Hansen's Northwest Native Plant Database

Northwest Native Wetlands

What are Wetlands?

We turned to the United States Environment Protection Agency's website for the official answer to this question:

"Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season.  Water saturation (hydrology) largely determines how the soil develops and the types of plant and animal communities living in and on the soil. Wetlands may support both aquatic and terrestrial species. The prolonged presence of water creates conditions that favor the growth of specially adapted plants (hydrophytes) and promote the development of characteristic wetland (hydric) soils.

"Wetlands vary widely because of regional and local differences in soils, topography, climate, hydrology, water chemistry, vegetation, and other factors, including human disturbance. Indeed, wetlands are found from the tundra to the tropics and on every continent except Antarctica. Two general categories of wetlands are recognized: coastal or tidal wetlands and inland or non-tidal wetlands.

"Coastal wetlands in the United States, as their name suggests, are found along the Atlantic, Pacific, Alaskan, and Gulf coasts. They are closely linked to our nation's estuaries, where sea water mixes with fresh water to form an environment of varying salinities.

The salt water and the fluctuating water levels (due to tidal action) combine to create a rather difficult environment for most plants. Consequently, many shallow coastal areas are unvegetated mud flats or sand flats.

Some plants, however, have successfully adapted to this environment. Certain grasses and grass-like plants that adapt to the saline conditions form the tidal salt marshes that are found along the Atlantic, Gulf, and Pacific coasts. Mangrove swamps, with salt-loving shrubs or trees, are common in tropical climates, such as in southern Florida and Puerto Rico. Some tidal freshwater wetlands form beyond the upper edges of tidal salt marshes where the influence of salt water ends.

"Inland wetlands are most common on floodplains along rivers and streams (riparian wetlands), in isolated depressions surrounded by dry land (for example, playas, basins, and "potholes"), along the margins of lakes and ponds, and in other low-lying areas where the groundwater intercepts the soil surface or where precipitation sufficiently saturates the soil (vernal pools and bogs). Inland wetlands include marshes and wet meadows dominated by herbaceous plants, swamps dominated by shrubs, and wooded swamps dominated by trees.

"Certain types of inland wetlands are common to particular regions of the country:

  • bogs and fens of the northeastern and north-central states and Alaska
  • wet meadows or wet prairies in the Midwest
  • inland saline and alkaline marshes and riparian wetlands of the arid and semiarid west
  • prairie potholes of Iowa, Minnesota and the Dakotas
  • alpine meadows of the west
  • playa lakes of the southwest and Great Plains
  • bottomland hardwood swamps of the south
  • pocosins and Carolina Bays of the southeast coastal states
  • tundra wetlands of Alaska.

"Many of these wetlands are seasonal (they are dry one or more seasons every year), and, particularly in the arid and semiarid West, may be wet only periodically. The quantity of water present and the timing of its presence in part determine the functions of a wetland and its role in the environment. Even wetlands that appear dry at times for significant parts of the year -- such as vernal pools-- often provide critical habitat for wildlife adapted to breeding exclusively in these areas.

See the EPA website: http://water.epa.gov/type/wetlands/what.cfm

The following article was written by Colleen Stuckey form Vancouver Island, British Columbia. It contains basic information to help those venturing into wetlands maintenance and restoration.

Wetlands General Information:

Wetlands are extremely rich ecosystems, and are able to support a vast number of plant and animal species. It is estimated that the wetlands of the United States support over 5,000 plant species, 270 bird species and 190 species of amphibians (McCormick, p. 20). Birds, mammals, amphibians, reptiles, fish, invertebrates and insects – a vast number of species from each group are dependent on wetlands for their survival.

Wetlands are not only valuable in sustaining wildlife populations; they are critical to the functioning of healthy watersheds. They do so by the following functions:

  • Slowing the flow of water and storing water during heavy rains or snow melts to reduce the risks of flooding.

  • Recharging the water table.

  • Purifying water and reducing pollution.

  • Reducing erosion.

