ENZYMATIC ANALYSIS OF RIVERINE BACTERIOPLANKTON PRODUCTION

Bacterial production is the entry point for detrital macronutrients in to aquatic food webs. Many factors affect productivity, but the hetero geneity of detrital substrates and the diversity of microbial communit ies confound simple relationships between carbon supply and growth. We tried to link the two by analyzing extracellular enzyme activities. W ater samples were collected from three rivers and assayed for bacteria l productivity and the activities of eight enzymes. Production varied among systems, peaking at 644, 170, and 68 mu mol C liter(-1) d(-1) in the Ottawa (Ohio), Maumee (Ohio), and Hudson (New York) Rivers. V-max values were generally correlated with productivity. The mean ratios o f productivity per unit peptidase and esterase activity were similar a mong rivers, whereas carbohydrase and phosphatase ratios varied widely . The data were used to evaluate a model that relates productivity to carbon Bow by using enzyme activities as indicators and assuming an op timum resource allocation relationship among C-, N-, and P-acquiring e nzymes. The data supported the model, but predictive power was low. Ba cterial productivity generally increased with inorganic nutrient avail ability, but high levels of productivity at any specific eutrophic sta te required sources of both saccharides and amino acids.