Glossary Flashcards
Abiotic
A non-living aspect of a system; e.g. geological or meteorological factors.
Ablation
The loss of mass from a glacier (e.g. by melting).
Abrasion
Physical wearing and grinding of a surface.
Abyssal plain
The flat part of the ocean floor that lies between about 4 and 6 km below the sea surface.
Accumulation
The gain of mass on a glacier (e.g. by snowfall).
Acidic cations
A positively charged ion that is able to interact with its surrounding water molecules to release one or more protons into solution, thus acting as an acid. An example is the Al3+ ion which is hydrated with six molecules of water, as [Al(H2O)6]3+, and can, depending on the solution pH, sequentially release protons, e.g.
[Al(H2O)6]3+ ⇌ [Al(H2O)5OH]2+ + H+
Acid rain
Liquid precipitation (rain) that is acidic; usually defined as having a pH of less than 5, to avoid confusion with natural acid rain. Emissions such as SO2 and NOx are oxidised in the atmosphere, and the oxidised products dissolve in water vapour, forming sulfuric and nitric acids. These acids increase the acidity of rainfall.
Actual evapotranspiration
The rate at which evapotranspiration occurs. It is dependent on a number of factors, including soil moisture content, vegetation type, rainfall and air temperature and movement.
adenosine triphosphate (ATP)
An energy-rich molecule which all cells use as a temporary store of energy. It is produced by respiration and used in a very wide array of biochemical processes.
Advection
In meteorology, the transport of air from one location to another. The term is generally applied to horizontal movement of air but vertical advection is also possible. Advection necessarily transfers atmospheric properties, such as humidity or cloudiness.
Aeolian
Pertaining to the wind.
Aerenchyma
Plant tissue type composed of hollow tubes. It is often abundant in the stems and roots of wetland species. It permits internal diffusion of gases within plants.
aerodynamic resistance
A measure of the effectiveness of air movement in aiding evaporation, as a function of the ‘roughness’ of the surface over which it blows.
A horizon
The surface horizon of a mineral soil consisting of organic matter mixed with mineral matter. The A horizon generally has maximum organic matter accumulation, maximum biological activity, and/or eluviation of materials such as iron and aluminium oxides and silicate clays.
Air
Approximately 80% nitrogen and 20% oxygen, plus a number of other gases present in trace quantities.
Air filled porosity
The proportion of a soil’s volume that is occupied by air.
Albedo
The reflection coefficient of a surface - the fraction of the amount of incoming radiation that is reflected from a surface.
algorithm
A calculation or formula that solves a recurrent problem.
aliquot
A small portion of a total amount of a solution.
alluvium
Loose (unconsolidated) sediments deposited by flowing water.
alteration
Change brought about by geological processes after initial rock formation, especially through the action of hydrothermal fluids.
aluminium buffer range
The soil solution pH (around pH 4.2–3.2) at which changes in pH are buffered by the dissolution of aluminium from clay minerals through the overall reaction:
AlOOH(s) + 3H+(aq) ⇌ Al3+(aq) + 2H2O(l)
Aluminium toxicity can be a major problem for soil biota and plant roots within this pH buffer range.
aluminosilicate
Minerals containing aluminium and silicon. In aluminosilicate minerals, aluminium (3+) replaces some silicon (4+), so one extra positive metal ion is needed for every silicon replaced.
aluminosilicate composition
Clay minerals containing aluminium and silicon. In aluminosilicate minerals, aluminium (3+) replaces some silicon (4+), so one extra positive metal ion is needed for every silicon replaced
ammonia volatilisation
The loss of NH3 from terrestrial ecosystems to the atmosphere.
Anabatic
Moving uphill, as in an anabatic wind, which is a warm wind that blows up a slope.
anaerobic
Oxygen-free conditions, typically found in waterlogged soils (bogs, swamps, marshes, etc.) and in the intestines of animals. The decomposition of organic matter (biomass) by bacteria adapted to these conditions (anaerobes) is the main natural source of atmospheric methane.
andesite
A fine-grained, intermediate, extrusive rock, with composition similar to diorite.
anemometer
An instrument for measuring wind speed.
aneroid barometer
An instrument for measuring barometric pressure.
angiosperms
A plant that produces flowers and whose seeds are covered by a protective layer of maternal tissue (e.g. fruit).
anion exchange capacity
The sum total of exchangeable anions that a soil can adsorb. Usually expressed as centimoles of charge per kilogram (cmolc kg-1) of soil (or of other adsorbing material, such as clay).
anions
Negatively charged ions.
anisotropy
The condition under which one or more of the hydraulic properties of an aquifer vary according to the direction of flow.
annual
A plant that completes its life cycle within a single year.
Anoxic
Oxygen-poor conditions, which can develop in soils and sediments if the supply of free oxygen is limited. The respiration of microbes adapted to these conditions releases trace gases containing nitrogen (N2, N2O and NO) and sulfur (H2S).
Antarctic
The region south of 66.6° S latitude, the Antarctic Circle.
Antarctic Bottom Water (AABW)
Antarctic Bottom Water (AABW)
Cold, dense bottom water mass that forms around the Antarctic continent (especially in the Ross and Weddell Seas) and spreads northwards in all three ocean basins.
anthropogenic
Produced as a result of human activity.
anticyclone
An extensive feature on a mean-sea-level pressure weather map around which air spirals out clockwise in the Northern Hemisphere (and anticlockwise in the Southern Hemisphere). Also referred to as a ‘high’.
aquifer
A porous or permeable, subterranean water-bearing body of rock through which water can flow easily to wells and springs. See also confined aquifer; perched aquifer; unconfined aquifer.
aragonite
A mineral with chemical composition CaCO3, but rarer than the other form of calcium carbonate, calcite.
Arctic
The region north of 66.6° N latitude, the Arctic Circle.
arête
A bedrock ridge formed by two glaciers eroding away on opposite sides.
artesian well
A well located within a confined aquifer.
assimilated
Describes material that has been incorporated into an organism’s tissues, either by photosynthesis or the uptake of food.
associates
A plant species that is neither constant within nor particularly characteristic of a particular community in which it occurs.
