Monday, May 26, 2008 - 2:00 PM
75

Stable isotope study of historical and present day fish communities in two arid river basins: Does river regulation alter carbon sources and feeding relationships of fishes?

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

We studied energy sources and trophic levels for fish communities in two major arid-land river basins: the Rio Grande (USA) and the Murray-Darling (Australia) by evaluating stable isotopes of carbon and nitrogen.   Natural history museums provided specimens that had been collected prior, during, and after large-scale river regulation, with the oldest specimens dating back to the late 1800s and the most recent collected in this decade. At present, both basins are heavily regulated for irrigation and flood control and consequently, the frequency and duration of flooding in both systems are diminished.  We hypothesized that terrestrial production in riparian forests provided the majority of carbon for the river food web prior to extensive regulation.  We also expected instream (algal) production to become the dominant source of carbon for the entire fish food web following river regulation.  Contrary to expectation, we found that instream production was most important over the entire study period in both systems.  Our results suggest that the major effect of river regulation is a reduced production capacity rather than a fundamental shift from riparian to instream production.


Web Page: floodplain, museum specimens, nutrient dynamics

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