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Natural Biogeochemical Cycles

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Dean Chigounis

on 17 December 2014

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Transcript of Natural Biogeochemical Cycles

Natural Biogeochemical Cycles
Carbon Cycle
Carbon is basic building block of life
Fundamental Element in:
nucleic acid
Cycles between all spheres
Carbon Cycle
Carbon is released back into atmpshere via:
Cellular respiration by plants and animals (converts glucose into CO2)
Anaerobic respiration, carbon is converted to methane (CH4)
Aerobic decomposition creates CO2
Anaerobic decomposition creates methane (CH4)
Combustion of Fossil Fuels, etc.
Weathering of rocks (especially limestone, marble, chalk) creates CO2 and Carbonic Acid (H2CO3)
Volcanic Eruptions
Release of CO2 by warm ocean waters
Nitrogen Cycle
Water Cycle
Major Reservoirs or "sinks":
plant matter
terrestrial biosphere: forests store 86% of planet's above-ground carbon and 73% of planet's soil carbon.
Oceans: dissolved inorganic carbon CO2.
Removing CO2 from water raises the pH.
Sedimentary Deposits: limestone and carbon trapped in fossil fuel s and coal. Limestone is largest reservoir of carbon in carbon cycle.
Prior to Industrial Revolution:
transfer rates between photosynthesis & cellular respiration balanced.
Post Industrial Revolution:
more CO2 being deposited in atmosphere than removed.
Two main causes:
burning of fossil fuels
Carbon Sinks
Carbon Sinks (billion of metric tons)
- marine sediment & rocks: 75,000,000 bmt
- ocean: 40,000 bmt
- fossil fuel deposits: 4,000 bmt
- soil: 1500 bmt
- atmosphere: 766 bmt
- terrestrial plants: 580 bmt
1. Nitrogen Fixation
2. Nitrification (2 steps)
3. Assimilation
4. Ammonification
5. Denitrification

Nitrogen Fixation
Nitrogen Fixation:
the conversion of atmospheric N2 gas to N03 or NH3. Both methods incorporate Rhizobium bacteria on roots of legumes.

Small percentage of atmospheric N (10% of nitrate) fixed by lightning, cosmic radiation, or meteorite trails, which combines N2 with O.
Rainfall then carries molecule back to Earth.

accounts for 90% of fixed nitrogen.
N2 split into two free nitrogen atoms (N2 -> N + N).
Nitrogen atoms then combine with hyrogen to yield ammonia (NH3)
N2 makes up 78% of the atmosphere.
Essential in creation of: amino acids, proteins, nucleic acids.
Some stores in sediment & organic material
1 million times more found in atmosphere than land or ocean

Nitrification: the process where ammonia is oxidized to nitrite (NO2) and nitrate (NO3), the form most usable by plants. * Ammonia (NH3) can also be used by some plants such as rice.
Two groups of bacteria involved:
Nitrosomonas: oxidizes ammonia t nitrite and water
Nitrobacter: oxidizes nitrite to nitrate
Nitrates (NO3) absorbed by root hairs of plants
Used to manufacture amino acids, oils, and nucleic acid.
Animals assimilate NO3 by consuming plants and animals that consume plants.
Some NO3 (soluble nitrogen) enter aquatic systems causing eutrophication.
Excessive nitrates & nitrites in groundwater can interfere with blood-oxygen levels in human infants.
Process occurs when organism dies or via excretion
Initial form of N is found in amino acids & nucleic acids
Bacteria & fungi convert these forms of N back into ammonia (NH3)
Process occurs when nitrates (NO3) reduced to gaseous nitrogen (N2)
Process aided by facultative anaerobes (bacteria capable of both aerobic and anaerobic respiration)
Ex. Pseudomonas bacteria and fungi
Nitrogen - Environmental Impact
Fossil fuel combustion contributed to sevenfold increase in nitrogen oxides (NOx) to atmosphere.
NOx is precursor to tropospheric ozone & contributes to smog, HNO3, and eutrophication
Ammonia (NH3) in atmosphere has tripled since Industrial Revolution . Ammonia acts as aerosol and decreases air quality
Nitrous oxide (N2O) is a GHG.
N20 breaks down stratospheric ozone
N20 emitted during nitrification (ammonia to NO2 & NO3) & denitrification (oxides back to N2 gas)
Largest N20 emissions result from nitrogen-rich fertilizer use
Humans have doubled tranfer of N to biological available forms via:
cultivation of legumes
auto emissions
biomass burning
cattle & feedlots
Industrial processes
Phosphorus Cycle
Phosphorus essential for production of nucleotides, ATP, fats in cell membranes, bones, teeth, and shells.
No atmospheric form
Major sink in sedimentary rocks
Usually found in form of phosphate ion (PO4) or hydrogen phosphate ion (HPO4)
Slowly released from terrestrial rocks via weathering and acid rain (leaches potassium from rock)
Dissolves in soil and absorbed by plants (limiting factor)
Major component in fertilizers
ex) 6-24-26 contains 6% N, 24% P, and 26% potassium

Phosphate - Environmental Impact
Anthropogenic impacts:
mining of rocks containing phosphorus for inorganic fertilizers
clear-cutting tropical habitats for agriculture
runoff from feedlots, fertilizers, and sewage plant discharge (causes eutrophication)
application of phosphorus-rich guano to fields
Sulfur Cycle
Elemental or pure sulfur found in underground deposits, natural hot-springs, and volcanoes.

