We measured tributary inputs, algal nutrient demand and excretion rates of consumers (gizzard shad and zooplankton) at a eutrophic river impoundment. During two summers with contrasting flow regimes, tributary inputs accounted for 38% (1998) and 3% (1999) of algal N demand and 95% (1998) and 17% (1999) of algal P demand. Gizzard shad contributions averaged 14% and 20% of algal demand for N whereas P contributions were 31% and 58% (1998, 1999; respectively). Zooplankton recycling accounted for a comparable fraction of algal P demand (47%) but a larger fraction of N demand (43%) because their excretia were N rich (N:P = 13:1) compared to fish (7:1). Nutrient release by one of the consumers (gizzard shad) was compared with tributary loading over a nine-year period to assess inter-annual variation in their relative importance. Historical records of inflow chemistry, discharge and gizzard shad biomass showed that variation in tributary inputs was the primary determinant of seasonal and inter-annual variation in nutrient loading. Consumer-derived nutrients were important in late-summer and during years when tributary inputs were low. We propose a conceptual model in which primary production is regulated by external nutrient loading and consumer recycling acts to stabilize and sustain production during periods of diminished external inputs.
|Original language||English (US)|
|Number of pages||15|
|State||Published - 2004|
Bibliographical noteFunding Information:
We are grateful to W. Pearson for assistance with electroshocking, G. Miller (KY Division of Water) for providing Salt River nutrient data, C. Prather and C. Mitchell (KY Department of Fish and Wildlife Resources) for Taylorsville Lake gizzard shad biomass estimates and Rich Schultz for assistance with laboratory analyses. The manuscript benefited from reviews by R. Drenner, D. Hamilton and M. Schaus. This research was supported in part by the University of Louisville’s Center for Watershed Research. Work on the manuscript was completed while P.A.B. was a Gledden Fellow at the Centre for Water Research, University of Western Australia.
Copyright 2012 Elsevier B.V., All rights reserved.
- Gizzard shad