Atom
The smallest component of a chemical element.
atomic number
The number of protons in the nucleus of an atom.
attrition
Wearing down of grains of rock by the impact of one against another.
autopippettes
Mechanical or battery operated calibrated tubes that are designed to measure and deliver precise volumes of solution. An autopipette is constructed from metal and plastic and uses disposable tips.
autotrophs
An organism able to build its tissues from simple molecules such as CO2 and H2O.
available water
Water that is held in a soil between field capacity and permanent wilting point. Plants are able to access this water.
available water capacity (AWC)
The proportion of a soil’s volume occupied by water that is available for plant uptake, i.e. at water potentials between field capacity (water potential = -5 kPa) and wilting point (water potential = -1500 kPa.)
axis
An imaginary line that indicates the orientation of a rotating object, such as the Earth.
background atmosphere
Air with a composition typical of that found in regions that are geographically remote from major anthropogenic sources of primary air pollutants.
backing
An anticlockwise change in wind direction at one place over time, or above one place at the same time.
ball-and-stick model
A molecular model used to display molecules in 3D by representing the atoms by spheres. Atoms are connected by cylindrical rods which represent the bonds.
ball clay
A valuable commercial clay deposit consisting mostly of kaolinite, found especially in the vicinity of Newton Abbot, in the Teign catchment.
barchan dune
A crescent-shaped sand dune with horns pointing downwind.
barchanoid ridges
A sand dune type that consists of several joined barchan dunes forming a connected ridged row – these occur when the sand supply is greater than in the conditions that create a barchan dune.
barrier island
A long, narrow, offshore deposit of sand or sediments that parallels the coastline. Saltmarshes develop on the side of the island that is protected from the force of waves.
basalt
A fine-grained, mafic, igneous rock. It is usually formed by cooling of lava erupted at the Earth’s surface, but may also be found in vertical or horizontal sheets of lava, which cooled very quickly. On cooling, it may develop characteristic polygonal joint patterns.
baseflow
The flow rate of a river in situations where there has been no recent precipitation or snowmelt.
base level
The fixed lowest level of a river where it has its outlet into a lake or ocean. It is therefore the limiting level below which a stream cannot erode the land. For many streams, this hypothetical elevation is sea level.
base saturation
The percentage of basic cations (Ca2+, Mg2+, K+, and Na+) that comprise the total exchangeable cations in soil.
bathymetry
The study of underwater depth of lake or ocean floor
bauxite
The end-product of weathering in the tropics through extreme weathering of silicate minerals, and kaolinite. Bauxite is composed of variable proportions of gibbsite and other aluminium hydroxides, as well as some iron hydroxides, kaolinite and resistant heavy metals. It is an important raw material for aluminium production.
bay barrier
A ridge of sand or gravel that completely blocks the mouth of a bay.
beach drift
The lateral movement of sediments on a beach when the angles of swash and backwash differ
beaufort scale
A practical scale that relates the force of the wind (as a number from 0 to 12) to disturbance of the sea surface, or features across a land surface.
B horizon
A soil horizon, usually beneath the A horizon, characterized by a concentration of silicate clays, iron and aluminium oxides, and humus, alone or in combination, and often a higher bulk density than the A horizon. Coatings of iron and aluminium oxides may give the B horizon a darker, stronger, or redder colour than the other mineral soil horizons.
bioaccumulate
When an organism absorbs a toxic substance at a rate greater than that at which the substance is eliminated.
biochemical oxygen demand (BOD)
The capacity of a water sample to take up oxygen as a result of its constituent organic matter being oxidised by microbial respiration. It is measured using a standard protocol in which the sample of water is incubated for five days at 20 °C. (The term is used interchangeably with ‘biological oxygen demand’)
biodiversity
A general term that encompasses all aspects of biological diversity, from genetic variability to ecosystem complexity.
biogenic elements
An element that is essential to the biosphere.
biogeochemical cycling
A cycle of a biogenic element, between living organisms (the biosphere) and the non-living environment (the atmosphere, geosphere and hydrosphere).
biologically active nitrogen
Nitrogen that can be used by organisms.
biological oxygen demand (BOD)
The capacity of a water sample to take up oxygen as a result of its constituent organic matter being oxidized by microbial respiration. It is measured using a standard protocol in which the sample of water is incubated for five days at 20 °C.
biological pump
The transfer of CO2 from the surface waters to the deep ocean as a consequence of photosynthesis in shallow waters, the settling of organic matter, and organic decomposition in deep waters.
biomass
The total mass of living organisms within an ecosystem (or other defined area) at a point in time. Because the chemical composition of all organisms can be approximated by the formula for carbohydrate, (CH2O)n (where n is a whole number), the term is also used to describe the dead organic matter (i.e. food) that is oxidized during aerobic respiration.
biomes
A region of the Earth’s terrestrial surface that has a characteristic climate, vegetation type and fauna. Examples include tundra, desert and tropical forest.
biosphere
The total range of environments on Earth that support living organisms. It includes much of the atmosphere, hydrosphere and the Earth’s crust.
biotic
Pertaining to a living organism within a system.
biotic index
A scoring system used for indicating the quality of an environment by taking into account the types of organisms present in it.
bioweathering
The fragmentation and decomposition of rocks as a result of biological (usually plant) activity. Caused by root development and the formation of plant acids, or through respiration and decay. It can be either chemical or physical. Examples include hydrogen ion pumping by plant roots, CO2 released by microbes, or roots breaking apart rocks.
black body
An ideal absorber of electromagnetic radiation that would absorb all the radiation that was incident upon it. Such a body would also be an ideal emitter, and would emit electromagnetic radiation with a spectrum that depended only on the temperature of the body.
blow out
A deflation hollow created when wind removes loose sediments.
bottom-up controls
Regulation of an organism’s population size by the availability of a resource, such as food supply or nesting sites.
boulder train
A deposit formed by large numbers of erratics that fan out from their source in areas that have been covered by ice sheets.
boundary layer
The layer of fluid (e.g. water or air) close to a solid surface, whose movement is constrained by frictional forces.
box model
A conceptual representation of a cycle (e.g. a hydrological cycle, or a geochemical cycle) in which reservoirs of a substance are depicted as boxes and transport between reservoirs is shown by arrows. No details about the processes that occur within the boxes are provided.