13th most abundant element in Earth's crust.
Percentage in rocks vary (sedimentary have most / igneous have least)
Released via weathering / erosion, runoff, etc.
Large deposits in oceans (migrate via rivers, etc.)
Sulfur Cycle
Main source in oceans (dissolved sulfate)
Most volatile compound in oceans (dimethyl sulfide (DMS).
DMS produced by algal & bacterial decay.
Highest concentrations in coastal marshes & wetlands
Sulfur is 2nd most abundant compound in rivers.
Rivers transport 110 million tons of sulfur per year to oceans
Nitrogen Cycle
Sulfur in Soil & Biosphere
Essential nutrient in biosphere
Concentrated mainly in soil where absorbed by plants (mainly in form of sulfate) & passed up food chain.
Main sources: deposition from atmosphere, weathering of rocks, decomposition of tissue, fertilizers, pesticides, and irrigation water.
Decomposition returns sulfate from biosphere to lithosphere.
Anaerobic decomposition releases hydrogen sulfide (H2S & dimethyl sulfide back into atmosphere.
Release of sulfur dependent upon warmer temperatures.

Sulfur in Atmosphere
Six sulfur compounds released into atmosphere:
1) Carbonyl sulfide (COS): most abundant sulfur species in atmosphere. Produced via decomposition & combustion. Persistent (44 years). Inert, less problematic.
2) Carbon disulfide (CS2): more reactive that COS, similar sources, 12 day lifetime, major sink in photochemical reactions, major source: microbial compounds in tropical soils.
3) Dimethyl sulfide (CH3)S: large stores released from oceans. Most of natural gas released from oceans is DMS. Concentrations peak at night.
4) Hydrogen sulfide (H2S): produced mainly via anaerobic decomposition. Highly reactive. Concentrations peak at night.
5) Sulfur Dioxide (SO2): natural source of oxidation of H2S. Major source of fossil fuel combustion. Form most influenced by anthropogenic emissions. Short-lived (2-4 days).
6) Sulfate aerosol: (S04): largest natural source of sulfate aerosol particles originate from sea spray. Most salt spray sulfates fall back to oceans but some migrates within atmosphere.
Forms of Nitrogen
N = nitrogen
N2 = nitrogen gas
NO2 = nitrite
NO3 = nitrate
NH3 = ammonia
HNO3 = nitric acid rain
Water Cycle - Facts
Water Cycle powered by sun
Evaporation occurs from: oceans, lakes, rivers, streams, soil & vegetation
97% of water held within oceans / source for 78% of all global precipitation & 87% of all global evaporation
Evaporation from oceans keeps Earth cooler
If no oceans, land surface temps would rise to 153' F
Warm air holds more vapor than cold air
: water goes from liquid to vapor (gaseous) state.

: the evaporation from plant parts (stomata via cellular respiration at night).

: water cools (both ground layer and upper atmosphere) and returns to liquid state.

water than has condensed, returns to Earth in form of rain, snow, sleet, etc.
Human Impact - Water Cycle
Withdrawing water from lakes, aquifers, and rivers: groundwater depletion & saltwater intrusion
Clearing of land for agriculture and urbanization: increased runoff, decreased infiltration, increased flood risk, accelerated soil erosion
Agriculture: eutrophication
Destruction of wetlands: disruption to natural processes that purify water
Pollution of water sources: infectious agents (cholera, dysentery, etc.)
Sewage runoff, feedlot runoff: eutrophication
Building power plants: increased thermal pollution
Phosphorus Cycle
Nitrogen Cycle
Sulfur Cycle
Quick Checklist Review
Carbon Cycle:
carbon sinks
Nitrogen Cycle:
nitrogen fixation
Phosphorus Cycle:
Sulfur Cycle:
Energy Flow:
Water Cycle:
Conservation of Matter & Energy
Conservation of Matter & Energy
Law of Conservation of Matter:
there is no detectable increase or decrease in quantity of matter.
total quantity of matter is fixed

Law of Conservation of Energy:
energy cannot be created or destroyed but can change form.
conversion of matter into another form is always accompanied by conversion of energy.
usually, heat is either emitted or absorbed.
sometimes conversion involves light or electrical energy in addition to heat.
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