Environmental Engineering Reference
In-Depth Information
Well-drained fine loamy and silty brown earths occur along the south Gower coast and are commonly
shallower than 30 centimetres on the cliffs themselves. The calcareous material and the relatively low
rainfall, together with additions of lime and basic slag on the agricultural land, result in these soils having
a near-neutral pH of 6.5 to 7.0. Brown podzolic soils are well-drained coarse loamy soils that can be dis-
tinguishedfromtheduller-colouredbrownearthsbylayersofbrightorange-brownsubsoil,whichcontain
larger proportions of iron and aluminium hydroxide.
All the soils on the salt marshes are affected by the high water table and are classed as alluvial gley
soils. They have different profiles depending on slight differences in elevation and there are four types
recognised, each with a distinctive vegetation community. At the lowest point on the shore there is an ex-
tensive areaofcommonsaltmarsh-grass
Puccinellia maritima
andtheupper20cmofthesoilsshowsome
structural development. On the mid-shore under red fescue the subsoil structures are well developed and
the upper 20cm is almost completely decalcified. The highest zone of the marsh, on the landward edge
with sea rush
Juncus maritimus
, the soils are completely decalcified with a pH value of 5.5 in the upper
50cm.
The raw sands of the dunes are composed largely of quartz grains and shell fragments and except on
the inland areas where they have been fixed by vegetation they are unstable and there is no visible struc-
turebelowthetopfewcentimetres.Asthedunesurfacesareveryunstablefreshsandfrequentlyburiesold
topsoils causing layering. On fixed dunes there can be more than 5cm of topsoil. In dune slacks humic-
sandy gley soils form, with surface layers rich in organic matter, overlying gleyed sand. Stabilised dunes
on cliff tops such as those at Pennard, where there is little accretion of fresh sand, are sometimes decalci-
fied below 30 cm and the soils are non-calcareous, resulting in an interesting flora.
PLANT COMMUNITIES
The plant life of every area, including Gower, is characteristic of the rock, soil and climate. Plants can
change their growth patterns relatively quickly, but because changes in the soil occur over long periods
there must be an equivalent slow change in plant growth. Plants adapted, for example, to growing on the
coarse loamy podzols of the commons may not be able to survive on the brown earths covering the lime-
stone.Someplants,however,cangrowequallywellonbothacidandneutralsoilsifthereisreducedcom-
petition. Manyexisting habitats inthepeninsula havebeenlargelyformedbyhumanactivity,buttheyare
so old and so traditional that they have come to be regarded as natural. So commons and heathlands are
described inthis topic asplantcommunities, eventhoughtheyneedconstant management toexist intheir
accepted form. The intervention of people is the subject of the next chapter.
