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Lowland Soil Catenas in Oxford

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All soils originate from rock – the parent material. The type of soil that is produced depends upon a number of factors, including changes in the parent rock, the soil’s position on a slope and drainage conditions in that location. This case study will examine the soil types and processes around the Oxford area, and how variations in soil sequences (catenas) produce an array of different soils.

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small globe iconOverview of soil types in Oxford

Figure 1 shows the range of soil types in the Oxford area and the influence of particular local conditions and processes:

  • Brasenose Wood, Shotover – the mix of sandstone, limestone and clay has produced a range of soil types, such as brown earth (on the sandstone), gley (waterlogged soils) on the clay, and rendzina on the limestone.
  • Port Meadow – on this low-lying floodplain that floods annually, groundwater gley predominates due to the high water table.
  • Summertown and Wolvercote – these outwash terraces initially comprised fluvio-glacial sand and gravel, and there is evidence of podzolisation producing podzolised brown earth in places.
  • Boars Hill and Wytham – the Corallian limestone parent rock has produced a mix of calcareous brown earths and rendzinas.
  • Within the urban, built-up area – human impacts can be seen in the way that soils are typically lime-rich (from mortar, cement and rubble), cultivated (ploughed in a general sense) and deficient in nutrients, as minerals are removed through the mowing of vegetation.
  • Agricultural area – this region shows the effects of intensive cultivation such as ploughing, draining, compaction and contamination from fertilisers and pesticides.

small globe iconSoil-forming processes

All soils originate from the parent rock. The passage of water through the soil profile and the consequent movement of materials significantly influence the type of soil that is formed. The parent rock determines the depth, texture and drainage of the soil. Hence, on a local scale, the processes effecting the formation of various soils are often the result of topography and climate.

Climate

The climate of the Oxford region is temperate. Average temperatures in winter are about 6–7°C and in the summer are 17–18°C. Rainfall is approximately 650 mm and evapotranspiration about 550 mm, so there is a net downward movement of water through the soil. This allows lessivage (the downwashing of materials in suspension), as well as leaching or solution (materials carried in soluble form). Soils that are determined by climate are called zonal soils. Solution or leaching is more common on the acidic sands and gravels of the terraces. Under conditions of extreme acidity (below pH 4.5) podzolisation may occur.

Drainage

Like most lowland areas in Britain, the Oxford region shows widespread gleying due to poor drainage and gentle relief features. There are two types of gleyed soil:

  • Groundwater gley – where waterlogging occurs as a result of a high water table, such as in the areas close to the rivers.
  • Surface water gley – where waterlogging occurs as a result of impermeable rock, such as those on the superficial clay deposits of Wytham and Shotover hills.

In addition, annual deposition by the Thames and Cherwell rivers leaves fine, grained material on the surface. Therefore, the soils in that area are still being formed and are described as ‘azonal’ or immature soils.

There are three soil types that have formed organically due to the particular micro-topography of their sites:

  • Eynsham area – the soil here was once covered by a layer of peat, which formed in the marshy conditions before the land was drained for agriculture. Now used for arable farming because of the lower water table, it has become a rich, organic ‘puff’ soil that is difficult to work once dry (a puffy, spongy surface does not readily wet again).
  • Oxey and Pixey Meads between the Thames and the Oxford northern bypass road between Wolvercote and Cassington – these are floodplain soils with a high water table, about 1 m lower than the puff soils of Eynsham. The meads are common land belonging to the villages of Begbroke and Yarnton that appear never to have been ploughed, only cut for hay. Organic matter has accumulated on their surface of enough depth to form a ‘floating meadow’.
  • Otmoor – this is a basin site in the floodplain of the River Ray that has carried down clay, mainly from Jurassic formations. The soil possesses a high water-holding capacity and is rich both in clay and humic colloids, exhibiting a range of wet soil profiles. Previously it was marshy grazing land, but since the Second World War it has been more effectively drained, partly by pumping to meet the water requirements of the Arncott Camp.

 

Figure 1. Soil types in the Oxford area.
Figure 1.
Soil types in the
Oxford area.
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Figure 2. An example of brown earth.

Figure 2.
An example of
brown earth.
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Figure 3. An example of clay-gleyed soil.
Figure 3.
An example of
clay-gleyed soil.
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Figure 4. An example of surface-gleyed soil.
Figure 4.
An example of
surface-gleyed soil.
Click here to enlarge.
 
 
 


 
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