Evidence for tight coupling between active bacteria and particulate organic carbon during seasonal stratification of Lake Michigan

Suspended particulate organic matter (POM) plays a critical role in the pla nktonic ecology of Lake Michigan during seasonal thermal stratification. We show, based on stable isotope and ribosomal RNA (rRNA) data, that the rela tionship between suspended POM and active biomass changes as thermal strati fication persists. Stable isotope data indicated that sources of suspended POM change between July and October, moving from primary production at a de ep chlorophyll layer to recycling-based production in surface waters. Conco mitant change in the distribution of active bacterial and eukaryotic biomas s was observed as indicated by rRNA abundances. Active bacterial and eukary otic biomass were highly correlated throughout the year. However, the corre lation be tween suspended POM and active bacterial biomass varied seasonall y and reflected the transitions in planktonic ecology. Suspended POM from d epths > 60 m was primarily of sedimentary origin. The combined application of stable isotope and rRNA analysis of suspended POM indicated a dynamic re lationship between the bulk POM reservoir and living planktonic biomass.