IAEA-SM-354/148P XA9951395 ALIPHATIC HYDROCARBONS AND 1 JOPANES AS BI.OMARKRRS OF THE PAST 120 YKARS SED1MBNT INPUTS IN A CORAL RBKF LAGOON (, FRENCH )

P,A. Harris Centre ORSTOM dc Tahiti, BP 529 Papeete, Tahiti, .

Pichez R., Fernandez J.-M. Centre ORSTOM tie Noumea, BP A5 Noumea Cedex New-Caledonia.

Saliot A. Laboratoire dc Physiques et Cbimie Marines, Universitc* Pierre ct Marie Curie, URA CNRS 2076, Tour 24, 4 place Jussieu, 75252 Paris Cedex 05, .

The study of sedimentary non-aromatic hydrocarbons (NAH) has been frequently used to determine of natural organic matter inputs, since a large fraction of these compounds derives from terrestrial and marine biological sources [J]. In addition, bopunes have been largely associated with petrochemical contamination [2]. Sediment cores were sampled in four sites in the coral reef lagoon surrounding the city of Papeete, Tahiti . French Polynesia. Sediment cores were dated by mean of 2l0Pb activity counting in order lo reconstruct past trends in environmental changes. This paper focuses on the historical evolution of NAH and hopanes in a sediment core sampled in the harbour which yielded results over a period covering J20 years, Geochronoly results evidenced a large inoease in sedimentation rates from 033 g.cm"V to 133 g.cniV «ncc 1967 ±4 y 13,4]. Total n-alkanes with carbon chain lenghts from CH to C35 increased from 0,4 ng.g'1 in the boUom of the core (dated 1880) to 1,7 u.gg' in the lop of the core (fig. J), When considering carbon chain number il is possible to distinguish between marine and terrestrial inputs. Marine contribution (£C]6-CM) stayed approximately constant over the whole 120 y considered period, concentrations ranging from 0.02 to 0.09 ng.g . Contribution from terrestrial higher plant n-alkanes was assessed by the sum of long and odd numbered carbon chains (Zodd C27-C(;<). Concentrations increased from 0.1 (jg.g"' in the bottom of Uie core- lo 0.65 Ug.g"1 in recent sediment layers.

^f- Hopanes 01, £ n-alkanes 3 o 1 S

192S J900 1950 1975 2000 Age of sediments

Fig. 1 : n-alkhnc et hopane concentrations relative to sediment age in Papeete Harbour,

Hopane compounds ranged from Cn to C,,s and only 17a(H), 2ip(H) configuration was found in our samples. The presence of 22S and 22R epimers w»s detected in (he C31-C35 J7a(H), 21p(H) extended hopanes. Homohopancs index, determined by the ratio between the two epimers (22S/ (22S + 22R), ranged from 0.50 to 0.65. These values were close to the equilibrium value at maturity (0.6, 1.5]). Totul hopanes concentrations increased from 0J5 to 1.8 fJg.g0 from the beginning to the end of the century (fig 1).

505 Concentrations in terrestrial n-alkanes and hopancs showed a very high correlation (fig. 2) suggesting that hopanc compounds derived from terrestrial (natural) inputs. This point was confirmed by the good correlation with iron or manganese derived from terrestrial inputs [6]. Enrichment factors for both classes of compounds from 1880 to present days were very similar in the sediment core (between 20-25). The flux of terrestrial n-alkanes in recent sediment layers (deposited during the past decades) was 0.85 (jg.on^.y1, while the flux of hopanes was about 3 times greater during the same time (2,45 ug.crn'2.y"'). These results are consistent with previous data showing an increased in terrestrial inputs since. J967 f7].

2 -i

Oil Ml

a cd o K

n-C^-C^alkancs (ng.g"')

Fig. 2 ; relationship between 11-C27-C33 alkane and hopane concentrations from the sediment core in Papeete harbour.

REFERENCES

11] Bouloubussi I. and A. Saliot (1993). Investigation of anthropogenic and natural organic inputs in cstunrinc .sediments using hydrocarbon markers (NAH, LAB, PAH). Occanologlca Acta, 16, 2, 145-161. 12] Peters K..E. and Moldowan J.M. (1993). The biomarker guide : Interpreting molecular fossils in petroleum and ancient sediments, Prentice-Hall, Englewwod Cliffs, NJ, 363 pp. |3] Fjchcz R., P. Harris, R. Jouen. Badie C, J.-M. Pernamicz, 1997. Sedimentary records of human induced environmental changes in the Tahiti lagoon. Proc. 8lh Jnl Coral Reef Sym, 2, 1833-1838. [4] Harris P. A., R. Ficht/., H. L. Oohcrinan and C. Badie (1998) Eutrophication process in the Papeete lagoon (Tahiti, French Polynesia): Using sediment gcochronology to reconstruct phosphorus cycling evolution during the past century. Oceanulogicn Ada, submitted. [5] Mackenzie A.S., R.L. Patience, J.R, Maxwell, M. vandenbroucke and D. Durand (1980). Molecular parameters ol' maturation in the Toarcinn shales, Paris Basin, France, i : Changes in the configurations of acyclic isoprcnoid alkanes, slwanos and trilcrpnncs. Gcochim. Csomochim. Acta, 44, 1709-1720. [6] Harris P. A. (199ft). Modification des caraclemliques chimiques du lagon dc Papeete lifies a I'aciivitd liumaine : int6r£t des traceurs eddimentaires gdochimiqucs ct biogdochimicjucs dans la rcconstilulinn de I'dvolulion tic l'environnemenl au cpurgidu XX' sieclc Ph. D. thesis, Univcrsiid Frnncaisc du Pacifique, in press, [7] Harm P.A.. R. l'ichez,, .T.-M. I'crnandc/. and C. Baiiie (1998). Heavy metals profiles hubied sediment cores Irom the lagoon of Pnpecsl (l'iihiii, French Polynesia): influence of mixing phenomenn. (Submitted to Jntcrtiatioal Symposium <;f Maiiue Pollution. Monaco, 5-9 ocl J998).

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