To characterize the dissolved organic matter (DOM) in tropical estuarine, optical properties of coloured and fluorescent matter of porewater were measured in New-Caledonia coastal ecosystem. Surface sediment pore waters were analysed in four coastal area under different ultramafic influences, strongly (VKP, South of Nouméa), few (Dumbéa) to not impacted (Ouegoa) by mining activities. Five stations in triplicate were sampled. Absorption coefficients were low in the two stations under ultramafic soil and remarkably high in Dumbéa and Ouegoa. Spectral slope and SR ratio indicators revealed high molecular weight molecules at the Ouegoa and Dumbéa and low in VKP. Fluorescence spectroscopy and parallel factor (PARAFAC) modeling indicate that pore water is mostly composed of 4 components, which combine both autochthonous (Humic-like-mangrove C1, Tryptophane-like C2) and allochthonous materials (Fulvic-acid C3, terrestrial-humic-like C4) in the whole sites. C1 was found in abundance at the Ouegoa and VKP which are strongly surrounded by mangroves. C2 had a homogeneous distribution along the sites with a higher concentration at VKP. The pseudo-concentration of compounds C3 and C4, were high for the Ouegoa and Dumbéa sites. The strong site effect could be explained by three main factors, presence of mangrove, size of the catchment areas, and geological conditions.