During the European's FP7, 19 European research projects focused on eutrophication, have been funded over 377 of the environment section, showing the relevance of the topic, which was recently listed as one of the most severe threat to human water security and biodiversity causing severe damages to the economies. Despite mitigation measures reducing the nutrients loads, harmful algal blooms still occur, possibly due to changes in fertilizer uses. Indeed organic matter (OM) and particularly N-containing organic matter like urea which is the most widely used fertilizer, is an important source of N for a large variety of marine phytoplankton, ranking often in importance greater than inorganic N like nitrate. Despite its lower concentration compared to nitrate, organic N (ON), a fraction of organic matter, could sustain the primary productivity due to its very fast regeneration by micro-heterotrophs. Hence, the DYNAMITE project will focus on the agricultural impact on the biogeochemical cycle of organic matter from land to ocean given that: (i) agricultural activities are obviously one of the major environmental pressures, (ii) the composition of organic matter is still poorly characterized and (iii) its behaviour in aquatic system is far to be understood. Thus DYNAMITE requires the following tasks: (1) to characterize the fine composition of riverine and estuarine OM considering the whole OM by transferring a water treatment technology in the field of marine chemistry, (2) to quantify the spatial and temporal release of OM from agricultural activities and relate the OM changes to specific land-use, (3) and to determine the dynamics of OM through temperate estuaries under strong agricultural activities and quantify the flux of OM and ON from the river to the ocean. DYNAMITE will be focused on Brittany region since in 2006 it was classified in Europe as a sensitive area to eutrophication with the highest threat to human water security and biodiversity.