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.

Why Do I need a Phase 1 Environmental Site Assessment?

A Phase 1 Environmental Site Assessment (ESA) is a critical and standard practice in real estate transactions, particularly when purchasing or financing commercial properties. This assessment plays a crucial role in identifying potential environmental liabilities associated with a property, offering invaluable insights for all parties involved in the transaction. The key reasons that that a Phase 1 ESA might be needed include:

  1. Securing Financing
  2. Regulatory Compliance
  3. Shield Against Liability
  4. Risk Management

One of the primary reasons for undertaking a Phase 1 ESA is its often-mandatory requirement for securing financing from lending institutions. Banks and financial entities seek assurance that the property being invested in doesn't harbor hidden environmental issues that could translate into financial risks down the road. By initiating a Phase 1 ESA early in the due diligence process, potential environmental concerns can be unearthed, allowing for well-informed decision-making by all involved parties.

The Phase 1 ESA serves as a crucial tool for ensuring regulatory compliance. It aids property buyers and developers in adhering to environmental regulations stipulated by agencies such as the Environmental Protection Agency (EPA). Failure to identify environmental liabilities can lead to legal and financial consequences. The assessment, by ensuring compliance with applicable environmental laws, acts as a preventive measure against these risks.

Additionally, the Phase 1 ESA acts as a protective shield against potential liability under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as the Superfund law. Should environmental contamination be discovered at a later stage, having conducted a Phase 1 ESA provides a potential defense against being designated as a responsible party for the contamination, provided the assessment adhered to established standards.

Beyond compliance and liability protection, the Phase 1 ESA serves as a valuable tool for risk management. It offers stakeholders a comprehensive understanding of the environmental history of a property, encompassing its past uses and any potentially hazardous activities that may have transpired. With this information, stakeholders can make well-informed decisions regarding property acquisition, development, and ongoing operations, thereby minimizing the risk of unforeseen environmental issues.

In summary, a Phase 1 Environmental Site Assessment stands as an indispensable component of due diligence in real estate transactions. It furnishes crucial information for financial institutions, buyers, and developers, facilitating informed decision-making, ensuring regulatory adherence, managing environmental risks, and safeguarding against potential liabilities associated with the property in question. Embracing this assessment early in the process is not just a best practice; it's a strategic imperative for a robust and risk-aware approach to real estate transactions.


Why Do I need a Permit to Build on Wetlands?

Requiring a permit to build on jurisdictional wetlands is a crucial aspect of environmental conservation and sustainable land use management. Wetlands play a vital role in maintaining ecological balance, providing habitat for diverse plant and animal species, improving water quality, and offering flood control. The need for a permit stems from the recognition that unregulated development in these sensitive areas can have significant and often irreversible impacts on the environment. In this blog post, we’ll delve into the why behind the need for permits and how they serve as guardians of these vital natural landscapes.

  1. Ecological Importance of Wetlands: Before we explore the intricacies of permits, it’s essential to understand why wetlands merit such stringent regulatory measures. Wetlands contribute significantly to ecological balance—they provide habitats for diverse plant and animal species, enhance water quality, and act as effective flood control mechanisms. Recognizing their irreplaceable role in the environment, various local, state, and federal regulations are in place to safeguard wetlands.
  2. Regulatory Oversight by Environmental Agencies: Agencies such as the Department of Environmental Quality (DEQ) and the Environmental Protection Agency (EPA) establish guidelines to ensure responsible usage and preservation of wetland ecosystems. Requiring a permit serves as a regulatory mechanism to evaluate proposed developments in or near jurisdictional wetlands, assessing potential environmental impacts and implementing measures to mitigate adverse effects.
  3. Comprehensive Review Process: Obtaining a permit involves a comprehensive review of the proposed project. This process considers factors such as wetland delineation, potential disturbance to habitat, changes in hydrology, and impacts on water quality. This careful evaluation helps regulatory authorities make informed decisions to balance human development needs with the protection of wetland ecosystems.
  4. Mitigation Measures and Sustainable Development: Permitting also allows for the incorporation of mitigation measures to offset any unavoidable impacts on jurisdictional wetlands. Developers may be required to implement strategies like creating new wetlands, restoring degraded ones, or establishing buffer zones to minimize the ecological consequences of the project. This approach aims to strike a balance between development and environmental conservation, ensuring that wetlands continue to provide their essential ecological functions.
  5. Preserving Biodiversity and Ecosystem Health: The requirement for a permit functions as a critical tool for sustainable land management. It acts as a safeguard against uncontrolled development that could lead to the degradation or loss of valuable wetland ecosystems. By navigating the permitting process, developers become active contributors to the broader goal of preserving biodiversity, maintaining water quality, and safeguarding the long-term health of these ecologically significant areas.

