Nutrient Circulation
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Waste is in the form of
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All can contain nutrients and/or energy
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If the nutrients are not made available again, the
ecosystem will decline
Open ocean productivity is low
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dead organisms: animals/ plants/ leaves
faeces
urine
Any dead organisms are removed from the ecosystem
sink to ocean floor
Failure to recycle nutrients, reduces future growth
within an ecosystem.
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Farmers need to replace harvested nutrients with
fertiliser
Nutrient Circulation
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During degradation wastes are
decomposed to release inorganic ions
This is called - Mineralisation
Can be absorbed by plants and used for
growth
Circulation depends on activities of 2
groups
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Detritivores
Decomposers
Detritivores
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Detritivores = detritus eating invertebrates e.g
Earthworms, woodlice
Turn large pieces of organic waste into small
pieces (gain energy & nutrients for growth in
doing so)
Make humus (important soil constituent –for
aeration, water retention/ drainage)
Because they in turn enter food chains by being
eaten by other animals (e.g birds), they recycle
the nutrients (and energy) back into the
ecosystem.
Also increase the surface area of the detritus, so
that decomposers can act more quickly
Decomposers
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These are bacteria and fungi
Saprophytic (obtain nutrients and energy
directly from dead or decaying matter)
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A range of microbes found within soil
Can secrete enzymes which degrade molecules
e.g cellulase
External digestion, forming a soluble soup
easily absorbed
Vital in e.g Nitrogen cycle, carbon cycle
Decomposers live freely in soil or can be
found in detritivore digestive tracts
Rate of Decomposition
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Type of detritus (coniferous litter is slower
than deciduous)
Type and abundance of decomposers
Abiotic factors
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temperature
moisture (humus)
aeration (humus)
nutrient availability (nitrogen)
Nutrient Cycling
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Animals gain nutrients from food
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Plants/ microbes gain nutrients from soil
Macronutrients
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required in large amounts
e.g N, P, S
Micronutrients
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birds, some animals go to salt licks
required in smaller amounts
e.g Se, Mo, Mn
All nutrients need to be soluble before they can
be absorbed
Lack of water can lead to nutrients not being
available
Biogeochemical Cycles
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Minerals can be part of living world (biota)
or non living environment (abiota)
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e.g. nitrogen as protein or atmospheric gas
chemically transformed by e.g. lightning
or biologically fixed by e.g. Rhizobium
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Soluble so often removed by leaching
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Three cycles:
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Carbon cycle
Nitrogen Cycle
Phosphorous cycle
Nitrogen Cycle
fixation
ammonification
Ammonium
assimilation
denitrification
nitrification
nitrification
nitrite
Nitrogen Cycle
converted into
plant protein,
nucleic acids
etc.
converted into
animal protein,
nucleic acids
etc.
Rhizobium sp.
Fungi & bacteria
uptake by plant roots of
soluble nitrates
Thiobacillus denitrificans,
Pseudomonas,
Nitrococcus,
Clostridium
Nitrobacter
Ammonium
Nitrosomonas
nitrite
Carbon cycle
Phosphorous Cycle
Phosphorous Cycle
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Phosphorous essential to cell biochemistry
Phosphorous minerals are rel. insoluble
Continuously weathered from rocks
Solubility pH dependent
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Plants obtain phosphorous from soil
Phosphorous absorption often aided by mycorrhizal
associations (mutualism)
Animals obtain phosphorous from plants
Phosphorous availability often limits growth
Hence use of NPK fertilisers
Algal blooms induced by detergent effluent
Nitrogen Cycle
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5 major processes:
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Fixation
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Assimilation
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breakdown of dead/ waste materials to give ammonia
bacteria & fungi (saprotrophic)
Nitrification
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uptake of nitrate into plant roots, incorporation into
nitrogen containing molecules (protein/ nucleic acid)
In the cycle this is animal’s source of nitrogen
Ammonification
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converting atmospheric nitrogen into soluble nitrate
rhizobium bacteria (free or in nodules), lightning
conversion of ammonia into nitrates
2 step process
ammonia to nitrite (nitrosomonas; nitroso species)
nitrite to nitrate (nitrococcus, nitrobacter; nitro species)
Denitrification
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fixed nitrate lost by bacterial reduction to gaseous oxides
of nitrogen (pseudomonas, clostridium) or nitrogen gas
(thiobacillus dentirificans)