Nitrogen bound to humic matter of terrestrial origin - a nitrogen pool for coastal phytoplankton?

Abstract

Micrograzers such as heterotrophic nanoflagellates, ciliates and copepod nauplii were present. Humic substances were isolated from river water. Trace metals, iron and vitamins were added. Phytoplankton biomass and primary production became significantly higher in treatments where nitrate or humic substances were added than in control flasks. Bacterial numbers became significantly higher in the treatments where humic substances were added. Ammonium concentrations became elevated in treatments where nitrate or humic substances were added. Humic substances were probably utilized by bacteria both as a carbon and a nitrogen source. Nitrogen was incorporated in bacteria and later regenerated as inorganic N due to the activity of bacterial grazers and other grazers of higher trophic levels. -from Authors