New insights into the size distribution of fluorescent dissolved organic matter in estuarine waters

The differences in fluorescence properties of the size fractions of DOM were further evaluated by determining three fluorescence indices: the fluorescence index (f450/f500), the humification index (HIX) and the index of recent autochthonous contribution (BIX). The origin and degree of transformation of DOM can be assessed through the calculation of these indices. We showed that the most humified OM was associated with different size fractions, depending on water sample origin, and was characterised by intermediate MW (higher for fresh than marine water). We also showed that DOM distribution and characteristics differ between the Gironde and Seine estuaries.