In this themed overview we are defining contaminants as both anthropogenic and naturally occurring substances with the potential to pollute, and we are considering the parameters which have the main impact upon fluxes of contaminants. We are not considering nitrogen and phosphorus when serving as nutrients. This distinction reflects that a separate themed overview on nutrient dynamics is being produced by the ELOISE secretariat, in which considerations of nitrogen as a nutrient will be better served. However, in certain forms nitrogen is not primarily a nutrient, and its potential polluting effects are unrelated to its role as a nutrient. The role of N2O as a greenhouse gas is one such case, and this themed overview will review ELOISE and IMPACTS progress in understanding these biogeochemical flows. The second boundary is drawn where the focus of interest shifts from biogeochemistry to climate change itself, as at this point a separate themed overview being produced on climate change is the more appropriate forum.
Greenhouse gas
Gases e.g. methane, carbon dioxide, chlorofluorocarbons (CFCs) emitted from a variety of sources and processes, said to contribute to global warming. Greenhouse gases and clouds prevent some of infrared radiation in the atmosphere from escaping,
trapping the heat near the Earth's surface where it warms the lower atmosphere.
Alteration of this natural barrier of atmospheric gases can raise or lower the
mean global temperature of the Earth.
See Glossary for complete list of all terms.
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Four broad contaminant groups have been considered by ELOISE and IMPACTS projects, being persistent organics and hydrocarbons, mercury, heavy metals in general, and biogenic gases. The issue to be considered in this themed overview is to what extent and in which way ELOISE and IMPACTS have added to our understanding of the factors affecting fluxes of these contaminant groups in the coast (Table 1).
A large number of ELOISE and IMPACTS projects have also focused on nitrogen flows. Whilst evaluated in a separate ELOISE themed overview, the processes and factors behind nitrogen flows can have parallel relevance to understanding of contaminant fluxes as defined here. Where appropriate, this themed overview also picks out findings of nitrogen projects for mention. In the table below the distribution of ELOISE and IMPACTS projects between the four contaminant groups plus nitrogen, and between the various European coastal sea regions is given.
There are thirty projects dealing directly with the contaminant groups selected, plus over twenty further projects dealing with nitrogen, and having potential relevance to understanding of systems or processes. This represents a sizeable fraction of the total of 56 ELOISE and 12 IMPACTS research projects
Contaminant issues often reduce to evaluating whether coastal zones are sources or sinks. Seeking to address this topic whilst collating the breadth of ELOISE /IMPACTS research in a succinct manner, this digest focuses solely on the transport routes of contaminants. The sections are thus: 1. Fluvial supply to the coast
2. Atmospheric pathways: from land to sea
3. Atmospheric pathways: from sea to land
4. Ground and sediment waters
Very few ELOISE and IMPACTS projects have focused on societal factors, and of those that have, scant attention has been given to interrelations with contaminants as understood in this digest. Thus, there is no separate discussion of the contribution of IMPACTS and ELOISE to the social parameters of contaminant flows. | 
