Chemical tracers of sediment organic matter origins in two coastal lagoons

The distribution of chemical tracers in two coastal lagoons was surveyed to assess changes in the contribution of autochthonous and allochthonous (terrestrial and marine) organic matter sources to sediments along a salinity gradient. C:N:P ratios of sediments from both lagoons were closer to the ratios of phytoplankton than to those of terrestrial plants, suggesting that the contribution of terrestrial organic matter was minor. A strong correlation between δ13C and the distance from the seawater entrance was attributed to changing δ13C of DIC sources used by autochthonous phytoplankton, because sediment N:P reflected the dominant phytoplankton inputs in each lagoon. These results suggest that autochthonous primary production controlled organic matter supply to sediments in both lagoons.