Jeremy Sueltenfuss GDPE MS Thesis Defense
Thursday, May 10, 2012, 03:00 PM
Forestry Building, Room 212

Irrigation has increased the agricultural productivity of the arid American West, but has also greatly altered the natural landscape. Irrigation canals transport water to 17 million ha of currently irrigated land. Because water is a limited resource in the west, and because irrigated agriculture uses approximately 90% of all the water diverted from rivers, much attention has been paid to the efficiency of irrigation systems. Irrigation canals have been shown to leak up to 50% of the water they transport, affecting both groundwater recharge and return flows to rivers, though little work has been done on the ecological effects of irrigation canal seepage on wetland ecosystems. This study sought to identify the hydrologic processes linking canals and reservoirs to wetlands, identify the types of wetlands supported by irrigation canal seepage, and document the area of wetlands supported by irrigation within the service area of an irrigation company. All wetlands within the North Poudre Irrigation Company in Larimer County were mapped and their hydrologic source determined from visual clues. Groundwater monitoring wells were installed in wetlands adjacent to canals and reservoirs to identify the hydrologic influence of canal seepage on wetland hydrologic regime. To further demonstrate the hydrologic source of wetlands, stable oxygen isotopes were analyzed within wetlands and possible adjacent water sources. Vegetation characteristics and species percent composition was related to environmental variables to highlight the types of wetlands supported by an irrigation infrastructure. A total of 176 wetlands covering 652.3 ha were mapped, over 91% of which was visually connected to the irrigation infrastructure. Wetland water tables fluctuated with adjacent canal flow, with increases in the water table when canals started transporting water, and decreases in water table depth during times when canals did not carry water. Isotopic data indicate that canal leakage is the hydrologic source for adjacent wetlands within the study area. The isotopic signature of canal water matched that of wetlands closer to canals. Wetland isotopic signatures became increasingly evaporatively enriched at further distances from canals, showing a linear relationship between isotopic signature and distance from canal. Wetland vegetation composition was related to both salinity and groundwater depth, with salt flats dominated by Atriplex spp. forming in areas with high salinity, marsh communities dominated by Typha latifolia and Schoenoplectus acutus forming in areas with low salinity and deeper standing water, and meadow communities dominated by Carex nebraskensis and Schoenoplectus pungens forming in areas with low salinity and water tables closer to the ground surface. Though agricultural land conversion and water diversions have led to dramatic reductions in historic wetland area and riparian corridors, it is clear from this study that current wetlands in agricultural landscapes rely on excess irrigation water for their hydrologic maintenance. Any future changes in irrigation practices or water distribution may have negative consequences on wetland ecosystems.

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Event Contact: Jeri Morgan can be reached at (970) 491-4373

Sponsored by teh Graduate Degree Program in Ecology