Columbia Southern Atmospheric Carbon Dioxide Levels Question Response QUESTION 7Describe how atmospheric carbon dioxide levels fluctuate daily, seasonally,

Columbia Southern Atmospheric Carbon Dioxide Levels Question Response QUESTION 7Describe how atmospheric carbon dioxide levels fluctuate daily, seasonally, and geographically. Explain why such fluctuation occurs. Your response should be at least 75 words in length.QUESTION 8Describe the movement of an atom of nitrogen from the leaf of a plant, through the process of decomposition, and back into the root of another plant.Your response should be at least 200 words in length. Adobe Captivate
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Unit VI: Part 2
Ecosystem Ecology: Energy Flow and
Nutrient Cycles
(Mploscar, 2016)
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Unit VI, Ecosystem Ecology: Energy Flow and Nutrient Cycles
Course Learning Outcome
4. Summarize the importance of biodiversity within the environment.
5. Detail the global exchange of nutrients through biogeochemical cycles
Unit Learning Outcomes
4.1. Describe the reciprocal effect that human activities have on community biodiversity.
5.1 Describe the process by which energy becomes fixed in an ecosystem.
5.2 Explain the purpose and process of decomposition in the energy cycle.
5.3 Summarize the routes by which different nutrients are taken up from the soil and water, incorporated into living tissues
and returned to the soil and water.
(Hansson, 2009)
(Welcome1to1the1jungle, 2014b)
(National Aeronautics and Space
Administration, 2014)
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Unit Lesson
Biogeochemical Cycles
So far, we have looked at the cycling of nutrients through an ecosystem by net primary productivity and decomposition. These are
biological processes. Now, let’s examine how abiotic components affect the cycling of nutrients, specifically rock, water, soil and the
atmosphere.
Many nutrients are found in their mineral form in rock. The weathering (breakdown) of rock releases minerals into the soil and water,
making them available for plant uptake. Water works to weather rock and transport minerals. Water, in the form of rainfall, can deposit
nutrients from the atmosphere, as well as leach away nutrients from the soil. Many minerals form salts in the soil, which then dissolve in
the water and eventually make their way to the ocean. Salts can remain in the ocean indefinitely or become incorporated into the Earth’s
crust through sedimentation (e.g., salt beds, limestone, silt deposits). Then, they become a part of the mineral rock again.
One of the largest stores of two essential nutrients, nitrogen and carbon, is the atmosphere. In fact, nitrogen is the dominant gas in the
Earth’s atmosphere (about 78%). Because of these atmospheric stores of nutrients, nitrogen and carbon cycles have to be studied on a
global scale. Other nutrients, such as phosphorus, do not have a gaseous state and can be studied on the ecosystem level. For all nutrient
cycles, energy is required at each stage. In order to understand the nutrient cycles on an ecosystem level, we first must find out the major
inputs and outputs.
Inputs and Outputs
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Since we generally study nutrient cycles at the ecosystem level, inputs into that system are anything that originates outside of the defined
ecosystem. As we just mentioned, a large source of nitrogen and carbon is the atmosphere. Therefore, atmospheric inputs must be
accounted for in these nutrient cycles. Calcium and phosphorus come mainly through the weathering of rock, creating mineral soil,
which is another major input. In addition to these large input sources, there are additional processes that bring smaller quantities of
nutrients into an ecosystem. As mentioned before, precipitation can capture nutrients in the form of dust particles and deposit them in the
canopy of trees or in the soil. This is called wetfall. Other airborne nutrient particles are blown in on the wind (referred to as dryfall). In
aquatic ecosystems, a major nutrient input is runoff from agriculture or dead organic matter from terrestrial ecosystems.
Dryfall is the dry deposition of nutrients from the atmosphere.
Wetfall is the deposition of nutrients from the atmosphere to the soil by means of precipitation.
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Unit Lesson
Nutrient outputs represent a loss to the ecosystem. In order for an ecosystem to remain in balance, the net inputs must equal the export of
nutrients. The loss of nutrients can occur in several ways, depending on the nutrient. Since carbon and nitrogen exist in a gaseous form,
they can also be lost to the atmosphere. Carbon is constantly being lost through the respiration of living organisms (carbon dioxide).
