Historically, loadings of nitrogen from the landscape, including overland flow, river and groundwater discharge, and direct discharges, have been considered to be the major sources of this nutrient. During the past decade, however, the role of the atmosphere in transporting 'new' nitrogen into coastal waters throughout North America and northern Europe has been documented. However, there are still high uncertainties associated with these estimates due to the current methods used to measure atmospheric nitrogen species. Therefore iron speciation and oxidation state are expected to change as aerosol particles are processed in clouds. Ultimately, it is important to understand this processing since the bioavailable fraction of iron is directly related to its chemical speciation and oxidation state.
Atmospheric processing is also important to nitrogen species.
Again, atmospheric processing can alter the fraction of ammonia in each phase and therefore effect its deposition rate. The scientific community is just beginning to understand some of the processes that link ocean productivity to atmospheric aerosols. It was only a little over ten years ago that the idea of atmospheric iron deposition controlling primary productivity really started to take off. In that time a great deal of interesting research has been done which has shed light on some of these issues. However, a great deal is left to be understood because of the complexity of atmospheric aerosols and marine ecosystems.