OutdoorNebraska

54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 GUIDE TO NEBRASKA'S WETLANDS starting just downstream of Ponca State Park caused the river channel to narrow and degrade (deepen) until where the Platte River joins the Missouri near the town of Plattsmouth. The bed is stable or aggrading downstream from Plattsmouth. Loss and Threats About 100,300 acres of aquatic habitats (mostly wetlands) and 65,300 acres of islands and sandbars have been converted to dry land or navigation channel between Sioux City, Iowa, and the river's confl uence with the Mississippi River (U.S. Fish and Wildlife Service 1980). Within Nebraska, losses were estimated at 18,200 acres of aquatic habitat and 18,700 acres of islands and sandbars. Channelization and measures to reduce the lateral movement of the river, along with the fl ood reduction efforts provided by mainstem and tributary reservoirs and levees, has fostered agricultural, urban, and industrial encroachment on 95% of the fl oodplain (Hesse et al. 1989), and this has contributed to the extensive wetland losses. The six huge mainstem dams in the Dakotas and Montana have had measurable infl uences on water quality, quantity, and timing along the Missouri River. The release of relatively silt-free waters from Gavins Point, the lowermost dam in the system, is contributing to riverbed degradation from below the dam to about Plattsmouth (U.S. Fish and Wildlife Service 1980). Riverbed degradation causes adjacent wetlands to become abnormally dry and isolates backwater areas from the main channel. In addition, control of the release of water from the dams has reduced the fl ood pulse that helps to maintain fl oodplain wetlands. Missouri River wetlands were given a Priority 1 ranking (due to very extensive past losses) in the Nebraska Wetlands Priority Plan (Gersib 1991). Channelization, loss of wetlands, and extensive development of the fl oodplain have reduced the natural fl ood-carrying capacity of the Missouri River system. As a result, fl ood stages have increased as was evidenced by the record fl oods in 1993, 2011, and 2019. In addition to the large events, due to the loss of the natural fl ood-carrying capacity, even smaller runoff events can result in moderate fl ooding. The Missouri River is a wetland complex where most of the destruction and degradation already has occurred. Categories of greatest threat along the Missouri River appear to be riverbed degradation, residential, agricultural, and commercial development, transportation, navigation maintenance projects, water pollution, water development projects, streambank stabilization, agricultural conversion, and drainage and fi lling. These factors have had a cumulative effect on river functions by isolating the fl oodplain from the river and reducing the natural dynamics. Invasive purple loosestrife has become well- established in the upper reaches of the Missouri River near Niobrara, Nebraska. Purple loosestrife's rapid expansion into the backwater areas of Lewis and Clark Lake is a threat to native plants all along the river. Zebra mussels are an invasive species that also are well established in the Missouri River, including the areas above Gavins Point Dam. Zebra mussels negatively affect several native mussel and fi sh species. Benefi ts The Missouri River, like many natural systems, is a whole that is greater than the sum of its parts. The interactions between the parts (e.g., wetlands, organic matter, sandbars, tree falls, side channels, etc.) form a complex interrelated system. Wetlands are an important component of this system because they produce invertebrates and other organic matter that provide energy and food to other parts of the river. Additionally, these wetlands provide spawning and nursery areas for many types of fi sh and are home for numerous wildlife species. Several state and federally listed threatened and endangered species regularly use the Missouri River in Nebraska. The state endangered least tern and state and federally threatened piping plover nest on unvegetated sandbars in the unchannelized reach of the river, a habitat type that has been eliminated downstream from Sioux City. The recovery plans for the piping plover (U.S. Fish and Wildlife Service 1988) include Missouri River nesting habitat as being essential to the recovery of this species. Several native fi sh species in the river are in severe decline, including the federally endangered pallid sturgeon, state endangered sturgeon chub, and state threatened lake sturgeon (Galet et al. 2005). Even so, the river still supports a self-sustaining paddlefi sh fi shery and good quality catfi sh fi shery. Other native fi shes (e.g., Prothonotary warblers use naturally wooded wetlands such as at Fontenelle Forest along the Missouri River in Bellevue. JASONONDREICKA

• Cover