SEASONAL CYCLING OF PUTRESCINE AND AMINO-ACIDS IN RELATION TO BIOLOGICAL PRODUCTION IN A STRATIFIED COASTAL SALT POND

Seasonal cycles of concentrations and microbial uptake of dissolved fr ee amino acids and the polyamine, putrescine, were followed during sum mer stratification of a coastal salt pond. Stratification began in May and was clearly seen in profiles of temperature, salinity, pH and alk alinity. Primary production exhibited a mid-August maximum and the O-2 -H2S interface shoaled at that time. POC and phytopigments roughly fol lowed the pattern of primary production. Cycling of putresince, like t he amino acids, was strongly influenced by primary production and micr obial decomposition. Putrescine concentration profiles appeared to fol low the pattern of primary production more closely, while amino acids appeared to follow the pattern of microbial production. The absence of production of putrescine during the decomposition of dissolved omithi ne and the correlation of putrescine concentration with primary produc tion suggest a direct source from algae in the water column. Microbial uptake of amino acids and putrescine together accounted for 60-90% of the bacterial C production measured in oxic waters and almost 300% of that measured in the anoxic bottom layer. Since other organic carbon and nitrogen compounds are also being taken up, these data suggest tha t tracer uptake methods as we used them may overestimate the true micr obial uptake rates, or release of other organic compounds by microbes occurs at the same time. Further work on carbon and nitrogen budgets i s needed to resolve the apparent imbalance between organic C and N inc orporation and bacterial production.