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Diploma of Environmental Monitoring & Technology
Study module 4
Matter in ecosystems
MSS024003A
Environmental
principles (Ecology)
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Ecological Principles (Ecology)
Study module 4 – Matter in ecosystems
MATTER IN ECOSYSTEMS
Introduction to Biogeochemical Cycles
What are nutrients?
NUTRIENT CYCLES
The carbon cycle
The Nitrogen Cycle
The Sulfur Cycle
The Phosphorus Cycle
2
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9
THE IMPORTANCE TO THE TECHNICIAN
10
ASSESSMENT & SUBMISSION
12
Knowledge questions
Assessor feedback
Assessment & submission rules
References & resources
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Study module 4 – Matter in ecosystems
Matter in ecosystems
Introduction to Biogeochemical Cycles
All of the previous sections have dealt with the laws, sources and uses of energy within
ecosystems, and how to depict the transfer of that energy through an ecosystem. To do this,
we have assumed that there were organisms (which, dead or alive are called biotic factors)
and their physical environments (abiotic factors) for the energy to flow through. We will
now focus on the matter found in those two factors. This leads to the following observation;
Energy flows in and out of an ecosystem in a linear fashion, yet matter is cycled within and
between ecosystems.
This statement will hopefully provide you with a platform of understanding about the
distinct difference between the pathways that energy and matter take in an ecosystem.
Remember that if energy did not dissipate, the Earth would continually absorb energy from
the Sun, and would get hotter and hotter. This does not happen, so the energy must go
elsewhere, it is only ever temporarily stored in an ecosystem.
Figure 4.1 – Theoretical flow diagram of energy (dashed lines) and matter (solid lines) in
ecosystems.
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Study module 4 – Matter in ecosystems
Matter, on the other hand, does not come from space in a continuous stream like sunlight
does, nor does it leave the Earth and go into space (like most energy does), so all the matter
on Earth must somehow just get used over, and over again, in accordance with Law of Mass
Conservation (or the first law of thermodynamics). This process of the continuous re-use of
Earths matter is called cycling.
If sunlight is the fuel and the engine of an ecosystem, then matter is the rest of the vehicle!
It follows that the movement of matter is energy driven via the processes of production and
of consumption. Figure 4.1 revisits the movement of matter and energy from earlier.
The word biogeochemical is a compound term consisting of the words biological, geological
and chemical, with the implication being that chemical matter is cycled through the
biosphere and the geosphere. Unfortunately, it fails to mention the atmosphere and the
hydrosphere, and rather than call it the biogeoatmohydrochemical cycle, we shall call them
nutrient cycles, as it is perfectly reasonable to assume that all of the major chemicals in an
unpolluted ecosystem are a) cyclic, and b) usable by organisms (even if only in trace
amounts). Figure 4.2 below shows how the concept of cycling occurs over a global scale.
Figure 4.2 – Generalised biogeochemical cycling (using phase change descriptors). The main
processes are production (via assimilation of nutrients), decomposition, gasification,
ionisation and sedimentation. Each individual nutrient will exhibit different transformations for
each phase.
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Study module 4 – Matter in ecosystems
The reason the term biogeochemical cycles exists is because of temporal and spatial scales –
large scale movements and cycles of materials over long timeframes (i.e. global, regional
etc) are termed biogeochemical, and catchments down to organism scale are termed
nutrient, presumably because the focus on the fate of the nutrient is different, either
organism or ecosystem based consumption as opposed to just the mass movement of the
chemicals.
What are nutrients?
We know from Study module 2 that every living organism requires certain materials to
either live (at all), or to at least live well. But what are these chemicals, and what do they
do? Table 4.1 below lists the most basic of chemical materials found in a generalised living
cell.
Element
Carbon
% of dry
Source
weight
50
organic compounds
or CO2
Oxygen
20
Nitrogen
14
Hydrogen
8
Function
Main constituent of cellular material
H2O, organic
compounds, CO2,
and O2
NH3, NO3, organic
compounds, N2
Constituent of cell material and cell water;
O2 is used in aerobic respiration
H2O, organic
compounds, H2
Main constituent of organic compounds and
cell water
Phosphorus 3
inorganic
phosphates (PO4)
Constituent of DNA and high energy bonds
Sulfur
1
SO4, H2S, S, organic
sulfur compounds
Constituent of proteins and coenzymes
Potassium
1
Potassium salts
Main inorganic cellular inorganic cation and
used for certain enzymes
Magnesium 0.5
Magnesium salts
Inorganic cellular cation, used in chlorophyll
(in a similar way to iron in a blood group)
Calcium
0.5
Calcium salts
Inorganic cellular cation, used in certain
enzymes
Iron
0.2
Iron salts
Component of blood proteins and certain
non-blood iron-proteins and used for some
enzymes
Constituent of proteins and enzymes
Table 4.1 – Average % composition of matter found in cells.
