Lornshill Academy Geography Department Higher Revision Physical Environments - Biosphere
Physical Environments Biosphere Properties and formation processes of podzol, brown earths and gley soils Natural vegetation deciduous forest vegetation provides deep leaf litter, which is broken down rapidly in mild/warm climate. Trees have roots which penetrate deep into the soil, ensuring the recycling of minerals back to the vegetation. Soil organisms soil biota break down leaf litter producing mildly acidic mull humus. They also ensure the mixing of the soil, aerating it and preventing the formation of distinct layers within the soil. Climate precipitation slightly exceeds evaporation, giving downward leaching of the most soluble minerals and the possibility of an iron pan forming, impeding drainage. Rock type determines the rate of weathering, with hard rocks such as schist taking longer to weather, producing thinner soils. Softer rocks, eg shale, weather more quickly. Relief greater altitude results in temperatures and the growing season being reduced and an increase in precipitation. Steeper slopes tend to produce thinner soils due to gravity. Drainage well drained with throughflow and little accumulation of excess water collecting, producing limited leaching. Interactions between factors: The A horizon is rich in nutrients, caused by the relatively quick decomposition of the litter of deciduous leaves and grasses in a mild climate. This produces a mull humus, well mixed with the soil minerals thanks to the activity of organisms such as worms. Soil colour varies from black humus to dark brown in A horizon to lighter brown in B horizon where humus content is less obvious. Texture is loamy and well-aerated in the A horizon but lighter in the B horizon. The C horizon is derived from a range of parent material, with limestone producing lighter-coloured alkaline soils. South-facing slopes with a greater amount of sunshine and higher temperatures increase the rate of humus production. 2 P a g e
Soil Types Podsol Soil (Sample Answer) Thin, black and acidic humus (ph 3 5 4) produced from the slow decomposition of coniferous needles and cones and cold climate. There is limited bacterial activity caused by the cold climate which results in the slow formation and hence thin/shallow soil. Precipitation is greater than evaporation and/or snowmelt results in the downward leaching of clays, humus, iron and aluminum resulting in an ash grey A horizon. An iron pan develops in the illuviation zone in the upper B horizon as a result of the redeposition of iron and this can impede drainage, resulting in waterlogging and gleying in the B horizon. Due to the cold climate present for most of the year, there are few soil biota to vertically mix the soil, so the horizons are well defined. The C horizon parent material is generally of weathered (fluvio) glacial material with a mixture of particle sizes and shapes. 3 P a g e
Gley Soil These are soils of a very cold, wet climate. They often are found on low, flat land, often near a river. They develop serious waterlogging that starves soil of oxygen; few plants can grow. They develop an extreme form of MOR (acid) humus. Their upper layers are blue-grey in colour due to oxygen deprivation. They have a poorly developed set of horizons due to freeze-thaw mixing the layers. They have virtually no soil organisms because of the acidic and anaerobic conditions. In extreme areas of the tundra, permafrost exists as the B and/or C horizons. Possible sample answer The plants that live on the surface are highly specialized, like heather, lichen and mosses. Trees are usually absent; tundra translates as without trees. The A horizon is poorly defined and is an unhealthy grey colour. Leaf litter seldom exists, and if there is a top layer, it is black; it decomposes so slowly it is virtually preserved. Leaching cannot happen, as the soil pore spaces are so clogged by water in the summer and ice in winter that movement cannot happen. There is no hard pan as a consequence. The B horizon- if it can be determined- is blueish, sticky, wet and almost lifeless. Angular fragments from the C horizon can often migrate upwards as boulders. The C horizon is the bedrock- usually ancient shield rocks like basalt or granite. They are hard and acidic, slow to break up and are usually impermeable. The whole profile usually has been set solid in permafrost since the Ice Age. 4 P a g e
Brown Earth (Sample Answer) These are soils of a milder, wettish climate. Widespread in Britain, except in highland areas. They often are found on gentle slopes rather than flat land. They develop best under vegetation that causes less acidic (MULL) conditions- like deciduous trees. These enrich the soil as they fall and decay in Autumn. The climate encourages more rapid decomposition and the resulting humus is mild and more alkaline. They may have a slightly-developed hardpan of iron and aluminium. Iron pans can develop where leaching is more active. Their upper layers are slightly leached and slightly waterlogged. They have a poorly developed set of horizons. They have quite a lot of soil organisms who mix the debris through the layers merging the boundaries between the layers. This also helps to aerate the soils. The roots of trees penetrate deep into the soil absorbing nutrients. And allowing good drainage. 5 P a g e