Chat Moss - Geography and Ecology

Geography and Ecology

At 53°27′46″N 2°25′54″W / 53.46278°N 2.43167°W / 53.46278; -2.43167 (53.4629, -2.4316), Chat Moss lies at the southern edge of the Lancashire Plain, an area of Bunter sandstones overlaid with marls laid down during the Late Triassic period. Those rocks are themselves overlaid by a layer of boulder clay deposited during the last ice age, about 10,000 years ago. The combination of the flat topography and the underlying clay resulted in extensive peat bogs developing along the Mersey Valley, and overflowing beyond the valley. The bogs in the area between the River Glaze in the west, and Worsley and Eccles in the east, to the north of what was the River Irwell – now the Manchester Ship Canal – are known collectively as Chat Moss.

Chat Moss is a lowland raised bog. In areas where drainage is poor, water-logging can slow down plant decomposition, producing peat, which over the years can raise the level of the bog above that of the surrounding land. The moss occupies an area of about 10.6 square miles (27.5 km2), and is about 5 miles (8 km) long, about 2.5 miles (4.0 km) across at its widest point, lying 75 feet (23 m) above sea level. Chat Moss lies mainly in Salford, but extends into Wigan. By the 1990s, an estimated 72 per cent of the bog had been reclaimed, most of it for agriculture. About 230 acres (93 ha) of degraded bog remain, with 766 acres (310 ha) of undamaged peat deposits in four former peat extraction sites. The peat varies in depth between 24 feet (7 m) and 30 feet (9 m).

The main bog mosses found in the peat of Chat Moss are Sphagnum cuspidatum, S. imbricatum, and S. acutifolia. The peat up to about 7 feet (2 m) from the surface is mainly humidified S. acutifolia, with fresher S. imbricatum peat nearer the surface.

A 228-acre (92 ha) area of Chat Moss, to the north of the Liverpool–Manchester railway line, notified as Astley & Bedford Mosses, was designated a Site of Special Scientific Interest in 1989. Astley & Bedford Mosses, along with Risley Moss and Holcroft Moss, is also a European Union designated Special Area of Conservation, known as Manchester Mosses.

The major habitats in the moss are bog, heathland, woodland and acidic grassland, subject to varying degrees of wetness depending on the local drainage. The remaining areas of bog are dominated by common cottongrass Eriophorum angustifolium and hare's-tail cottongrass E. vaginatum. Bog mosses are more scarce, but Sphagnum cuspidatum, S. recurvum, S. tenellum, S. fimbriatum and S. subnitens occur in patches. As the peat has become drier, areas have been taken over by purple moor grass Molinia caerulea and by downy birch Betula pubescens. The moss also supports several bird species, and is particularly important for wintering raptors such as the hen harrier Circus cyaneus cyaneus, the short-eared owl Asio flammeus and the merlin Falco columbarius, along with breeding species such as the curlew Numenius arquata and the long-eared owl Asio otus. There is a large heronry in Botany Bay Wood, the largest area of woodland in Greater Manchester.

The domestic and industrial waste dumped on Chat Moss resulted in very high levels of heavy metals such as lead and copper in the soil, raising concerns that crops grown there may pose a health risk. However, the high pH of the peaty soil limits the mobility of the metals and so prevents them being taken up by crops.