The very green bottle in the photo to the right is of a water sample collected from a bloom of phytoplankton in western Lake Erie (August 2003). How do you study natural processes occurring in lakes and oceans without disturbing any of the system components? This is the challenge.

Conceptual changes in the distribution of organisms and nutrients across a productivity gradient: 

In low-productivity systems, nutrients are primarily organic and dissolved (small prokaryotic autotrophs and osmotrophic heterotrophs dominate), and autotrophic-heterotrophic coupling (A-H coupling) is strong - that is, prokaryotic heterotrophic respiration is equal to or greater than primary production, with little organic matter remaining for export to the sediments. In eutrophic systems, nutrients are primarily inorganic and particulate (larger eukaryotic autotrophs and phagotrophic metazoans dominate), and A-H coupling is weak, - that is, high export production.