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Content archived on 2024-05-21

Marine effects of atmospheric deposition


Problems to be Solved The coastal seas represent one of the most valuable resources on the planet. However, this ecosystem is threatened as a result of human pressure. In Europe high population densities and high levels of industrial activity mean that the pressures arising from these activities are particularly acute. Globally we have probably doubled nitrogen fixation as a result of human activities and increased nitrogen emissions five fold. On a regional scale in Europe the increases have been greater than this, leading to real concern over eutrophication threats to coastal waters. Atmospheric inputs deliver 20->50% of the total input of nitrogen from land to coastal waters. Atmospheric inputs differ from riverine inputs in many ways and may produce different effects on the marine ecosystem. However, we have almost no information on the direct effects of atmospheric deposition on marine ecosystems. Policy makers are concerned to regulate nitrogen inputs to coastal waters to avoid unacceptable damage to the ecosystems. However, current scientific understanding is inadequate to allow rational decisions to be made over whether increased regulation is necessary, and if so how to do this most cost-effectively. The results from MEAD will help identify the most effective way to achieve this. Scientific Objectives and Approach MEAD is based on one specific area - the Kattegat in the Baltic, an area where there is particular concern over the possible effects of atmospheric deposition on the marine ecosystem. MEAD involves fieldwork, modelling and a retrospective study. All of the work involves both atmospheric and water column studies that will be closely integrated. The fieldwork includes studies to understand atmospheric transport and deposition over the coastal seas and the response of phytoplankton communities to variable nutrient levels. The retrospective analysis involves comparing results from atmospheric deposition monitoring around the Kattegat to monitoring data on phytoplankton abundance and species composition in the coastal waters of the area. Archived satellite images of the area will also be studied for evidence of past algal blooms. This retrospective study will investigate if there is evidence of links between atmospheric deposition and algal blooms. The data from the fieldwork will be used to develop models to describe atmospheric deposition over coastal waters and the response of the plankton community to this deposition. Expected Impacts The model developed in MEAD is specifically designed to describe the linkage between atmospheric deposition and eutrophication problems in coastal waters. Although developed for the Kattegat, the principles of the model should be transferable to other areas. The model will be used in conjunction with local environmental regulators around the Kattegat to investigate the impact of atmospheric emission control strategies on marine eutrophication.
MEAD has managed to successfully meet its objectives. MEAD has documented that the phytoplankton community of the Kattegat responds to increased nitrogen inputs with increased biomass. We have documented that the atmosphere represents an important source of nitrogen to the Kattegat, particularly in summer. Oxidised (primarily nitric acid and nitrate) and reduced (primarily ammonia and ammonium aerosol) nitrogen are of approximately equal importance. This atmospheric input is regulated by a complex series of chemical and physical processes, which can act to focus deposition to certain regions. These complex processes, coupled to the geography of the Kattegat, mean that atmospheric inputs are highly variable in space and time. Models developed and improved within MEAD can now describe reasonably well this complex deposition pattern. In MEAD, the analysis of data sets from routine monitoring activities have been used to show for the first time the distribution and frequency of algal blooms in the Kattegat.

Models developed in MEAD can simulate the pattern of algal activity seen in this area. The combination of MEAD field studies and modelling of the marine ecosystem, together with the retrospective studies of monitoring data, lead us to conclude that atmospheric deposition events are generally too small to trigger blooms in this region. Rather we conclude that mixing of nutrients from deep water is the primary mechanism responsible for bloom formation. However, atmospheric deposition does make an important contribution to the overall input of nitrogen to this region and hence contributes to the overall levels of phytoplankton activity and to eutrophication problems. In MEAD we have been able to evaluate the effects of various nitrogen emission control strategies on phytoplankton levels in the Kattegat. We show that regulation of local sources will primarily impact ammonia deposition, while Europe wide emission control will be required to reduce the input of oxidised nitrogen. The methodologies and improved conceptual understanding developed in MEAD will provide a framework to evaluate the importance of atmospheric inputs in other European marine areas.

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United Kingdom

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