Monday, May 26, 2008 - 4:30 PM
110

Community responses to variable flows in an arid-land river (Rio Grande, New Mexico)

Ayesha S. Burdett, Thomas F. Turner, and Monica K. Tellez. Department of Biology and Museum of Southwestern Biology, University of New Mexico, MSC 03-2020, 1 University of New Mexico, Albuquerque, NM 87131

Flows in the Rio Grande are unpredictable and flashy.  In spring and summer, high flows can alternate with nearly dry conditions.  We conducted two types of surveys to examine questions about aquatic community responses to differing flow conditions through the year. Weekly surveys at Bosque del Apache NWR began when flows were high in May, continuing until the river was nearly dry in August. Occasional high flows from monsoonal rains in tributaries added sediment to the system, making turbidity excessively high and limiting instream primary production. We used stable isotopes (C, N) to examine the switch between in-stream and riparian production related to causal effects (flow, turbidity) and biotic outcomes (fish life stages, invertebrate communities). The biofilm isotope signatures changed through the summer, which may indicate changes in biofilm community composition. We also surveyed five sites along the length of the middle Rio Grande for community composition (biofilm, invertebrates, fishes) and conducted similar analyses of food web structure. This longitudinal survey was repeated several times in the year as flow conditions changed, providing information about differences related to location and flow regime. These longitudinal surveys complement our single site observations in an attempt to examine river-wide responses to flow variability.


Web Page: stable isotopes, arid-land river, community dynamics

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