What’s a wetland?


Adam Janke | Assistant Professor in Natural Resource Ecology and Management and Extension Wildlife Specialist, Iowa State University

In keeping with a theme from my last blog titled “What the heck is habitat”, this month I explore another critical question within the language of conservation. What’s a wetland?

Wildlife biologists like me adopt a broad definition of a wetland because so too do the wetland-dependent wildlife we study. We find often that a migrating flock of Greater Yellowlegs in August are apathetic whether a wet spot in a crop field has drainage infrastructure underneath it. And that a nesting pair of Soras care little about the motivation or permits behind the construction of a water-treatment wetland in town. To wildlife, and thus to a wildlife biologist like me, what makes a wetland is how it functions. And to describe that critical wetland function we need to consider two factors: water and plants.

Put simply, a wetland is a place where water and water-loving plants interact to create shallow pools that vary in depth and duration of flooding. In some years, a wetland may be feet deep and hold water from ice-off to freeze-up. In others, it may hold water for a few weeks or be entirely dry.

Wetland compare-01

Healthy wetlands transition between wet and dry cycles and have a diversity of water-loving plants in and around them.

Given this broad definition, we can look to the land to find a wide variety of wetland types.

  • Floodplain wetlands capture flood waters adjacent to over-filled rivers and streams.
  • Oxbow wetlands were once part of a stream or river channel and today reconnect only occasionally.
  • Ephemeral pools are found in woodlands where the deafening call of breeding frogs in spring is a distant memory when the spot is dry weeks later in June.
  • Prairie potholes take all shapes and sizes from problem areas in a crop fields to iconic lakes like Clear Lake, Spirit Lake, and Black Hawk Lake.
  • Engineered wetlands are designed to use natural wetland processes to clean water or sequester floods in strategic areas in agricultural and urban landscapes.
  • Fens are outlets of groundwater on slopes with unique chemistry and biological adaptions of many plants found there.

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All these wetlands and more share two common characteristics; their tendency for dynamic water levels (fluctuating between wet and dry periods) and their harboring of water-loving plants that cycle through time.

When these two characteristics manifest, the accolades for wetland function are long and include:

  • Removing nutrients in water, including nitrogen and phosphorus.
  • Removing contaminants in water, including sediment and chemicals used in urban and agricultural environments.
  • Providing habitat for a wide range of wildlife including many wetland dependent organisms and even terrestrial animals like bees, bats, and insectivorous birds.
  • Providing recreational opportunities like kayaking, canoeing, swimming, bird watching, and hunting.
  • Capturing and slowly releasing flood waters, reducing downstream flood peaks.
  • Providing for conditions for ground-water recharge.
  • Sequestering carbon from the atmosphere.

Scientists and policy makers call this long list of accolades “ecosystem goods and services.” According to economists who have estimated the values of these ecosystem goods and services, inland wetlands only lag behind coral reefs and coastal ecosystems for their financial returns to society.

This recognition of the critical roles of wetlands as “nature’s kidneys” (to say nothing of their value as “nature’s playgrounds” for many) has led to extensive and growing efforts to protect existing wetlands and restore others. In an ironic turn of tides, today the same forces that claimed over 90% of Iowa’s original wetlands — the excavator, drain tile, and bulldozer – are being employed to put wetlands back into our agricultural landscapes in areas of the farm that generally underperform for farmers and have potential to accrue the valuable functions described above for society.

Once water levels begin to fluctuate again and the vegetation follows in kind, you can be sure the Soras, Yellowlegs, and many more wildlife will contently reassert their satisfaction with these restored oases in Iowa’s landscape, happily calling the spot where uniquely adapted plants and dynamic water levels meet a wetland once again.

Adam Janke