Higher Biosphere

Natural vegetation - Thin, black and acidic humus (pH 3·5–4) produced from the slow decomposition of coniferous needles and cones. 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 aluminium resulting in an ash grey A horizon. Soil organisims - 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. Drainage - 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. Rock type - The C horizon parent material is generally of weathered (fluvio) glacial material with a mixture of particle sizes and shapes.&nbsp;&nbsp;

The A horizon may be further subdivided. &nbsp;(L) leaf litter &nbsp;(F) fermenting leaf litter &nbsp;(H) humus &nbsp;(E) eluvial (not always present) These lie above the B horizon.

Dead vegetation-Litter (L)

A soil profile is a vertical cross-section of a soil. It is divided into a number of distinct layers, referred to as horizons. The horizons are normally designated by letters.&nbsp; O Horizon – Organic layer A Horizon – Topsoil B Horizon – Sub soil C Horizon – Parent material (bedrock)

Characteristics of&nbsp;Brown Earths

Free draining Brown/reddish brown Deciduous woodland Litter rich in nutrients Intense biological activity e.g. earthworms Mull humus

Soil texture is a term used to describe the distribution of the different sizes of mineral particles in a soil. Textures range from clay, sand, and silt at the extremes, to a loam which has all three sized fractions present. The main influence of texture is on permeability which generally decreases with decreasing particle size.&nbsp; Soil high in silt and clay with compact subsoil lacking in pore spaces

Biosphere 2 – Brown Earth

Look at Diagram Explain the main conditions and processes which have led to the formation of a Brown Earth soil. 8

Look at Diagram Explain the main conditions and processes which have led to the formation of a Gley soil. 8

Although there are a number of different soil types in Scotland. The main three soils are: •Brown Earth •Podzols •Gleys

Vegetation &amp; Biota

Plants influence the soil in many ways: The nature of the soil humus is determined by the vegetation cover and resultant leaf litter. Roots contribute dead roots to the soil, bind soil particles together and can redistribute and compress soil.

Organisms influencing soil development range from microscopic bacteria to large animals: Micro organisms such as bacteria and fungi assist in the decomposition of plant litter.&nbsp; This litter is mixed into the soil by macro organisms (soil animals) such as worms and beetles. Soil horizons are less distinct when there is much soil organism activity.

This refers to the breakdown and decomposition of rocks and minerals by factors including air, water, sun and frost. Physical weathering involves continual breakdown or rocks into smaller and smaller particles. Chemical weathering involves alteration of the chemical composition of rock minerals.&nbsp;

Gley-from the Russian word; glei= compact bluish grey Poorly drained Periodic or permanent waterlogging Lack of oxygen in pore space = anaerobic conditions Chemical reduction occurs prior to translocation Grey or bluish grey colour to subsoil

Where gleying is intermittent, orange/yellow coloured mottling can occur Horizons generally rich in organic matter intergrading into peat deposits - peaty gley to peat

Ao/A - Slow rate of decomposition of organic matter because of waterlogged anaerobic conditions.&nbsp;This forms a mor humus. Plant roots do not penetrate deeply as most nutrients found near the surface. Red brown mottling occurs along root channels where pockets of oxygen accumulate. Anaerobic conditions means few organisms living in soil.&nbsp;This leads to clearly defined layers. B - Blue grey colour due to waterlogging -&nbsp;the iron compounds in the soil are changed from red/brown due to this.&nbsp;Red mottling as air pockets reoxygenise the iron in the soil. C – impermeable clay impedes drainage and causes waterlogging.&nbsp;High input of precipitation has filtered through horizons and cannot drain away. Soils are often found on moorland or at foot of steep slopes, valley floors.&nbsp;Relief&nbsp;causes drainage problems.

Draw a fully annotated soil profile of a Brown Earth soil to show its main characteristics (including horizons, colour, texture and drainage), and associated vegetation. 8

Relief influences soil formation in several ways: It influences soil profile thickness i.e. as angle of slope increases so does the erosion hazard. It has an effect on climate which is also a soil forming factor gradient affects run-off, percolation and mass movement. It influences aspect which creates microclimatic conditions.

O Horizon - Thick black humus layer.&nbsp;Mild Mull humus. A Horizon - Dark brown with loamy texture.&nbsp; B Horizon - Lighter brown with some staining from organic matter above.&nbsp; C Horizon - Limestone or schist rock allowing for more drainage.&nbsp;

Associated vegetation is deciduous forest and shrubs. Poorly-defined horizons. Large amount of soil biota to mix soil. Plants have long deep roots. Well drained but an iron pan may be present in the B horizon.

The Ao horizon is a layer of pine needles, heather and mosses, which generates a mor humus with a pH of 3.5 – 4. There is a thin layer of acid humus due to the nature of the waxy vegetation which is difficult to break down and the low temperatures. The A horizon is a far more distinct layer due to the short roots of the vegetation which do not penetrate and the lack of soil biota which reduce mixing. The horizon is an ash / grey colour as the nutrients and minerals have been leached out by the excessive rainfall (podsolization) this is referred to as the zone of eluviation. The B horizon the iron and aluminium oxides collect (illuviation) where the iron oxides can accumulate to form a thin layer of hardpan, which impedes drainage through the soil. Some iron and aluminium oxides get through the iron/hardpan, giving this its dull orange colour. The C horizon is derived from more acidic glacial / till rocks, this can further impede drainage.