BP
Years before present.
braided channel
Shallow stream channel that is subdivided into a number of continually shifting smaller channels that are separated by bar deposits.
breccia
A coarse- or very coarse-grained fragmental (sedimentary) rock in which individual fragments are angular
brown earth
A soil type formed under temperate forest, in which nutrients (especially cations) are recycled by the vegetation and podzolization is avoided. The soils are usually deep and even in colour, with rather indistinct horizons.
brown soils
Well drained soils with brownish to reddish-brown subsurface horizons denoting iron oxide formation. One of the six categories of the current classification of British Soils (Avery, 1990).
bryophytes
A plant without specialized conducting (vascular) tissue, such as xylem vessels or phloem sieve tubes. All mosses and liverworts are bryophytes.
buds
The growing point of a plant, which survives hostile periods, such as winter or the dry season, in a dormant state.
buffered
Protected against fluctuations in pH. Buffering is a feedback mechanism in which a small change in pH initiates a chemical reaction to counteract that change; e.g. increasing acidity in a carbonate-rich soil solution results in the formation of hydrogen carbonate ions and a reduction of the acidity.
buffer strips
A strip of land that has permanent vegetation that helps to control environmental problems. It works by trapping sediment; this slows down runoff that could enter the local surface waters, which enhances filtration of nutrient and pesticides.
bulbs
A perennating organ, usually below the soil surface, which is composed of thickened leaf bases protecting a dormant bud. (e.g. daffodil or onion).
Butterfly Monitoring Scheme
Method of monitoring the relative abundance of British butterflies, undertaken at a large number of sites throughout the year.
C2 cycle
A metabolic process occurring in leaves receiving excess light, which results in the loss of previously fixed carbon. It is based on the oxygenase activity of the enzyme rubisco and was formerly referred to as photorespiration.
calcareous
Description of rocks or soils that have a high pH and abundant calcium. They generally contain large amounts of calcium carbonate (e.g. chalk, limestone).
calcicoles
A plant adapted to grow on calcareous soils (e.g. the rock-rose, Helianthemum nummularium).
calcifuges
A plant adapted to grow on soils of low pH, where calcium is in short supply (e.g. the cross-leaved heath, Erica tetralix).
calcite
A mineral with the composition calcium carbonate (CaCO3).
calving
The breaking off of icebergs from a glacier terminating in tidewater.
campos
Type of natural, temperate grassland found in Uruguay and Brazil.
canopy
The vegetation layer that intercepts direct sunlight.
canopy resistance
The resistance to evaporation of the overall vegetation canopy.
capillary retention
A process whereby water clings to the walls of narrow openings.
carbonate buffer range
In soils dominated by carbonate rock, the soil solution pH (around pH 8–6) at which changes in pH are buffered by the dissolution of calcium carbonate:
CaCO3(s) + H+(aq) = Ca2+(aq) + HCO3-(aq)
Within this buffer range, soils and soil organisms generally are little affected by acid deposition.
carbonate compensation depth (CCD)
The level below which the rate of carbonate dissolution exceeds the rate of its introduction.
carboxylic acid group
A functional group (–COOH) having one oxygen bonded to carbon by a double bond and the oxygen of an –OH group bonded by a single bond. Carboxylic acid groups are abundant in the constituents of humus.
carnivores
An organism that consumes animals as a major part of its diet.
carotenoids
Yellow or orange pigments that have a role in light absorption and in protecting plant cells from light-induced damage.
carrying capacity
The maximum density of mature individuals that can be supported by a given level of resource.
catalyst
A substance that speeds up a chemical reaction without being consumed itself.
catalytic cycle
Pictorial way of representing a catalytic reaction mechanism sequence where the catalyst appears at the top of the cycle and the reactions are connected in a cyclic manner. The catalyst always remains within the cycle pathway whereas reactants join the cycle at given points and products leave at other points.
catchment
An area from which any precipitation either evaporates or appears in a flow out of the catchment. Typically, a catchment is a valley or series of valleys containing a river system.
cation exchange capacity
The total amount of exchangeable cations that a soil can absorb; usually expressed as millimoles charge or centimoles charge per kilogram.
cations
Positively charged ions.
cellulose
A structural molecule composed of sugar subunits, which is the main component of plant cell walls. It is a complex carbohydrate that is very difficult for animals to digest.
cement
Mineral crystals that grow within the pore spaces of a sedimentary rock, holding together the fragmentary grains. Usually calcite or silica in composition.
chalk
A very fine-grained limestone which is often quite soft and usually white or cream in colour. Chalk is usually composed of the minute skeletal plates (known as coccoliths) of tiny marine algae or foraminifera.
chamaephytes
A woody plant that holds its buds above the ground, but is usually not more than 25 cm high; one of Raunkaier’s plant life-forms.
channelised flow
The flow of water in channels. Water flowing in this manner can become turbulent, thus scouring the soil surface and accelerating erosion.
channel precipitation
(Abbreviation: Qp) Precipitation that falls directly into drainage channels.
Chapman mechanism
A set of reactions representing the formation and destruction of ozone in the stratosphere, first proposed in 1930 by the British scientist Sydney Chapman.
charge density
The ratio between the charge of an exchange surface and its area in direct contact with the soil solution or soil air; usually measured as cmol charge m-2.
chelating agent
An organic compound that donates or shares one or more of its electrons through covalent bonds with a metal atom or ion.
chemical weathering
The gradual decomposition of rocks and minerals as the result of chemical reactions with dilute aqueous acid (especially solutions of CO2) and dissolved oxygen, in rainwater or groundwater.
chemoautotrophs
An organism able to build its tissues from simple molecules (autotroph), using energy from chemical transformations such as the oxidation of sulfur compounds.
chlorophyll
A green photosynthetic pigment able to absorb light energy and convert it into chemical energy
chloroplast
An organelle within a cell that contains chlorophyll and is the site of photosynthesis.
