Sedimentation of particulate matter in the south-west lagoon of New Caledonia: Spatial and temporal patterns

Suspended and sedimented particulate materials were assessed monthly at five sites on the south-west lagoon of New Caledonia, from May 1986 to April 1987. Sedimentation of particulate matter was measured using sediment traps for 24 h. Resuspension, which accounted for more than 80% of the total sedimentation, was distinguished to calculate net sedimentation values. The mean net sedimentation rate for the lagoon varied according to the site from 0.481 to 1.157 g C m−2 day−1 with a general mean value of 0.756 g C m−2 day−1. An increasing gradient from the reef to the shore stations was observed for both suspended and sedimented particles. The standing stocks and the fluxes of suspended particles were maximal in February, during the warm season associated with maximal rainfall, and minimal in August. The high C/N ratio in sedimented material (26) compared to suspended particles (11) indicated that organic matter degradation had occurred preferentially in the water column. The mean particulate organic carbon flux was about twice the lagoon pelagic primary production; sedimented plant material only accounted for a small part of the organic carbon flux. The major source of sedimented organic carbon was therefore allochthonous and derived both from the reef and the shore. The latter seemed to predominate. Relative uncoupling between benthos and pelagos is suggested.