Sewage

Oil

Synthetic organics and heavy metals

Pollution is clearly a major concern in the management of SACs, but problems posed are considerably more complex than those which arise in relation to other human activities. Activities such as fishing are relatively clear-cut in terms of origin, effects and potential for control. By contrast pollution may be difficult to analyse on all these counts, and can pose major problems for effective management, because:

• The origin of pollution may not be a known point source, with a limited distribution, but may have uncertain origins and be diffuse over a wide area.
• A pollutant may affect the CFT community in situ, or it may affect the pelagic larval phase whilst in the water column, possibly in a different location. In either case little is known of the sensitivity of CFT species to concentrations of specific pollutants, and even less of synergistic effects.
• Pollutants may build up in organisms and through the food chain, so that concentrations in the water or sediment may be of little direct relevance.
• Most pollution will arise outside the SAC, limiting management options.

The following pollutants will be considered - sewage (and other organic based effluents with the same basic effects), oil, synthetic organic compounds, and heavy metals.

Sewage and other organic-based effluents present several environmental problems.

• They contain inorganic plant nutrients, and induce potentially serious impacts which are considered below under eutrophication.
• They add dissolved and particulate material to the water which will reduce light penetration and deposit sediment onto the substratum.
• Perhaps most importantly, they utilise the dissolved oxygen in the water.

The majority of CFT biotopes occur on open coasts in areas of vigorous water movement, and either in or close to waters of considerable depth. They are not generally near sources of discharge of organic pollutants, such as sewage, and even if they were, they would be considered as Higher Natural Dispersion Areas, and therefore apparently at little risk. The only exceptions are the limited CFT biotopes in sheltered semi-enclosed situations such as in the Scottish sea lochs and south western rias. These would be exposed to risk of depletion of dissolved oxygen if there was a substantial organic input, and because of their scarcity, have a high conservation value. Past experience in Scandinavian fjords and bays has shown this to be a real threat. The choice of SACs is based upon the existing quality of environment, which means that they are not currently in an area receiving excess organic input. Any proposed change in effluent treatment or discharge regimes, or new source of organic input (e.g. intensive fish farming) would be a management concern, and must be evaluated in the context of the water dispersion patterns within the SAC. Fortunately all such proposals will (it is to be hoped) be subject to strict consent conditions.

Another important form of organic pollution is oil, and in contrast to the above, serious oil pollution incidents are quite unpredictable. For the purposes of SAC management, the treatment of oil pollution can present conflicts of interests for different biotopes, and the optimal measures for CFT biotopes cannot be pursued in isolation. Untreated oil is not a risk, since it is concentrated mainly at the surface, and the CFT biotopes are protected by their depth. If oil is treated by dispersant the resulting emulsion will penetrate down the water column, especially under the influence of turbulence. However, the target response of the Marine Pollution Control Unit is to spray offshore when spraying is required, and spraying inshore should be a last resort. An oil spill contingency plan is an integral part of every SAC management programme, but it will concentrate on vulnerable (or valuable) components of the system - marine birds and mammals, soft intertidal sediments, aquaculture developments, and amenity sites. CFTs will inevitably, and realistically, come low on the list of considerations.

Synthetic organic compounds include pesticides, PCBs and TBT antifouling. Heavy metals include cadmium, lead, and mercury. All are known to have toxic effects in low concentrations, with larval stages being particularly sensitive, and to be capable of high levels of bioaccumulation. Because of this bioaccumulation they often affect higher trophic levels most severely, and become a serious consideration in any species used for human consumption. If there are any suspected point sources within or near the area of the SAC, then they will have to be a feature of management plans. Their potential impact upon the dispersive larval stages means that there influence cannot be ignored beyond the boundaries of SACs, since they may affect recruitment to the communities.

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