Respiration and the carbon-to-nitrogen ratio of a phytoplankton bloom

During the 1995 spring bloom in Bedford Basin, Nova Scotia, Canada, dissolved organic carbon (DOC) and nitrogen (DON) in surface waters were separated by cross-flow ultrafiltration into low molecular weight and colloidal size fractions. In order to obtain realistic estimates of the total standing stock of organic carbon and nitrogen during the bloom, measurements of DOC and DON in the ultrafiltered size fractions were combined with particulate organic carbon (POC) and nitrogen (PON) measurements. The combined C:N ratio of the total standing stock of organic matter (TOM) increased from near-Redfield values to a maximum during the early bloom as carbon-rich diatom exudates accumulated in the dissolved (primarily the colloidal) size fraction. Even though the colloidal exudates were only a small fraction (