Managing Iowa Habitats

Fen Wetlands

Introduction Why should I be concerned? Fens are the rarest of Iowa’s wetland commu- Fens are an important and unique wetland nities and of great scientific interest. While type. Not only are the fens themselves rare, but their geology varies, they all are the products they shelter over 200 plant species, 20 of which of the seepage of groundwater to the surface. are Iowa endangered and threatened species. Because the water is rich in calcium and other Many of the plant species have been in these minerals, only a select group of plants is able to areas for thousands of years. The fen’s vegeta- grow there. As a result, fens contain many tion, in turn, shelters wildlife by providing plant species considered endangered or valuable habitat. threatened in Iowa. Fens are valuable to humans as well. They are A few of the oldest fens contain plant remains important as sites of groundwater discharge — that date back 10,000 years, though most Iowa good indicators of shallow aquifers. Vegetation fens are less than 5,000 years old. A few of in all wetlands plays an important role in these “younger” fens may have existed 10,000 recycling nutrients, trapping eroding soil, and years ago, but because of dramatic climate filtering out polluting chemicals such as changes, they may have dried up and lost the nitrates. However, the rarity of fens and their plant remains (by burning or erosion) that relatively small size makes it important could prove their age. When the climate grew to protect them from overloading by wetter again about 5,000 years ago, these fens these materials. Too many nutrients may have reappeared. Most Iowa fens, how- or other chemicals can irreparably ever, are thought to be of rather recent origin, damage fens. As miners watched geologically speaking. It is likely they were their canaries for signs of poisoned formed in the last 5,000 years and are related to air, it is wise for humans to watch the changes in geology brought by the receding closely the health of plant and animal of the last glaciers from Iowa. life in ecosystems such as fens, which are good indicators of environmental quality. The condition of plants and animals in fens can help us mon- itor the quality of groundwater resources.

Fringed gentian

IOWA STATE UNIVERSITY Extension and Outreach Pm- 1351f | February 1993 What are fen wetlands? Fen characteristics The name fen is not as commonly used in the Fens differ substantially from other wetlands. United States as in Europe where these Some of these differences cannot be directly wetlands are not as rare. In Iowa, fens have observed because they are deep below the soil been called marshes, seeps, side-hill seeps, surface. mound springs, wet prairies, sedge mead- ows, and sloughs. They also have been Geological settings - underground mistakenly called bogs, hanging bogs, and structure hillside bogs. Fens are typically found on Fens can form where a groundwater source hillsides, though occasionally in low areas rich in minerals is exposed to the surface. between hills. Depending on a fen’s location in the state, its foundation was laid either during a glacial Fens differ There are many different kinds of wetlands. period hundreds of thousands of years ago substantially Certain characteristics make fens unique. (and since eroded), or during the most recent from other Typically, the water in fens is neutral to glacial period — about 10,000 years ago. In wetlands. alkaline (the pH is 7 or greater) and rich in either case, the geology provided an ideal nutrients. The water comes from groundwa- setting for the development of a fen. There are ter that saturates the fens’ organic soils — basically two settings: layers of partially decomposed plant material • The most common setting is one in which the called peat. In certain areas this peat is so groundwater source is a buried sand and saturated with water it sometimes is called gravel deposit located in debris left behind “quaking soil” because the ground trembles by glaciers (see Figure 1). Over time, when walked on. Sometimes the water that erosion exposed portions of this sand and saturatesthis soil carries enough dissolved gravel resulting in a seep area — calcium carbonate to form a grayish-white, a place where the groundwater is near the lime-rich substance called marl or tufa when surface. Peat soil is characteristic of fens it comes to the surface. Because of this formed over the seep area. calcium deposit, these wetlands are some- • A less common setting is one in which the times referred to as calcareous. groundwater source is in sand and gravel that was deposited on the surface by Because of the dissolved calcium and other flowing water from the melting glaciers. minerals in the water, fen plants are very distinctive. The most common plants in the These geological settings of fens are important fen are sedges that often hide some rare and because they relate to the likelihood of con- beautiful wild flowers. Other plants that live tamination by chemicals and other pollutants. in the fen include grasses, forbs (broad-leaved Fens with groundwater sources near the plants), and a few shrubs and trees. surface (second setting) can be contaminated by surface-derived pollutants much more easily than fens whose source of groundwater is buried (first setting). However, the glacial deposits surrounding the buried groundwater plants sources of eastern Iowa fens are old and glacial debris weathered. This makes them more fractured, pools allowing pollutants moving through the peat ground to enter the fen easily and rapidly. Thus eastern Iowa fens are more likely to be seep area sand and gravel deposit water flow contaminated by surface pollutants that move into and through the fractures than similar western Iowa fens, whose glacial debris geologic setting is younger and not as weathered.

