Agricultural uses of wetlands

Mires, marshes and bogs have some of the highest levels of productivity to be found in any natural ecosystem. Although not generally part of mainstream agriculture they have long been skilfully diverted to human needs, particularly in areas of marginal farming. Marshes that dry out sufficiently in summer can provide grazing or in some cases a crop of hay. Well-managed water meadows

Fig. 11.22 An Indian island dwelling on Lake Titicaca (3810 m). The present-day descendants of the Uro Indians who retreated onto islands on the lake due to the expansion of the Inca Empire still make use of these islands where they construct houses and build boats made of dried bundles of the South American bulrush, the totora (Schoenoplectus californicus).

Fig. 11.22 An Indian island dwelling on Lake Titicaca (3810 m). The present-day descendants of the Uro Indians who retreated onto islands on the lake due to the expansion of the Inca Empire still make use of these islands where they construct houses and build boats made of dried bundles of the South American bulrush, the totora (Schoenoplectus californicus).

Fig. 11.23 Shallow water navigation of Lake Titicaca. Manoeuvring a boat made from totora reeds (Schoenoplectus californicus) by means of punting with a pole.

can add greatly to grass production for hay in areas where gross production is limited by drought in summer. However, the management of these water meadows requires careful attention and they are now much less used than in the past.

An outstanding example of extensive water meadows that are still in use is found along the banks of the Shannon in Ireland. The River Shannon traces a long S-shaped course through the centre of Ireland where it receives the waters of 12 counties. Along its 205 km journey to the sea it falls only 12 m, which gives it the shallowest gradient of any large river in Europe. Consequently, given this extensive catchment area and Ireland's plentiful rainfall, the Shannon pours nutrient-rich floodwaters across 35 square kilometres of fields every winter. The flooded fields are called the Callows (Irish Caladh means either water meadow or meeting place depending on context) and offer a refuge for large numbers of wildfowl and wading birds in winter while in summer they provide hay and pasturage for cattle (Heery, 1993).

Peat bogs, although in large measure created by human disturbance through deforestation, have eventually earned a wilderness conservation status as well as being a useful source of fuel for inhabitants of marginal areas. Peat has provided fuel for fires and bedding for livestock for centuries. Cutting, drying and carrying peat is very labour intensive, and peat cutting for domestic use is much reduced from what it was in earlier centuries. In the British Isles extensive clearing of peatlands took place with land improvement schemes in the seventeenth and eighteenth centuries of which Flanders Moss at the head of the River Forth is a well-documented Scottish example. The eradication of smallpox caused the human population of neighbouring areas to the north in the Scottish Highlands to increase to such an extent that there was an acute shortage of land. Highlanders were offered land on the bog rent-free for life if they cleared the peat. The peat provided material for building their homes, fuel for their fires and bedding for their animals. What was not needed was cast into the upper waters of the Forth. This eventually proved detrimental to downstream salmon fishings, and further clearance was halted leaving the considerable expanse of undisturbed raised bog that is now preserved by conservation regulations. Modern peat harvesting for industrial use unfortunately leaves a wetland that is of very little use either for agriculture or wildlife (Fig. 11.24).

When properly managed the interface between wet and dry land can provide a double resource that has been exploited since the beginnings of human settlement. When fenland or raised bogs are drained and cleared of peat a nutrient-rich organic soil of great agricultural potential is left. The neighbouring wetland provides grazing in dry summers when the surface of the bog is dry enough to bear livestock. Marshes and peatlands also provide ample opportunity for dietary supplements from wildfowling and fishing. Such a multi-use habitat is typified by the Fenlands of southeast England which were formed by the silting-up of a bay of the North Sea to form a flat lowland extending west and south of the Wash and becoming the largest swampland in England. The lower peat levels were

Fig. 11.24 Effect of the industrial removal of peat from a bog in Caithness (Scotland) — a landscape in which the only remaining commercial resource is wind.

deposited from 7500 BC onwards but widespread coverage did not occur until c. 3500 BC. Due to the wetland being at a maximum during the Iron Age human settlements were limited to the edge of the Fenlands although lowering of the water table by the Romans who attempted drainage and built a few roads across the Fens brought about a denser occupation of the edges and islands - only to be followed by drowning of many settlements after their departure (Hall & Coles, 1994). Cornelius Vermuyden, a Dutch engineer, developed the first effective drainage systems in the seventeenth century. Drainage and construction of dikes and channels in the various sections or 'levels' continued through the nineteenth century despite problems of land sinkage, water accumulation, and periodic flooding. Agriculture is now plentiful on the fertile alluvial soils, with vegetables, fruit and wheat being the principal crops.

A somewhat different interaction of people with the edges of wetlands is found in south-west England on the area of marshes and moors known as the Somerset Levels. With the rise in sea level at the end of the last glaciation this area was flooded and remained under water until c. 4500 BC when peat deposits began to form in the salt marsh, leading gradually to the development of fens and raised bogs. To cross these wetlands and reach the islands of rock and sand in the valleys, prehistoric people built wooden trackways, remains of which survive to the present day due to the waterlogging of the peat. The oldest is the Sweet Track which was a raised walkway built in 3806 BC. In the Roman period the first sea and river defences were built, but as with the Norfolk Fenlands, the end of the Roman period saw large-scale flooding. Despite the constant risk of flooding, islands in the moors were chosen as sites for monastic centres and for pasturing sheep on the flood-enriched summer grazing. It was this principal use of the wetlands in summer that was probably the origin of the regional name 'Somerset' from the Anglo-Saxon 'Sumersatan' - land of the Summer People (Dunning, 2004).

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