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

2007 
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 (ad). 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 ad 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%).
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