DISSOLVED AND PARTICULATE ORGANIC-CARBON IN CHESAPEAKE BAY

We measured dissolved and particulate organic carbon (DOC and POC) in samples collected along 13 transects of the salinity gradient of Chesa peake Bay. Riverine DOC and POC end-members averaged 232 +/- 19 mu M a nd 151 +/- 53 mu M, respectively, and coastal DOC and POC end-members averaged 172 +/- 19 mu M and 43 +/- 6 mu M, respectively. Within the c hlorophyll maximum, POC accumulated to concentrations 50-150 mu M abov e those expected from conservative mixing and it was significantly cor related with chlorophyll a, indicating phytoplankton origin. POC accum ulated primarily in bottom waters in spring, and primarily in surface waters in summer. Net DOC accumulation (60-120 mu M) was observed with in and downstream of the chlorophyll maximum, primarily during spring and summer in both surface and bottom waters, and it also appeared to be derived from phytoplankton. In the turbidity maximum, there were al so net decreases in chlorophyll a (-3 mu g l(-1) to -22 mu g l(-1)) an d POC concentrations (-2 mu M to -89 mu M) and transient DOC increases (9-88 mu M), primarily in summer. These occurred as freshwater plankt on blooms mixed with turbid, low salinity seawater, and we attribute t he observed POC and DOC changes to lysis and sedimentation of freshwat er plankton. DOC accumulation in both regions of Chesapeake Bay was es timated to be greater than atmospheric or terrestrial organic carbon i nputs and was equivalent to similar to 10% of estuarine primary produc tion.