The Value of Wetlands and Wetland Delineation

 

     In recent years the value of wetlands to local ecosystems has become established. Far into the past wetlands and “swampy” areas in some places in the U.S. were drained to remove unwanted effects such as mosquitoes, black flies, and other undesirable wildlife. Another major past benefit of draining swamps was that this resulted in big decreases in cases of malaria, which comes from a parasite spread by mosquitoes. After WWII when anti-malarial drugs and pesticides were developed and became more widely available, case of malaria dropped drastically. Swamps were also drained for agriculture and in a few cases to mine peat from bogs. Arguably, this resulted in some positive effects on nearby human habitation such as less mosquito-borne illness. However, it also degraded wetlands that provide environmental benefits.

 

 

The Value of Wetlands

 

     Wetlands preserve unique ecosystems and habitats. The species that inhabit wetlands perform ecosystem services. Wetlands are among the most biologically diverse ecosystems. The EPA notes that “wetlands are among the most productive ecosystems in the world, comparable to rain forests and coral reefs.” Wetlands can include large varieties of species of microbes, plants, insects, amphibians, reptiles, birds, fish and mammals. Dead plant material decomposes into small fragments of organic matter known as detritus that feeds many aquatic species. Wetlands are part of a geographic area known as a watershed where water drains from uplands to lowlands. The presence of shallow water, abundance of nutrients, and primary productivity lead to wetlands providing thriving food webs. Wetlands are involved in global water, nitrogen, and sulfur cycles and likely in atmospheric maintenance and carbon cycles as well. Wetlands are considered to be among the most threatened ecosystems.

     Not all functions and impacts of wetlands are benign. Wetlands preserve organic matter in low oxygen (hypoxic) or no oxygen (anoxic) conditions. This initiates anaerobic decomposition which results in release of methane into the atmosphere which has a high global warming potential. Methane contributes to global warming. Human-made wetlands such as rice paddies and reservoirs for dammed hydroelectric plants also release methane in significant amounts. Draining wetlands has the benefit of slowing methane release. However, in most cases the benefits of wetlands are seen to outweigh the detriments of wetlands. Even though they release methane they also sequester more CO2 than other environments, so the net greenhouse gas emissions of wetlands are more complicated to determine.

     Wetlands protect against floods by acting as buffer zones that can take in and store significant amounts of water. Coastal wetlands protect against storm surges from tropical storms and hurricanes. Wetlands support fishing economies. They provide critical habitat for migrating birds as rest areas and nesting sites. Wetlands can improve water quality and reduce contaminant concentrations.

 

Wetland Delineation

 

     The U.S. Army Corp. of Engineers and the U.S. Environmental Protection Agency define wetlands according to the Clean Water Act (CWA) as follows:

 

“Wetlands are areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas.”

 

     Wetland delineation involves detailed study of the soils, surface water, vegetation, and wildlife of a wetland. A key goal is to define the boundaries of the wetland. Another goal is to determine the function and value of the particular wetland and what kinds of impacts any development would have on that wetland. Another goal is to determine the jurisdiction of the wetland, whether it qualifies as part of the “Waters of the United States.” According to Section 404 a wetland has three characteristics: 1) presence of hydrophytes or plants that grow in or near water; 2) presence of hydric soils. Hydric soils are soils that are “saturated, flooded or ponded long enough during the growing season to develop anaerobic conditions in the upper part of the soil profile that favor the growth and regeneration of hydrophytic vegetation (USDA - SCS, 1991).”; and 3) a non-soil substrate such as sand or peat that is soaked or submerged for part of every year.

     Wetland boundaries need to be determined before jurisdiction can be established. Wetland delineations can be required before permitting building and development activities. Another function of wetland delineation is “identifying mitigation opportunities for mitigation banks – accounts of credits for restoring and protecting wetlands – as well as determining the boundaries of compensatory mitigation areas required by Section 404 permits. Compensatory mitigation areas help ensure that any project’s wetland impacts can be mitigated by reducing or removing the impact elsewhere in the watershed. For example, if a project causes significant wetland impacts, these areas help ensure that other projects within the watershed are not negatively impacted in the same way.” This seems to be a kind of impact trading – trading negative impacts in one area by assuring no impacts in another area by protecting that area or by restoring an impacted area. Wetland delineations can also help states and federal agencies to place certain wetlands off limits to any development or to certain kinds of development.

