VIRAL ABUNDANCE IN AQUATIC SYSTEMS - A COMPARISON BETWEEN MARINE AND FRESH-WATERS

In order to investigate the factors controlling viral abundance, 22 la kes in Quebec were surveyed. We measured viral and bacterial abundance , bacterial production, chlorophyll a, total phosphorus and DOC (disso lved organic carbon) concentrations. Regression models built with thes e data were compared to models based on literature data, which to date have been collected largely from marine sites. Positive empirical rel ationships were found between viral abundance and (1) chlorophyll a co ncentrations, (2) bacterial abundances, (3) bacterial production, and (4) total phosphorus concentration. There was little to no trend in th e virus-to-bacteria ratio with increasing trophy. Analysis of covarian ce revealed significant differences between relations in marine and fr eshwater systems. The virus-to-bacteria ratio was significantly higher in freshwater (mode = 22.5) than marine environments (mode = 2.5), an d there were significantly more bacteria per unit chlorophyll in our f reshwater samples. We suggest that this difference is related to the i ncreased dependence of freshwater bacteria on allochthonous material r elative to marine systems, as well as the increased relative importanc e of photosynthetic cyanobacteria in lakes.