Fen Management Handbook - Scottish Natural Heritage

nutrients. For example, at high concentrations, calcium can react with soluble
orthophosphates to form insoluble calcium phosphates, thus helping remove
bio-available phosphorus from the system. Calcium concentrations are largely
determined by the local geology and groundwater inputs.
Magnesium (Mg 2+ ) and sodium (Na + ) have similar effects as calcium, such as
ameliorating acidic conditions via their associated carbonate and bicarbonate
ions, but they are less commonly observed in high concentrations in fen systems.
Exceptions include fen systems close to the coast, where aerial precipitation of
salts from the sea, and brackish influences on groundwater can increase sodium
concentrations in fen systems. Fens that occur in areas of dolorite-rich geology (e.g.
Magnesian Limestone that is found in parts of Nottinghamshire, South and West
Yorkshire and County Durham) can have elevated magnesium concentrations.
Chloride (Cl - ) can be found in elevated concentrations in some fen habitats that
are close to the sea, where concentrations of sodium are similarly increased.
However, increased Cl - can also indicate pollution inputs via ground or surface
water. Aluminium (Al 3+ ) and iron (Fe) concentrations are also important in fen
habitats, but this is due to their potential toxicity rather than their role as nutrients.
Both aluminium and iron are soluble under acidic conditions and in base-poor fen
systems these ions might therefore become bio-available in concentrations that limit
productivity or are directly toxic to plants.
Key processes relating to nutrients
Mineralisation Conversion of nutrients to inorganic and often plant-available forms – for example organic
nitrogen to nitrate or organic phosphorus to phosphate, undertaken by microorganisms..
Ammonification
Conversion of organic nitrogen to ammonia by microorganisms.
Nitrification Conversion of ammonia to nitrites and nitrate by microorganisms.
Denitrification Conversion of nitrate to gaseous nitrogen by microorganisms.
Nitrogen fixation Conversion of gaseous nitrogen to ammonia and then to organic nitrogen, requires specialist
microorganisms often in a symbiotic relationship with plants (e.g. nitrogen-fixing bacteria and
legumes).
Nitrate reduction Conversion of nitrate to ammonium under highly anaerobic conditions.
Absorption The process whereby atoms or molecules enter the bulk volume of a gas, liquid or solid.
Adsorption The mechanism by which nutrients are chemically bound to soil particles. This can be an
important mechanism of P immobilisation.
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