AME 22:1-12 (2000)  -  doi:10.3354/ame022001

ABSTRACT: Bacterial utilization of natural levels of dissolved organic carbon (DOC) was measured in the York River estuary, a sub-estuary of the Chesapeake Bay. This study was undertaken in order to elucidate spatial and temporal changes in bacterial carbon utilization and to evaluate its importance as a pathway for organic matter transformation in estuaries. Multiple pools of DOC were defined based on decomposition kinetics. The first pool (G₁) made up a mean of 2.8% of total DOC and had turnover times of ≤5 d. The second pool (G₂) comprised an average of 4.9% of total DOC and had turnover times of ~1 mo. Our data indicate that although the total amount of DOC utilized was low, there was a continual supply of both the G₁ and G₂ fractions within the estuary. Bacterial growth efficiency on the G₁ pool averaged 28%. The production of CO₂ through bacterial respiration of the G₁ pool could not balance CO₂ evasion for the majority of the estuary. Bacterial DOC degradation in the York River estuary was limited by temperature for the majority of the year. This temperature constraint coupled with relatively short hydrologic residence times resulted in the export of labile DOC from the estuary prior to complete bacterial decomposition. We estimate that ~10% of the riverine DOC exported annually from estuaries to the mid-Atlantic Bight (MAB) is a labile fraction of DOC that is not utilized within the estuaries due to temperature constraints on estuarine bacteria. This DOC is not inherently recalcitrant and is an allochthonous source of labile DOC for the coastal Mid-Atlantic Ocean.

KEY WORDS: Dissolved organic carbon (DOC) · Heterotrophy · Mid-Atlantic Bight · Carbon export · Chesapeake Bay · York River