Ultimately, the permit requirement serves as a critical tool for sustainable land management. It helps prevent uncontrolled development that could lead to the degradation or loss of valuable wetland ecosystems. By obtaining a permit, developers contribute to the broader goal of preserving biodiversity, maintaining water quality, and safeguarding the long-term health of these ecologically significant areas.


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.

Mandeville Monitoring

Comite field crew Jason Day and Joel Mancuso carried out monitoring at the Bayou Chinchuba and Tchefuncte Marsh assimilation wetlands. Leaf Litter biomass was collected from each forested site (M-Tmt, M-Mid, M-Ref & TM-Tmt). Dissolved oxygen, conductivity, temperature, salinity and pH were measured at all sites. TM-T discharge is off. Water nutrient and water metals samples were taken at all sites TM-Out. Water nutrients were delivered to Curtis Environmental in LaPlace, LA. Free chlorine measurements were made at the package plant that discharges into a canal that leads out to the Mandeville TM assimilation wetland. Measurements were made at the package plant discharge pipe (0.2 ppm) and where the canal meets the wetland (0.0 ppm). Vegetation percent cover estimates were done at all sites. Accretion measurements were taken at the TM-T site. The TM-Mid site was not visited due to land access issues.

Jason Day at the TM-Ref site on August 21, 2018.
Jason Day at the TM-Ref site on August 21, 2018.

St. Charles Monitoring

St. Charles Parish has been using wetlands assimilation since 2008. The wastewater treatment facility consists of a facultative oxidation pond with a chlorination and dechlorination disinfection system with an average discharge of 1.6 million-gallons-per-day. Before 2008, the treatment plant discharged into Cousin Canal, which drains into Lake Cataouatche via the Louisiana Cypress Lumber Canal. Starting in 2008, the treated municipal effluent was piped approximately 150 ft to a 1439 ha cypress-tupelo dominated forested wetland. Effluent is retained within the project boundaries by low-lying levees running along the northern, eastern, and western boundaries that prevent hydrological exchange with the surrounding landscape, except at the southern most extent of the project area where water flows out of the project area into the Louisiana Cypress Lumber Canal and then to Lake Cataouatche.

Comite Resources carried out a carbon sequestration study at the St. Charles assimilation wetlands. Changes in carbon stocks of trees and soils as well as methane and nitrous oxide emissions were measured over a one-year period and compared to baseline conditions derived from the scientific literature (see Carbon Sequestration). Methods and equations were applied from the American Carbon Registry (ACR) wetland carbon offset methodology ‘Restoration of Degraded Deltaic Wetlands of the Mississippi Delta’. The results of the study demonstrate that wetland assimilation increases wetland productivity and enhances carbon sequestration. See Lane et al. 2017 for the peer-reviewed scientific study.

Comite Resources has been carrying out wetlands assessment of the site since effluent was diverted into the wetlands in 2008. Monitoring includes measurements of tree growth (dbh & leaf) and productivity, water hydrology, soil accretion, and nutrients and metals concentrations of surface waters, soils and vegetation. These measurements are made at permanent plots located in the forest directly impacted by the effluent (termed the Discharge site), where the surface water exits the assimilation wetland (termed the Out site), and a site in between these two sites (termed the Mid site), as well as a nearby Reference site that is not impacted by the effluent for comparison (see Hunter et al. 2009b and Hunter et al. 2018). Below are monitoring reports from this site describing work carried out and preliminary data.

