Relevance of the Fleet to other lagoons

In considering and extrapolating the lessons from The Fleet study, it is prudent to note both the similarities and differences between the Fleet and other lagoons sites. Whilst every site is unique in some way there are also a number of characteristics of the Fleet which are common to a range of other lagoon sites.

Physiography and habitat: Whilst the Fleet lies near the mid-range for size of lagoons in the UK (from less than 0.1 ha to 860 ha) it is larger than most lagoons. As a consequence, the communities it supports may be less sensitive to change (natural and anthropogenic) than those of smaller lagoon sites. Conversely, where change does occur it may be more difficult to reverse the impacts of such change than in smaller lagoons. The Fleet is representative of the main lagoon type, by area, within the UK. However, because of the clear divisions across the site, the western part of the Fleet in particular has some characteristics of smaller and more enclosed lagoons such as percolation lagoons.

Biological communities: Larger lagoons tend to include a greater diversity of habitat types and, therefore, to support a more diverse community of species. In that sense, the Fleet is representative of larger lagoons. However, as a result, the site also includes many of the communities and species found in most lagoons in the UK, e.g. both UK species of Zostera and of Ruppia, 5 of the 10 lagoonal species protected under the UK=s Wildlife & Countryside Act 1981. It therefore provides a useful model from which to extrapolate on the impacts of nutrients on particular communities and species such as Lamprothamnium papulosum (See table below).

Nutrient sources: The Fleet is bordered by agricultural land, with several freshwater stream inputs B many other lagoon sites are more isolated from agricultural land, and have more diffuse freshwater inputs (e.g. percolation, groundwater seepage), which may be much more difficult to measure and quantify, yet may be significant sources. Where the population is more spread out and not connected to mains sewerage there may be numerous septic tanks which may discharge to a lagoon. Where urban areas are adjacent to a lagoon, or border a stream input to a lagoon, there may be storm sewage outfalls whose location may not be known, and which may contribute significant amounts of nutrients sporadically during storm events. Whilst the presence of the swannery is unique in the UK, the work on the input from the swans is relevant to estimating inputs from wildfowl on other sites. On small sites, in particular, wildfowl populations may be relatively significant to the nutrient budget.

Level of study: The study of historical information from the Fleet has been greatly assisted by the existence of the Fleet Study Group and its archive at Weymouth College, which has meant that data relating to the Fleet from various sources is collected together and easily accessible. This situation is unlikely to exist for other lagoon sites. It is unlikely that much historical information exists for other sites, and what does exist may be difficult to identify and obtain as it is likely to be spread amongst different agencies and locations.

Concerning more current studies and identification of potential sources of nutrient inputs, this has been relatively easy as a result of the work carried out by the Environment Agency on sewage discharges and freshwater flows. For some lagoon sites, identification and measurement of potential sources may be much more difficult, for example where:

  • groundwater may be a major source of water input to a lagoon, flows and nutrient content of such inputs may be difficult and/or expensive to measure;
  • seawater percolation is a major source of water input to a lagoon, flows may be very difficult to trace, measure or estimate;
  • significant water exchange only occurs during extreme events, e.g. storms affecting isolated lagoons, which is very difficult to predict and measure, but which may, nevertheless, bring in or export significant quantities of nutrients.

Management: In addition, most of the land bordering the Fleet has been owned and managed for many years by a private estate, which has meant that few significant changes in its management have occurred, and those that have, have been documented. It is likely that there have been minimal changes in management at many lagoon sites. It is less likely that on many other lagoon sites, such changes have been have documented, although the information is probably available for some sites in Scotland (Downie pers. comm.).

Saline lagoons in which the foxtail stonewort Lamprothamnium

papulosum is known to occur (based on DETR 1999, Thorpe et al 1998, Martin pers. comm. and authors= own information).

* = sites within SACs


Fleet (lagoonal inlet)*

Fort Gilkicker Moat (sluiced)*

Harbour Farm lagoons (isolated)*

Great Deep (sluiced)

Normandy Farm (sluiced)*

Eight Acre Pond (sluiced)*

Ardmore lagoon (sluiced)

Loch Ceann a= Bhaigh (sluiced)

Loch a= Bharp (lagoonal inlet)

Loch Ba Alasdair (silled)

Oban nan Stearnan (silled)*

Oban a= Chlachain (sluiced)

Oban nam Fiadh (silled)*

Oban na Curra (sluiced)

Alioter Lagoon (sluiced)*

Oban Honary (lagoonal inlet)

Lochan Sticir (sluiced)

Loch an Duin (sluiced)*

Loch Strumore (sluiced)*

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