HYDROCARBON INFLUENCE ON DENITRIFICATION IN BIOTURBATED MEDITERRANEANCOASTAL SEDIMENTS

An in situ experiment was carried out in bioturbated Mediterranean coa stal marine sediments (Gulf of Fos) in order to study the influence of hydrocarbons on denitrification after 1, 4 and 6 months. In the absen ce of hydrocarbons in the control sediments, the presence of macrofaun a stimulated denitrification by 160%. This stimulation is induced by s ediment reworking that favours both direct NO3- supply from the water column and the penetration of O-2, which in turn stimulated nitrificat ion, the other source of NO3- in sediment. The presence of hydrocarbon s in the experimental sediments either stimulated or inhibited the den itrification. The denitrification response to the presence of hydrocar bon is dependent on the quantity of matter buried by the macrofauna ac tivity. In small quantities, the organic matter related to hydrocarbon s 120% enhanced the denitrification compared to the controls. On the o ther hand, when buried hydrocarbon concentrations were higher (>100 mg saturated hydrocarbon fraction kg(-1) dry sediment), the denitrificat ion was inhibited. On the basis of the results obtained, a descriptive model of the patterns of denitrification in relation to the presence of macrofauna and the distribution of hydrocarbons in sediments is pro posed.