Documentation of Existing Conditions in the Central Platte Valley

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1 SECTIONTWO Environmental Setting cattail and brush marshes, wetland swales, ponds and sloughs, and lowland savannas are all aspects of wet meadows ... The common thread among these diverse types of wet meadows is a high groundwater table, a surrounding matrix of prairie, and the presence of scattered wetlands, poor drainage, and nutrient -rich soils." The term "wet meadow" is more widely used in the central and western U.S. to describe herbaceous meadows on mineral soils of seasonally flooded or saturated flats, which are usually dry for a portion of the growing season (Windell et al. 1986; Hansen et al. 1995; Stewart and Kantrud 1971, 1972). Stewart and Kantrud described the wet meadow zone as intermediate between wetland -low prairie and shallow marsh. Under the National Wetlands Inventory (NWI), wet meadows would typically be mapped as PEMA (palustrine, emergent, temporarily flooded) (Cowardin et al. 1979). NWI would not map Stewart and Kantrud's wetland -low prairie zone as wetland and would identify shallow marsh as PEMC ( palustrine, emergent, seasonally flooded) or PEMF ( palustrine, emergent, semi - permanently flooded). Wet meadows in this usage are a type of wetland, which is "an ecosystem that depends on constant or recurrent, shallow inundation or saturation at or near the surface of the substrate" (National Research Council 1995). The term "wet meadow" has been used to refer to both non - wetland bottomland grassland and to wetlands ranging from true wet meadows to ponds and sloughs. This may be due in part to evidence that wetlands were far more prevalent in the bottomlands prior to agricultural development and water diversions. However, since many of these areas are not currently wetlands and the term "wet meadow" has been applied both to wetlands and to non - wetlands in bottomland areas along the Platte River, the following section will use the term "bottomland grassland" except where it is clear that the literature being discussed refers only to wet meadows as a type of wetland. 2.7.2 Location and Distribution Mapping of bottomland grasslands "wet meadows" was included as art of the WELUT PP� g � ( ) p database (Currier et al. 1985) and is being included in the current BOR study. These areas were defined as grasslands with emergents or open water within the floodplain. The WELUT database did not include wet meadows or bottomland grassland outside of the Platte River floodplain; these areas were counted as upland grassland (Sidle et al. 1989). The National Wetlands Inventory has also mapped wetlands on all of the U.S. Geological Survey (USGS) quads in the study area. The currently available maps were prepared in 1987 based on May, July, or September 1981 aerial photography (NWI 1987). Although these maps are not up to date and may not be accurate, they are useful for identifying general areas of wet meadows and bottomland grasslands. Bottomland grasslands and wet meadows occur throughout the study area but are much more prevalent in the eastern portion of the study area. Currier et al. (1985) reported that about 75 percent of the bottomland grasslands and wet meadows in the WELUT study area (Segments 1 to 11) occurs in Bridge Segments 1, 2, 3, 4, and 7. The largest area is on Mormon Island in Segment 3, most of which (about 2,000 acres) is mapped as wet meadow (about 90 percent ME AWW Woodward A)* 2-8 68FOD9728600/rl.doc 6/211999(9:52 AMUURSGWCFS/2 swvfts