Particulate beam attenuation coefficient, bacteria abundance and production in marine nearshore waters

摘要

Variability of particulate beam attenuation coefficient at 532 nm (c_p (532)) and microbial planktonic community (heterotrophic bacteria and phytoplankton) was analyzed in coastal waters of Southern California. The goal of this study was to explore heterotrophic bacteria (HB) response (cell abundance, BA, and carbon production, BCP) with respect to different particle characteristics (concentration, size distribution, and composition) related with c_p(532). We observed a fairly complex pattern of HB response and particle dynamics during seven experiments throughout the summer and winter, which reflected variations in c_p(532). The first experiment showed relatively high values of c_p(532), in conjunction with high chlorophyll a concentration (chl) of about 5.4 mg m~(-3). For experiments 2 and 3, a sharp decrease of chl was accompanied by an increased role of detrital particles (non-living matter) as evidenced by increased detrital absorption (a_d). The highest values of particle-attached ( ＞ 1 μm) and free living ( ＜ 1 μm) BA and BCP were observed in experiment 3. These changes in particle assemblage including HB maintained c_p(532) at relatively high level, comparable to that observed when phytoplankton dominated. A significant decrease of c_p(532) was observed in experiment 4 and 5, which coincided with relatively low BA, BCP, and a_d values. In experiment 7, c_p(532) magnitude was comparable to the first experiment and was accompanied by high chl, BA and SPM (suspended particulate matter). Greatest changes in c_p(532) coincided with greatest variations in BA, even though our estimates of the direct contribution of heterotrophic bacteria to c_p(532) for all experiments remained quite low ( ＜ 10%).