Tuesday, June 5, 2007 - 9:15 AM
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River food webs during summer dry-down in the Middle Rio Grande: a study using stable isotope analysis

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

The temporal dynamics of food webs in arid-zone rivers are poorly understood. This study examined temporal variation in the food web in the Rio Grande at the Bosque del Apache National Wildlife Refuge, New Mexico. Food web constituents (terrestrial detritus, algae, meiofauna, macroinvertebrates, fish) were sampled from low flow habitats at weekly intervals during spring-summer 2006. Water flows decreased significantly from May to June and then increased dramatically following monsoon rains in late June and July. Fish abundance and taxonomic richness were variable over time, while invertebrate abundance and richness decreased following monsoonal flooding. Stable isotope analysis was used to identify primary carbon sources (d13C) and trophic level (d15N) for each of the constituents. There was a shift in carbon source as the river dried, from algal-derived production to riparian-derived plant detritus. This shift may be driven by changes in the edibility of algae in the river, either related to a species turnover in the algal community or related to top-down limitations of microinvertebrate grazing on algae. Following flooding, there was a shift back to algal-derived production as the primary carbon source in the food web.