| Summary |
The distribution, sources and sinks of organic carbon were studied in the Pamlico River Estuary during 1975-1977. The main source of organic carbon was from phytoplankton productivity, which, together with other sources from within the estuary, provided 64% of the organic carbon inputs. The remaining 36% was mainly from tributaries. Organic carbon losses (sinks) were 80% as water column respiration and 20% as outflow. Sedimentation and benthic respiration are undetermined losses. Total organic carbon (TOC) varied seasonally with the highest levels occurring during the summer months when flow rates were low. Also, TOC normally displayed a gradient with the highest levels consistently in the upper reaches near Washington, N.C. Approximately 79% of the TOC in the estuary consisted of dissolved organic carbon (DOC) which accounted for most of the seasonal variations in TOC. Levels of particulate organic carbon (POC) were fairly constant throughout the year with the exception of sporatic increases in phytoplankton biomass. The dry and calm summers of 1976 and 1977 provided an excellent opportunity to study deoxygenation in the estuary. The normally sluggish circulation of the Pamlico River depends primarily on wind stress for mixing, and both wind speed and direction are important in determining the extent of mixing. Deoxygenation was observed spanning the entire length of the estuary and well into Pamlico Sound, and has even been observed during the winter in association with an intense algal bloom. Deoxygenation is normally limited to the deeper mid-channel regions of the estuary except in the upper reaches where it may extend throughout much of the water column and into relatively shallow areas in extreme cases. The largest input of organic carbon to the estuary is from productivity of phytoplankton which is more readily available to organisms utilizing oxygen than the less abundant and more refractory inputs from tributaries. Because of this, the regulation of inorganic nutrient sources (especially nitrogen) is more important for controlling increases in organic loading than are tributary inputs of organic carbon. Although deoxygenation depends on physical conditions which result in stratification of the water column, episodes of oxygen depletion may be more severe and occur more frequently if conditions become more favorable for higher phytoplankton production. |