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Nutrient Cycles
As mentioned in Study module 2, a nutrient is any chemical that aids the growth of an
organism. Nutrients are physical abiotic factors, and as such can determine the presence or
absence, and the health of organisms in an environment, but do not generally determine
whether an organism lives or dies. In this section we will examine the following key points;
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The key nutrients cycled in the environment
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The reservoirs of the nutrients
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The pathways the nutrients take through an ecosystem (or to a sink)
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The changing of one species of chemical into another species (chemical speciation)
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How the flow of material controlled.
When examining and drawing nutrient cycles, it is best to use a compartmental approach
(box diagrams) so that boundaries are easily defined. With this in mind, we draw the three
abiotic spheres and define the chemical species in each sphere of the element in question.
Once this is done, we can look at the biotic interactions which are responsible for the
movement of the nutrients. You will examine the interaction of the anthrosphere and
ecosystems (i.e. pollution effects) in another program of study.
There are four major elements that are moved around the environment which act as
nutrients: carbon, nitrogen, sulfur and phosphorus.
The carbon cycle
The largest store of carbon dioxide is found in the Earth’s oceans and freshwater bodies. It is
from these ‘stores’ that carbon is distributed and transformed into the other forms of
carbon. Carbon is removed from the ocean into the atmosphere in several ways, including
pH and temperature, but the main way is by simple exchange with CO2 in the atmosphere.
As carbon is used in the creation of terrestrial biomass via photosynthesis, CO2 is ‘pulled’ out
of the water to replace it in process scientists call equilibrium. A very similar process occurs
in the water between aqueous carbon dioxide (bicarbonate, HCO3-) and photosynthetic
aquatic organisms.
In its most simplistic form, there are only four major processes controlling the carbon cycle;
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Biomass production (primary and secondary)
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Biomass consumption (primary and secondary)
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Mineralisation
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Sedimentation
As we have learnt, biomass production comes primarily in the form of glucose from
photosynthesis, and the production of carbohydrates, proteins and lipids from the
secondary production of consumers. This is illustrated in figure 4.3 as the lines from plants
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Study module 4 – Matter in ecosystems
to the atmosphere (which involves photosynthesis and respiration), and from the line from
plants to animals (secondary production). Note that respiration is also observed from
animals to the atmosphere.
Figure 4.3 – Illustration of the Carbon Cycle, showing the four major cycling processes;
production, consumption, mineralisation and sedimentation. Relative storage times for
atmosphere, biosphere and geosphere (and lithosphere) are also indicated.
Biomass consumption is performed via secondary production (the line from plants to
animals), but is also found in the detritus cycle (the lines from plants and animals to soil).
Both of these processes occur equally on land as they do in the ocean.
Mineralisation occurs when CO2 dissolved in water reacts with calcium and other minerals
to form metal carbonates such as limestone (CaCO3). These mineral deposits form another
‘sink’ by which carbon is stored. The mineralisation process, by which the carbon is released
as CO2 is pH dependant and can occur in any aqueous environment (such as lakes, rivers and
oceans). Mineralisation is found as the lines from water to soils and sediments.
The Nitrogen Cycle
Nitrogen is required by all organisms and is used in many biochemical reactions, as is found
in the production of chemicals such as chlorophyll in plants and hormones, enzymes and
tissues in all organisms. Nitrogen compounds are often the limiting factor for many species,
as found in algal blooms. Of all the major nutrient cycles, the nitrogen cycle is perhaps the
most complex. Although the atmosphere is approximately 78 % nitrogen (which makes the
atmosphere the largest repository for nitrogen), it is completely inert to heterotrophs and
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can only be assimilated from the gaseous form by autotrophic species. Figure 4.2 below
shows five of the major processes in the nitrogen cycle.
