Document: GEO-3-74-22

Investigating the utilization of benthic versus pelagic primary production in Lake Roosevelt, WA: A stable isotope analysis.

BARLOW, G.W.* and A.R.BLACK

Eastern Washington University, Cheney, WA 99004, USA ¹

Abstract:
Food web components of Lake Roosevelt, WA, were examined using carbon and nitrogen stable isotopes in an effort to determine the extent of pelagic versus benthic carbon in the diet of commonly occurring species in the lake. Lake Roosevelt is a long, deep reservoir of the Columbia River, located behind Grand Coulee Dam. Every spring the water level of the reservoir is lowered by as much as 80 feet in order to create room for peak runoff from the surrounding mountains, and returned to full pool by mid summer. Strong fluctuations in water level severely inhibit benthic production from becoming permanently established in the reservoir. Isotopic data shows Lake Roosevelt to be primarily a pelagically driven system. Benthic primary producer carbon signatures were isotopically heavier than pelagic primary producer carbon signatures. Organisms demonstrating a purely benthic diet included only primary consumers (YOY carp, chironomids, and snails). Fish which are typically considered to be obligate benthivores (adult carp and large-scale suckers) had carbon signatures indicating a mixed diet between the benthic and pelagic regions. Those fish that are typically considered to have a mixed diet (lake whitefish and yellow perch) demonstrated a diet resulting from pelagically derived carbon. Fish that were expected to have a pelagically derived diet did so.

Keywords: Food webs, stable isotope, reservoirs

This abstract is being presented at: 10:30 AM in session:
Poster Session #9: Fish, Lakes, Streams and Wetlands.