Pills, Pools and Marshes - Gower - page 235

MARSH MANAGEMENT
Marshes are immensely dynamic, complex and productive systems, but are quite short-lived. Although
Oxwich Marsh, in its current form, is only about eighty years old, the habitats change quite rapidly as
plant succession takes place. At present reed, iris and bulrush are invading open water, scrub is invading
reedswamp and fen and reed is invading fen. At the same time the whole area is gradually silting up due
to material being washed down by the inflowing streams. The marsh would inevitably develop into damp
deciduous woodland if left unmanaged and there would be a serious decline in the wildlife value of the
area, with the loss of various habitats. Over the last twenty years or so therefore control of scrub in the
reedswamp and fen has taken place and reed has been cut back in the channels and ponds.
The plant succession is also influenced by the type and behaviour of the water because the different
stages require different regimes. Common reed for example grows best in nutrient-enriched water at high
fluctuating levels, whereas fen vegetation does best if the water is at a lower level and is stable and low
in nutrients. The solution to these issues depends on being able to control the quality, flow and level of
the water in the marsh and therefore a lot of marsh management is about engineering, building weirs and
bunds, cleaning ditches, and repairing culverts, the sea wall and the sluice.
In 1963, when Oxwich became a National Nature Reserve, extensive reedbeds had developed in the
west marsh, though mixed and poor fen, open water and carr woodland were still present. At the time this
was considered to represent a good balance of habitats, especially as the area was valued mainly for its
rich bird life, particularly the various warblers. The marsh was also felt to have potential for becoming
a breeding area for a number of species rare in western Britain, including bittern, marsh harrier, bearded
reedling and purple heron, all of which, as described previously, were regular visitors. In addition the wa-
ter quality was excellent and there was little invasion by scrub. Management of the area was therefore
low-key and there was little direct intervention. By the middle of the 1970s, however, there was concern
abouttherate atwhichscrubandemergentvegetation intheditches andpondswasspreading. Scrubcon-
trol by cutting and chemically treating the stumps was introduced and common reed in the main ditches
wascutusingasmallpurpose-builtraftwithamotorisedscythemountedatthefront(Fig.132).Attempts
to use this raft to control water-lilies Nymphaea spp. failed, as did using a suction pump to remove silt.
In the early 1980s another concern emerged, that of water quality. Some deterioration had been noted
earlier, thought to be associated with the increasing sediment in the ditches and open water and the high
silt content of winter floodwater. Then a series of isolated events, involving accidental releases of sewage
and farm slurry, together with fertiliser runoff, compounded the problem and there were algal blooms and
a rapid spread of dense carpets of greater water-moss Fontinalis antipyretica . This nutrient enrichment
and its impact on the various plant communities became the main influence on the management of the
area. A detailed survey of the marsh in 1981 showed that the fen vegetation was rapidly being overtaken
by common reed as a result of the nutrient-rich waters spreading throughout the marsh. A programme
of works was therefore designed to provide control over water levels and the flow of water through the
marsh. Towards the end of the decade, when budgets for management were reduced, the emphasis moved
towards developing ways of ensuring that future maintenance was viable and cost-effective. For the last
ten years or so the marsh has been managed on a 'care and maintenance' basis, with the sluices and weirs
kept in good working order and an annual programme of scrub control. The scrub, mainly alder and wil-
low, is invasive, particularly around the fringes of the marsh and alongside recently re-excavated ditches.
Small stands and lines of scrub are left and this benefits both reed and Cetti's warbler by providing a
spread of feeding opportunities throughout the marsh.