CHEMICAL-COMPOSITION OF BIODEGRADABLE DISSOLVED ORGANIC-MATTER IN STREAMWATER

Plug-flow biofilm reactors colonized by microorganisms in streamwater were used to measure the concentration and composition of biodegradabl e dissolved organic C (BDOC) in White Clay Creek. During the 4-month s tudy period, DOC ranged from 0.8 to 10.4 mg C liter(-1) and was, on av erage, composed of 75% humic substances, 13% carbohydrates, 2% amino a cids, and 18% > 100 kDa. The carbohydrates were predominantly polysacc harides, nearly all amino acids were present in the combined form, and most carbohydrates and amino acids were humic bound. BDOC ranged from 0.2 to 2.9 mg C liter(-1), averaged 25% of the DOG, and was composed of 75% humic substances, 30% carbohydrates, 4% amino acids, and 39% DO C > 100 kDa. The carbohydrate portion of the BDOC was primarily polysa ccharide or humic bound. Similarly, the amino acid portion of the BDOC was overwhelmingly present in the combined form and primarily humic b ound. Glycine and aspartic acid were the dominant amino acids in White Clay Creek DOC and in the BDOC pool. Our data broaden the perspective on substrates important to microbial metabolism and energy Bow in str eams and provide the first direct evidence that humic substances, alth ough largely refractory, are an important component of streamwater BDO C.