  • Encouraging precipitation and air humidity

Storing water:

All wetlands have the capacity to store large amounts of water. Wetlands that develop over a clay soil retain vast amounts of water as water drains slowly through clay. Peat bogs similarly retain water as decomposed peat has small particles and does not easily drain. Wetland plants retain more water in their roots, leaves and stems than dry land plants. Therefore, in times of heavy rain, wetlands absorb water and hold it, reducing the likelihood and severity of flooding. As an example, A. McCormick estimates that a single ten-acre marsh can hold 1.5 million gallons of water (McCormick, p.41).

Slowing the flow of water:

Stems of plants slow the flow of water. The slower the flow of water, the more water is absorbed into the subsoil and underground aquifers. Furthermore, the slower the flow of water, the less likely flooding is to occur. Lastly, this stored water is slowly released in times of drought.

Another advantage to a slowed flow of water is that solid particles settle before entering streams, rivers and oceans. Both heavy metals and pathogens from agricultural runoff and sewage are found in particulates and are potentially very dangerous to life forms when they enter the water system. Once settled, the roots of certain wetland plants secrete substances that kill pathogens. Heavy metals, on the other hand, bind chemically to the clay that forms the substrate of the wetland and are stored there, similar to the way carbon is stored.

Incidentally, designers of wetlands can select different types of clay to absorb specific metals. This clay layer may need to be removed, disposed of and replaced periodically to ensure proper functioning.

Not only do pollutants from industrial, agricultural and household wastes kill animal populations, but so do an excess of nutrients. Nutrients are often broken down by the wetland and if not, they are stored within the wetland, accumulating during the growing season when water levels are lower. When water levels rise after a period of heavy rain or snow melt, the wetland is flooded and the nutrients that have built up enter the larger bodies of water, feeding the aquatic plants and micro-organisms. This is important because the nutrients are entering the body of water only after water levels have risen and are therefore diluted.

Consider how critical this function is by exploring what happens in a water system when there is no wetland present to catch excess nutrients. As water flows over land (during rains or via irrigation), it picks up minerals, nutrients and fertilizers, pesticides, and pathogens. An excess of nutrients entering a body of water causes a rapid burst of plant growth, a process called “algae bloom.” This plant growth is either consumed by zooplankton (microscopic animals) or dies and sinks to the bottom of the body of water. If water levels are low, the situation becomes dire. As the zooplankton manure or dead plant material decompose, all of the available oxygen in the water is used. Without sufficient oxygen, fish die and this, in turn, kills the species that depend on the fish – the herons, kingfishers, otters and many more. Wetlands break down nutrients and store excessive levels of nutrients to be released only when water levels rise and can therefore support the nutrient charge.

Recharging the water table:

The slowed water flow recharges the water table by seeping through the ground. Wetlands also have a profound effect on hydraulic pressure – the pressure needed to force water upwards from underground aquifers/reservoirs to springs or drilled wells.

Reducing pollution:

Wetland plants perform the vital task of storing toxins and chemicals. Organic matter is aerobically (using oxygen) broken down and the nutrients made available to plant life. When soils become waterlogged, as in a wetland, the oxygen is used up in the decomposition process and an anaerobic condition occurs. However, wetland plants have adapted to this condition and they have developed “aerenchymous” tissue, or aerating tissue, which enables oxygen to transfer quickly between the leaves and the roots. The oxygen is released through the roots of the plants and this creates an environment in which micro-organisms (and other animals and fish) can live. These micro-organisms feed on the dissolved nutrients so that decomposition can continue.

Another crucial function of a wetland is its ability to store carbons. Bogs and fens are two types of wetlands that are characterized by vast layers of peat. Peat forms in waterlogged areas with low oxygen, high acidity and low levels of nutrients. This is obviously a condition that is not conducive to plant growth. Plants then begin dying and as there is little aerobic activity, the plants decompose very slowly, forming layers of half-rotted, carbon-rich organic matter. Because peat breaks down so slowly, the carbons are held rather than released into the air as carbon dioxide (greenhouse gas). Conversely, when a wetland is excavated, mined or drained, oxygen levels increase and decomposition is accelerated, releasing the stored carbons into the atmosphere as carbon monoxide. In his introduction to the book Wetlands in Danger, David Bellamy warns us that if we disturb the world’s peat lands in a large-scale manner, we would release double the amount of carbon dioxide into the atmosphere than is already present and thereby profoundly increase the greenhouse effect (Dugan, p.8).

