Intense winter heterotrophic production stimulated by benthic resuspension

Abstract

A major episodic sediment resuspension event (25‐yr high), which was triggered by atmospheric and water column instability in an El Niň;o year, temporarily altered the dynamics of autotrophy and heterotrophy in Lake Michigan. Resuspended sediments, rich in organic and inorganic nutrients, especially phosphorus, stimulated heterotrophic production despite low water temperatures (2ºC or less). During the resuspension event, southern basin winter heterotrophic bacterial productivity was high (64% of summertime productivity), especially along the margins of the lake. The mean bacterial cell size increased in regions where productivity was highest during the resuspension event. Although resuspended sediments stimulated bacterial secondary productivity, they simultaneously decreased water‐column light availability and autotroph biomass. Consequently, heterotrophic bacteria were temporally decoupled from the commonly recognized source of organic matter for bacterial production—photoautotrophy. Variation in the magnitude and frequency of these resuspension events likely influences variation in interannual productivity in this system. Such previously underappreciated, intermittent, and ephemeral benthic‐pelagic exchange events may significantly influence plankton dynamics and biogeochemical cycling in coastal marine and freshwater ecosystems.