Assessment of nitrogen cycling in coastal benthic ecosystems

The economic development of coastal zones and changes in land use (e.g., agricultural drainage) have significantly increased nutrients inputs in coastal water. This increase may lead to eutrophication, a rise of organic matter supply to the ecosystem, altering its natural equilibrium. The most obvious expressions of eutrophication are disproportionate algae blooms, deoxygenation and acidification of water, with far-reaching consequences on the mortality of marine organisms with potential economic interest. To date, more than 400 impacted coastal ecosystems have been reported as an oxygen-poor or dead zone, including the Lower St. Lawrence Estuary. Although biogeochemical processes involved in sedimentary nitrogen cycling (NC) are now well discriminated, little is known about the influence of environmental context on their occurrences and rates. Many parameters influence NC, such as NO3 and O2 concentrations in bottom water, the reactivity of organic matter delivered to sediments as well as the community structure of the 3 ecosystems. Moreover, the ongoing climate change and associated alterations of biodiversity are likely to change the rate and the dominant pathways of NC.