Nitrogen can also be released as a gas through microbial processes. As we just mentioned, dead organic matter can be carried away in
streams, along with the nutrients still embedded in the tissue. Herbivores can also remove plants from an ecosystem and deposit the
waste in aquatic systems to be carried downstream. (Fecal matter that remains in the ecosystem is not considered an output.) Nutrients
can also be leached from the soil in rainwater and carried away in the water table. One of the biggest losses of nutrients comes from
harvesting organic material, as in agriculture and logging activities. In both of these activities, a large quantity of biomass is removed from
the ecosystem. The subsequent loss of topsoil also results in the further export of soil nutrients. Fire also results in a large loss of
nutrients, depending on the severity of the fire. Although many nutrients will remain in the ash, there is a loss through airborne or volatile
nutrients. With the loss of vegetation, there is an increase in leaching of minerals, as well as the loss of mineral soil through erosion.
In each of these examples, however, you can see that the loss of nutrients in one ecosystem results in nutrient inputs into another
ecosystem. On a global scale, nutrients are neither exported nor imported; rather, they are simply cycled in different forms in different
ecosystems. Let’s look at how each of the major nutrients are cycled globally.
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Unit Lesson
Carbon Cycle
When we study the energy flow through an ecosystem, we are tracking how energy is fixed (photosynthesis) and how energy is released
(respiration). Essentially, we are tracking how carbon is fixed and how carbon is released. The energy cycle and the carbon cycle are
essentially the same cycle.
The source of all carbon is carbon dioxide from the atmosphere (or water in aquatic systems). This is the source of carbon for
photosynthesis. Once carbon is fixed in photosynthesis, it can be converted to many different compounds (e.g., carbohydrates, proteins,
fats, amino acids). As carbon passes from plants to herbivores, and then to carnivores, it is incorporated into every living tissue. As living
organisms use stored energy, they release carbon dioxide into the atmosphere/water through respiration. Carbon in the living tissues will
be broken down as organisms die. Decomposers also release carbon into the atmosphere/water by respiration.
An overview of the carbon cycle is shown in the video on the next slide. Please note you will need to use your myCSU login and password
in order to access the video.
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Unit Lesson Introduction
Video
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Knowledge Check
(Mploscar, 2016)
What is the source of all carbon in living organisms?
A) Simple sugars
B) Carbon dioxide from the atmosphere and water
C) Carbon-fixing bacteria
D) Sedimentary rocks
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Unit Lesson
We can measure the productivity of an ecosystem by determining the difference in carbon that is fixed during photosynthesis and the
carbon released through respiration (net ecosystem productivity). Just as the rates of primary productivity and decomposition are
influenced by environmental constraints (e.g., temperature, precipitation, humidity, nutrients), so are rates of carbon cycling. In tropical
climates, carbon cycling happens very quickly. These ecosystems are some of the most productive in the world, as far as the rate of
carbon being fixed and recycled. Deserts and cold climates have much slower rates of carbon cycling. As was mentioned before, very wet
environments, such as swamps and marshes, inhibit the rate of decomposition. In these ecosystems, carbon cycles move very slowly, but
there is still a high rate of primary productivity. This creates a high
net ecosystem productivity. As carbon builds up, it can form deep layers of peat or humus. Over geologic time, these swamps may form
deposits of fossil fuels.
When we look at carbon cycling on a daily or seasonal basis, we can see patterns form. Since photosynthesis takes place during daylight
hours, this is when the most carbon dioxide is taken up (except in climates with a high density of crassulacean acid metabolism [CAM]
plants, which take in and store carbon dioxide at night). Therefore, atmospheric carbon dioxide is greatest during the night and lowest
during the day in most heavily vegetated areas. A similar pattern is evident in aquatic ecosystems.
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For the same reason, we also see seasonal variation in atmospheric carbon dioxide levels around the globe. During the growing season,
when carbon dioxide is constantly taken up by plants, atmospheric carbon dioxide levels will be lower than during winter months (see
figure). Of course, in equatorial regions, where plants are constantly taking up carbon dioxide year-round, these fluctuations are less
evident. It is interesting to note that these fluctuations are most evident in the Northern Hemisphere since there is greater land area, and
these patterns are most pronounced in terrestrial ecosystems.
The net gain in carbon is represented by the difference between the rates of NPP and carbon lost through respiration (both consumer and
decomposer).