Throughout the United States, industry and municipal planners are developing artificial wetlands to purify water. Paper mills and mining companies construct wetlands to clean industrial waste from waters before they are returned to the watershed. Similarly, residential planners are building wetlands to filter sewage. The town of Arcata, California, constructed a 96-acre artificial wetland to purify waste after research revealed that this system was far more efficient and less expensive than a traditional sewage-treatment plant (McCormick, pp.47-48). In fact, it is estimated that “one hectare (2.5 acres) of tidal wetland can do the job of US $123,000 worth of state of the art waste-water treatment,” (Bellamy, in Dugan p. 8). Furthermore, wetlands can be constructed to treat landfill leacheate, agricultural effluent, and to curb the effects of flooding.

Increasing precipitation:

Plants absorb water and release it into the air through a process called evapotranspiration. This adds humidity to the air and, in a large area, can increase precipitation.

Sulfates entering a wetland are converted to sulfide and released into the air in various forms. One way they are released is in the form of dimethyl sulfide, which acts as a catalyst for cloud formation.

NOTE: Oregon's two native turtles, the Western Pond Turtle and the Painted Turtle, are in danger of disappearing. Oregon Zoo's conservation project for the Western Pond Turtle. See http://www.oregonzoo.org/Conservation/westernpondturtle.htm Oregon State's Extension Service has more information about how you can make a real difference for these two little natives. See http://extension.oregonstate.edu/gardening/things-you-can-do-your-property-help-native-turtles

Reducing Erosion:

The roots of wetland plants stabilize the shores of streams, rivers, lakes and oceans. Rushes, Sedges and Cattails have quickly spreading root systems to anchor them in periods when water flows fast or when waves from lakes push hard against them.

Words of wisdom from An incomplete and ever-changing catalog of native Plants of Montara Mountain:

"Sedges have edges. The rule to remember in identifying members of Cyperaceae - and although those edges are sometime pretty subtle, it holds true for our native species.

They all grow in wet areas, if not right in creeks and ponds, which is another clue. Stems are usually solid and three-angled (those edges - you may have to slice it toward the base to really see it). The leaves, when present, are slender but with a substantial stem clasping basal sheath with fused edges.

The flowers (or florets in this case) are clustered in spikelets, with bracts at each floret as well as the spikelet itself. There is usually 3 stamens, and 2 to 4 feathery stigmas on the pistil.

See www.plants.montara.com

For a list of Pacific northwest wetland plants, click here.


Other northwest natives that work well in the bog garden or pond:



Delesalle, Bruno in cooperation with Ducks Unlimited and Environment Canada. Understanding Wetlands: A Wetland Handbook for British Columbia’s Interior. BC, Canada: Ducks Unlimited Canada, 1998.

Dugan, Patrick, ed. Wetlands in Danger: a World Conservation Atlas. New York: Oxford University Press, 1993.

Logsdon, Gene. Getting Food From Water: A Guide to Backyard Aquaculture. Pennsylvania, USA: Rodale Press, 1978.

McCormick, Anita Louise. Vanishing Wetlands. San Diego, California: Lucent Books, Inc., 1995.

Pettinger, April. Native Plants in the Coastal Garden: A Guide for Gardeners in British Columbia and the Pacific Northwest. Vancouver, British Columbia: Whitecap Books, 1996.

Pojar, Jim and MacKinnon, Andy. Plants of Coastal British Columbia including Washington, Oregon and Alaska. Vancouver, BC: Lone Pine Publishing, 1994.

Thompson, G. and Coldrey, J. with photos by G. Bernard and illustrations by G. Thompson. The Pond. Toronto: William Collins Sons & Co. Ltd., 1984.

Weller, Milton W. Freshwater Marshes: Ecology and Wildlife Management. Minneapolis, Minnesota: University of Minnesota Press, 1981.

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