Vitamin B 12 production and depletion in a naturally occurring eutrophic lake.

The distribution of vitamin B(12) within Upper Klamath Lake was surveyed at approximately monthly intervals during a period from September 1968 to November 1969. High concentrations (up to 1.8 mug/g of dry sediment) characteristically occurred at the water-sediment interface, with a sharp decline below this area. A heavy bloom of Aphanizomenon flos-aquae occurred from the latter part of May through October 1969. B(12) concentrations of the uppermost sediments, from all but one sampling site, increased gradually through the bloom, followed by a drastic increase during the die-off period. B(12) is probably not a limiting factor for primary productivity, since sufficient levels of this vitamin were found to occur throughout the year. Of 42 cultures isolated from Upper Klamath Lake water and sediments, 20 were found capable of producing 50 pg or more of B(12)/ml of medium. Phytoplankton samples were found to contain up to 5 mug of B(12)/g of dry material. Degradation of B(12) occurred in sterilized as well as fresh sediment samples.