Non-tidal Wetlands Conservation

Creating wetlands on the Mainland Unit of Julia Butler Hansen Refuge/USFWS

Over 120 acres of freshwater wetlands support a variety of species including, Columbian white-tailed deer, waterfowl, other water birds, amphibians.


Non-tidal marshes on the refuges have no direct connection to the Columbia River and thus are not affected, or are affected very little, by the tides. These marshes occur primarily on the diked areas of the Julia Butler Hansen Refuge (the Mainland and Tenasillahe Island units). They are seasonal in nature and form in depressions where winter rainfall creates pools. The non-tidal marshes tend to be small in size and vegetated with undesirable invasive plants such as reed canarygrass and common rush (tussock). Since 1999, the refuge has been enhancing some of these marshes by shallow excavation and the installation of water control structures. To date, 20 areas totaling 129 acres have been improved. The excavation and water control installations result in establishing more desirable wetland plants. Species include creeping spike rush, cattail, bur-reed, smartweed, beggars-tick, soft-stem bulrush, water purslane, tapered rush, water foxtail, wapato, mannagrass, and water plantain. Less desirable plants such as reed canarygrass and common rush also flourish and are periodically controlled by mowing and cultivating.

The non-tidal marshes have many of the same biological functions as the tidal marshes that were present prior to the construction of dikes. The plants provide food for thousands of migratory ducks and geese. Bald eagles and peregrine falcons are attracted to the abundance of prey. Water draining from the marshes carries nutrients that reach the Columbia River and help feed the organisms of the estuary, including salmon. Columbian white-tailed deer feed on water foxtail and other marsh plants. The non-tidal marshes also provide ideal breeding habitat for several species of amphibians, such as long-toed salamanders, red-legged frogs, and Pacific tree frogs.

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When Nature is not at its Best 

Unmanaged freshwater wetlands are generally 1-2 feet lower than the surrounding pasture lands, have standing water from early fall through late spring, and are dominated by monotypic stands of common rush (Juncus effusus). This rush limits availability of open water resting sites for waterfowl. In less disturbed sites, wetlands may also be dominated by dense stands of reed canarygrass (Phalaris arundinacea). Soils in these wetland sites are mostly clay, which drains poorly and is a source for silt deposition in ditches and sloughs. Management of water levels in these natural wetlands is not possible. 

Managing Wetlands for Wildlife Success 

Managed wetlands are similar to unmanaged wetlands with some significant differences. These wetlands have been constructed to manage water levels and reduce infestations of weedy plant species. Managed wetlands have water structures which allow for control of the water levels, which are generally maintained at around 18 inches or less. The wetlands are usually drawn down during the summer months to mimic natural cycles and if necessary, they can be disked or plowed to reduce noxious plant infestations and to provide a good ratio of vegetative cover to open water. There are currently 13 managed wetlands sites on the mainland unit of the refuge. 

Wetland enhancement work takes place in late spring through early fall, the driest portion of the year. Work begins as soon as soil conditions allow, with disking and plowing of the wetland sites and adjacent pastures occurring first. As the sites dry, more extensive dozer and scraper work is initiated. In the wetter locations some of the more extensive heavy equipment activity may be delayed until during the months of July and August. Since 1999, over 100 acres on the Mainland Unit and 25 acres on the Tenasillahe Island Unit have been modified to allow for managed wetlands.

Learn more about how the Refuge manages freshwater wetlands... 

Wetlands are managed as summer feeding sites for the deer with the secondary goals of providing overwintering feeding and loafing sites for waterfowl and springtime breeding and larval rearing sites for pond-adapted amphibians. Water inflows at these sites will occur from precipitation and subsequent runoff into the wetland areas. Water levels will be maintained at relatively shallow depths (2-3 feet) to promote use by dabbling ducks. During periods of high precipitation, wetlands may serve as overflow areas, i.e., places that can be flooded instead of allowing the entire refuge to be inundated. These managed wetlands help to control invasive plant species by allowing the refuge to control water levels and to some degree the timing of the water inundation. Consideration is also given to management of water levels and management schemes for amphibian species. Species identified on the refuge include the long-toed salamander, northwestern salamander and Pacific tree frog and red-legged frog. Further survey work is planned to identify additional species as well as determine their relative population abundance. Particular emphasis will be placed on breeding water depth and larval use in wetlands. The expansion of bullfrog populations, which require water for two or more years to complete their life cycles, is limited by drying the wetlands during the summer. 

Emergent wetland species such as smartweed and cattails benefit from the enhanced wetlands and provide valuable cover and food for waterfowl. Other wetland species such as manna grass provide a food source for the CWTD when the wetlands dry during the summertime. Emergent plants are encouraged to develop through natural succession. During late spring, the water is removed from wetlands and the growth of species such as reed canarygrass, Juncus and sedges will likely accelerate. Management of the wetland bottoms depends on the type and amount of vegetation cover and involves periodic mowing and disking of the sites.