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This carbon cycle diagram shows the storage and annual exchange of carbon between the atmosphere, hydrosphere, and geosphere in
gigatons – or billions of tons – of carbon (GtC). Burning fossil fuels by people adds about 5.5 GtC of carbon per year into the atmosphere.
(Saff, 2006)
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Unit Lesson
This figure shows the carbon cycle in terms of the carbon budget—the relative amount of carbon in storage (black numbers) and in flux
(blue numbers). Notice that the largest storage of carbon is in the deep ocean at 38,100 Gt
(gigaton, the equivalent of 1 billion metric tons). This is mainly in the form of bicarbonate or carbonate ions. The surface ocean holds
another 1,020 Gt. Soils hold approximately 1,580 Gt, both as dead organic matter and mineral soil. This varies depending on the rate of
decomposition. In general, northern boreal forests will hold more carbon in the soil compared to tropical forests because decomposition is
slower in colder areas.
As mentioned earlier, swamps and marshes usually hold the highest amount of carbon in the soil. The atmosphere actually only stores
about 750 Gt, though there is a high rate of flux between the atmosphere and all other stores.
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Knowledge Check
(Mploscar, 2016)
Atmospheric carbon dioxide concentrations in a forest are greater during the day than during the night.
A) True
B) False
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Knowledge Check
(Mploscar, 2016)
What is the largest active carbon pool?
A) The atmosphere
B) The oceans
C) Living organisms
D) Dead organisms
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The graphic depicts the global nitrogen cycle, showing the various forms of nitrogen and the processes involved.
(Chicano, 2015)
Unit Lesson
Nitrogen Cycle
As we have discussed previously, nitrogen is an important component of every ecosystem. Since nitrogen makes up amino acids, which
form proteins, nitrogen is an essential part of all living tissues. Although nitrogen gas (N 2) makes up almost 80% of the atmosphere, it can
only be taken up by plants in the form of ammonium (NH4+) or nitrate (NO3-). This figure shows the global nitrogen cycle and how organic
and atmospheric nitrogen can be converted to forms useable by plants.
Inorganic nitrogen can enter the ecosystem by two ways. The first is called nitrogen deposition. Nitrogen deposition is simply when
particles of nitrogen fall to the soil. This can take place through wetfall or dryfall, as mentioned earlier. Wetfall comes through some form of
precipitation or fog, while dryfall is dust or particles. When the nitrogen eventually makes its way to the soil, it is in a form available for
plant uptake.
The second pathway is through nitrogen fixation. Nitrogen fixation is the conversion of free nitrogen (N2) to ammonium (NH4+) or nitrate
(NO3-). Atmospheric nitrogen can be fixed in one of two processes. The first is through a high-energy reaction in which the nitrogen
combines with other elements in the air. This can happen through lightning strikes, meteorites, or ultraviolet rays.
This accounts for about 10% of the nitrogen fixed.
Nitrogen fixation is the conversion of atmospheric nitrogen to forms used by organisms (ammonium and nitrate).
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Unit Lesson
The remaining 90% of nitrogen fixation is a result of biological processes. Most commonly, nitrogen is fixed by bacteria—symbiotic
bacteria, cyanobacteria, or free-living soil bacteria. Symbiotic bacteria form a mutualistic relationship in the roots of many species. The
plants provide energy, through glucose, to allow the bacteria to split N 2 into two atoms of free nitrogen, which then combine with hydrogen
to form ammonia (NH3). The most common symbiotic bacteria is rhizobium, which forms a mutualistic relationship with leguminous plants.
Some lichens also form symbiotic relationships with nitrogen-fixing cyanobacteria.
Ammonia (NH3) is the gas formed by these bacteria as a waste product. It is easily converted to (NH 4+), which is a solid and can be taken
up by plants when excess H+ ions are found in slightly acidic soil. This process is called ammonification. If the soil is neutral, some of the
ammonia gas will be released back into the atmosphere (volatilization). This is common in agriculture fields when lime (which decreases
soil acidity) and nitrogen fertilizers are used in high amounts.
The video segment on the next slide shows each step of the nitrogen cycle. Please note that you will need to use your myCSU login and
password in order to access the video.
Ammonification is the breakdown of proteins and amino acids by decomposers, which releases ammonia as a by-product.