 

Source: Corps of Engineers Wetlands Delineation Manual. by Environmental Laboratory. Wetlands Research Program Technical Report Y-87-1 (on-line edition). U.S. Army Corps of Engineers. January 1987. Wetlands Delineation Manual (army.mil)

Source: Corps of Engineers Wetlands Delineation Manual. by Environmental Laboratory. Wetlands Research Program Technical Report Y-87-1 (on-line edition). U.S. Army Corps of Engineers. January 1987. Wetlands Delineation Manual (army.mil)

 

Types of Wetlands

 

     The U.S. Fish and Wildlife Service classifies wetlands according to the scheme developed by Cowardin as described in the publication Classification of Wetlands and Deepwater Habitats of the United States which divides wetlands into five types: marine, estuarine, lacustrine, palustrine and riverine. The U.S. Army Corps of Engineers classifies wetlands according to the scheme of Brinson in the publication A Hydrogeomorphic Classification for Wetlands which divides wetlands into the following types: marshes, swamps, bogs, and fens. According to the EPA marshes are defined as follows:

 

“Marshes are defined as wetlands frequently or continually inundated with water, characterized by emergent soft-stemmed vegetation adapted to saturated soil conditions. There are many different kinds of marshes, ranging from the prairie potholes to the Everglades, coastal to inland, freshwater to saltwater. All types receive most of their water from surface water, and many marshes are also fed by groundwater. Nutrients are plentiful and the pH is usually neutral leading to an abundance of plant and animal life. We have divided marshes into two primary categories: non-tidal and tidal.”

    

Non-tidal marshes are mostly freshwater marshes, but some may be brackish or salty. They are the most common wetlands type in North America. They often occur along existing streams. Due to their high level of nutrients freshwater marshes are among the most productive ecosystems on the planet with phenomenal biodiversity. They are also among the wetlands most impacted by humans. Tidal marshes occur mostly along the Atlantic Coast and the Gulf Coast. In tidal marshes the lower part of the marsh is typically covered daily by tides. Some are freshwater, some brackish, and some saline. These ecosystems are also impacted and threatened by human development. The Everglades in Florida are an example of a freshwater marsh.

     A swamp is a wetland dominated by woody plants. Swamps are of two types: forested swamps and shrub swamps. These swamps are typically bottomland forests along sluggish rivers with low gradients. They are common in the Southeast. Forested swamps occur throughout the U.S. The Great Dismal Swamp of coastal Virginia is one example that I have visited. One example of a shrub swamp is a mangrove swamp. Mangrove swamps cover vast distances along the Florida coast. Mangrove swamps are also noted for their ecosystem services of protecting against erosion and sequestering carbon. So-called blue carbon credits in carbon trading systems can involve the restoration and expansion of mangrove swamps.

     The EPA describes bogs this way:

 

“Bogs are one of North America's most distinctive kinds of wetlands. They are characterized by spongy peat deposits, acidic waters and a floor covered by a thick carpet of sphagnum moss. Bogs receive all or most of their water from precipitation rather than from runoff, groundwater or streams. As a result, bogs are low in the nutrients needed for plant growth, a condition that is enhanced by acid forming peat mosses.”

 

Thus, we can see that bogs are much different than swamps and marshes. Bogs are often inhabited by specifically adapted plants and animals due to the physically and chemically demanding conditions and low nutrient levels. Northern bogs occur in the Northern U.S., along the Great Lakes, and in Alaska. Most of the wetlands in Alaska are undisturbed by human encroachment. Pocosins are a type of bog that occurs in the U.S. Southeast. Many bogs and pocosins have been drained for agriculture and mined for peat. Pocosins often occur in broad flat uplands away from large streams and like northern bogs most of their moisture comes from precipitation. They may have significant charcoal layers due to past burning.

     Fens are peat-forming wetlands that receive moisture from sources other than precipitation, usually drainage from mineral soils and groundwater. They differ from bogs in being less acidic and having more nutrients. They develop a more diverse community of plants and animals. If they become separated from their water source, they can become bogs. Fens have also been impacted by human development.