C horizon
Deepest soil horizon, composed of unweathered, or only slightly weathered, substrate. The C horizon is relatively unaffected by biological activity and soil development and is lacking properties diagnostic of an A and B horizon. The A and B may or may not be formed from material weathered from the C horizon.
cirques
(also called corries) These are bowl-shaped depressions on mountainsides which are produced by erosion at the head of a glacier. They start to develop beneath a snowfield where frost shattering eats away at the rock and meltwater removes the resulting debris. As the snowfield becomes a glacier, plucking and abrasion enlarge the depression.
cirrus
A high cloud composed of ice crystals with a wispy, fibrous appearance.
class
A level of classification intermediate between order and phylum.
clay mineral
A sedimentary aluminosilicate mineral formed by the chemical decomposition of other aluminosilicate minerals such as feldspars, pyroxenes and amphiboles, with sheet structures related to that of the mica, biotite.
climax
The end point of an initial succession when the most productive vegetation has established itself. This is rarely a stable position however.
climax community
The vegetation type produced by successional processes that is regarded as being stable and self-perpetuating.
climbers
A plant that relies on other species for support (e.g. honeysuckle, Lonicera periclymenum).
clods
Soil aggregates formed by artificial processes, such as ploughing or digging.
closed
(ecosystem) Used to describe ecosystems that do not exchange material with the wider environment.
cloud base
The lowest level at which cloud droplets or ice crystals are observed, often corresponding to the level at which condensation occurs.
Course fish
Fresh water fish other than game, for example, pike, carp and bream.
cold front
The leading edge of cold air within a frontal depression.
community
A group of populations living together in the same habitat.
competitive exclusion
This term refers to the interaction between two species that require identical resources from the environment, when one or more of those resources is limiting. The result is that one species may outcompete and replace the other.
competitors
Plant species whose survival strategy is based on maximizing its capture of resources from the environment at the expense of its neighbours.
complexation
In soil science, the formation of a chemical bond between an ion in solution and the surface of a soil particle. Anions that form complexes include phosphate, silicate, and probably sulfate and choride. Metal ions can also form complexes with organic molecules.
conductivity
The measure of the amount of electrical current a material can carry; expressed in μS cm−1.
cone of depression
cone of depression
The fall of the water table around a well from which water is being pumped. The shape and extent of the cone of depression depend on the hydraulic conductivity of the rock, the rate of pumping, and the duration of pumping.
confined aquifers
Aquifers that are overlain by an impermeable bed.
conglomerate
A coarse- or very coarse-grained sedimentary rock in which individual fragments are rounded.
constancy of composition
The principle for seawater that, although the concentration of dissolved salts can vary from place to place, the relative proportions of the ions remains virtually constant.
constants
Plant species that occurs at a consistently high frequency through all variants of a plant community type.
consumers
Any heterotrophic organism. The term can be applied to herbivores, carnivores or detritivores.
contact metamorphism
Metamorphism resulting from the intrusion of hot magma into colder, surrounding rocks, usually limited to the area immediately surrounding an igneous intrusion (the metamorphic aureole).
contamination
Introduction of material or compounds into the environment or water supply at levels that may or may not harm the living organisms that live in or consume it.
continental
(Of an air mass) An air mass that forms over a surface that is predominantly dry land.
continental crust
The crust from which the Earth’s continental landmasses and surrounding continental shelves are composed. On average, it is of intermediate chemical composition, and is thus richer in silica than the oceanic crust.
continental shelf
The part of the ocean floor bordering the continents at a depth of 200 m or less below the sea surface.
continental slope
The part of the ocean floor extending from the edge of the continental shelf to the start of the continental rise. The continental slope has an average gradient of around 4deg.
convection
convection
Heat transfer process in which air is heated at a hot surface and rises, then cools and sinks again in a circulatory fashion.
core
The dense, iron-rich distinct central part of the Earth. The Earth’s core has an inner solid part of iron and nickel, and an outer liquid part of molten iron diluted by a less dense element (probably O, S or K).
Coriolis effect
The influence of the Earth’s rotation on the motion of air across its surface which produces an apparent deflection of air to the right of the direction of motion in the Northern Hemisphere, and to the left of the direction of motion in the Southern Hemisphere.
Coriolis force
An apparent force invented to explain the deflection of bodies moving over the surface of the Earth without being frictionally bound to it. It acts 90° to the right of the direction of motion in the Northern Hemisphere, and 90° to the left in the Southern Hemisphere.
corms
A short, swollen underground stem with one or more dormant buds, that lies dormant during unfavourable periods and contains a food store for rapid growth when conditions improve (e.g. Crocus spp.).
covalent bond
A chemical bond formed by sharing a pair of electrons, like the silicon-oxygen bond in the silicate etrahedral of silicate minerals.
crag and tail
A resistant rock knob with glacial deposits sited in its downstream shadow region.
