The urbanization of the coast is generating significant environmental issues, including increasing nutrient runoff that promotes eutrophication and hypoxic conditions in estuaries. At the same time, the excessive input of nutrients is also responsible for an increase acidification of coastal waters, as denitrification in sediments typically generates acidity. This project will attempt to quantify the impact of nutrient addition to coastal marine sediments and predict its effect on biogeochemical processes, including alkalinity and CO2 release from the sediment which either buffer or acidify the overlying waters. Mesocosms with circulating overlying seawater to maintain suboxic conditions in the sediments will be established in the laboratory. These mesocosms will be systematically manipulated to investigate the effect of increasing inputs of nutrients in overlying waters on sediment diagenesis. Depth profiles of the main redox species will be obtained over time in the sediments with voltammetric microelectrodes, and overlying water alkalinity, dissolved inorganic carbon, and pH will be monitored over time. Microbial abundance and diversity, as well as the activity of nitrifiers and denitrifiers will be determined using molecular techniques at the end of each experiment. The diagenetic code MATSEDLAB will be used to reproduce the evolution of early diagenetic processes in the mesocosms to calculate the resulting flux of alkalinity or acidity to the overlying waters.