Wetlands: Definitions, Classification, and Conservation

This blog post consists of my lecture notes from Wetlands: Definitions, Classification, and Conservation, presented by Kim Blaszak, a resource technician with the Forest Preserves of Cook County.  The lecture took place on July 29, 2015 at Sand Ridge Nature Center in South Holland, Illinois.  

What once was:  Chicago's Vast Wetlands

Chicago was incorporated as a town in 1833.  The word 'chicago' refers to wild onions (Alium spp.).  Chicago was originally a small town surrounded by wetlands (figure 1).  

Figure 1:  Map of the city of Chicago, circa 1833.  

Early inhabitants despised the wetlands due to the high volume of mosquitoes and frequent flooding.  This distaste for Chicago's swampy conditions led to several pieces of legislation that sought to resolve Chicago's wetland "problem."  The Flood Control Act of 1944 was one of the first major pieces of legislation that negatively impacted wetlands.  The development of Federal Crop Insurance was another.  Later, the National Flood Insurance Program encouraged development in flood plains and other flood-prone areas with government funding.  

Starting in the mid-20th century, a more positive view of wetlands started developing, as people began to see the benefits that wetlands provide to the environment.  As such, legislation shifted more towards wetland conservation.  The Migratory Bird Conservation Act (1929) was one of the earliest pieces of pro-wetland legislation, which helped protect wetland habitat for migratory birds on a global scale.  The Clean Water Act, the Endangered Species Act (1973), the Comprehensive Environmental Response Compensation, and Liability ACT (Superfund, 1980), the Flood Security Act of 1985, and the Federal Water Pollution Control Act were all key pieces of federal legislation that helped protect and restore America's wetlands.  The Interagency Wetlands Policy Act of 1989 was adopted exclusively by the state of Illinois, although the federal government created a similar policy.  

What is a wetland?

The term wetland was derived around 1956.  One of the earliest definitions of a wetland was lowlands covered with shallow or intermittent waters with emergent vegetation, as opposed to open water or a deep lake.  Also, wetlands had to be wet for most of the year.  Later, the U.S. Army Corps of Engineers developed an official legal definition of wetlands:

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

Wetland Characteristics

Three criteria need to be considered when classifying wetlands:  (1) hydrology, (2) soils, and (3) vegetation.  

Soils.  When examining the soil profile,saturated soil should be present.  If one digs a hole in wetland soils, water should quickly fill it in.  Another indication is a foul, rotten-egg like odor of the soil, which indicates anaerobic conditions.  Soil pores that are filled with water contain low amounts of O2. Redoximorphic features of wetland soils include gray and orange color variegation.  Organic hydric soils can be:

• Peat - brown to black in color.  Has some leaf tissue material mixed in.  
• Musk - black and greasy when moist
• Musky peat - in between peat and musk in color and texture

Secondary indicators include the presence of crayfish holes as well as cracking of surface soil during dry periods.  Leaves covered with silt is another secondary indicator.  

Vegetation.  The presence of obligate wetland species such as lotuses and water lilies are good indicators of wetlands (figure 2).  Less obvious indicators are facultative wetland species which are found in wetlands most of the time.  Other plants are obligate upland species and are not indicators of wetlands.  

Figure 2:  Water lotuses (Nelumbo sp.) growing in a floodplain wetland.  

There are different types of wetland plants.  Emergent wetland plants are rooted into the substrate and common examples include cattails (Typha spp.), bulrushes, and sedges (figure 3).  Submerged wetland plants are underwater except for the flowering parts.  The leaves on submerged plants are highly modified into thin and divided structures.  Floating leaf plants, such as the lotuses pictured in figure 2, have circular or heart shaped leaves with entire leaf margins as an adaptation to prevent tearing from wave action.  

Figure 3:  A wetland with emergent vegetation. 

Free-floating wetland plants take in nutrients from water column, such as Duckweed (Lemna spp.) (see figure 4).  

Figure 4:  Duckweed (green layer on pond), a free-floating wetland plant

Wetland plants have several adaptations to living in water.  The presence of arenchyma, hollow tubes in the middle of the stems, allow oxygen entry and gas exchange in wetlands plants such as Spadderdock (Nuphar variegata).  Many wetland plants have bimorphic leaves (differences in shape on submerged leaves versus emergent leaves).  Floating leaves, such as those on water lilies (Nymphaea spp.), have stomata on the upper side of the leaves instead of on the lower side as in most terrestrial plants.   

Wetland Classification

Marine Wetlands include rocky intertidal zones and subtidal zones.  Estuarine wetlands are in between freshwater and marine systems, are are influenced by tides.  Riverine wetland systems are contained within a channel.  Laucustrine systems are wetlands situated in a depression, often the result of a dammed river channel. In a laucustrine wetland system, emergent plants are less than 30% of the vegetative cover.  

