ORGANIC MATTER IN ANOXIC PORE WATER FROM GREAT BAY, NEW HAMPSHIRE

Shallow and deep cores were obtained from a number of sampling sites within the Great Bay Estuary, and pore water obtained by high speed centrifugation of the samples. All sample handling and processing was conducted under oxygen free conditions. It was shown that failure to exclude oxygen from anoxic sediment samples results in changes in both the amounts and nature of the organic matter in the pore water. In addition, the loss of iron, phosphate and titration alkalinity from the pore water of oxygen exposed samples was reaffirmed. From measured depth profiles of sulfate, ammonia and phosphate in Great Bay pore waters, rates of sulphate reduction and ammonia and phosphate production were calculated using a kinetic model (Berner, 1980). Calculated values of sulphate reduction at two sites in Great Bay agreed quite well with measured rates (Hines, 1981). Dissolved organic carbon (DOC), in Great Bay pore waters was shown to vary laterally, vertically and seasonally. In surface sediments, the seasonal variation in DOC was coupled to seasonal changes in microbial activities and the bioturbation of marine benthic organisms. In deeper sediments, the seasonal changes in DOC were hypothesized to be coupled to a temperature induce adsorption/desorption mechanism. The molecular size of pore water organic matter was observed to be relatively large, with the dominant molecular weight range in many cores between 50,000 and 1,000. A method for the fractionation of pore water organic matter using reversed phase high pressure liquid chromatography was developed, and the usefullness of this technique for qualitative studies of this material was demonstrated