COMBINED CARBON-ISOTOPE AND C N RATIOS AS INDICATORS OF SOURCE AND FATE OF ORGANIC-MATTER IN A POORLY FLUSHED, TROPICAL ESTUARY - HUNTS BAY, KINGSTON HARBOR, JAMAICA/

Stable carbon isotopes and C/N ratios of particulate organic matter (P OM) in suspended solids, surficial sediments and sediment cores were u sed to define the spatial and temporal variability of POM in a poorly flushed, urbanized, eutrophic tropical estuary (Hunts Bay, Kingston Ha rbour, Jamaica). C/N Variation in the sediment surface POM is a functi on of initial suspended particulate organic matter (SPOM) (or other PO M) type and the alteration of CM ratios in the water column or on the sediment surface. The delta(13)C(SPOM) (- 20 to - 25 parts per thousan d) values suggest that this material is a mixture of: (1) in situ phyt oplankton organic matter; (2) terrestrial river-borne SPOM; (3) terres trial river-borne bottom sediment POM; and (4) sewage. Downcore variat ion in organic carbon content, C/N and delta(13)C is attributed mainly to change in the supply rate and type of organic matter. In the NE of Hunts Bay, down core variation in sedimentology and geochemistry are consistent with a change fi om fully marine to freshwater runoff-domin ated sedimentation with increasing organic matter input from sewage in recent times. Despite large overlaps in the C/N and delta(13)C(org) ' end-members' pollutant POM, in this case sewage, was the only source w hich could account for the amount of POM deposited, the surface sedime nt C/N and delta(13)C(org) values and the trajectories of evolution in C/N and delta(13)C(org) values in cores. The data show that the combi ned delta(13)C and C/N successfully identifies the source, fate and hi story of POM even in a poorly-mixed estuary. (C) 1998 Academic Press L imited.