  

 

Hydrophytic Plants

 

     Hydrophytic or aquatic plants, or hydrophyes, are plants that are adapted to growing in inundated and low-oxygen environments. These plants have evolved mechanisms for collecting oxygen including hypertrophied lenticels (Speckled Alder), hollow stems (rushes and grasses), and air-filled cells, or aerenchyma (cattail roots).  

     Other ways plants have adapted to oxygen-starved aquatic environments include developing long, hollow stems that reach the surface of the water; developing large, flat, waxy leaves that allow the top of the plant to float; floating on the surface of the water; developing air sacs or large spaces between cells, which provide buoyancy that allows the plant to float; and developing the ability to be completely submerged in water and rooted in the mud.

     Hydrophytes provide food and habitat for many species including algae, macroinvertebrates, amphibians, fish, birds, and more. Hydrophytes can also improve water quality by taking up nutrients, metals, and contaminants. Thus, they perform what is known as ecosystem services.  

     Wetland vegetation can also help with flood control and shoreline erosion. Wetlands are of different types that are inhabited by different hydrophytes. These different kinds of wetlands include salt marshes and sandy beaches, ponds, lakes, marshes, swamps, savannahs, bays, estuaries, bogs, fens, quiet streams, and tidal flats that are commonly flooded with at least a foot of water.

     Plants are given wetlands indicator statuses or categories. These are defined as follows:

 

-         Obligate wetland (OBL) - Almost always occurs in wetlands under natural conditions (estimated probability > 99%).

-         Facultative wetland (FACW) - Usually occurs in wetlands (estimated probability 67% – 99%), but occasionally found in non-wetlands (estimated probability 1% – 33%).

-         Facultative (FAC) - Equally likely to occur in wetlands and non-wetlands (estimated probability 34% – 66%).

-         Facultative upland (FACU) - Usually occurs in non-wetlands (estimated probability 67% – 99%), but occasionally found in wetlands (estimated probability 1% – 33%).

-         Obligate upland (UPL) - Almost always occurs in non-wetlands under natural conditions (estimated probability > 99%).

 

“A positive (+) or negative (−) sign is used for the facultative categories. The (+) sign indicates a frequency towards the wetter end of the category (more frequently found in wetlands) and the (−) sign indicates a frequency towards the drier end of the category (less frequently found in wetlands).”

 

 

Hydric Soils

 

     The National Technical Committee for Hydric Soils defines hydric soil as: “soils that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part.”    

     A particular soil is inundated when the water table is at or above the soil surface. A water table may be steady throughout the year, or it may change seasonally. Thus, determining the position of the water table varies by area and sometimes by time of year. In a wetland the soil is submerged for at least part of every year. If the soil is submerged with no water movement as occurs in depressions, it is considered to be ponded. A soil is considered to be saturated if the water table is within six inches of the soil surface for sandy textured soils or within 12 inches for loamy or clayey textured soils. These depths differ for each grain size and texture since at those depths the textures will support a capillary rise to the surface. More capillary action occurs with smaller pore size.  If the water is saturated for at least several weeks during the growing season, then the oxygen in the soil will deplete and anaerobic conditions will develop. This will lead to an accumulation of organic matter and the reduction and movement of iron which in turn produces a soil structure that will be identifiable as a hydric soil. Hydric soil indicators are muck, mucky texture, gley colors and sulfidic odor. Gley color refers to a color from the Munsell soil color chart. It is a greenish-blue-gray color due to the anoxic conditions of wetland soils. Other hydric soil indicators include dark surface, organic accretions, oxidized rhizospheres, polychromatic matrix (matrix stripping), stratified layers, iron and manganese concretions, distinct and prominent mottles, and marl. The last three occur in loamy or clayey textured soils only. Basically, color and texture are the two main indicators of hydric soils.

     Many hydric soil indicators are based on biogeochemical processes. These include iron reduction, transformation, and differential accumulation; manganese reduction, translocation, and accumulation; carbon accumulation and differential decomposition; sulfur reduction; precipitation of calcium carbonate by algae; and various combinations of these processes. Hydric soils are classified according to a schema where A refers to all soils, S refers to sandy soils, and F refers to loamy or clayey soils. A number follows each letter and refers to other indicators.

