Coastal Nitrogen Cycling – Biogeochemical Processes and the Impacts of Human Activities and Climate Change

In coastal zones, intense organic matter cycling occurs due to land proximity, water – sediment interaction, and exchange processes with the open ocean. Nitrogen sources include atmospheric deposition, submarine groundwater discharge, wetlands, rivers/estuaries and the open ocean. All sources are highly impacted by human activities, such as food production. The nitrogen cycle consists of mostly microbial processes, including nitrogen fixation, nitrification, denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA), which interact in different ways depending on environmental factors, in particular, the availability of oxygen. At present, human-induced production of reactive nitrogen globally equals the natural one, and a large part of it is introduced into the coastal ocean, where it strongly affects ecology, for example, through eutrophication. In the future, unless anthropogenic nitrogen inputs are reduced, a deterioration of the ecological situation can be expected when rising temperatures and declining oxygen exacerbate the effects of the anthropogenic nitrogen inputs.