Aquatic Sciences Meeting, Albuquerque 2001

CS40 Nutrients, Primary Production, and Aquatic Ecosystems

Date: Wednesday, February 14, 2001, Time: 3:00:00 PM

Location: La Cienega

Aguilar, C, , Great Lakes WATER Institute of the University of Wisconsin-Milwaukee, Milwaukee, USA, aguilar@uwm.edu

Cuhel, R, L, Great Lakes WATER Institute of the University of Wisconsin-Milwaukee, Milwaukee, USA, rcuhel@uwm.edu

SMALL LAKE PHYTOPLANKTON COMMUNITY ECOLOGICAL RESPONSES TO LARGE SCALE ECOSYSTEM PERTURBATIONS

Elkhart Lake, WI, has been studied for 10 years, providing a basis for long term analysis of water quality and phytoplankton community changes. It is a deep lake (35 m) with >70% of its area deeper than 10 m. It was invaded by zebra mussels in 1994. Phytoplankton respond to changes in nutrient availability, grazing, and other ecosystem perturbations including a recent El Nino event. Spatial and temporal photosynthetic parameters as well as chlorophyll a concentration, phytoplankton community, and nutrient changes were measured before, and since the onset of zebra mussel invasion, punctuated by the 1998 El Niño. Areal productivity declined by 25 %. Chl a showed a pronounced spring bloom (12 µg/L) that has decreased consistently since 1996. Due to warmer winters since 1997, ice-out is earlier, leading to diminished spring blooms. Changes in phytoplankton composition show lower diatom abundance, with bigger cells particularly scarce. Increasing abundance of small Synechococcus cells has been observed. Oscillatoria filaments are an important component of the deep chlorophyll maximum in the lake and their abundance has decreased over 90% since 1994.

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Aquatic Sciences Meeting, Albuquerque 2001

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