Impact of Irrigation Cessation on Wetland Communities within the Elk Ranch, Grand Teton National Park, Moose, Wyoming

Riparian ecology research in Arizona and California has documented the likelihood of a subsurface linkage between irrigation, especially flood-irrigation, and riparian function (Smith et al. 1989; Stromberg et al. 1996). Initial groundwater monitoring results from rural New Mexico indicate water tables rose 1 to 2m after the onset of field irrigation and subsurface flow paths towards the Rio Grande River developed soon after (Fernald et al. 2008). Results from a study of wetlands in southeastern Wyoming suggest that declining flood-irrigation levels would lead to a reduction in the total area of wetlands and related areas of wetland vegetation types in the Laramie Basin (Peck and Lovvorn 2001). Stringham et al. (1998) have reported further evidence for a linkage between irrigation and riparian function . These Oregon researchers noted lower water temperatures in stream reaches receiving subsurface return flows from irrigated hayfields than similar reaches flowing through non-irrigated lands. This information is timely because Grand Teton National Park (GTNP) managers have begun an evaluation of historic irrigation operations within the Park and are endeavoring to learn how cessation of flood irrigation will affect Park wetlands. The historically irrigated hayfields at the Elk Ranch provide an opportunity to address the Park Service's informational needs through identification of vegetation composition, soil physical characteristics and groundwater patterns associated with irrigated and naturally occurring wetlands. Successful description of patterns unique to natural wetlands will provide an avenue for predicting which Park wetlands would remain functional should irrigation efforts be brought to a close. Development of criteria for identifying naturally occurring wetlands could also serve as a basis for identifying areas for wetland mitigation and rehabilitation elsewhere in GTNP and the mountain valleys of the Northern Rocky Mountains.