Crassulacean acid metabolism
Crassulacean acid metabolism (CAM)
A photosynthetic pathway that allows plants in arid environments to harvest CO2 from the atmosphere during the night and store it for use during the day, thereby reducing water loss (e.g. many cacti and succulents).
crescentic dunes
These are crescent-shaped mounds or segments of sand ridges. Each segment is wider than it is long and is bounded on its concave side by a slip face. Such dunes are found in areas with a single wind direction
crevasses
Fractures in the surface of a glacier arising from the flow of the ice.
crust
The compositionally distinct layer overlying the mantle. In the terrestrial planets, the crust is richer in silica than the mantle. The Earth has two kinds of crust; oceanic crust and continental crust.
cryosphere
Those portions of the Earth’s surface where water is in solid form.
cryoturbation
The mixing of materials between various soil horizons affected by freeze-thaw processes.
crystalline rocks
Rocks composed of an interlocking mosaic of crystals, produced in igneous rocks by crystallisation from a magma, and in metamorphic rocks by the recrystallisation and growth of new minerals without melting.
cumulonimbus
A low cloud with a horizontal base and often an anvil-like, icy upper surface, which reaches to great heights. It produces showers of rain, snow, hail or sleet, or thunder and lightning.
cumulus
A type of low cloud with a flat base and heaped upper layers.
cuvette
A small tube of square cross-section, sealed at one end, made of plastic, glass or quartz and designed to hold samples for spectroscopic experiments.
cyclone
An extensive region of low pressure on a mean sea-level pressure weather map into which the air spirals anticlockwise in the Northern Hemisphere (and clockwise in the Southern Hemisphere). Also referred to as a ‘low’.
cyprinid
Cyprinidae is a family of freshwater fish and its members are commonly called cyprinids.
Darcys law
A relationship that, in various forms, can be used to predict the rate of flow or the mass flux of a liquid through a porous medium. One version of Darcy’s law states that the speed of water movement, v, down a slope through saturated soil between two points in a catchment that are a distance l metres apart, is partly determined by the difference in height, h, between them and the hydraulic conductivity of the soil, K, such that:
dark reactions
The second part of photosynthesis. These biochemical processes consume the hydrogen atoms and the high-energy electrons formed in the light reactions of photosynthesis, by combining them with carbon dioxide to make sugars.
decomposers
Organisms, primarily bacteria and fungi, that feeds on dead organic matter by secreting enzymes which digest it externally, releasing simple inorganic compounds such as CO2, water, NO3-, NH4+ and PO43-.
deflation
Erosion of unconsolidated material by wind.
deflected
(climax). A stable result of successional change in vegetation when external forces (usually human-derived) have prevented the development of the climatic climax vegetation type - typically by repeatedly grazing, mowing or burning an area. In the Teign catchment, grassland is a deflected climax because the climatic climax of deciduous forest is prevented from developing by grazing.
delayed throughflow
(Abbreviation: Qdt) The fraction of throughflow water (Qt) that travels slowly through the less permeable underground layers, see also quick throughflow (Qqt).
delta
A body of sediment deposited by a stream where it flows into standing water.
denitrification
Process in the nitrogen cycle carried out by microbes in anaerobic conditions, where nitrate acts as an oxidizing agent, resulting in the loss of nitrogen as it is converted to nitrous oxide (N2O) and nitrogen gas.
dependent variable
The variable plotted on a graph that depends on the variable fixed by the investigator, called the independent variable. The dependant variable is normally plotted on the y-axis (vertical axis) of a graph.
desert pavement
A natural residual concentration of closely packed pebbles, boulders, and other rock fragments on a desert surface where wind and water action has removed all smaller particles (by deflation).
detritivores
Soil organisms, primarily invertebrates including earthworms, centipedes, nematodes and mites, that consume dead or waste organic matter (detritus).
detritus
Fragments of dead or waste organic matter (such as fallen leaves, dead bodies, faeces).
dewpoint temperature
The temperature to which the drybulb temperature of an air sample must fall to produce saturation, at constant barometric pressure and absolute humidity.
diamicton
An unsorted, unstratified sediment regardless of origin.
diatoms
One of the most common type of phytoplankton and a major group of algae.
diffuse layer
Heterogeneous, loosely-held ions forming a layer of electric charge between an exchange surface and the soil solution.
diffuse source
Diffuse pollution can be caused by a variety of activity that has no specific point of discharge, for example, agriculture.
discharge
Water that runs from the land along channels such as streams and rivers. It is also referred to as streamflow or runoff.
dolomite
Carbonate rock-forming mineral of composition CaMg(CO3)2, or carbonate rock composed predominantly of this mineral. It occurs in limestone that has been dolomitised by the action of magnesium-bearing fluids.
Doppler effect
Where waves (of any kind, e.g. electromagnetic radiation, sound) have been reflected off an object and are then shifted in wavelength by an amount proportional to the object’s speed. An object moving towards an observer will produce a reduction in wavelength, whereas an object moving away will increase the wavelength.
Doppler Radars
Radars designed to sense the component of the wind that moves towards or away from them, by tracing particulate material suspended in the flow - such as raindrops.
Draas
Large-scale dunes with wavelengths measured in kilometres and heights measured in tens or hundreds of metres.
Drainable water
The amount of water in a soil between saturation and field capacity - i.e. the amount that drains out of a saturated soil under gravity.
drawdown
A lowering of the water table of an unconfined aquifer or a lowering of the potentiometric surface of a confined aquifer, caused by the pumping of ground-water from wells.
drift
All glacial, glaciofluvial and glaciomarine deposits
drumlin
A long streamlined hill composed of rock debris moulded into a mound by a glacial ice sheet.
dry adiabatic lapse rate
(Abbreviation: DALR) The rate at which an unsaturated parcel of air drops in temperature as it ascends through the atmosphere, exchanging no heat (i.e. adiabatic) with its surroundings. The DALR is 9.8 °C km−1.
dry air
All constituents of air, except water.
drybulb temperature
The temperature of air, usually measured inside a weather screen.
dry bulk density
The oven-dry mass of soil per unit bulk volume. The dry bulk density (sometimes referred to simply as bulk density) of a soil depends on the density of the soil particles and on their packing arrangement.
dry deposition
The transfer of airborne particles or gas directly from the atmosphere to the Earth’s surface (be it plant, soil, ocean, etc.).
Dystrophic
dystrophic
In this content, dystrophic is used to describe a brown water lake that is low in oxygen and supports little life due to the high levels of organic matter.
ecological dynamics
Processes by which species distributions change in time and space.
ecosystem
A unit of any size (e.g. a cowpat or the Earth itself) in which living organisms interact with one another and their abiotic environment. The defined unit is used to study food webs, energy flows and nutrient cycles.