Figure 1. Generalized cross-section diagram of an Iowa fen.

2 Soils was first thought to Fen soil contains a large quantity of decompos- reflect an east-west ing plant and animal material called humus. gradient across the state. Soils with a high humus content are called Currently, researchers organic soils. Fen organic soil is saturated with feel it is more likely due water, and the humus is so rotted that it is to differences in the difficult to discern any bits of plant or animal nature of the geology material. Such organic soil is called muck. In of the sites. contrast, the true peat soils of bogs show recognizable bits of plant stems and other Water-response to material. Two soil series are typical of Iowa rainfall. fens: Palms muck and Houghton muck. How- A fens’s response ever, some exceptions exist; these soil series do to rainfall is related to its not always have fens, and some fens are found geological setting. Moist- on other soil series. ure levels in eastern Iowa fens tend to reflect the Water — pH current quantity of rainfall. A particular water chemistry also characterizes Most eastern fens are a fen. For example, its pH is alkaline, neutral, drier during drought or only slightly acidic, whereas a bog is very periods and recover quickly acidic. Fen soils are saturated with water after wet periods because coming directly from groundwater sources. the geological materials Grass of Parnassus This groundwater supplies most of the nutri- around the groundwater ents needed by fen plants. Classification of sources allow water to move Iowa fens is based on the quantity of available rapidly through to the fens after nutrients and the water pH. There are three a rainfall. At the same time, distinct types: these materials do not hold water • nutrient-poor (slightly acidic), well enough and the groundwater • nutrient-rich (neutral), and storage volume is not large enough to maintain • very nutrient-rich (alkaline). moisture levels during droughts.

Only two nutrient-poor fens are known to exist Some western Iowa fens have geological in Iowa. One of these is located in Pilot Knob materials surrounding them that cause water State Park. Nutrient-rich fens are located to move through more slowly. These materials chiefly in the types of geological settings hold water better and the groundwater sources typical of eastern Iowa. Most of the very can store more water. These conditions can nutrient-rich fens are found in northwestern help maintain a more constant moisture level Iowa. Very nutrient-rich fens also may be and cause a more delayed response to changes characterized by calcium carbonate (lime- in rainfall patterns. stone) deposits of marl or tufa. Plant life Water — hardness Certain species of plants, such as beak-rush, The hardness of water is largely defined by the Grass of Parnassus, and brook lobelia, can be quantity of dissolved calcium and magnesium used as indicators of fens. (See page 8 for ions in the water. The more dissolved ions scientific names of plants.) Of those plant present, the harder the water. Hard water tends species peculiar to fens, 80 percent occur in to be more alkaline. As a result, slightly both eastern Iowa and western Iowa fens. alkaline, very nutrient-rich fen have higher These include upright sedge, inland sedge, bull concentrations of dissolved calcium carbonate, sedge, purple-stemmed aster, flat-topped white sulfate and silica than neutral, nutrient-rich aster, Muhly, and Grass of Parnassus. Most fens. The different water chemistry among fens fens in Iowa are dominated by upright sedge.

