Study module 4
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Ecological Principles (Ecology)
MATTER IN ECOSYSTEMS
Introduction to Biogeochemical Cycles
What are nutrients?
NUTRIENT CYCLES
The carbon cycle
The Nitrogen Cycle
The Sulfur Cycle
The Phosphorus Cycle
THE IMPORTANCE TO THE TECHNICIAN
ASSESSMENT & SUBMISSION
Knowledge questions
Assessor feedback
Assessment & submission rules
References & resources
Study module 4 – Matter in ecosystems
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Ecological Principles (Ecology)
Study module 4 – Matter in ecosystems
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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Ecological Principles (Ecology) 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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Ecological Principles (Ecology) 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.
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 % of dry weight
Carbon 50
Source organic compounds or CO
2
Oxygen
Nitrogen
20
14
H
2
O, organic compounds, CO
2
, and O
2
NH
3
, NO
3
, organic compounds, N
2
Function
Main constituent of cellular material
Constituent of cell material and cell water;
O
2
is used in aerobic respiration
Constituent of proteins and enzymes
Hydrogen 8
Phosphorus 3
Sulfur 1
H
2
O, organic compounds, H inorganic
2 phosphates (PO
4
)
SO
4
, H
2
S, S, organic sulfur compounds
Main constituent of organic compounds and cell water
Constituent of DNA and high energy bonds
Constituent of proteins and coenzymes
Potassium 1
Magnesium 0.5
Calcium 0.5
Potassium salts
Magnesium salts
Calcium salts
Main inorganic cellular inorganic cation and used for certain enzymes
Inorganic cellular cation, used in chlorophyll
(in a similar way to iron in a blood group)
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
Table 4.1 – Average % composition of matter found in cells.
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Ecological Principles (Ecology)
Study module 4 – Matter in ecosystems
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;
◗
The key nutrients cycled in the environment
◗
The reservoirs of the nutrients
◗
The pathways the nutrients take through an ecosystem (or to a sink)
◗
The changing of one species of chemical into another species (chemical speciation)
◗
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 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 CO
2
in the atmosphere.
As carbon is used in the creation of terrestrial biomass via photosynthesis, CO
2
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, HCO
3
) and photosynthetic aquatic organisms.
In its most simplistic form, there are only four major processes controlling the carbon cycle;
◗
Biomass production (primary and secondary)
◗
Biomass consumption (primary and secondary)
◗
Mineralisation
◗
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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Ecological Principles (Ecology) 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 CO
2
dissolved in water reacts with calcium and other minerals to form metal carbonates such as limestone (CaCO
3
). These mineral deposits form another
‘sink’ by which carbon is stored. The mineralisation process, by which the carbon is released as CO
2
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.
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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Ecological Principles (Ecology) Study module 4 – Matter in ecosystems 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 (NH
4
+ ), which is then assimilated and transformed into the form of amino nitrogen (NH
2
) 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 (NH
4
+ ) ions. The next step involves bacteria which transform the ammonia into nitrate (NO
3
) via the nitrification step.
Depending upon the species of plant, either (or both) ammonium ions (NH
4
+ ) and nitrate ions (NO
3
) 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 NH
4
+ or NO
3
)
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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Ecological Principles (Ecology) Study module 4 – Matter in ecosystems available for the start of a new cycle. A summary of these simplified processes is found in
Table 4.2.
Process
Fixation
Ammonification
Nitrification
Assimilation
De-nitrification
Transformation
Conversion of gaseous elemental nitrogen N
2
to ammonia NH
3
Organic nitrogen, ON (e.g. proteins) is transformed to ammonia, NH
3
Conversion of ammonia NH
3
to nitrate NO
3
-
Conversion of ammonia, NH
3
or nitrate, NO
3
- to organic nitrogen ON
Conversion of nitrate, NO
3
to gaseous elemental nitrogen, N
2
Table 4.2 – Summary of the five major transformations found in the Nitrogen 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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Ecological Principles (Ecology) Study module 4 – Matter in ecosystems
If we start with decomposed material, then the essential steps of the sulfur cycle are:
◗
Desulfuration of organic sulfur to the inorganic form, hydrogen sulfide (H
2
S), which occurs after decomposition. These materials can also be ‘locked’ in sedimentation processes.
◗
Microbial oxidation of sulfides (S 2) and elemental sulfur (S
8
) and related compounds to sulfate (SO
4
2– ).
◗
Microbial reduction of sulfate (SO
4
2) to for use in organic compounds (i.e. proteins etc)
◗
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.
Phosphorus is an essential nutrient for plants and animals in the form of ions PO
4
3 and
HPO
4
2. 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: PO
4
3. 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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Ecological Principles (Ecology) Study module 4 – Matter in ecosystems
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 ]
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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Ecological Principles (Ecology) Study module 4 – Matter in ecosystems 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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Ecological Principles (Ecology)
Study module 4 – Matter in ecosystems
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.
◗
Type brief answers to each of the questions posed below.
◗
All answers should come from the theory found in this document only unless the question specifies other.
◗
Marks shown next to the question should act as a guide as to the relative length or complexity of your answer.
1.
Does matter dissipate through an ecosystem or is it cycled around ecosystems? 1mk
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2.
What is meant by the term ‘cycling’ as it pertains to an ecosystem? 2mk
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3.
What is the difference between a ‘biogeochemical’ cycle and a ‘nutrient cycle’? 1mk
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4.
Provide a simple example of how anthropogenic activity has affected the nutrient cycles? 2mk
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Ecological Principles (Ecology) Study module 4 – Matter in ecosystems
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 (N
2
). 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 sulphur cycle? 4mk
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10.
What form of sulphur is created by human activity that can adversely affect the quality of the atmosphere? 2
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Ecological Principles (Ecology) Study module 4 – Matter in ecosystems
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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 answer, identify which components of an ecosystem phosphates move through ‘quickly’ and those in which it moves ‘slowly’. 6mk
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13.
Provide an example of one use of phosphate by humans. 1mk
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14.
Why is a rudimentary understanding of nutrient cycles important to an environmental technician? 2mk
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Ecological Principles (Ecology)
◗
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Study module 4 – Matter in ecosystems
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Resources
◗ http://www.environment.gov.au/parks/nrs/science/bioregionframework/ibra/index.html
◗ http://www.environment.gov.au/
◗ http://www.botany.uwc.ac.za/sci_ed/grade10/ecology/abiotic/abiot.htm
◗ http://www.umanitoba.ca/institutes/fisheries/
◗ http://www.physicalgeography.net/fundamentals/9e.html
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Ecological Principles (Ecology)
References
Study module 4 – Matter in ecosystems
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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