Ecosystem services
Services provided by ecosystems that are of benefit to humans (e.g. flood prevention).
ecotones
Habitats that are transitional between two distinct vegetation types and form a vegetation gradient between them.
ectothermic
Relating to an organism that typically operates at the ambient temperature of its environment.
eddy viscocity
Internal friction between the molecules of a liquid that transfers momentum.
E horizon
E horizon
Horizon characterised by maximum eluviation (washing out) of silicate clays and iron and aluminium oxides; commonly occurs above the B horizon and below the A horizon.
Ekman drift
Ekman drift
The mean current across the Ekman layer.
Ekman layer
The depth of influence of the Ekman spiral.
Ekman spiral
The vertical spiral pattern of water velocities that develops in the upper ocean as a result of the Coriolis force acting on moving water. The pattern develops to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere.
Ekman transport
The volume of water transported by the Ekman drift.
electromagnetic radiation
A form of radiation that involves variations in electric and magnetic effects, and is emitted by all objects with a temperature above zero kelvin. Electromagnetic radiation is divided into subranges according to the wavelength of the waves that comprise the radiation, and includes radio waves, microwaves, infrared radiation, visible light, ultraviolet (uv) radiation, X-rays and gamma rays.
electromagnetic spectrum
The range of electromagnetic radiation, ranging from gamma rays at short wavelengths (high frequencies) through X-rays, ultraviolet radiation, visible light, infrared radiation and microwaves to radio waves at long wavelengths (low frequencies).
electron
electrons
A negatively charged particles, found outside the nucleus of an atom.
Eluvial
eluvial
Meaning ‘washed out’, describes where material has been removed in solution and suspension from a layer of the soil. (Elluvial contrasts with ‘illuvial’ which means ‘washed into’.
Endemic
endemic
Term describing a species whose range is confined to a given region.
endocrine disruptors
endocrine disruptors
Chemical that at certain doses, can interfere with the hormone system in animals (including humans) causing cancerous tumours, birth defects and other developmental disorders.
endotherm
An organism that raises its internal temperature by increased rates of respiration.
endothermic
Relating to an organism that maintains a stable body temperature by generating heat internally as required.
englacial
Refers to any location within the body of a glacier.
enzymes
Specialised proteins that catalyse a biochemical reaction.
epiphytes
epiphytes
A plant that does not normally root in the soil but grows upon another plant, or other object, remaining independent of it except for support.
equatorial
equatorial
The region at and near to the Equator, between the tropics at 23.4° N and 23.4° S.
equatorial trough
An west-east elongated pressure minimum, which stretches around the Earth’s surface within the lower latitudes of the tropics. It is associated with a belt of cloud and showery rain.
Permalink: Equatorial Trough
equilibrium line
equilibrium line
Conceptual line on a glacier surface separating accumulation and ablation areas, where net accumulation equals net ablation and net mass balance is therefore zero.
Erg
erg
Wind-blown deposits of sand greater than 30 000 km2 in area.
erosion
The process by which weathered rock is transported by wind, water or ice and deposited elsewhere.
Permalink: erosion
erratics
erratics
Rocks that have been transported by glaciers away from their origin and deposited in a region of dissimilar rock.
esker
esker
A long, narrow, often sinuous ridge of stratified glacial drift.
Eukaryotes
eukaryotes
Organisms that have their DNA packaged within a nucleus rather than free in their cytoplasm. Examples are protists, plants, animals and fungi. All multicellular organisms are eukaryotes.
eutrophic
eutrophic
Term describing water that is rich in nutrients.
eutrophication
eutrophication
The process of nutrient enrichment and its effect on living organisms.
evaporation
evaporation
The process of a liquid changing into a gas.
evaporite
evaporite
Evaporite deposits are rocks created by evaporation of seawater (e.g. gypsum, CaSO4).
evapotranspiration
evapotranspiration
The process by which water moves from the land surface into the atmosphere as vapour. It combines both direct evaporation from wet surfaces and transpiration from vegetation.
excess precipitation
excess precipitation
(Abbreviation: Pe) Term used in the context of the Horton and Hewlett hypotheses to represent the difference between the rate at which water falls on the ground and the rate at which infiltration occurs. Excess precipitation is then identified as overland flow.
Exchangeable cation buffer range
exchangeable cation buffer range
The soil solution pH at which changes in pH are buffered by the release of basic cations from pH-dependent exchange sites (primarily on organic matter), in exchange for hydrogen ions in solution. Occurs across the range of commonly occurring pH levels in soil.
exploitable storage
exploitable storage
The exploitable storage of water in an aquifer is the volume of water it will yield. It is described by
V multiplied by Y divided by 100
where V is the volume of the aquifer that is being exploited, and Y is the specific yield.
extrusive
extrusive
Description of igneous rocks that have been erupted as magma at the Earth’s surface.
eye
eye
The central core of intense tropical cyclones that have reached hurricane strength. The eye is typically -50km in diameter and is characterised by deep sinking motion, generally clear skies and light winds.
eyewall cloud
eyewall cloud
The cylinder-like ring of deep, extremely vigorous thunderclouds that encircles the eye of a hurricane, typhoon or cyclone. It is associated with the ring of most devastating surface winds and most intense precipitation.
