Widewater Lagoon Management Plan Comments

14 April 2005



Widewater Lagoon does not contain any really special species to be of precise concern. The most important aquatic species is the Lagoon Cockle, Cerastoderma glaucum. This species is buried in the mud, although the young stages are attached to weed, especially Cladophora (blanketweed). It is a food resource for Shelducks (a rare visitor). 

This would probably benefit from elevated water levels to avoid large losses through desiccation. There is a possible danger of predation from introduced crabs. However, this is not of practical concern. Widewater is too small a body of water to be self supporting and its biodiversity depends on recruitment from the open sea. The pipeline is clearly advantageous. 

 

Summary:  monitoring of the Lagoon Cockle population would be desirable for scientific interest and research, rather than active management. 

 

Glasswort, Salicornia, is a common species (or several species) of flowering plant that occupies a distinct zone on the edge of Widewater and is a distinctive visible feature. This could be altered by elevated water levels, but this unpredictable and in erratic in natural estuaries. I expect, in the long term; over five to ten years, the plant would favour decreased water levels. This must be balanced against the aquatic organisms including the buried Lagoon Cockle, which will favour elevated levels. 

The level of the lagoon can effect the distribution of wild plants on the flood plain as some will not tolerate an increased immersion in salty water.

 

Summary:  monitoring of the Glasswort, Salicornia, population would be desirable for scientific interest and research, rather than active management. 

 

Salinity:  the old salinity records are questionable. The BMLSS records indicate that the lagoon attained normal sea water 34.5 in the main body of the lagoon and some side pools, but this was never exceeded. This would only be possible it the lagoon dried out to a few puddles. 

 

Summary:  the pipeline would expect to increase the average salinity, and increase the minimum winter figure, but not the maximum summer salinity. This could have some effect on the relative proportion of aquatic critters but it is not important. 

Salinity monitoring would be would be desirable for scientific interest and research, rather than active management. 

 

Species list: these should be noted where taken in short term surveys and show small shortcomings, e.g. species present at other times would not be noted. The common prawn Palaemonetes varians is a fully aquatic lagoon indicator species of low salinity. Therefore, its presence and absence could indicate a change of conditions. However, to do so with Widewater would not be precise. The prawn Palaemon elegans is present in greater numbers and this species can tolerate greater salinities and it is difficult to differentiate these species. Natural fluctuations of salinity are greater than could be practically managed so it is not important.

 

Summary: Species monitoring would be would be desirable for scientific interest and research, rather than active management. 

 

Phaeocystis plankton blooms at sea occur in May and June and plankton blooms also occur in autumn. This is not toxic but can cause localised anoxic conditions in inlets and lagoons. It can also be unsightly and smelly in once a decade conditions. It would only have minimal short term environmental effects. The main problem is that the strings of the dying plankton look like human sewage and give rise to public complaints. 

 

Summary:  it usually occurs when the tides are below six metres in May and June. If a particularly bad bloom occurs, it may be desirable to close the pipeline. Visual sea monitoring during May would minimise rather than prevent if the pipeline is letting in water. The benefits of the pipeline outweigh the small risk.

 

Avian presence.

This is an important amenity resource of the lagoon. I would defer to bird experts.

My observations indicate that the increased food resource of the elevated water levels attracts more birds than the minimal reduced feeding opportunities.

 

Summary: Bird species monitoring would be would be desirable for scientific interest and research, rather than active management. 

 

Andy Horton

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