Grazing • Access and amenity • Pollution • Coastal defence maintenance • Alternative uses

Pollution (cont)

Oil • Chemicals • Sewage and other enrichment • Litter

Sewage and other enrichment

Estuaries have been used for many years as a convenient place to dispose sewage. The enriching effects (eutrophication) of these effluents, when combined with the agricultural run-off of fertilisers, can cause excessive growth of green algae. This may help to decrease the diversity of life in the estuary and can have a detrimental affect on saltmarsh habitat as higher marsh vegetation may become smothered by excess plant material. The extent to which these types of enrichment can be beneficial, i.e. increase productivity within an estuary, is not clear, although there is some evidence that this may result in higher numbers of some bird species feeding in these areas.

The drive over the past two decades to improve the water quality of inputs into estuary systems may reduce the overall nutrient loadings and hence potential productivity, but may lead to an increase in species diversity. This may have possibly caused, or be causing, a reduction in carrying capacity of estuaries for some populations of birds, although this is very difficult to prove and must be set against a return to a more “natural” system and potential increase in the range and diversity of species that these non-eutrophic systems support, together with an improvement in water quality.