Since viral lysis and nanoflagellate grazing differ in their impact on the aquatic food web, it is important to assess the relative importance of both bacterial mortality factors. In this study, an adapted version of the modified dilution method was applied to simultaneously estimate the impact of both virus and nanoflagellate grazing on the mortality of heterotrophic bacteria. A series of experiments was conducted monthly from April to December 2011 and April to October 2012. The growth rates of bacteria we measured ranged from 0.078 h⁻¹ (April 2011) to 0.42 h⁻¹ (September 2011), indicating that temperature can be important in controlling the seasonal variations of bacterial growth. Furthermore, it appeared that seasonal changes in nanoflagellate grazing and viral lysis could account for 34% to 68% and 13% to 138% of the daily removal of bacterial production, respectively. We suggest that nanoflagellate grazing might play a key role in controlling bacterial biomass and might exceed the impact of viral lysis during the summer period (July to August) because of the higher abundance of nanoflagellates at that time. Viral lysis, on the other hand, was identified as the main cause of bacterial mortality between September and December. Based on these findings in this study, the seasonal variations in bacterial abundance we observed can be explained by a scenario in which both growth rates and loss rates (grazing + viral lysis) influence the dynamics of the bacteria community

Since viral lysis and nanoflagellate grazing differ in their impact on the aquatic food web, it is important to assess the relative importance of both bacterial mortality factors. In this study, an adapted version of the modified dilution method was applied to simultaneously estimate the impact of both viral and nanoflagellate grazing on the mortality of heterotrophic bacteria. A series of experiments was conducted monthly from April to December 2011 and April to October 2012. The growth rates of bacteria we measured ranged from 0.078 h⁻¹ (April 2011) to 0.42 h⁻¹ (September 2011), indicating that temperature can be important in controlling the seasonal variations of bacterial growth. Furthermore, it appeared that seasonal changes in nanoflagellate grazing and viral lysis could account for 34% to 68% and 13% to 138% of the daily removal of bacterial production, respectively. We suggest that nanoflagellates grazing might play a key role in controlling bacterial biomass and might exceed the impact of viral lysis during the summer period (July to August), because of the higher abundance of nanoflagellates at that time. Viral lysis, on the other hand, was identified as the main cause of bacterial mortality between September and December. Based on these findings in this study, the seasonal variations in bacterial abundance we observed can be explained by a scenario in which both growth rates and loss rates (grazing + viral lysis) influence the dynamics of the bacteria community

This contrac t involve d 4 man-mon ths of work during the period indicat ed above. The objecti ve was to purchas e and set up a pyrolys is unit for the analysi s of hydroca rbons in sedimen ts from the offshor e contine ntal margins of the United States. Funds were receive d for the project in July, 1977 at which time the pyrolys is unit origina lly request ed was no longer available. After conside rable investi gation, we ordered a Chemica l Data Systems unit for $12,600. This arrived and was put into operatio n in January , 1978. This unit has more flexibi lity in operati ng conditi ons than the one origina lly conside red. We borrowe d a gas chromat ograph and electro nic integra ter from another project and began testing the system with samples from Walvis Bay off southwe st Africa and the Persian Gulf. We also examine d a few samples of known source rocks provide d by oil compani es. 4. RESULTS AND DISCUSS ION: After several weeks of experim entatio n, we finally settled on the flow plan shown in Figure 1. A descrip tion of the procedu re is as follows: DISTRI BUTION OF THIS DOC UOUW T 19 UNI,IMI XEQ I DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government.