     Hydric soils have been mapped all over the U.S., but these may not be in enough detail for specific properties. The main source of information and classification of hydric soils is the USDA Soil Conservation Services’ Field Indicators of Hydric Soils in the United States.

 

Source: Field Indicators of Hydric Soils in the United States: A Guide for Identifying and Delineating Hydric Soils, Version 8.2, 2018. USDA Soil Conservation Service. pdf.aspx (usda.gov)

 

Hydrology and Determination of the Water Table

 

     Water table determination can vary according to the reason the water table is being determined. The definition of a water table can be somewhat different for a soil scientist than for a hydrologist. For a hydrologist the water table can mean “… the level at which water stands in a well penetrating the aquifer.” The water table, or phreatic surface, is also defined as the surface that “forms the upper surface of the zone of saturation.” Typically, there is a single – zone of aeration – where the soil voids are occupied by both air and water and below that a single – zone of saturation – where the voids are occupied solely by water. The water table can be different for determining the suitability of a septic system than for design and construction of a storm water management system or for the suitability for the construction of an oil & gas well pad.

     A water table may be permanent or seasonal. In cases where standing water is less common one might want to find the seasonal water table. Although some soil scientists may refer to a high seasonal water table as a “perched water table,” a groundwater scientist will point out that a true perched water table is rare in nature, where an aquifer of limited extent is perched above the regional water table.     

     Saturated conditions show different features and characteristics in different soils and rocks including differences in hydraulic conductivity, groundwater flow rates, maybe different hydraulic gradients, and different degrees of anisotropy. Type of soil, in terms of composition and grain size distribution and degree of saturation are the two most important ground conditions that affect construction projects. They are also two of the most important factors in assessing contaminant transport. Heavy rains can also create temporary, or perched water tables that can lead to slips or landslides.

     Ideal determination of saturation conditions would require some degree of understanding saturation of the site throughout the year, type of soil, and the type of project. Detailed info could best be gathered by drilling test wells, but excavated soil profiles are typically the main approach. Soil scientists would correlate colors (a key indicator of saturated conditions) and look for mottling (often in gray vertical streaks) and other redoximorphic features, particularly those that indicate the reducing conditions brought about by newly saturated soil. “Redoximorphic features are formed by the reduction, translocation and oxidation of iron and manganese compounds in the soil after water saturation and desaturation, respectively.” Redoximorphic features are used to determine seasonal water tables and to identify anaerobic soils. The percentage of redoximorphic features in wetland soils are used to determine the frequency and duration of saturation in those soils. Since redoximorphic features are common in saturated soils they are extensively used in making land use decisions, particularly regarding on-site waste disposal and wetlands.

Example of the Redoximorphic Feature known as Mottling

     Reducing reactions take place in chemical order and so the degree of reduced chemicals can hint at how often and how long conditions are saturated. If there is sufficient organic matter present the sequence begins with aerobic decomposition by oxygen-consuming bacteria (aerobes). When saturated conditions and subsequent low oxygen conditions occur for long enough then anaerobic decomposition begins with reducing reactions in decomposition by anaerobes. The chemical sequence of reducing reactions begins with oxygen to nitrogen, to iron, to manganese, to sulfur, to carbon, and then to microbial gas. These constituents and their relative percentages can be clues to past saturation conditions. For instance, a sulfur smelling soil indicates enough saturation and saturation-time to have reduced significant amounts of sulfur, which is closer to generation of microbial gas, typically referred to as “swamp gas,” ie. methane. This indicates prolonged submergence.

     Saturated conditions close to surface, whether seasonal or permanent, can create problems for construction, drainage, landslide potential, and be more easily contaminated by spills. Structures built on or partially on saturated soil can be subject to hydrostatic uplift pressures which is buoyancy derived from saturated pore water pressures. In order for structures such as underground tanks to avoid hydrostatic uplift they must be built heavy enough to withstand those pressures – typically 1.5 times the pore water pressure. Spills are easier to clean up in unsaturated soils where they can be excavated, and the soil treated offsite. When contaminants enter groundwater, they can be more mobile and much more difficult to remediate. Saturated clay soils are the most problematic as they swell when wet and shrink when dry, but saturation can cause issues with other soils as well.

