Aquatic Sciences Meeting, Albuquerque 2001

CS40 Nutrients, Primary Production, and Aquatic Ecosystems

Date: Wednesday, February 14, 2001, Time: 2:45:00 PM

Location: La Cienega

Horgan, M, J, Miami University, Oxford, USA, horganm1@muohio.edu

Vanni, M, J, Miami University, Oxford, USA, vannimj@muohio.edu

Layne, C, D, Dartmouth College, Hanover, USA, craig.d.layne@dartmouth.edu

Renwick, W, H, Miami University, Oxford, USA, renwicwh@muohio.edu

INFLUENCE OF WATERSHED NUTRIENT INPUTS AND NUTRIENT REGENERATION BY OMNIVOROUS FISH ON PHYTOPLANKTON COMMUNITY DYNAMICS IN A RESERVOIR

In Acton Lake, Ohio, gizzard shad (Dorosoma cepedianum) ingest sediments and provide a consistent source of new pelagic nutrients through excretion, while watershed nutrient inputs vary with rainfall through stream discharge. We related discharge records and gizzard shad biomass estimates to phytoplankton community structure and biovolume during the growing season in Acton Lake for an eight year (1992 – 1999) period. Phytoplankton community biovolume follows a unimodal pattern in Acton Lake with a summer cyanobacteria (Oscillatoria, Raphidiopsis) peak. The timing and magnitude of the peak is associated with summer rainfall. The relative abundance of cyanobacteria is related to shad biomass. However, in 1996 gizzard shad biomass was unusually low resulting in drastic differences in the phytoplankton community. In 1996, peak phytoplankton biovolume was much lower than other years and cyanobacteria were never dominant, appearing much later in the year even with high rainfall. The stable effects of gizzard shad may determine one of two general states of the summer phytoplankton community, whereas the variable effects of rainfall modify the timing and magnitude of within-season community dynamics.

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Aquatic Sciences Meeting, Albuquerque 2001

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