Sources of Organic Matter for Reservoir Fish Production: A Trophic-Dynamics Analysis

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Abstract
A trophic-dynamics approach was used to examine the relationships of phytoplankton production, other autochthonous primary producers, and allochthonous organic matter to the organic carbon supply necessary to support the fish community production in 17 southeastern and midwestern U.S. reservoirs. Fish community carbon requirements were estimated using average efficiencies of 10 and 15% per trophic transfer to bracket the range of efficiencies that probably occur in reservoir food webs. At 10% efficiency, most of the reservoir food webs considered appeared to be supplemented significantly by allochthonous organic matter. At 15% efficiency, phytoplankton production accounted for the organic carbon required for fish production in 10 of the 17 reservoirs. In this case, supplementary organic carbon sources were invoked to meet fish production requirements in the remaining seven reservoirs. Our results suggest that, depending on the actual food web efficiencies, autochthonous primary production can often account for the organic carbon supply required for reservoir fish production and that the importance of allochthonous organic matter to reservoir biological productivity may have been previously overemphasized. Although both the morphoedaphic index (MEI) and phytoplankton productivity were strongly correlated with reservoir fish production, a simple relationship does not appear to exist between the MEI and phytoplankton productivity, probably because of the complex aggregate nature of the MEI descriptor.