Elemental nitrogen must be fixed into a usable form before it can begin its cycle through the
environment. The fixation of nitrogen occurs via micro-organisms into a soluble form of
nitrogen called ammonium (NH4+), which is then assimilated and transformed into the form
of amino nitrogen (NH2) species which is used in proteins and the like in plants. Secondary
consumption carries the nitrogen into higher trophic organisms via secondary production
mechanisms.
Figure 4.4 – A generalised nitrogen cycle showing five major transformation processes. A
complete picture of a nitrogen cycle is dependent upon both the ecosystem type (i.e.
terrestrial or aquatic) and the species within it.
The next step in the cycle is ammonification, which releases the biochemical nitrogen into
ammonium (NH4+) ions. The next step involves bacteria which transform the ammonia into
nitrate (NO3-) via the nitrification step.
Depending upon the species of plant, either (or both) ammonium ions (NH4+) and nitrate
ions (NO3-) can be used by the plant via assimilation to make organic nitrogen compounds
such as proteins (e.g. chlorophyll) in much the same way as seen in the fixation process (it is
only the starting form of nitrogen that is different, N 2 versus either NH4+ or NO3-)
The final step in the nitrogen cycle takes the nitrate form of nitrogen and converts it back to
elemental (and other forms) of nitrogen in a process called de-nitrification, which becomes
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available for the start of a new cycle. A summary of these simplified processes is found in
Table 4.2.
Process
Transformation
Fixation
Conversion of gaseous elemental nitrogen N2 to ammonia NH3
Ammonification
Organic nitrogen, ON (e.g. proteins) is transformed to ammonia, NH3
Nitrification
Conversion of ammonia NH3 to nitrate NO3-
Assimilation
Conversion of ammonia, NH3 or nitrate, NO3- to organic nitrogen ON
De-nitrification
Conversion of nitrate, NO3- to gaseous elemental nitrogen, N2
Table 4.2 – Summary of the five major transformations found in the Nitrogen Cycle.
The Sulfur Cycle
Sulfur is one of the constituents of some proteins, vitamins and hormones (as seen in Table
4.1). It is an essential element, and many limitations are imposed on organisms that exhibit
sulfur deficiencies. The sulfur cycle is in many ways as comprehensive as the nitrogen cycle
as there are many forms sulfur, and therefore many microbial transformations that can take
place.
Figure 4.5 – The Sulfur Cycle
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If we start with decomposed material, then the essential steps of the sulfur cycle are:
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Desulfuration of organic sulfur to the inorganic form, hydrogen sulfide (H2S), which
occurs after decomposition. These materials can also be ‘locked’ in sedimentation
processes.
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Microbial oxidation of sulfides (S2-) and elemental sulfur (S8) and related compounds to
sulfate (SO42–).
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Microbial reduction of sulfate (SO42-) to for use in organic compounds (i.e. proteins etc)
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Sulfuration (microbial immobilization) of the sulfur compounds into the organic form of
sulfur as found in plants, and in animals after secondary productivity.
Human impact on the sulfur cycle is primarily in the production of sulfur dioxide (SO 2) from
industry (e.g. burning coal) and the internal combustion engine. Sulfur dioxide can
precipitate onto surfaces where it can be oxidized to sulfate in the soil (it is also toxic to
some plants), reduced to sulfide in the atmosphere, or oxidized to sulfate in the atmosphere
as sulfuric acid, a principal component of acid rain.
The Phosphorus Cycle
Phosphorus is an essential nutrient for plants and animals in the form of ions PO 43- and
HPO42-. It is a part of DNA-molecules, of molecules that store energy (ATP and ADP) and of
fats of cell membranes. Phosphorus is also a building block of certain parts of the human
and animal body, such as the bones and teeth.
Phosphorus normally occurs in nature as part of a phosphate ion, consisting of a phosphorus
atom and some number of oxygen atoms, the most abundant form (called orthophosphate)
having four oxygens: PO43-. Most phosphates are found as salts in ocean sediments or in
rocks. Over time, geologic processes can bring ocean sediments to land, and weathering will
carry terrestrial. Plants absorb phosphates from the soil. The plants may then be consumed
by herbivores that in turn may be consumed by carnivores. After death, the animal or plant
decays, and the phosphates are returned to the soil. Runoff may carry them back to the
ocean or they may be reincorporated into rock.
