Aquatic Sciences Meeting, Albuquerque 2001

SS44 Auto-Heterotrophic Coupling Across Trophic Gradients In Lakes and Oceans (Spatial and Temporal Connections)

Date: Monday, February 12, 2001, Time: 4:15:00 PM

Location: Sandia/Santa Ana

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

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

Waples, J, T, Great Lakes WATER Institute of the University of Wisconsin-Milwaukee, Milwaukee, USA, jwaples@uwm.edu

Klump, J, V, Great Lakes WATER Institute of the University of Wisconsin-Milwaukee, Milwaukee, USA, vklump@uwm.edu

HIGH-FREQUENCY SAMPLING OF PRODUCTIVITY PARAMETERS ALONG A COASTAL DEPTH GRADIENT DURING EARLY SPRING BLOOM CONDITIONS IN LAKE MICHIGAN

Three groups of 8-10 NOAA-EEGLE daily cruises interspersed with visits for other projects provided high-frequency coverage of a nearshore-offshore gradient during April-May 2000. Productivity indices (leucine heterotrophy, photosynthesis-irradiance rate assays, and phosphorus uptake kinetics) were combined with hydrographic and standing crop (biomass and nutrients) parameters to analyze spring bloom development at daily and kilometer scales. Storm events and associated cross-shelf transport punctuated relatively consistent progressions in biological productivity. Algal biomass was greatest offshore. Two 3-8-fold spikes in bacterial production coincided with increases in Pmax and phosphorus kinetics suggestive of upwelling. Both heterotrophic activity and photosynthetic rate trends at more offshore (deeper water) stations lagged inshore activities by one to two days, while high phosphorus uptake potential occurred earlier at offshore stations. Fluctuations in Vmax for phosphorus were associated with storms, followed by continuous increase during extended periods of tranquility in inshore stations. As spring progressed, spatial gradients decreased to near homogeneity, only to reverse in early summer. Nonetheless it appears that biweekly to monthly monitoring provides a fair synopsis of events, if more frequent measurements are made during transitional periods.

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Aquatic Sciences Meeting, Albuquerque 2001

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