34.3 global biogeochemical cycles. overview all organisms require a variety of organic and inorganic...
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34.3 Global Biogeochemical Cycles
Overview
All organisms require a variety of organic and inorganic nutrients to survive:
Carbon dioxide (CO₂) and water are used in photosynthesis
Nitrogen is found in all structural and functional proteins, and nucleic acids that sustain living tissues
Phosphorus is needed for ATP and nucleotide production
Together, they are known as biogeochemical cycles because they involve both living and nonliving components. Each element can cycle through 3 possible areas:
A reservoir – normally unavailable to produces (ex. fossils, rocks, sediment)
An exchange pool – sources where chemicals are taken from (ex. atmosphere, soil)
The biotic community – chemicals move along food chains; could bypass the exchange pool
2 types of biogeocheical cycles: Gaseous cycle – carbon and nitrogen cycles
Element returns to/is withdrawn from atmosphere as a gas
Sedimentary cycle – phosphorus cycle Element absorbed from sediment by roots,
passed to heterotrophs, and returned to soil by decomposers
The nutrients are not limited to one ecosystem. They can flow between terrestrial and aquatic systems very easily.
The Water (Hydrologic) Cycle
In the ocean...Sun causes fresh water to evaporate from
salt water Vaporized fresh water rises, cools, then falls
as rain over land and sea
On the land...Sun causes water to evaporate from land and
transpire from plants Vaporized water rises, cools, then falls as rain
Water sources exists as standing water (lakes, ponds), flowing water (streams, rivers), and groundwater
Water from precipitation (rain, snow, hail, etc.) can sink or percolate into the ground, saturating the Earth Top of saturation zone called groundwater table or
the water table Groundwater also found in aquifers – rock layers
that contain water and release it in wells/springs Groundwater mining – took much water is removed
from aquifers, destroying possibility of refilling
The Carbon Cycle
On land...Plants use CO₂ from the air
Use photosynthesis to turn CO₂ into organic nutrients When individuals respire (or breathe), CO₂ returns
to the atmosphere
In the water...CO₂ from the air combines with H₂O (water) to
create bicarbonate ions (HCO₃) – food for protists When individuals respire, CO₂ is released and
becomes bicarbonate ions (HCO₃)
Living and dead organisms are carbon reservoirs Remains that don’t decompose turn into coal, oil,
and natural gas (fossil fuels) Calcium carbonate shells from marine organisms
gather in ocean bottom sediment
Global Warming
Transfer Rate: amount of nutrients that move from one component of environment to another within a specified time frame
Transfer rates from photosynthesis and respiration are about equal
Human activity (burning of fossil fuels/wood, destruction of forests) has caused more CO₂ being placed in atmosphere than being removed
Human activity has resulted in release of greenhouse gases Nitrous oxide – fertilizers, animal wastes Methane – bacterial decomposition, flooded rice paddies,
sediments)
Results in global warming due to the greenhouse effect allows solar radiation in but slows the escape of infrared
rays, causing the temperature to rise dangerous because water vapour is also a
greenhouse gas increased temp. = more water evaporation = more cloud
cover that could further increase temperature Effects of global warming include melting glaciers,
rising sea level, increase water evaporation leading to more rainfall on coast with dry conditions inland, droughts, etc.
The Nitrogen Cycle
Nitrogen is the most abundant element in the atmosphere (about 78%). Having a nitrogen deficiency can limit plant growth.
Nitrogen Fixation: occurs when nitrogen (N₂) is converted into a form that plants can use
Nitrogen-fixing bacteria living in legumes roots make nitrogen compounds available to host
Free-living bacteria in water and soil fix nitrogen gas into ammonium (NH4), which is used by plants
Plants also use nitrates (NO₃), which will reduce to ammonium and be used to produce amino acids and nucleic acids
Nitrification: production of nitratesPlants also use nitrates (NO₃), which will reduce
to ammonium and be used to produce amino acids and nucleic acids
Nitrogen gas (N₂) converted to nitrate(NO₃) in atmosphere due to high energy events (cosmic radiation, meteor trails, lightning)
Ammonium in soil converted into nitrate by chemoautotrophic soil bacteria Nitrite producing bacteria convert ammonium to
nitrite (NO₂), then nitrate producing bacteria convert nitrite to nitrate
Subcycle using dead organism and animal wastes, ammonium, nitrites, nitrates, and plants doesn’t necessarily depend on nitrogen gas
Denitrification: conversion of nitrate to nitrous oxide and nitrogen gas
Occurs in aquatic and terrestrial environments
Almost balances nitrogen fixation
Nitrogen and Air Pollution Human activity has resulted in 3x more
nitrogen oxides in atmosphere than there should be. Fossil fuel combustion puts sulfur dioxide (SO₂) in the atmosphere. Both turn into acids when combined with water vapour. They return to the Earth as wet deposition (acid rain/snow) or dry deposition (sulfate and nitrate salts).
Acid Deposition: reduce agricultural yields and causes corrosion (marble, metal, stonework)
Nitrogen oxides (NO) + hydrocarbons (HC) + sunlight Photochemical Smog
Photochemical smog contains ozone and PAN (peroxyacetylnitrate), which can affect the respirator and nervous systems. Ozone is also harmful to plants.
Thermal Inversion: warm air is unable to escape into atmosphere, which then traps pollutants under a layer of warm, stagnant air
The Phosphorus Cycle
The Phosphorus Cycle only occurs on land, which is why it is also called the sedimentary cycle.
On land...Weathering of rocks makes phosphate ions
(PO4, HPO3) available to plants from soil Some runs into aquatic systems where it’s used
by algae Phosphate in sediments only available when
geological upheaval exposes them to weathering
Phosphate taken in by producers and used for organic molecules like phospholipids, ATP, and nucleotides
Animals eat producers and use phosphate in teeth, bones, and shells
Decomposition returns phosphate ions available for producers again
Is a limiting inorganic nutrients because it regulates growth due to its short supply
Phosphorus and Water Pollution
Phosphorus and Water Pollution Human activity has increased amount of
phosphate(used in fertilizer and detergent) Phosphate and nitrogen runoff (from fertilizer use,
animal wastes, and sewage discharge) causes eutrophication (over-enrichment) of waterways Causes algal blooms – decomposers use up all oxygen ,
resulting in fish death
Point sources of pollution are specific, while nonpoint sources are caused by runoff from the land.
Biological Magnification: elements builds up in the body over time and is not excreted; become more concentrated as you move up the food chain
Ex. presence of DDT and PCB’s in fish