Permalink: eyewall cloud
facilitation
facilitation
One model of ecological succession in which early successional species alter their environment in such a way that it becomes more favourable for other (late successional) species to become established.
family
family
A level of biological classification intermediate between genus and order.
felsenmeer
felsenmeer
A surface of angular, shattered rock produced by frost weathering.
felsic
felsic
A pale-coloured igneous rock, with a high proportion of feldspars and quartz (silica). Examples are rhyolite and granite.
ferromagnesian
ferromagnesian
Minerals which are rich in magnesium and iron. Also described as mafic. They are characteristically dark.
fertility
fertility
The quality of a soil that enables it to provide essential chemical elements in quantities and proportions for the growth of specified plants.
fetch
fetch
The distance of open water in one direction over which wind can blow.
field capacity
field capacity
The amount of water retained in soil after it has been saturated and allowed to drain freely for two or three days. At field capacity, the forces holding water to soil particles are approximately equal to the downward forces of gravitational pull.
fixed nitrogen
fixed nitrogen
Collective term for nitrogen compounds that are biologically active.
fjord
fjord
Where U-shaped glacial trough valleys with steep sides and a flat floor meet the coast, the resulting bay is called fjord.
flocculation
flocculation
Separation of colloidal particles from a liquid to form loose aggregations (Flocs).
floodplain
floodplain
That portion of a river valley, adjacent to the channel, that is built of unconsolidated sediments derived from the river and that may be submerged periodically by flooding.
flowers
flowers
Structures that aid the sexual reproduction of plants and encourage animals, particularly insects, to transport pollen between them.
food chain
food chains
A sequence of organisms, starting with a primary producer or detritus, with the following organisms in the chain all heterotrophs: some chains feature a sequence of herbivores and carnivores, and some a sequence of detritivores and decomposers.
food web
food web
A network of organisms within a particular community, which demonstrates the reliance of each on other organisms (or a source of detritus) in the web as a food source.
fractional crystallisation
fractional crystallisation
The physical separation of crystals from the magma in which they occur. Because the first crystals to form are less rich in silica than the remaining magma, fractional crystallisation leads magma to become enriched in silica.
fragmentary rocks
fragmentary rocks
See sedimentary rocks.
frazil ice
frazil ice
The initial form of sea ice: a slurry-like suspension of ice crystals.
freeze thaw weathering
freeze–thaw weathering
A form of physical weathering through the pressure generated by the expansion of freezing water within cracks or pores in rocks as it freezes.
frequency
frequency
(Of a wave, f) The number of complete cycles of a wave that pass a fixed point in unit time. Conventionally measured in the unit s−1.
(Of a species) The proportion of samples in which a given species occurs.
frost cracking
frost cracking
Fracturing of the ground by thermal contraction at sub-freezing temperatures.
frost heave
frost heave
An upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface.
frost shattering
frost shattering
See freeze thaw weathering.
fruit
fruit
The material surrounding the seeds of angiosperm plants. It is derived from maternal tissue.
fully mixed (or vertically mixed) estuaries
fully mixed (or vertically mixed) estuaries An estuary type dominated by large tidal currents and having low river flow, such that the waters are well mixed and the salinity does not vary with depth in the estuary channel, but increases towards the sea.
functional group
functional group
A group of covalently bonded atoms that exist together in a molecule, which usually behaves chemically in a particular way, i.e. shows a specific chemical functionality.
functional redundancy
functional redundancy
A term describing ecosystems in which there are several species performing the same function. Therefore, if one species declines or disappears, another species replaces it (e.g. insects as food for the greater horseshoe bat). It is an important factor in determining ecosystem stability.
functional types
functional types
Grouping of species that perform similar functions or employ similar survival strategies.
fundamental niche
fundamental niche
The range of environments in which a given species could survive in the absence of competition from other species.
gelifluction
gelifluction
The seasonal freeze–thaw action upon waterlogged soils which induces downslope movement.
Genera
genera
The plural form of genus. A classification by type, in this case of clouds.
Genus
genus
A level of classification intermediate between species and family. It is a group of species that have many features in common and can on occasion interbreed.
Geoconservation
geoconservation
Geological and geomorphological conservation or Earth heritage conservation.
Geodiversity
geodiversity
The variety of rocks, minerals, fossils, landforms, sediments and soils in an area, together with natural processes, such as erosion and landslips.
Geopark
geopark
An area with an outstanding geological heritage that is internationally significant.
geophytes
geophytes
Plant that has its buds below ground during its dormant phase; one of Raunkaier’s plant life-forms.
geostationary orbit
geostationary orbit
An orbit at 6.7 Earth radii from the centre of the Earth above the Equator, such that a satellite completes one orbit in 24 hours and hence remains stationary above a fixed point on the Earth’s surface.
gibbsite
gibbsite
An aluminium oxide clay mineral, in which aluminium ions form octahedra by sharing OH− ions. These octahedra combine to form sheets that are stacked on top of each other and held in place by hydrogen bonds. Gibbsite is common in highly weathered soils, such as oxisols.
Glacial marine drift
glacial marine drift
Drift deposited in the sea from floating ice bodies.
Glacial trough valley
glacial trough valleys
A glacially eroded U-shaped valley.
Glaciated
glaciated
Terrain formerly covered by glaciers or ice sheets, bearing their imprint in terms of landforms and sediments.
Glaciarised
glacierised
Terrain currently covered by glaciers or ice sheets.
Gley soils
gley soils
Soils that developed under poor drainage; the waterlogging and anaerobic conditions resulting in the reduction of iron to give the soils a characteristic blue-grey colour.
gneiss
gneiss
A medium- or coarse-grained metamorphic rock, composed of alternating bands of felsic and mafic minerals, formed at very high pressures and temperatures during regional metamorphism.
goethite
goethite
A common iron oxide clay mineral, in which Fe3+ ions share O2− and OH− ions and are arranged in octahedra. Goethite is a weathering product of moderate climates, and gives many mid-latitude soils their characteristic brown colour.
graded stream
graded stream A stream (or river) that has a concave longitudinal profile (i.e. a gradient that decreases from source to mouth) and in which inputs and outputs of sediment load are balanced.
granite
granite
A coarse-grained, felsic, intrusive, igneous rock with a chemical composition similar to that of rhyolite; formed as the result of slow cooling at depth beneath the Earth’s surface.
ground layer
ground layer
The lowest layer of a plant community, usually comprising mosses and rosette herbs (e.g. less than 0.1 m above the ground surface).
ground moraine
ground moraine
Unconsolidated material deposited directly beneath the base of a glacier.
groundwater
groundwater
The water that penetrates the ground surface and is contained in pore spaces in rocks located below the water table, or located in a confined aquifer.
groundwater flow
groundwater flow
(Abbreviation: Qg) The flow of water through a saturated underground region.
