INTRODUCTION TO SALINE LAGOONS

Definitions and descriptions

Saline lagoons develop behind shingle (and sometimes sand) bars where saline water peculates through the beach or from occasional overtopping by waves. These are usually small and ephemeral as beach roll-over or changes in salinity reduce the brackish conditions in the water. Larger lagoons also develop in tidal inlets sheltered from storm waves by enclosing spits and bars. They are usually defined by their physical situation and salinity. There are 5 main physical types: Isolated lagoons; Percolation lagoons; Silled lagoons; Sluiced lagoons and Lagoonal inlets. The definition is based on their physiography, i.e. by the nature of the separating barrier (Section 2.2 of the Saline Lagoon Guide describes each of these).

Traditional management

Water quality and salinity levels are critical to their value for the specialist marine plants and animals they support. Management is usually concerned with ensuring both of these are appropriate to the interest present on the site. There are differences in the requirements but the preference of most marine related species is for salinities approaching that found in the sea, i.e. 35%. (Section 3.1 of the Saline Lagoon Guide provides more detailed information on the salinity management requirements.)

Reasons to restore

Lagoons are rare habitats and in the UK generally small in size. Some 30 - 40 lagoons are estimated to have been lost in England alone in the 1980s. These losses, which can be exacerbated by 'natural' change continue to effect the remaining sites today and provide powerful incentives for restoration. Depending on the definition used in the Mediterranean there are many examples of large lagoonal areas associated with the deltas such as the Rhone (Carmargue) in France, The Ebro in Spain or the Po delta and Venice lagoons in Italy. These have also been adversely affected by a number of activities which have greatly reduced their area. These activities include conversion to rice cultivation, artificially drained for agriculture (Sacchi 1979), fish-farming as well as use for saltmaking.

States and values

The state of a particular lagoon is largely determined by the salinity of the water. Thus three states have been identified:

1. State 1 - Low salinity, 6-10%;
2. State 2 - Intermediate salinity, 18-24%;
3. State 3 - Hypersaline.

Guidance (routes to restoration)

Changes in salinity cause changes in the species composition of the habitat. Moving the lagoon to the preferred state by the control of salinity is the primary focus for restoration. Other factors which are important include: the size and shape of the lagoon; the substratum type and the need to control encroaching vegetation such as common reed.

Publications

• Guides: This section of the "Coastal habitat restoration, towards good practice" leans heavily on the recent comprehensive guide to the restoration of saline lagoons. Rather than repeating what is in that guide it provides a general introduction to the main issues and details of where the information can be found in the saline lagoon guide. The full contents list is provided. See also the Royal Society for the Protection of Birds (RSPB) saline lagoon guides on creating and managing saline lagoons for birds and for specialist invertebrates and plants.
• Ongoing projects: The RSPB-led 'Conserving saline lagoons and their birds on ten Natura 2000 sites in England' LIFE Nature Project (LIFE99 NAT/UK/006086)

References

Sacchi, C.F. 1979. The coastal lagoons of Italy. In: Ecological Processes in Coastal Environments, ed.Jefferies, R.L. & Davy, A.J.Blackwell Scientific Publications, Oxford, 593-601.