3 However, some well-developed western fens plant species found in fens are valerian, brook contain a variety of dominant sedges that lobelia, tall cottongrass, and sage or hoary include water and beaked sedge. Beak-rush willow. These plants are listed so that they will also is frequent in western fens, but not in be more closely studied and monitored in the eastern fens. There are a number of forbs found state. Iowa fens in eastern fens that are rare or absent in west- shelter more ern fens. These include marsh-marigold or Zonation of plants is an unusual phenomenon than 200 cowslip, swamp saxifrage, sensitive fern, and found in fen plant communities. Plants in fens species of marsh fern. Eastern fens have twenty-two can be grouped into three distinct zones: the wildflowers, species of trees and shrubs while western fens discharge zone, the sedge mat zone, and the border some of contain only two. zone (see Figure 2). Much like the concentric which only growth rings in a tree trunk, the first zone live in fens. It is likely that the differences in plant popula- forms around the groundwater seepage area, tions found in eastern and western fens are due the second zone forms around the first, and the chiefly to differences in climate and moisture, third around the second. Actual presence af all though variations in geology and water three zones, as well as how distinctly they are chemistry may also play a part. In some defined, varies among fens. In Iowa, only a few individual cases, plant population characteris- large, well-developed fens such as Silver Lake tics may reflect land use, such as loss of plant and Excelsior fens in the northwest, fully species due to grazing. demonstrate this phenomenon. Some other western Iowa fens have three zones, but the Iowa fens shelter more than 200 species of sedge mat zone is narrow and not as well wildflowers, some of which only live in fens. defined. Zonation becomes less distinct in fens This encompasses approximately 13 percent of from west to east across the state. Eastern Iowa the state’s native wildflowers. Recent searches fens are primarily made up of border zone of fens have discovered over 20 species of with small discharge zones, if any. Most do not plants that are considered rare in Iowa. Three have sedge mat zones. of the species had previously been listed as extirpated (gone from the state completely). Animal Life State endangered plants (species in danger of All wetland types are important habitat for a being extirpated) found in fens include bog large number of wildlife species. Many birds, bedstraw and bogbean. The seven state threat- such as the sora rail, yellow-headed blackbird, ened plants (species becoming very rare in the marsh wren, and common snipe depend on state) found in fens are bog birch, yellow fens and other wetlands. Fens have been monkey flower, beak-rush, narrow-leaved found to shelter a great variety of butterflies. fringed gentian, bog willow, small arrow grass, This includes the rare Baltimore checkerspot and large arrow grass. State special concern butterfly. Unique communities of microscopic border zone plants and animals, such as diatoms, also have been found in fens.

border zone Where are Iowa’s fens? Formerly, fens were thought to occur only in sedge mat zone northwest Iowa. However, fens in Iowa include some peaty wetlands found in the northeastern discharge zone part of the state. A statewide fen inventory found 200 fens in 37 Iowa counties. The search pools identified many other possible fen sites that had been destroyed by cultivation, grazing, mining, or impoundments.

Of the 200 existing fens, about 25 are consid- ered high quality — those that have suffered Figure 2. Aerial view of zonation in a large, little or no damage, and exhibit a large number well-developed fen.

4 and wide variety of plant species charac- teristic of fens. Ranging in size from less than 1 /2 acre to 25 acres, most of these fens are located in privately-owned pastures surrounded by cropland.

This location has been detrimental to fens. Most have been altered in some way through grazing or drainage for farming. Damage to fens can occur from direct use as a water source for livestock, mining for peat or gravel, or from runoff and drift of pesticides and fertilizers from surrounding Figure 3. Counties in Counties with high quality fens fields. These are major threats to Iowa’s Iowa that contain at least one identified fen. remaining fens unless something is done soon. Other counties with existing fens

The future of this rare wetland type is en- trusted to your hands — the landowner.

What assistance is available for land- nient to sell a small parcel. When the land- owners for maintaining fens? owner does not wish to sell, but does want to maintain the fen in its native state, there are Financial assistance options that provide tax credits for the land- Some landowners are in a financial position owner. These include conservation easements that allows them to set this land aside or sell that allow the landowner to retain ownership the fen property. And there are various pro- and the right to use the property in ways grams that provide cost assistance for doing so. agreed upon with the agency providing the easement payment. The landowner may use The future Acquisition of property such as fens is a high the land for recreation such as bird watching, of this rare priority for some agencies and organizations. but may not farm, drain, or fill the fen. In wetland The Iowa Department of Natural Resources is return, the landowner benefits by retaining type is active in acquiring fens for the state from ownership of the property, gaining tax benefits, entrusted willing sellers. Private organizations such as and controlling access. The easement is usually to your The Nature Conservancy, the Iowa Natural permanent to ensure that the land is main- hands — Heritage Foundation, and Pheasants Forever tained as a natural area. the land- also work toward buying fens. Rather than owner. managing the fens themselves, these organiza- Reserved life estates are another way of setting tions sometimes turn them over to the local aside property. The landowner gives the deed County Conservation Board. to the land to a qualifying organization, but reserves lifetime use of the property. Again this However, the landowner may not wish to sell. use must not destroy the natural state of the When a fen is located, for example, in the property. Reserved life estates also provide the middle of pasture or cropland, it is not conve- landowner with tax benefits. For more options,

