Acknowledgements UNM Hydrogeoecology Group NSF Grant DEB-9903973

1. HYDROLOGIC CONNECTIVITY OF NATIVE RIPARIAN FORESTS ALONG THE MIDDLE RIO GRANDE, NEW MEXICO S.F. Gray, J.F. Schuetz, and M.C. Molles, Jr. Department of Biology, University of New Mexico, Albuquerque, NM 87131 Abstract The native riparian ecosystem of the Middle Rio Grande in New Mexico is in decline and is aging. This riparian forest, or bosque, is dependent on the annual flood pulse that in the past 50 years has been nearly eliminated by dams, diversions and drought. We are studying the difference in hydrologic connectivity between four flood sties and four nonflood sites within a 160 km stretch of the middle Rio Grande from Cochiti Dam to the Elephant Butte Reservoir. These hydrologic factors include river levels, groundwater depth and soil moisture. The relationship among these factors will help us understand hydrologic differences in flood and nonflood sites and what is critical in maintaining the native riparian ecosystem. Results from this study will be used to help inform policy makers on potential tool such as managed floods that could be used to restore the native bosque of the Middle Rio Grande. • Introduction • The flood pulse that once normally occurred throughout the Rio Grande Valley has been greatly diminished. This has a negative impact on native plant and animal populations, wood and leaf decomposition rates and soil bacteria and fungi (Ellis, Crawford, and Molles 2002). • Life cycles of plants and animals in floodplain ecosystems are correlated to the annual timing, duration and river levels produced from the flood pulse (Junk, Bayley, and Sparks 1989). • Natural overbank flooding has been severely restricted in the past 60 years, and the last major floods that produced large-scale cottonwood establishments occurred in 1941and 1942. • Flooding has been shown to decrease air and soil temperatures and increase water holding capacities of soils. These factors may be important to the life cycles and activities of soil and surface organisms (Ellis, Molles, and Crawford 1996). • Three years of experimental flooding indicates a strong relationship between surface water and ground water. Increased ammonium levels in the soil, increased soil respiration, and changing soil structure and composition were observed, including lowered salinity (Ellis, Molles, and Crawford 1996). • Reinstating the historical hydrograph of the Rio Grande can help restore the native riparian ecosystem, supported by results from three years of experimental and natural flooding (Ellis, Molles, and Crawford 1996). Groundwater depths were significantly higher at flood sites than nonflood sites in 2001 (p=0.001) and 2002 (p=0.032) View of Rio Grande under normal flow conditions Recording water table depths Literature Cited Ellis L.M., Crawford C.S. and M.C. Molles Jr.. 2002.The role of the flood pulse in ecosystem-level processes in southwestern riparian forests: a case study from the Middle Rio Grande.Flood pulsing in wetlands: restoring the natural hydrological balance, p. 51. Ellis L.M., Molles M.C., Jr., and C.S. Crawford. 1996. Seasonal flooding and riparian forest restoration in the Middle Rio Grande Valley. Final report, U.S Fish and Wildlife Service, District 2, Albuquerque, New Mexico. Junk, W.L., Bayley P.B. and R.E. Sparks. 1989. The flood pulse concept in river-floodplain systems, p.110-127. In D.P. Dodge Proceedings of the International Large River Symposium. Can. Spec. Publ. Fish. Aquat.Sci. 106. Obtaining soil moisture readings Acknowledgements UNM Hydrogeoecology Group NSF Grant DEB-9903973 Middle Rio Grande Conservancy District Bosque del Apache National Wildlife Refuge City of Albuquerque Open Space Division New Mexico State Land Office Rio Grande Nature Center Belen Consolidated Schools Contacts Samuel F. Gray 505-277-5732 samgray@unm.edu Jennifer F. Schuetz 505-277-5732 jschuetz@sevilleta.unm.edu Manuel C. Molles, Jr. 505-277-3050 molles@sevilleta.unm.edu Dry river bed of the Rio Grande at Bosque del Apache 7/17/02