Aquatic Sciences Meeting, Albuquerque 2001

PC07 Spatial and Temporal Connections

Date: Wednesday, February 14, 2001

Location: Southwest Hall

Koch, R, W, Department of Biology, University of Louisville, Louisville, KY, USA, rick.koch@louisville.edu

Bukaveckas, P, A, Department of Biology, University of Louisville, Louisville, KY, USA,

NUTRIENT, LIGHT AND TEMPERATURE LIMITATION OF PHYTOPLANKTON AND BACTERIA IN LARGE RIVERS AND THEIR IMPOUNDMENTS.

Seasonal and spatial variations of nutrient, light and temperature limitation were assessed monthly in 1999 within the Ohio River and two tributary impoundments. Laboratory dilution assays with light and nutrient manipulations indicated light as the dominant factor limiting riverine phytoplankton, with nutrients (silica) becoming limiting during extended low discharge. Reservoir phytoplankton were nutrient limited throughout the growing season, shifting from a spring phosphorus to an autumn nitrogen limitation. Ambient daily growth rates of phytoplankton, ranging from 0.1-1.5 in main stem and 0.2-0.6 in reservoirs, were greatest at the onset of base pool and decreased throughout the growing season as nutrient depletion occurred. Temperature and nutrient assays indicated that bacterioplankton shifted from temperature to carbon limitation as ambient water temperatures rose above 20C. Inorganic nutrients were important, especially in low nutrient environment of reservoirs. Our findings indicate that multiple factors regulate autotrophic and heterotrophic activity and that spatial complexity may arise from differences in water aging and river geomorphology.

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Aquatic Sciences Meeting, Albuquerque 2001

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