5 see the booklet: The Landowner’s Options: a guide als who have Pesticide Applicator Training and to the voluntary protection of land in Iowa, avail- who are willing to sign liability release forms. able from the Iowa Natural Heritage Founda- tion, Des Moines, Iowa 50319, (515) 288-1846. How should fens be managed? One of the primary techniques in fen manage- Technical assistance ment is avoiding land-use practices that are For help in managing fens or in identifying damaging to fens, such as grazing, draining, or plants, there is a wide range of assistance tilling the fen. Also avoid farming practices available. The primary source is the Bureau of outside the fen that allow excessive soil and Preserves and Ecological Services, Iowa chemical runoff and pesticide drift. Department of Natural Resources, Wallace State Office Building, Des Moines, IA 50319, Attempts at draining fens for farming can (515) 281-3891 (technical assistance, fen inven- cause irreversible damage, as well as often tory, initial management plans). Other sources being illegal. The real tragedy is that after include: spending a large quantity of money tiling a fen • Environmental Protection Agency, Wetlands to drain it, the land often remains wet. The Protection Section (technical assistance); land is still untillable and the fen is lost. • Geological Survey Bureau, Iowa Department Therefore, it is important to avoid trying to of Natural Resources (technical assistance); crop these areas. • U.S. Fish and Wildlife Service, Private Lands Office, Walnut Creek National Wildlife Refuge Livestock grazing and watering also can (technical assistance); damage fens. Many fens are located in pastures • Iowa Prairie Network (source of volunteers that are grazed by cattle. Some landowners for implementing management plans such as allow cattle access to fens. In wet years, cattle prescribed burns and weed control); do not venture far into the fen because of the • Iowa State University Exten- wet, unstable ground. However, during dry sion (technical assistance); years, cattle trampling can cause uneven • The Nature Conservancy surfaces and trails that allow undesirable (financial and technical exotic weeds to invade the fen. It is best to assistance); fence off the fen and devise an alternative • Wetlands for Iowa, Iowa Natural water source. Heritage Foundation (financial and technical assistance); Protect water quality • local Agricultural Stabilization and In a recent study of 20 Iowa fens, it was found Conservation Service (ASCS) and that some of the most important techniques in Soil Conservation Service (SCS) managing fens were those that managed the (financial and technical assistance); land around the fen. In particular, land man- • local County Conservation Board agement practices that safeguard water quality (technical assistance, possible source of help maintain quality fens. Because many fens financial assistance and volunteers); have row crops upslope from them, it is critical • local hunting groups such as to protect fens from the runoff or drift of Pheasants Forever and Ducks agricultural chemicals. Of 20 fens studied, 10 Unlimited (financial assistance and contained pesticides and 14 exhibited high source of volunteers); levels of nitrates. These chemicals can be • local Master Gardener groups harmful to the wildlife and plants of the fen. (sources of volunteers for implementing Excess nitrogen and herbicide runoff, with management plans); and resultant changes in pH, can weaken and kill • other conservation groups. Local sensitive plant species, making room for the college botany, biology, or animal ecology invasion of less desirable species. Pesticides departments and even local Scout troops Bogbean can affect wildlife in many ways. For more are possible sources of assistance in pre- information see the ISU Extension brochure: serving these rare, natural areas. For some Agricultural Pesticides and Wildlife: A Balancing management practices, such as weed control, Act . you may have to find groups with individu- Buffer strips of grass at least 20 feet wide 6 (preferably 66-99 feet wide), can help reduce combat certain weed species effectively. For the quantity of chemicals carried into fens from example, Canada thistle is best controlled by nearby farming areas. Buffer strips are most late spring burns-between May and June. Early effective when used in conjunction with other spring burns can actually increase sprouting farming practices that help reduce runoff. and reproduction. Annual burns may be These practices include conservation tillage, necessary during the first three years of control strip cropping, and terracing. Because fens get efforts. Hand-cutting of individual plants can their water directly from the groundwater, be an effective control if done at least three farming practices that reduce the quantity of times each year-in June, August, and Septem- fertilizer and pesticides entering groundwater ber. Careful spot-spraying of the amine formu- sources will reduce the quantity that enters lation of 2,4-D can be used in heavy infesta- fens. Crop rotations and use of Integrated Pest tions. Use all herbicides according to label There is wide Management (IPM) are among these practices. directions. agreement There is wide agreement that maintaining that maintain- Control weeds steady water levels, fencing out livestock, and ing steady protecting the fen from runoff and contami- water levels, and woody vegetation fencing out nated groundwater are all critical to maintain- We are still learning about the best way to livestock, and maintain fen plant communities. Researchers ing high quality fens. With your help, Iowans protecting are experimenting with careful burning once will have this important resource for many the fen from every four or five years to remove invading generations to come. runoff and woody vegetation. Burning must be done only contaminated groundwater during wet periods so that the organic soils For more information Wetland Plants and Plant Communities of Minne- are all critical (the peat) is not burned. Effects of burning on to maintaining sota and Wisconsin is a guide to fen plants, rare insect populations is a concern that needs high quality further study. including those in Iowa fens. It can be obtained fens. for $6.50 from Dept. of the Army, St. Paul Burning for weed control is not always the best District, Corps of Engineers, ATTN: CENCS- option. Each fen must be considered on an LM/SALES AGENT, U.S. Post Office and individual basis. Some fens seem to benefit Custom House, St. Paul, MN 55101-1479 most from careful spot spraying or the mowing of undesirable plants. Woody vegetation can Vegetation ManagementManual and Guidelines sometimes be controlled by cutting or girdling. for 25 aggressive woody and herbaceous Herbicides should only be used when burning, species can be obtained from the Illinois mowing, cutting, and girdling are not effective Nature Preserves Commission, 524 So. Second options. St., Lincoln Tower Plaza, Springfield, IL 62701- 1787, (217) 785-8686. The timing of control attempts is important to

