Harris, P; Fichez, R; Fernandez, JM; Golterman, H; Badie, C
During the past century, the sediment deposition rate has been assessed by measuring excess super(210)Pb activity in a sediment core sampled in the harbour area of the Papeete Lagoon (Tahiti, French Polynesia). Dated sediment samples were analysed following a sequential extraction method to quantify five sedimentary phosphorus pools: loosely sorbed or exchangeable phosphorus, ferric iron-bound phosphorus, authigenic calcium carbonate associated phosphorus, detrital apatite and detritic inorganic phosphorus, and organic phosphorus. Results from sediment dating showed the core to cover the period from 1865 to 1995, with a sharp change around 1957 corresponding to a doubling in sediment deposition rates. From the bottom to the top of the core, concentrations decreased for authigenic calcium carbonate-associated phosphorus, were almost constant for exchangeable phosphorus, and increased significantly for iron-bound phosphorus, detritic inorganic phosphorus and organic phosphorus. As a consequence, the calculated phosphorus total accumulation rate was multiplied by four from top to bottom. Those trends were related to modifications in the relative importance of the five phosphorus reservoirs, especially for organic phosphorus, which contribution increased to 30% of total phosphorus in recent sediments. From the sequential extraction approach it is possible to estimate that phosphorus with a terrestrial origin represented 54% of total phosphorus in recent sediment, while it only represented 30% at the beginning of the century. Present particulate phosphorus inputs were also assessed from a sediment trap approach and a budget of phosphorus burial efficiency is proposed.Original Abstract: Le taux de sedimentation a ete evalue par la mesure de l'activite du super(210)Pb en exces dans une carotte de sediment prelevee dans la zone portuaire du lagon de Papeete (Tahiti, Polynesie francaise). Les echantillons de sediments dates ont ete soumis a une extraction sequentielle afin de determiner cinq fractions sedimentaires de phosphore: faiblement adsorbe ou echangeable, associe au fer ferrique, lie au carbonate de calcium authigene, detritique et organique. Les resultats de dataion montrent que la carotte couvre la periode 1865-1996, avec un changement majeur vers 1957 correspondant a un doublement du taux de sedimentation. Entre la base et le haut de la carotte, les concentrations diminuent pour le phosphore lie au carbonate de sodium, restent constantes pour le phosphore faiblement echangeable, et augmentent pour le phosphore associe au fer ferrique, le phosphore detritique et organique. Les augmentations conjointes du taux de sedimentation et de la concentration en phosphore ont pour consequence de multiplier par quatre le taux d'accumulation de phosphore total. Ces tendances correspondent a des modifications importantes de la contribution relative de chaque fraction, en particulier pour le phosphore organique qui represente plus de 30% du phosphore total dans les sediments recents. Sur la base des extractions sequentielles, il est possible d'estimer que le phosphore d'origine terrestre represente 54% du phosphore total dans les sediments recents, contre seulement 30% au debut du siecle. Le depot actuel de phosphore particulaire a egalement ete evalue au moyen de pieges a particules, et un bilan de la diagenese du phosphore est presente.
ISE, Pacific, French Polynesia, Society Is., Iles du Vent, Tahiti, Papeete Lagoon; Calcium carbonates; Phosphorus; Suspended particulate matter; Sediment traps; Geochronometry; Core analysis; Sediment samples; Organic phosphorus; Nonpoint Pollution Sources; Pollution Load; Sediment Contamination; Nutrients; Harbors; Lead Radioisotopes; French Polynesia; 2001)