Carbohydrate dynamics and contributions to the carbon budget of an organic-rich coastal sediment

Potential hydrolysis rates of three different polysaccharides, pullulan, la minarin, and xylan, were measured in intact sediment cores from Cape Lookou t Eight, North Carolina, in order to constrain the rates at which a fractio n of the high-molecular-weight sedimentary carbon pool may be hydrolyzed to lower molecular weights. Potential hydrolysis rates of pullulan were somew hat higher than those of laminarin and xylan. Highest potential rates were measured in surface sediments; rates at depths of 5-7 and 14-16 cm differed relatively little from one another. Total dissolved carbohydrates, dissolv ed organic carbon (DOC), sulfate, and sulfate reduction rates were also mea sured and compared with data previously collected at Cape Lookout Eight in order to investigate carbohydrate dynamics and establish the relative contr ibution of carbohydrates to the sedimentary carbon budget. Total porewater carbohydrates constitute a disproportionate fraction of DOC, ranging from a maximum of 855 in near-surface intervals to 24% at depths of 14-16 cm. A c omparison of potential hydrolysis rates, dissolved carbohydrate concentrati ons, DOG, and sulfate reduction rates, along with results from a wide range of studies previously conducted at this site suggests that hydrolysis of h igh-molecular-weight polysaccharides can potentially be very rapid relative to carbon remineralization rates. Dissolved porewater carbohydrates form a dynamic pool that is likely turned over on short timescales in Cape Lookou t Bight sediments. Copyright (C) 1999 Elsevier Science Ltd.