6 - Processes
a
Absorption
Uptake of matter or energy by a substance.
Adsorption
Process by which atoms, molecules or ions are retained on the surfaces of solids by chemical or physical bonding.
Ammonification
Conversion of organically bound N into ammonium-N by soil biota.
b
Buffering of fields
The presence of terraces, treelines, buffer zones, riparian zones, which all contribute to intercepting overland flow.
d
Denitrification
Conversion of nitrate-N into N2O-N and dinitrogen-N.
Drainage (artificial)
Man-made adjustments to a field directed at the removal of excess water by ditches, subsoiling, pipes.
e
Eutrophication
Process through which a waterbody, such as a lake or a soil solution, becomes enriched with dissolved nutrients. This can be natural, but is often due to pollution. Eutrophication may result in algal blooms which finally promote anaerobic conditions which may harm fish life.
f
Flooding
Inundation of land beside a watercourse, as a result of an excessive water table. This may incur addition of sediment onto the land surface as well as into the water.
h
Humification
Process whereby the carbon of organic residues is transformed and converted to humic substances through biochemical and abiotic processes.
i
Immobilisation
Conversion of water-soluble elements into organic compounds by soil biota.
l
Leaching
Removal of soluble materials from one zone in soil to another via water downward movement in the profile.
m
Mineralisation
The degradation of organically bound elements (N, P, S) by soil biota into plant-available (inorganic) forms.
n
Nitrification
Conversion of ammonium-N into nitrite-N and nitrate-N by soil biota.
o
Overland flow
Excess water leaving a field horizontally across the soil surface because it cannot infiltrate into the soil, eventually ending up in a ditch or stream (= surface runoff).
Oxidation
The addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. In the environment, organic matter is oxidized to more stable substances. Oxidation is the opposite of ‘reduction’. Oxidation of organic matter is termed ‘burning’, and that of iron ‘rusting’.
p
Percolation
The movement of water through the soil.
r
Reduction
The addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic conditions (where there is no dissolved oxygen present) such as in ‘gley’ soils, sulphur compounds are reduced to odour-producing hydrogen sulphide (H2S) and other compounds. Reduction is the opposite of oxidation.
Runoff
The precipitation discharged into stream channels from an area. The water that flows off the surface of the land without sinking into the soil is called surface runoff. Water that enters the soil before reaching surface streams is called groundwater runoff or seepage flow from groundwater.
s
w
Weathering
The process by which materials in rocks or other deposits are broken down into smaller parts and ultimately their constituents. An example is ‘freeze thaw’ expansion and cracking. There are physical, chemical and biological weathering processes.