Lithosphere Ecology lecture notes KVB
Lithosphere and Soil Science
Lithosphere
The lithosphere is the solid component of the Earth, encompassing the crust and the uppermost layer of the mantle.
The Earth is a solid, cooled, spherical planet revolving around the sun and rotating on its axis at a constant distance, creating day and night.
It consists of multiple layers: the outer crust, the mantle, and the core.
Core
The core is a nearly spherical, fluid or vaporized region approximately 2,500 km in diameter, believed to be primarily composed of Nickel and Iron. It is divided into two parts: the outer core, which is liquid, and the inner core, which is solid due to immense pressure.
Mantle and Crust
The mantle extends about 2,900 km above the core and is mainly in a molten state, allowing for the movement of tectonic plates.
The crust is the thin, outermost solid layer of the Earth, varying from 8 to 40 km in thickness, and it is divided into continental and oceanic crust.
The crust is complex, with surfaces covered by soil, which is crucial for supporting diverse biological communities by providing essential elements like food, shelter, and concealment from predators.
Soil Science
Soil Science encompasses various disciplines such as Pedology (the study of soils in their natural environment) and Edaphology (the study of the influence of soil on living things). It plays an essential role in agriculture, ecology, and environmental science, focusing on soil formation, classification, and mapping.
Soil Formation and Types of Rocks
Types of Rocks
Igneous Rocks: Formed through the cooling and solidification of molten magma or lava. Common examples include granite (intrusive) and basalt (extrusive).
Sedimentary Rocks: Created from the accumulation and consolidation of sediments, often containing fossils. Examples include shales, sandstone, and limestone.
Metamorphic Rocks: Formed by the alteration of existing rocks due to heat and pressure, resulting in textures and mineral compositions that differ from the original rocks. Examples include gneiss, schist, slate, quartzite, and marble.
Weathering of Rocks
Physical Weathering: Involves mechanical processes like temperature fluctuations, ice expansion, gravity, and the action of water and wind.
Chemical Weathering: Includes processes such as hydrolysis, oxidation, and carbonation, leading to the breakdown of minerals through chemical reactions.
Biological Weathering: Involves the actions of living organisms, such as lichens and mosses, which can break down rocks and extract minerals, facilitating soil development.
Lichens and mosses are often pioneers in ecological succession, promoting soil nutrient cycling through decomposition.
Chemistry of Soil-Forming Rocks
Rocks are complex chemical mixtures made up of numerous minerals, contributing to the soil's overall texture and fertility.
Types and Examples of Rocks
Igneous Rocks
Examples include basalt, pumice, obsidian, rhyolite, granite, and gabbro, each with unique cooling histories and mineral compositions.
Metamorphic Rocks
Examples include marble (from limestone), gneiss (from granite), schist, slate, and anthracite, showing varied textures and structures.
Sedimentary Rocks
Formed by deposition processes; examples include bituminous coal, chalk, conglomerate, diatomite, flint, limestone, silicious limestone, rock phosphate, rock salt, and red sandstone.
Structure of Soil
Soil Layers
O Horizon: The top layer composed mainly of organic matter like decomposed leaves and twigs, typically appearing brown or black, crucial for nutrient cycling.
A Horizon: The uppermost soil layer rich in humus and minerals, darker and looser than deeper layers; essential for supporting plant roots and storing moisture.
B Horizon: Subsoil layer with limited organic material compared to the A horizon, often contains minerals leached from above layers.
C Horizon: Composed of weathered parent material, containing few or no organic materials; its chemistry plays a critical role in the soil's pH and capacity for water retention.
Soil Morphology and Texture
Soil Texture Types
Coarse Textured Soils: Consisting mainly of sand and gravel, they retain little moisture and are typically well-draining.
Moderately Coarse Soils: Include sandy loam and very fine sandy loam, providing a balance of drainage and moisture retention.
Medium Textured Soils: A blend of sand, silt, and clay, ideal for retaining water and nutrients for plant growth.
Moderately Fine Textured Soils: High clay content leads to stickiness and plasticity when wet, holding significant moisture.
Fine Textured Soils: Composed of over 40% clay, they may restrict internal drainage but are nutrient-rich, enhancing fertility.
Soil Colour
Soil colour can reflect the mineral composition inherited from the parent material or result from soil-forming processes. While it does not directly influence soil functionalities, it can aid in distinguishing various soil types.
Red/Yellow Soils: Indicate the presence of iron oxides, often providing clues about the soil's drainage and aeration properties.
Dark Coloured Soils: Typically richer in organic matter, contributing to better fertility and soil structure.
Grey Soils: Often associated with water saturation and reduced iron, affecting nutrient availability.
Physical Properties of Soil
Soil Density: The average density of soils is typically 2.65 g/cm³, varying by texture and mineral composition.
Porosity: Refers to the volume fraction of pores (micro-pore and macro-pore) between soil particles, impacting water retention and aeration.
Permeability: Fundamental in determining water movement through the soil profile, significant for assessing drainage capabilities.
Soil Temperature: Influenced by solar radiation and the decomposition of organic matter; dark soils absorb more heat compared to light-coloured soils.
Soil Water: Integral for maintaining soil texture and livability, including gravitational, capillary, hygroscopic, and combined water—aiding in nutrient transport and root health.
Soil Permeability
Classified further based on permeability levels: non-porous, porous, non-permeable, and permeable, affecting irrigation and drainage practices in agriculture.
Soil Atmosphere and Chemistry
Soil Atmosphere
Contains essential gases including O₂, CO₂, and N₂, with higher moisture and CO₂ levels compared to the atmosphere, vital for microbial activities and plant growth.
Soil Solution
The soil solution is a mixture of dissolved minerals and nutrients necessary for plant development, influencing soil fertility and biological activity.
Soils can be classified based on nutrient concentrations:
Eutrophic: Optimal for nutrient content, supporting healthy plant growth.
Oligotrophic: Suboptimal nutrient levels, which may limit plant productivity.
Chemical Properties of Soil
Inorganic and Organic Components:(a) Major inorganic elements include aluminum (Al), silicon (Si), calcium (Ca), magnesium (Mg), iron (Fe), potassium (K), and sodium (Na). Additionally, trace elements like boron (B), copper (Cu), and zinc (Zn) are vital for plant growth.(b) Organic Matter: Primarily consists of humus, which is rich in proteins, sugars, and fats, characterized by its dark colour and absence of odour.(c) Colloidal Properties: Soils comprise crystalloids and colloids, exhibiting unique physico-chemical properties crucial for nutrient retention and exchange.(d) Soil pH: Typically ranges from 2.2 to 9.6, influencing soil reactions and biological activity, with effects of being acidic, neutral, or alkaline.
Soil Fauna and Flora
Microfauna: Includes organisms sized from 20µm to 200µm, such as protozoa and small mites, playing key roles in nutrient cycling.
Microflora: Dominated by bacteria (90%), also hosting soil fungi and actinomycetes, essential for organic matter decomposition and nutrient uptake.
Soil Fauna
Mesofauna: Comprising animals sized from 200µm to 1cm, including microarthropods, arachnids, and small insects, contributing to detritus breakdown and soil structure improvement.
Macrofauna: Larger organisms over 1cm, such as earthworms, molluscs, and larger insects, which aerate the soil, enhance fertility, and assist in organic material decomposition.