Paulustrine wetlands include all non-tidal wetlands that are connected to a riverine system.  Paulustrine wetlands must exhibit the following characteristics:

• Contains fresh water
• Less than 20 acres in size
• No bedrock shoreline
• Water depth greater than or equal to 2.5 meters

Wetland vegetation can include plants that are persistent and those that are nonpersistent.  Persistent vegetation can still be seen in winter.  Nonpersitent vegetation dies back in the winter and is only visible during the growing season,  

The U.S Fish and Wildlife Service's National Wetlands Inventory Map can be viewed at the following web address:

http://www.fws.gov/wetlands/Data/Mapper.html

The inventory uses a coding system to classify wetlands.  The code is formatted as such:

(SYSTEM, SUBSYSTEM, CLASS, WATER REGIME, SPECIAL MODIFIER)

The codes uses one character of each characteristic.  For example, in a wetland with this code:

E2AMB

E means that the system is an estuarine system, 2 indicates that the subsystem is a subtidal system, AB means the class is an aquatic bed, and M is the water regime.  This wetland has no modifier assigned to it,  A modifier would indicate some sort of wetland modification by people or beavers (e.g. dams, quarries, etc.).  

Illinois Wetlands

Wetland fauna that associate with wetlands in Illinois consists of 78% of mammals, 90% of amphibians, 78% of reptiles, 105 species of birds, and 50% of all Illinois invertebrates.  

A wet meadow, or sedge meadow, has brief periods of standing water with vegetation dominated by sedges (figure 5).  Wet meadows contain less than 30% woody plants.  Wet meadows are often located adjacent to other wetland types.  Presently, only 630 acres of wet meadow habitat remain in Cook County, Illinois.  

Figure 5:  Restored wet meadow on the Chicago Lakefront.  

Fens are a rare type of wetland where ground water percolates through calcareous bedrock leading to highly alkaline conditions.  Fens are restricted to the northern 1/3rd of Illinois and along some parts of the Illinois River valley.  Presently, only 250 acres of fens remain in Illinois.  Figure 6 shows a fen in nearby Northwest Indiana.  Bluff Spring Fen, located in the far western section of Cook County, is the only natural fen in the county.  

Figure 6:  A fen in the Indiana Dunes region.  

Important fen species include shrubby cinquefoil (Dasiphora fruticosa) (see figure 7), Kalm's Lobelia (Lobelia kalmii), and Queen of the Prairie (see figure 8).  

Figure 7:  Shrubby cinquefoil in a restored coastal wetland along Lake Michigan in Chicago

Figure 8:  Queen-of-the-prairie

Seeps and springs is the next type of Illinois wetland.  Wetlands fed by seeps and springs in Cook County can be found at Black Partridge Woods.  Seeps and springs are caused by upwellings of groundwater.  Important plant species include Skunk Cabbage (Symplocarpus foetidus), Jewelweed (Impatients spp.), and Great Angelica (Angelica atropurpurea). 

Bogs are wetlands that have restricted drainage.  Volo Bog is a local example.  Bogs are very acidic (low pH) due to the fact that their only source of water is rain water, which is naturally acidic.  The soils contain peat, which is also acidic.  Bogs have ample presence of Sphagnum moss.  Cranberry Slough was the only bog in Cook County, but was destroyed several years ago by dynamite.  Important bog plant species include sphagnum moss, Northern Pitcher Plants (Sarracenia purpurea) (see figure 9), Sundew (Drosera spp.), and various species of orchids (figure 10).  

Figure 9:  Northern Pitcher Plants

Figure 10:  An orchid growing along a coastal wetland near Lake Superior.  

Orchids have adapted to nutrient poor bog conditions by relying on mycorrhizae fungus for nutrient absorption.  Orchids do not have their own endosperm, and so they must gain their carbohydrate source for seed production from outside sources.  Tamaracks (Larix laracina) have ectomycorrhizae, which attach to the outside of the roots instead of the roots.

A marsh includes emergent plants such as cattails and reeds (see figure 3).  Shrub-scrub wetlands are plant communities in transition from marsh to swamp.  Shrub-scrub wetlands in Illinois contain a lot of Buttonbush (Cephalanthus occidentalis) shrubs (see figure 11).  Woody coverage in shrub-scrub wetlands is greater than or equal to 30 %.

Figure 11:  The blossom of a Buttonbush.  

Swamps are wetlands with woody vegetation in the form of trees that provide an aerial cover of at least 30% and where the trees are over 20 feet tall (figure 12).

Figure 12:  Myself kayaking through a swamp in North Carolina.  

Forested wetlands are similar to swamps, but lack year-long standing water, experience frequent flooding and have lots of debris at the bottom, and contain distinct layering's of vegetation including an understory and herbaceous layer of plants (figure 13).  Important plant species include silver maples (Acer sachharinum), Sycamores (Platanus occidentalis), and Eastern Cottonwoods (Populas deltoides).

Figure 13:  Forested wetland

Ecosystem Services of Wetlands
Wetlands can act as carbon sinks - perhaps better than rain forests, as peat stores a lot of CO2. Nutrient farming is an emerging concept that involves "growing" wetlands to "harvest" excess nutrients such as nitrogen, phosphorous, and CO2.  Nutrient farms sell reduction credits to farmers and/or municipalities that release excess nutrients.  Nutrient farming could prove to be a novel approach to funding wetland restoration.

Major Threats to Wetlands
Major threats to wetlands include hydrological alterations, exotic species, global climate change, habitat loss, and sea level rise (for coastal wetlands).