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Unit Lesson Introduction
Video
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Knowledge Check
The nitrogen cycle is a series of chemical transformations, which makes it relatively insensitive to environmental conditions
such as temperature and moisture.
A) True
B) False
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Knowledge Check
Lightning converts N2 to a nitrogen form that enters soil and can be readily assimilated by plants.
A) True
B) False
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Knowledge Check
The process of nitrification produces a form of nitrogen that is easily lost from soil through leaching.
A) True
B) False
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Unit Lesson
Because of the high demand for nitrate by both plants and bacteria, it is generally taken up as quickly as it is produced. However, human
inputs of nitrogen in agriculture often create an excess of nitrates. These excess nitrates are carried away from agriculture fields in runoff
and end up in streams and waterways. Eventually, these nitrates end up in the ocean and allow for excessive growth of phytoplankton in
the ocean (eutrophication). This very high level of phytoplankton growth will result in a lot of dead organic material that sinks to the
bottom on the ocean. As this matter decomposes, the decomposers with deplete oxygen with their high levels of respiration. This can
create dead zones in the ocean where oxygen is depleted and marine organisms cannot survive. Dead zones are often found in areas
around the world where major rivers drain a populated area. The video below highlights this problem and how it is monitored. Excess
nitrates can also lead to nitrogen saturation in ecosystems, which lead to decreased productivity and excessive denitrification.
Phosphorus Cycle
The phosphorus cycle differs from the carbon and nitrogen cycles in that there is no gaseous form of phosphorus found in the
atmosphere. Trace amounts of phosphorus exist as dust in the atmosphere but has very little impact on the phosphorus cycle.
The main sources of phosphorus are mineral rock (calcium phosphate) and natural phosphate deposits. As rock is weathered, phosphorus
is released. It can also be mined from natural deposits. In terrestrial ecosystems, phosphorus is in high demand for plant growth. Like
nitrogen, it can only be taken up in its inorganic form. Because phosphorus is often limited in natural ecosystems, it is conserved by plants
through resorption prior to leaf senescence. Phosphorus in dead organic matter is converted to inorganic phosphorus by bacteria through
the process of decomposition. The video segment on the next slide gives an overview of the phosphorus cycle.
Eutrophication is the introduction of high levels of nutrients into a body of water.
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Unit Lesson Introduction
Video
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Knowledge Check
The phosphorus cycle is a sedimentary cycle with essentially no gaseous cycle.
A) True
B) False
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Knowledge Check
The main reservoir of plant-available phosphorus is organic matter in the soil.
A) True
B) False
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Unit Lesson
Sulfur Cycle
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The sulfur cycle is not understood as well as other nutrient cycles. Like nitrogen and carbon, sulfur exists as a gas (SO2) in the
atmosphere, though in very small concentrations. (It is generally considered a pollutant when it exists in the atmosphere in any significant
amount.) Sulfate particles are also in the atmosphere and can be deposited through dryfall and wetfall. Sulfur is taken up in small amounts
by plants to be used in proteins. Like other nutrients, it is only taken up in its inorganic form, where it is assimilated into organic sulfur.
Organic sulfur is broken down by bacteria and becomes available for uptake or is released back into the atmosphere. However, the
majority of sulfur is found in the oceans and sediments. As it accumulates in ocean sediments and salts, it will eventually become rock
once again. Other sources of sulfur include volcanoes and hydrothermal vents in the ocean. With industrial emissions, sulfur can be
released in large amounts and pose health concerns.
Each Biogeochemical Cycle Is Linked
Although we study each cycle independently, the various nutrient cycles (including nutrient cycles that were not specifically covered in this
unit) are linked together. Often the various nutrients are linked as they join to form minerals and organic matter. The various molecules
essential for life (e.g., proteins, carbohydrates, lipids, amino acids) require a specific ratio of these nutrients. With the absence of just one
nutrient, life if not possible. If one nutrient is limited in an ecosystem, the entire ecosystem becomes limited—all the way up the food chain.
By understanding the relationship of ecosystems and their essential nutrients, we can identify critical processes that impact all living
organisms.
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Unit Lesson
Review Concepts for Unit VI
Energy from the sun is captured through photosynthesis. This energy is fixed, or stored, in biomass (the gr…
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