Location of wetland monitoring sites at the St. Charles assimilation wetlands. R = Reference site, D = Discharge site, M = Mid site, and O = Out site.


Hammond Monitoring

The Hammond assimilation wetlands consist of 121 ha of mostly emergent wetlands located just north of the Joyce Wildlife Management Area, which encompasses about 14,000 ha. Once effluent exits the assimilation wetlands it then flows through this much larger wetland complex. Hammond’s treatment system has a design capacity of 8 million-gallons-per-day with a three-cell aerated lagoon. A 1.2 km effluent distribution system disperses effluent along the northern edge of the assimilation wetlands.

The Joyce Wildlife Management Area used to be a thriving cypress-tupelo forested wetland (see Shaffer et al. 2015). During the past century and a half, there have been a number of significant modifications to the landscape that substantially altered the hydrology of the region (see Lane et al. 2015). Now most trees are dead due saltwater intrusion and the lack of freshwater, and the area has converted to emergent wetlands dominated by smooth cordgrass (Spartina alterniflora). The living cypress that are left are confined to the northern reaches where the addition of municipal effluent has created a freshwater buffer that counters higher salinities coming from the south. Comite Resources planted several hundred cypress seedlings directly in the path of the municipal effluent over a decade ago, and now these trees are growing very fast at 2 cm/yr in diameter (see Hillman et al. 2018).

Comite Resources has been carrying out wetlands monitoring at the Hammond assimilation wetlands since discharge began in 2006. Monitoring includes measurements of tree growth (dbh & leaf) and productivity, water hydrology, soil accretion, and nutrients and metals concentrations of surface waters, soils and vegetation. These measurements are made at permanent plots located in the area directly impacted by the effluent (termed the Discharge site, taken at the boardwalks), where the surface water exits the wetland complex (termed the Out site), and a site in between these two sites (termed the Mid site). Since the Mid site is forested and the Discharge and Out sites are emergent wetlands, there are two Reference sites, an emergent and forested, not impacted by the effluent. Below are monitoring reports from this site describing work carried out and preliminary data.

Location of wetland monitoring sites at the Hammond assimilation wetlands. D = Discharge site, M = Mid site, and O = Out site, Rf = Forested Reference site, Re = Emergent Reference Site.

CHS Monitoring

Comite Resources designed two stormwater wetlands directly north and south of CHS, Inc. bulk grain transfer terminal, which handles both grain and grain by-products. The facility transfers grain from barges to ocean going vessels and services about 2 to 3 ships per day. Because of the high volume of grain handled by the facility, grain dust and spilled grain is deposited on the site and washed into the stormwater system. To address this problem, CHS partnered with Comite Resources to construct two wetlands totaling 2.5 acres to reduce total organic carbon (TOC) from stormwater runoff. Herbaceous species were planted and also colonized the area naturally, and baldcypress seedlings were planted at a density of 200 per acre, for a total of 500 trees. Hillman et al. (2018) reported a mean diameter growth increase of 2.5 cm/yr for these seedlings, which is very high. The use of wetlands to remove pollutants from stormwater runoff has great potential as a cost- and energy efficient method of improving water quality while also providing habitat for wildlife (see Stormwater Wetlands). The CHS stormwater wetlands have many species of birds living in the wetlands along with alligators, fish and frogs. Comite Resources visits CHS stormwater wetlands quarterly to carry out stormwater wetlands assessment and environmental monitoring to assess TOC reduction efficiency, vegetation growth, and overall health and system performance. Below are monitoring reports from this site describing work carried out and preliminary data.

Imagery of the CHS facility with the stormwater wetlands, labeled as North and South ponds, located on either side of the facility.