Extensive measurements of material concentrahons and water velocities at a transect across North Inlet, South C a r o h a (USA) allowed the estimation of net material and water fluxes. Sampling periods were distnbuted seasonally and according to tidal height. Statistical and hydrodynanlic models were used to develop flux estimates for specific tidal cycles. There was a net discharge of water from the marsh-estuanne system to the Atlantic Ocean which is attributed to rainfall runoff and freshwater input from an adjacent estuary. All constitutents were exported seasonally and annually from the system -except total semments, imported during fall and winter, and chlorophyll a and zooplankton, imported in summer and fall. ATP, bird biomass and macrodetritus were exported throughout the year. Export of carbon, nitrogen and phosphorus from North Inlet is high compared to other systems studied to date. Large net fluxes of DOC during winter imply coupling with the uplands. The high rates of export of ammonium and orthophosphate along with detritus and microorganisms suggest major decomposition processes are taking place within the system. Export of ammonium and orthophosphate to the coastal ocean also suggest a feedback loop with phytoplankton utilizing these materials, then in turn phytoplankton are imported into the estuary where they are consumed and remineralized. Previous explanations of outwehng and tidal transport are examined and found to be individually lacking. It is proposed that any comprehensive explanahon of the magnitude and direction of transport must include a physical explanation of water motion and the biological and physical mechanisms by which materials are added or removed from tidal waters. A comprehensive explanation of outwelling in North Inlet IS proposed which describes this system as an ebb-dominated, bar-built estuary with good flow connection to the sea and with some freshwater input. It is also a fertile system with high productivity providing materials for export to the coastal ocean and utilization of other imported materials.

ABSTRACT. Simultaneous annual fluxes of carbon, nitrogen and phosphorus were studied on an intertidal oyster reef In Bly Creek, South Carolina, USA. We observed material fluxes every 10.2 d (33 tidal cycles) over 1 yr and used regression estimation to compute annual estimates. The reef appeared to take up 1200 g C m-' yr-' from tidal waters. It had an estimated net removal of 189 g N m-' yr-' from the water column with the majority of this nitrogen released as ammonium (125 g N m-' y~' ) , and a net uptake of 98 g P m-2 yr-l. As indicated by the C : N : P ratio of the fluxes, proportionally more phosphorus was taken up than would be expected. Oyster reefs process carbon, nitrogen und phosphorus at high rates and appear to function as retention mechanisms for nitrogen and phosphorus in estuaries.

A synthesis of a comprehensive annual study of material processing in the Bly Creek marsh-estuarine basln is described. The project design provides statistical estimates of material fluxes for the water column, salt marsh, and oyster reef subsystems. Fluxes from a freshwater stream, groundwater, and rain are also presented Material processing by the Bly Creek marsh-estuarine basin is constituent-and subsystem-specific Inflows of material via rain, streamwater. and groundwater are small and relatively unin~portant compared to tidal fluxes. The salt marsh dominates the basin in aerial extent and in terms of net material fluxes. Most constituents exhibit significant net annual import to the salt marsh. Only DON is exported from the marsh and from the basin at significant levels. The salt marsh appears to recycle most of the nitrogen and phosphorus needed for marsh grass primary production. Sufficient inorganic particulate material is imported to allow the salt marsh to maintain its elevation with respect to ongoing sea-level rise. As a result of metabolic processes, the oyster reef imports particulate materials and releases dissolved nutrients. The reef is a significant consumer of chl a and produces enough dissolved inorganic nitrogen and phosphorus to support water column primary production The N:P ratio of Bly Creek dissolved inorganic nutrients is lower than that of North Inlet or ocean waters and implies nitrogen conservation or mobilization of particulate phosphorus into orthophosphate. In contrast to human-impacted coastal systems, this prist~ne basin reduces the N : P rat10 as water passes through it Differences in the N:P ratio are probably the result of DON export, denitnfication, and phosphorus import by the basin

Exchange of organic carbon (DOC and POC) between a euhaline vegetated marsh and an adjacent tidal creek (North Inlet, South Carolina) was studled on 40 tidal cycles between 15 Apr 1983 and 19 Jun 1984. A flume was utilized to evaluate the role of the vegetated marsh in processing carbon during tidal inundation and a drainage weir was used to measure export from the marsh via runoff and seepage during low tide exposure (including storm events). Mean flood water DOC concentrations varied seasonally from 3.1 to 18.6 ppm. Maximum concentrations were observed in late w n t e r and early spring, and were associated with freshwater discharge from the adjacent forest. There was a stahstically insignificant (a = 0.05) DOC import to the vegetated marsh during tidal inundation of 2.9 g C m-' yr-l. Mean flood water POC concentrations varied seasonally between 0.7 and 4.6 ppm with the highest values observed during the summer The vegetated marsh was a sink for POC during tidal inundation except when storm events occurred on the ebb tide. There was a statistically significant (a = 0.05) import of POC to the vegetated marsh of 83.3 g C m-2 yr-' with the largest removal rate observed when the tidal water resided on the low marsh (tall Spartina alterniflora) Exports of DOC and POC from the marsh via runoff and seepage d u r~n g low tide exposure (including rain events) were 36.2 g C m-' yr-l and 30.6 g C m-' yr-' The annual net exchange (inports-exports) of carbon between the marsh and the adjacent tidal creek suggests thls system is a sink for POC and a source for DOC, the total organic carbon exchange being negligible. This study implies the vegetated marsh may not be the source of carbon which was found to outwell from this and other marsh-estuarine systems.

Tidal fluctuations and transports of particulate organlc carbon (POC) were investigated at 3 marsh creeks (near Georgetown, South Carolina, USA) comprising the major transfer points between the North Inlet Marsh and the adjoining aquatic ecosystems. Two creeks, Town and North Jones, form the inlet mouth and are the only marsh-ocean exchange points. The third creek, South Jones, connects to a brackish water embayment. The creeks were simultaneously sampled every 1.5 h for 50 consecutive hours during neap tides (4 tldal cycles) and 50 consecutive hours during corresponding spring tides of each season. At the inlet. POC concentrations fluctuated in-phase with the tide during the winter and out-of-phase with the tide during the summer Combinations of in-phase and out-of-phase patterns occurred in spring and fall. The fluctuations at the brackish water location were irregular POC concentrations were similar in each season with values averaging about 1.4 g mP3. Net transports varied from tidal cycle to tidal cycle with regard to direction of transport (import or export) and magnitude, ranging from a net import of 240 g POC S-' to a net export of 228 g POC S-'. Annual budgets revealed Town Creek to export POC at a rate of 2.6 ? 0.5 X log g yr-'; North Jones Creek imported POC at a rate of 3.8 ? 0.7 X 10a g yr-l; and South Jones Creek exported POC at a rate of 5.5 k 0.8 X 108 g yr-' The 3222 ha North Inlet marsh serves as a source of POC to the ocean at a rate of 87 2 16 g of POC per m2 yr-l.