Wherever rainfall exceeds evaporation and there is free downward movement of water through the soil pore system. Soluble minerals are leached or moved from the soil profile. Continual leaching tends to impoverish the upper mineral horizons by removal of basic minerals.&nbsp;

Draw a fully annotated soil profile of a Podzol soil to show its main characteristics (including horizons, colour, texture and drainage), and associated vegetation. 8

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 — softer rocks weathering more quickly with more drainage, producing thicker soils. Relief — lower altitudes results in warmer temperatures and a decrease 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.&nbsp;

Draw a fully annotated soil profile of a Gley soil to show its main characteristics (including horizons, colour, texture and drainage), and associated vegetation. 8

O Horizon - Thin black, acidic mor humus A Horizon – poorly drained.&nbsp;Darker colour.&nbsp; B Horizon – blue, grey colour.&nbsp;&nbsp;Almost continually waterlogged. Red brown mottling along root channels. C Horizon – impermeable clay

Clearly defined layers. Few soil biota to mix soil.

properties and formation processes of Podzol soils Brown earth soils Gley soils

Soil climate has two major components; Precipitation and temperature, influencing evaporation.&nbsp;When precipitation exceeds evaporation, leaching of the soil will occur. When evaporation exceeds rainfall capillary action will take place. Temperature determines the rate of reaction. In a warmer climate vegetation breaks down more quickly and enable lots of biota to survive.&nbsp;Colder climates cause a much slower breakdown of chemicals.

Look at Diagram Explain the main conditions and processes which have led to the formation of a Podzol soil. 8

Associated vegetation is coniferous forest or heather moorland. Plants have shallow, spreading roots. Well-defined horizons. Few soil biota to mix soil.

O Horizon - Thin black humus layer. Mor/acidic humus. A Horizon - Some darker staining in upper A horizon from humus. Ash-grey lower A horizon with sandy texture. E Horizon - Iron pan develops in impeding drainage and causing water logging. B Horizon -&nbsp;reddish-brown with denser texture due to downward leaching. C Horizon - is parent material, generally glacial weathered rock.

BIOSPHERE Higher Geography

Where evaporation exceeds precipitation, moisture moves upwards within the soil profile by capillary action. The takes with it certain minerals in the soil. It is therefore in the reverse direction to leaching. In Britain precipitation generally exceeds evaporation.&nbsp;As a result capillary action in British soils rarely occurs, apart from in very sandy soils.

The O horizon is a thick layer of humus particularly in autumn due to the varied and large amount of deciduous vegetation. This produces a mull humus, well mixed with the soil minerals thanks to the rapid decomposition due to bacteria and biota. 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. Indistinct layers within the soil. The B horizon&nbsp;has a lighter soil colour, varying 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.

Generally, the soil colour is determined by the amount of oxygen and the state of the iron. When oxygen mixes with the iron in the soils it oxidizes (rusts) forming red / brown soils. This happens in well aerated soils with lots of biota. This cant happen in soils which are heavily waterlogged as the pores are filled with water and forms grey soils (Gleys), although if pockets of oxygen occur a mottled effect happens of red speckles.&nbsp;

The parent material can influence the soil in several ways: colour texture&nbsp; structure mineral composition permeability/drainage

This soil has developed on Old Red Sandstone and so has derived its distinctive colour from its parent material.

The movement of material in solution from one horizon to another is referred to as translocation. 

The upper mineral horizon losing the material is the ELUVIAL or E horizon. This is where maximum leaching or eluviation (from the Latin word ex or e meaning out, and luv meaning washed) takes place. The E horizon near the surface of a podzol is a good example of an eluvial horizon. The lower horizon gaining the material is the ILLUVIAL horizon (often a subsoil or B horizon) (from the latin words il, meaning in, and luv, meaning washed).&nbsp;This is the zone of maximum accumulation.

Soils develop as a result of 5 factors:&nbsp;

The AO horizon - Acidic mor humus Juncus (rushes) and grass vegetation Plant roots do not penetrate deeply The A horizon – poorly drained.&nbsp;Darker colour.&nbsp;Red brown mottling along root channels. The B horizon – blue, grey colour.&nbsp;Iron compounds in soil are changed from normal red brown colour to blue grey. Almost continually waterlogged. The C horizon – impermeable clay Clearly defined layers

Soils develop very slowly.&nbsp;In Britain it takes about 400 years for 10mm of soil to develop. Young soils retain many of the characteristics of the parent material.&nbsp;Over time they acquire other features resulting from the addition of organic matter and the activity of organisms. The soils of Britain are relatively young because they are largely post-glacial.

Decomposition and Humification

Decomposition is the breakdown of plant derived material into its simpler organic constituents.&nbsp;This is accomplished by enzymes, earthworms, mites and other organisms. Humification is the breakdown of plant remains- leading to the formation of different types of humus.

MULL humus develops under deciduous woodland, where base-rich plant remains are actively broken down by a prolific soil biota. MODER humus is intermediate between mor and mull. MOR humus usually develops beneath coniferous woodland or heather moorland, under cool, wet climatic conditions. Breakdown is slow due to the absence of soil biota.

Characteristics of Podzol

Podzol - from the Russian words; pod = under zola = ash Extensive group of leached, acidic soils Distinctive light-coloured horizon found immediately below organic debris - eluvial horizon formed due to loss of iron/aluminium by leaching Mor humus with no recognisable plant remains Brightly coloured zone of iron/aluminium deposition - illuvial horizon

Darker zone of organic deposition Relatively unaltered C horizon at variable depth Most podzols are free draining

Name

Safari may block some audio or video from playing automatically and ‘read to me’ will skip these. You can configure this in Safari’s preferences.