Fen Plants 7 Scientific names* for Iowa fen plants listed in text

Common name Scientific name

beak-rush ...... Rhynchospora capillacea beaked sedge ...... Carex rostrata bog bedstraw ...... Galium labradoricum bog birch ...... Betula pumila bog willow ...... Salix pedicellaris bogbean ...... Menyanthes trifoliata Sora rail among brook lobelia...... Lobelia kalmii fen plants bull sedge...... Carex lanuginosa bulrush ...... Scirpus spp. cattails ...... Typha spp. common boneset ...... Eupatorim perfoliatum flat-topped white aster ...... Aster umbellatus fringed gentian ...... Gentianopsis crinata Grass of Parnassus ...... Parnassia glauca inland sedge ...... Carex interior large arrow grass ...... Triglochin maritimum marsh fern ...... Thelypteris thelypteroides marsh-marigold or cowslip ...... Caltha palustris Muhly or barnyard grass...... Muhlenbergia glomerata narrow-leaved fringed gentian ...... Gentianopsis procera northern bog violet...... Viola nephrophylla Olney’s bulrush ...... Scirpus americanus purple-stemmed aster ...... Aster puniceus reedgrass (common reed) ...... Phragmites australis sage or hoary willow ...... Salix candida sensitive fern ...... Onoclea sensibilis small arrow grass ...... Triglochin palustre spotted Joe-Pye-Weed ...... Eupatoriadelphus maculatus swamp saxifrage ...... Saxifraga pensylvanica tall cottongrass ...... Eriophorum angustifolium upright sedge ...... Carex stricta The information in this document has been valerian ...... Valeriana edulis funded wholly or in part water sedge ...... Carex aquatilis by the United State yellow monkey flower ...... Mimulus glabratus Environmental Protection Agency under assistance * Nomenclature follows: Reed, Jr., P. J. 1988. National list of plant agreement X007576 01 to ISU Extension. It has species that occur in wetlands: Iowa. U. S. Fish and Wildlife Service been subjected to the Biological Report NERC-88/18. 15. A copy can be viewed at your local Agency’s peer and U.S. Soil Conservation Service office. administrative review and has been approved for Prepared by Georgia Bryan, ISU Extension wildlife associate. Reviewed by James Pease, ISU publication as an EPA Extension wildlife specialist; John Pearson, Iowa DNR Bureau of Preserves and Ecological document. Mention of Services; Carol Thompson and Jean Prior, Iowa DNR Geological Survey Bureau; and Arnold trade names or commer- cial products does not Van der Valk, ISU professor of botany. Edited by Marilyn Vaughan, ISU Extension communica- constitute endorsement tions specialist. Designed by Dennis Melchert, ISU Extension Communications. Artwork by or recommendation for Mark Muller. Special thanks to Gerry Shimek, Project Manager, EPA. use.

File: Wildlife

This institution is an equal opportunity provider. For the full non-discrimination statement or accommodation inquiries, go to www.extension.iastate.edu/diversity/ext.