     The main redoximorphic feature that can indicate seasonal water tables is mottling which is more or less synonymous. They can form quickly in newly saturated conditions. Oxidized iron which is most often red and insoluble changing to a reduced gray form that is more soluble indicates saturation. Mottles can indicate soil water level, whether recent or in the past as in relict mottles. Another saturation indicator, as mentioned, is a gleyed (greenish gray) matrix. The Munsell color chart can be helpful in these determinations but is better for determining the A, S, or F soil number for hydric soils.

  

 Example of the Munsell Color Chart

Defining Wetlands According to the Clean Water Act

 

     The main source for defining wetlands used by the EPA and Army Corp. of Engineers for Section 404 of the CWA is the 1987 Corps of Engineers Wetlands Delineation Manual and Regional Supplements. It is organized into three categories: soils, vegetation, and hydrology. The regional supplements divide the U.S. into 10 regions with more specific regional delineation characteristics.

 

 

Jurisdictional Determination

 

     Since wetlands defined as Waters of the United States are protected and regulated under Section 404 of the CWA it is necessary to determine if a particular delineated wetland falls under that jurisdiction. Wetlands delineated by ecologists and environmental consultants must be submitted to the Army Corp. of Engineers for verification. They will then determine jurisdiction. First, there is a verified preliminary determination, which may be satisfactory for some projects and uses. A more detailed final approved delineation may be required for projects with more potential impacts.

     Anyone who buys land with the presence of hydric soils and other wetlands indicators should be aware of possible restrictions on building and development on those parts of the land. A wetland delineation will determine if there are any jurisdictional issues.

     The U.S. Fish and Wildlife Service has developed a National Wetlands Inventory. This may be used to determine preliminary suitability for a project, but more detailed analysis will likely be required to obtain permits. Environmental due diligence software can help to determine where a property is in relation wetlands inventories and previously mapped or delineated wetlands through GIS layers.

     Since wetlands can change due to changing saturation conditions, a wetland delineation is typically good for 5 years before a new delineation is required. This can perhaps be cumbersome for developers and landowners. This 5-year permit term is built into Section 404. Desired activities such as draining a wet area for agricultural use often require wetland delineation as well.

     It should also be determined whether a wetland is a human-made wetland such as results from damming or diverting water from one place to another. These may result from irrigation, impoundment, wetlands resulting from filling of formerly deepwater habitats, dredged material disposal areas, and wetlands resulting from stream channel realignment. Some of these human-made wetlands may be subject to Section 404. Of the three indicators of wetlands: hydrophytic plants, hydric soils, and hydrology, the presence of hydric soils is usually absent in human-made wetlands.

 

 

Wetland Restoration and Protection

 

     According to the EPA:

 

“Wetland restoration is the manipulation of a former or degraded wetland's physical, chemical, or biological characteristics to return its natural functions.”  

 

These include re-establishment which is rebuilding of a former wetland, and rehabilitation which refers to repairing a degraded wetland. Wetland protection refers to removing threats to wetlands and preventing the decline of a wetland. Wetland restoration can increase all the benefits of wetlands by adding to the total. Restoration and protection can be either voluntary or regulatory. Both can and do play a role in supporting the Clean Water Act and the Safe Drinking Water Act. Non-profits, local governments, and industry can collaborate in wetland protection and restoration. Partnerships with many federal agencies can aid in voluntary wetlands protection and restoration. Regarding restoration EPA notes that:

 

“… constructed treatment wetlands use natural processes involving wetland vegetation, soils, and their associated microbial life to improve water quality. They are often less expensive to build than traditional stormwater treatment options, have low operating and maintenance expenses, and can handle fluctuating water levels.”

 

References:

 

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Corps of Engineers Wetlands Delineation Manual. by Environmental Laboratory. Wetlands Research Program Technical Report Y-87-1 (on-line edition). U.S. Army Corps of Engineers. January 1987. Wetlands Delineation Manual (army.mil)

Classification and Types of Wetlands. U.S. EPA. Classification and Types of Wetlands | US EPA

National List of Plant Species That Occur in Wetlands -- North Central (Region 3). Reed P. 1988. National Wetland Inventory, U.S. Department of the Interior, Fish and Wildlife Service, St. Petersburg, FL. 90 pp.

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