guild
guild
A group of species that exploit the same kind of resources in comparable ways e.g. snakes that hunt anuran prey using venom.
gullyy erosion
gully erosion
Process whereby water accumulates in narrow channels and, over short periods, may remove soil from these channels to considerable depths.
gymnosperms
gymnosperms
A plant with vascular tissue and which produces seeds, but the seeds are naked (i.e. not covered by fruit). All conifers are gymnosperms.
gyre
gyre
A large-scale circulatory feature of the ocean circulation, usually extending across many thousands of kilometres.
habitat
habitat
The environment in which an organism lives. The term is most strictly applied to the range of environments a particular species inhabits, but in practical use it is often defined by reference to a community rather than an individual species.
habitat fragmentation
habitat fragmentation
The process by which once extensive areas of relatively uniform habitat are broken up (usually by human activity) into small blocks separated by tracts of a very different habitat type.
hadley cells
Hadley cells
The cellular motion of air in the north-south vertical plane that occurs within the tropics.
half life
half-life
The time taken for half of the number of atoms of the parent radioactive isotope to decay into its daughter isotope.
halophytes
halophytes
Any plant that grows in saline environments and readily takes up salts.
hanging valley
hanging valley
A valley eroded by a small tributary glacier that joins the main valley of the larger glacier at a higher elevation than the larger valley floor.
hazard
hazard
A substance or environmental agent or condition with a potential to cause harm
head
head
(In the context of water) The difference in height between two points on a sloping water table.
helical flow
helical flow
Movement of water within a stream that occurs as spiral flows.
hemicryptophytes
hemicryptophytes
Plant that has its buds at the level of the ground surface (often hidden by snow or litter) during its dormant phase; one of Raunkaier’s plant life-forms.
hemisphere
hemisphere
One of two halves of the Earth, divided by the Equator; known as the Northern and Southern Hemispheres. The Western and Eastern Hemispheres are separated by the prime meridian (0° of longitude).
herbivore
herbivores
Organism that primarily eats plant material (e.g. the water vole, Arvicola terrestris).
herb layer
herb layer
The layer of a plant community composed primarily of herbaceous species including grasses (e.g. 0.1–1.0 m above the ground surface).
heterogeneous
heterogeneous
Term describing a substance that has different characteristics in different locations (i.e. non-uniform).
heterotrophs
heterotrophs
Organisms that obtain energy and materials from eating the tissues or products of other organisms.
homogenous
homogeneous
Term describing a substance that has identical characteristics everywhere (i.e. uniform).
horizons
horizons
A soil layer approximately parallel to the land surface with characteristic features that often gives information about the processes that formed the soil.
horn
horn
A pyramid-shaped mountain peak created by several glaciers eroding away different sides of the same mountain.
horton hypothesis
Horton hypothesis
An explanation of the way that rainfall reaching the surface of the ground divides into a component that flows over the surface and a component that penetrates the ground. The idea is based on the way that the ability of the ground to absorb water changes with the progress of a rainstorm.
humidity
humidity
A measure of how close the air is to saturation with water vapour.
humus
humus
The stable, dark-coloured organic material that accumulates as a by-product of decomposition of plant or animal residues added to soil. The term is often used synonymously with soil organic matter.
hurricane
hurricane
A tropical cyclone in the North Atlantic or the northeast Pacific Ocean. Hurricanes in the Atlantic Ocean can have landfalls in southeastern USA, the Caribbean and Central America.
hybrids
hybrids
The offspring of parents from different genetic lines. These may be from within a species, from different species (interspecific hybrid) or even different genera (intergeneric hybrid).
hydrated oxide-clay minerals
hydrated oxide-clay minerals
Alteration minerals formed by severe weathering, including hydrated iron (III) oxides (goethite and hematite) and hydrated aluminium oxide (gibbsite). Dominant in highly weathered soils, especially in the tropics.
hydration
hydration
Part-physical, part-chemical union between an ion or compound and one or more water molecules, the association being stimulated by the attraction of the ion or compound for either the hydrogen or the unshared electrons of the oxygen in the water.
hydraulic conductivity
hydraulic conductivity
The volume of water that will flow through a unit cross-sectional area of rock per unit time, under a unit hydraulic gradient and at a specified temperature.
hydraulic gradient
hydraulic gradient
The slope of the water table, defined as h/l, where h is the height difference and l is the length difference between two points.
hydraulic radius
hydraulic radius (R) A characteristic of a cross-section of a river, defined as the cross-sectional area of the river divided by the wetted perimeter.
hydrogen-abstraction reactions
hydrogen-abstraction reactions
In an atmospheric context, a reaction in which the hydroxyl radical reverts back to a stable water molecule by abstracting a hydrogen atom from some other molecule (e.g. methane or other hydrocarbons).
hydrogen bond
hydrogen bond
Weak, directional bond formed between slightly positively charged hydrogen atoms (attached to strongly electron-attracting atoms like oxygen and nitrogen), and similar strongly electron-attracting (and therefore slightly negatively charged) atoms, usually in other molecule.
hydrograph
hydrograph
A plot of river discharge at a particular cross-section of river against time.
hydrographic section
hydrographic section
The standard way for presenting a series of CTD (seawater conductivity and temperature, and depth) measurements taken across an ocean or a feature in the ocean.
hydrological cycle
hydrological cycle
Also called the water cycle. Circulation of water from the ocean through the atmosphere to the land and ultimately back to the ocean.
hydrologically effective precipitation
hydrologically effective precipitation
Effective precipitation. The difference between precipitation and actual evapotranspiration.
hydrology
hydrology
The study of the occurrence, distribution and chemistry of all waters of the Earth.
hydrolysis
hydrolysis
The reaction between water and a compound (commonly a salt or mineral) in which the hydroxyl from the water combines with the cation from the compound undergoing hydrolysis to form a base; the hydrogen ion from the water combines with the anion from the compound to form an acid. In this way, metal cations within mineral structures are replaced by hydrogen ions in soil water.
