The word “wetland” is a bit mysterious. It can evoke images of gnarled trees dripping with moss, misty mires, or serene ponds. Some people are drawn to wetlands, while others do not care for them. Many people are familiar with the terms wetland, marsh, swamp, and bog, but if you ask someone to define those terms, their response may be hesitant. The simplest definition of a wetland is an area of land saturated with water. While this definition is not wrong, neither is it fully accurate.

Wetlands are liminal zones; they are neither upland nor aquatic but a transition between them. For most people, that is all they really need to know. However, for wetland scientists and anyone fascinated by these incredible habitats, accurately defining and classifying a wetland is a bit murky.

determination

The word “wetland” is often used to describe any area with some water and is perhaps mucky, but there are plenty of muddy tracts of land that are not true wetlands. To qualify as a wetland, an area must meet three criteria:

1. The land, for at least a period, supports hydrophytes (water-loving plants).
2. The ground is mostly hydric soil (soil whose chemistry has been altered by standing water).
3. The soil is covered or saturated by water during at least part of the growing season every year.

These criteria make things about as clear as mud. Determining if an area is a wetland is a bit like Goldilocks’ attempt to find the right bed. If there is too much water, it is not a wetland; if there is not enough water, it is not a wetland, but if the amount and timing of the water is just right and it has the right plants, you have a wetland.

Hydrophytic plants can survive in areas where other plants cannot. They have special adaptions that allow their roots to be constantly or seasonally submerged in water. Some adaptations include elongated stems, shallow roots, adventitious roots (roots growing from the plant’s stem/trunk), and aerenchyma (tissue that creates air pockets).

Washington State’s native yellow pond lily (Nuphar polysepala) has a large surface area to allow for photosynthesis while the rest of the plant is submerged. These water lilies also have flexible stems, which allow them to stay afloat even when the water level changes. photo by John F. Williams

The iconic western red cedar (Thuja plicata) is in the cypress family and provides an example of buttress roots, a portion of the tree’s roots that are above ground and have contact with air. photo by John F. Williams

Sundew plant. photo by SeanGentle via Pixabay

 In the United States, the US Army Corps of Engineers publishes the National Wetland Plant List, which is available for the whole country or by region. The guide lists plants, both native and non-native, found in the US and ranks them based on how likely they are to be found in wetlands using a code (see table). The greater Puget Sound area lies within the Western Mountains, Valleys & Coast (WMVC) region.

classification

For wetland scientists, once it is determined that an area is a wetland, they must then classify it. Several classification systems exist, and not all government agencies use the same one. Here we will use the Cowardin classification system used by the U.S. Fish and Wildlife Service. It focuses on the landscape position, the type of vegetation, and the source of water.

Of course, several other classification systems exist, and not all government agencies use the same one. Another commonly used classification system is the Hydrogeomorphic (HGM) system.

Cowardin Map: A map showing the different wetland types within the Three Forks Natural Area in Snoqualmie. map courtesy of UW Wetland Science & Management Students Joy Wood, Meagan Watson, Kelly O’Callahan, and Sarah Ottino

Since most people are not wetland scientists, they use common terms such as swamp or marsh to classify a wetland. While these terms are not strictly scientific, they represent wetlands with certain vegetation types and/or water sources.

The problem with common terminology is that not everyone uses it the same way, and it is not always the most accurate classification. For example, a wet meadow can be used in reference to a soggy field, but that field can also be called a marsh. Both a marsh and wet meadow can be classified as a lacustrine wetland with emergent vegetation.

Another example is the term swamp. A swamp can be dominated by shrubs and receive freshwater from a lake, but a swamp can also be dominated by trees and receive saltwater from the ocean, such as a mangrove swamp. Thankfully, unless you are a wetland scientist or a real estate developer, there is not much of a reason to be concerned with the proper classifications and terminology of wetlands.

rating

After a wetland has been determined and classified, it is rated. The Washington Department of Ecology has separate rating forms for Eastern and Western Washington. The assessor goes through the list, and points are assigned for the wetland classification type, type of plants present, soil characteristics, water quality function, and more. The wetland is then ranked as one of four categories:

• Category 1 Wetlands: unique/rare, more sensitive to disturbance, less disturbed, or high level of functions
• Category 2 Wetlands: difficult but not impossible to replace, or high level of some functions
• Category 3 Wetlands: moderate level of functions or can be adequately replaced
• Category 4 Wetlands: lowest level of functions and often heavily disturbed

Even though plants and animals living in the wetland, mainly threatened or endangered species, are taken into consideration, the whole extent of species supported by the wetland is not assessed. Bacteria and fungi are crucial for nutrient cycling and the breakdown of chemicals, however, neither group of organisms is considered.

wetlands for wildlife

Wetlands are sanctuaries for numerous species across all taxonomic kingdoms. They provide refuge for migrating birds and are nurseries for many juvenile species of animal. Some animals spend their whole lives in or next to wetlands, while others visit them seasonally.

The great blue heron (Ardea herodias) is just one of the countless species that are dependent on wetlands. These birds primarily eat fish but also snack on amphibians, reptiles, and small rodents. Since most of their diet is found in or near shallow water, a great blue heron would not easily survive in an upland habitat.

Red-winged blackbird in a wetland full of cattail. photo by John F. Williams

Dragonfly Larva: A dragonfly (Anisoptera family) larva collected from a wetland. photo by Sarah Ottino

Pacific tree frog. photo by John F. Williams

A Cascades frog (Rana cascadae) in a seasonal alpine wetland. photo by Sarah Ottino

Beavers, like humans, are landscape engineers. They are so important that April 7 is International Beaver Day. Beavers do not like moving water, so much so, that the sound of running water is used as a beaver deterrent. When a beaver hears running water, they build a dam to slow it down. The creation of a dam creates a reservoir. If left undisturbed for long enough, that reservoir becomes a wetland. “Problem” beavers are sometimes relocated to areas purposely to create a wetland.

wetland benefits

If providing vital habitat is not enough reason to appreciate wetlands, don’t worry; they have even more benefits. Coastal wetlands decrease shoreline erosion by slowing down wind and waves. Another major benefit is their ability to clean water. Wetlands are just as, if not more, effective at treating wastewater than wastewater treatment facilities, and they are cheaper. Wetlands also help mitigate climate change by sequestering carbon and other greenhouse gases.

Rough-Skinned Newt: A rough-skinned newt  (Taricha granulosa) crossing a road to access a wetland. photo by Sarah Ottino

In Western Washington, wetlands are all over, and it is easy to visit parks to experience them. Here are some ways to find a wetland park to visit:

• Search “wetland” in Google Maps
• Search “wetland” in Washington Trails Association’s hiking guide
• Check with your county’s land bank/trust
• Check with your county’s and/or city’s parks department

Since wetlands provide so much for us, it’s only right that we give back. There are many ways to help protect, restore, and preserve wetlands:

• Volunteer at a work party
• Pick up litter you find on and near trails and throw it away
• Bag pet waste and throw it in the garbage
• Leave only footprints and take only memories
• Learn more about wetlands
• Teach others about wetlands

Additional Resources:
EPA: Classification and Types of Wetlands
US Army Corps of Engineers: Plant List
U.S. Fish & Wildlife: National Wetlands Inventory
U.S. Fish & Wildlife: Wetlands Mapper
WA Dept. of Ecology: Wetland Rating System
WA Dept. of Ecology: Wetlands & Climate Change
WA Dept. of Fish & Wildlife: Priority Habitats and Species List
Beavers: Wetlands & Wildlife
Seattle’s Child: 5 Wetland Boardwalks to Explore with Your Family

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Thanks so much for your interest and your support.