The primary biological importance of phosphates is as a component of nucleotides, which
serve as energy storage within cells (ATP) or when linked together, form the nucleic acids
DNA and RNA. Phosphorus is also found in bones, whose strength is derived from calcium
phosphate, and in phospholipids (found in all biological membranes).
Phosphates move quickly through plants and animals; however, the processes that move
them through the soil or ocean are very slow, making the phosphorus cycle overall one of
the slowest biogeochemical cycles.
However, recent findings suggest that phosphorus is cycled through the ocean on the
timescale of 10,000yr, suggesting that the phosphorus cycle may play a role in global
warming.
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Unlike other cycles of matter compounds, phosphorus cannot be found in air in the as a gas.
This is because at normal temperature and circumstances, it is a liquid. It usually cycles
through water, soil and sediments. In the atmosphere phosphorus is mainly small dust
particles.
Phosphorus is one of the longest cycles, and takes a long time to move from sediments to
living organisms and back to sediments.
Figure 4.6 – The Phosphorus Cycle [source]
The importance to the technician
A comparison can be made between the earth's surface system and a giant chemical
factory. In nature, material circulation is driven by energy from the sun. This is a mechanical
and inorganic view of the earth. In another and more realistic sense, the earth has a natural
metabolism; materials have circulated about its surface for millions of years in a complex,
interconnected web of biogeochemical cycles.
An array of physical, chemical, and biological processes weather and erode rocks and
transfer materials in and out of the atmosphere, from the atmosphere to the land and biota
and back again. Each element has a natural biogeochemical cycle. Life has evolved in this
system and plays a strong role in the development and maintenance of the system through
processes, fluxes, and feedbacks.
Human activities have contributed materials to the biogeochemical cycles. Some of these
materials enter element cycles already naturally in operation; they are the same chemical
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species that have circulated for millions of years. Other materials are synthetic compounds
and are foreign to the natural environment. These anthropogenic materials are leading to a
number and variety of environmental issues, including the possibility of global climate
change.
As environmental technicians you need to have a good understanding of how the ecosystem
works. You need to comprehend that human activities do change the way nature works, and
that as a result, environmental laws are put into actions which requires continuous
monitoring of the environment. This will be your job.
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Assessment & Submission
This section provides formative assessment of the theory. Answer all questions by typing
the answer in the boxes provided. Speak to your teacher if you are having technical
problems with this document.
Knowledge questions
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Type brief answers to each of the questions posed below.
◗
All answers should come from the theory found in this document only unless the
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1. Does matter dissipate through an ecosystem or is it cycled around ecosystems? 1mk
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5. What are the ‘big four’ nutrient cycles? 4mk
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6. The carbon cycle exhibits four main processes. List each one and describe what the
process is. 8mk
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7. List and describe the five nitrogen transformations. In your answer state the two
transformations that involve elemental nitrogen gas (N2). 10mk
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8. Provide one example of how human activity has altered the nitrogen cycle. 2mk
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9. What is the difference between ‘sulfuration’ and ‘desulfuration’ as it applies to the
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10. What form of sulphur is created by human activity that can adversely affect the quality
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11. What is the name of the common form of phosphate found in the environment? 1mk
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12. Explain why the phosphorus cycle can be one of the longest nutrient cycles? In your
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13. Provide an example of one use of phosphate by humans. 1mk
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Use the documents ‘Save As…’ function to save the document to your computer using
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References & resources
Resources
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http://www.environment.gov.au/parks/nrs/science/bioregionframework/ibra/index.html
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http://www.environment.gov.au/
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http://www.botany.uwc.ac.za/sci_ed/grade10/ecology/abiotic/abiot.htm
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http://www.umanitoba.ca/institutes/fisheries/
◗
http://www.physicalgeography.net/fundamentals/9e.html
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References
Note that some of these resources might be available from your teacher or library
Krohne.D.T. 2001. General Ecology 2nd Ed. Brooks Cole Publishing. Pacific Grove CA USA.
Manahan, S.E. 1999. Environmental Chemistry 7th Ed. CRC Press LLC. Boca Raton. USA.
Sturman. A. Tapper. N. The Weather & Climate of Australia & New Zealand. Oxford
Publishing, Melbourne, Australia.
Carlton, C. Chalson J. 2002. Plant Survey Methods (Comprehensive). NPWS (National Parks
Association of NSW inc. Canberra. Australia.
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