schedules can amplify the pressure. Recognizing the significance of meeting deadlines is crucial, along with harnessing cutting-edge technology and tools to enhance efficiency and accuracy.
  4. Cost Considerations: Wetland delineation may seem like an added expense, particularly for larger projects. However, investing in this process upfront can prevent substantial costs and complications later on if a wetland that was not known about is disturbed during construction.
  5. Potential for Disruptions: Delineations may reveal previously unidentified wetland boundaries, potentially causing delays or interruptions during permitting. Addressing these discoveries early is key to minimizing project disruptions.

The process of identifying and delineating wetlands is complex. Contact Comite Resources, an environmental consulting company with a knowledgeable and experienced staff, to provide expertise and support throughout the entire process.

What is a Wetland?

A wetland is an area where water is present either on the soil surface or within the plant root zone for a portion of the year and contains vegetation adapted to wet soils. Wetlands are diverse ecosystems that bridge the gap between terrestrial and aquatic environments. They’re incredibly important because they provide habitat for a wide variety of plant and animal species, help control flooding by absorbing excess water, improve water quality by removing pollutants such as excess nutrients, and help maintain biodiversity.

Wetlands include marshes, swamps, bogs, and areas along water bodies such as bayous or lakes. Wetlands dominated by trees are called swamps and wetlands dominated by herbaceous (i.e., non-woody plants) plants are called marshes. Wetland vegetation species distribution is determined by hydrology, specifically length and depth of soil surface flooding.  A typical wetland will emerge from an adjacent water body into the shallow aquatic zone where floating or rooted plants grow to the marsh zone where herbaceous (non-woody) plants grow.  Beyond the marsh, at a slightly higher elevation, may be a shrub/scrub area with short woody and herbaceous vegetation that, grades to swamp dominated by bald cypress trees at lower elevations and longer flooding times.

A schematic of wetland donation from aquatic to upland (top panel), and a photograph of the zonation in the wild (bottom).
Schematic of idealized freshwater wetland zonation (top). Actual freshwater wetland zonation in a coastal Louisiana wetland (bottom).

There are seven major types of wetlands, classified as either coastal or inland, in the United States. These wetlands exhibit considerable diversity due to variations in soil type, topography, climate, hydrology, water chemistry, vegetation, and various other factors. They support a rich biodiversity and span across diverse landscapes and range from the icy tundra to the lush tropics, and are present on every continent except Antarctica.


Wetland Type Dominant Vegetation Dominant Hydrology
Coastal Wetlands

Tidal Salt Marsh

Herbaceous – ex: smooth cordgrass  


Tidal Freshwater Marsh Herbaceous – ex: maiden cane Tidal
Mangroves Woody – Mangrove trees Tidal
Inland Wetlands

Inland Freshwater Marsh


Herbaceous – ex: cattails

Rivers, streams, precipitation, watershed runoff
Northern Peatlands Herbaceous – ex: moss Precipitation

Southern Deepwater Swamps

Woody – ex: bald cypress, water tupelo Rivers, streams, precipitation, watershed runoff

Riparian Wetlands

Woody – shrubs and trees, ex: buttonbush and willow, Rivers, streams, precipitation, watershed runoff


Wetlands are important and diverse ecosystems that provide economic benefits to society.  For example, coastal mangrove wetlands can protect houses from intense wind and storm surge (Figure 2).

A schematic of how storm waves are attenuated by wetlands.
Figure 2. Coastal forested wetlands provide protection from wind and storm surge (Image from D. E. Marois and W.J. Mitsch (2015). Coastal protection from tsunamis and cyclones provided by mangrove wetlands – a review. International Journal of Biodiversity Science, Ecosystem Services & Management 11:1:71-83.

State and federal legislation, such as Section 404 of the Clean Water Act (CWA), exists to protect wetlands.  Wetlands determined to be ‘jurisdictional wetlands’ (as delineated using Section 404 of the CWA) have their uses regulated by agencies such as the U.S. Army Corp of Engineers, including wetlands on private property.  So, What is a jurisdictional wetland?  Sign up to receive additional information.