Evaluating PAH Biodegradation Relative to Bacterial Carbon Demand in Coastal Ecosystems: Are PAHs Truly Recalcitrant?

Various techniques have been used to evaluate microbial metabolic activity in natural environments. In recent years, tracer additions of radiolabeled substrates coupled with short term, environmentally-relevant incubation experiments have become standard for assessing overall microbial growth rates as well as utilization rates for specific components of the bioavailable carbon pool. Using these techniques, microbial activities have been determined over a wide range of spatial and temporal scales in a variety of estuarine settings, providing valuable insight into carbon cycling in these dynamic systems. In this paper, we focus on patterns of microbial carbon consumption in estuarine sediments and relate these to the utilization of polyaromatic hydrocarbons (PAHs) as a recalcitrant, yet microbially available component of the carbon pool. Drawing on extensive field studies and those published in the literature, we relate microbial metabolic activities to the utilization of specific carbon species, discuss the partitioning of carbon between bacterial production and respiration (utilization efficiency), address the substrate-activity relationship for utilization of recalcitrant organic carbon and identify seasonal effects on the utilization of natural and anthropogenic carbon pools. These studies elucidate the advantages, disadvantages and caveats of relating microbial consumption of bulk labile organic carbon to the utilization of specific components and improve our ability to predict the fate of organic contaminants in estuarine systems. No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services. Thomas J. Boyd, David C. Smith, Jude K. Apple et al. 2