Environmental Engineering Reference
In-Depth Information
five or six crops. False teeth were tried and fitted to the sheep some years ago, but they did not appear
to be successful. But salt-washed mutton is a local delicacy and some butchers place special orders for
marsh sheep and lambs. Until about 1904 the fleeces from the sheep were spun into yarn and woven into
quilts and blankets in the mills at Llanrhidian; today they are virtually worthless.
Nearer the enclosed fields bounding the upper shore, the 'inbye' land, there are large areas ofsea rush
where there is always some well-sheltered grass for the harder winter weather. Little is known, however,
about the grazing behaviour of animals in salt marshes. Selective grazing, trampling, dunging, nutrient
redistribution and the interactions of different grazing species are all likely to be important factors in de-
termining the nature of the saltmarsh vegetation. Some initial studies of pony grazing on the salt marsh
were undertaken by the University of Swansea in 1975 and 1976, but these have never been followed up.
These preliminary studies showed that a wide range of saltmarsh plants was grazed and that the preferred
plantsvariedwidelybetweendifferentindividualsandatdifferenttimesofyear.Analysisofdungshowed
that in general saltmarsh-grass and red fescue form the major part of the diet. Some groups of ponies do
grazeandtramplecommoncord-grass,maintainingshort,openswardsinplaces,whileotherareasremain
ungrazed. Similar work undertaken in the early 1970s in Bridgwater Bay, Somerset, found that areas of
cord-grass could be converted into saltmarsh-grass pasture in five to ten years by sheep grazing, but there
does not seem to be enough grazing pressure on the Gower marshes for this approach to be effective.
THE FUTURE
Attheheightofconcernabouttheinvasionofcommoncord-grassandshortlyaftertheoystercatchercull,
itwasnotedthattheinletandestuaryhad'ahistoryofthoughtlessinterference'(Nelson-Smith&Bridges,
1977), with proposals intended to favour only one interest conflicting with the needs of others. Also in
the writer's mind at the time was the proposal by the Loughor Boating Club for a tidal barrage across
theLoughor.TheClubhadcontractedSwanseaUniversity'sEngineeringDepartmentin1969tocarryout
a feasibility study for a barrage 'to contain a freshwater lake of 400-600 acres [162-243 hectares] with
a new Swansea to Llanelli link road across the top'. The intention was to use the area for water sports.
Although no further progress was made the issue is still raised in the local newspapers every few years.
Today, with the international importance of the estuary well understood and better liaison and consulta-
tionbetweenthevariouslocalandregionalinterests,thebarrageisunlikelytobebuilt.Thereis,however,
growing concern about an issue that was scarcely recognised in the 1970s, and that is a rise in sea level.
Changes in sea level due to global warming are likely to cause great changes to the inlet and estuary over
the next hundred years.
Sea level is currently rising at a rate of about 2 millimetres per year and the forecast is that the level
will rise approximately 40 centimetres by 2100. The rate of the rise depends on three different factors,
some of which researchers are more confident in than others. The first definite factor is that increasing
global temperatures are causing sea water to expand as it warms. Secondly there is a moderate certainty
that melting glaciers will add to the volume of the sea, and finally there is a concern that the instability of
ice sheets could contribute to large-scale and sudden sea-level rise.
Saltmarshesandintertidal areasareobviouslysensitive toariseinsealevels,buttheyarenotpassive
elementsofthelandscapeandasthesealevelrisesthesurfaceofthemarshandsandswillalsorisedueto
inputs of sediment and organic material. If this input keeps pace with sea level then the marsh and sands
will grow upwards. If it does not, then they will be steadily submerged. In this situation vegetation will
be covered by the tide for progressively longer periods and it may die, giving way to bare intertidal areas
or even open water. Direct losses of habitat due to sea-level rise can be offset by higher areas converting
to marsh, but there is comparatively little room for this on the south side of the estuary. If current predic-
