Download - Bio Geo Chem Cycles
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Biogeochemical Cycles
Water, Nitrogen, Carbon, Phosphorous, Sulphur
ENV200
Environmental Studies
Lecture Slides
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Position In Syllabus
Global Environmental Crisis, Biogeochemical Cycles, Climate
Change, Ozone Hole, Overpopulation, Energy Crisis, Water Crisis.
Periodical 1
Ecology, Biodiversity Loss, Deforestation and Land Degradation,
Food Crisis, Pollution (Water, Air, Land, Thermal, Noise), Sewage
Domestic and Industrial and Effluent treatment
Periodical 2
Solid waste (municipal, medical, e-waste, nuclear), Environmental
Management, Conventions, Regulations and Impact Assessment,
Sustainable Development.
Final Exam
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Outline
• Segments of the Environment
• Gaia Theory
• Biogeochemical Cycles
• Hydrologic Cycle
• Nitrogen Cycle
• Carbon Cycle
• Phosphorous Cycle
• Sulphur Cycle
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What is the Environment?
• The physical and biological habitat
surrounding us is the environment
• Abiotic Environment: Air, land, water,
rocks
• Biotic Environment: Living organisms
such as plants, microorganisms, animals,
birds etc.
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Segments of the Environment
• Lithosphere: Earth’s Crust, rocks, minerals. Huge
reservoir, less transport (conveyer)
• Pedosphere: soil
• Hydrosphere: oceans and water, huge reservoir
and transporter
• Biosphere: small reservoir, moderate transporter;
huge impact on the environment.
• Atmosphere: small reservoir, efficient
transporter.
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Zones of the Atmosphere
• Exosphere: 500 – 1000 km up to 10,000 km,
• Thermosphere: from 80 – 85 km to 640+ km temperature increasing with height. • Ionosphere: auroras, long distance radiowave
propagation.
• Mesosphere: 50 km to 80 to 85 km temperature decreasing with height. Meteors burn up when entering the atmosphere.
• Stratosphere: 7 to 17 km range to about 50 km Temperature increases with height. Ozone—few ppm (Mainly 15 to 35 km)
• Troposphere: Surface to between 7 km at the poles and 17 km at equator, • Weather variations , vertical mixing
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Temperature Distribution in the Atmosphere
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Outline
• Segments of the Environment
• Gaia Theory
• Biogeochemical Cycles
• Hydrologic Cycle
• Nitrogen Cycle
• Carbon Cycle
• Phosphorous Cycle
• Sulphur Cycle
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Inter-relationships
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Gaia Theory
• By James Lovelock; Greek Earth Goddess
• Earth with all intricate and interacting systems is like a Super-Organism
• Self regulation: chemistry of oceans, atmosphere, temperature, living beings
• Earth behaves as if it had a purpose
• Purpose is to nurture life and maintain life-friendly conditions.
• This perspective brings a new awareness that can be the foundation of all future development
• It will enable the further evolution of mankind
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Outline
• Segments of the Environment
• Gaia Theory
• Biogeochemical Cycles
• Hydrologic Cycle
• Nitrogen Cycle
• Carbon Cycle
• Phosphorous Cycle
• Sulphur Cycle
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Biogeochemical Cycles
• Matter (chemicals) are recycled through the
ecosystem by both biological and geological
processes
• Reservoir: Large quantities of chemical; long
residence time (e.g. ocean)
• Exchange pool: short residence time (e.g. cloud)
• Transportation of nutrient
• Biotic community serves as exchange pool and in
transport (e.g. trees transpire: water from soil to
air)
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Outline
• Segments of the Environment
• Gaia Theory
• Biogeochemical Cycles
• Hydrologic Cycle
• Nitrogen Cycle
• Carbon Cycle
• Phosphorous Cycle
• Sulphur Cycle
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Global Hydrologic Cycle
Source: Adapted from Clarke, R. Water: The International Crisis. London, Earthscan Publications Limited, 1991. (30)
Fluxes: km3/yr
Pools: km3
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Sat, July 19, 2008 AM220 Lecture 3
Water a Scarce Resource
• 70% of earth’s surface covered with salty water
• 3% by vol. is freshwater;
• 79 % of it is locked in polar ice.
• 20% is underground.
• Only 1% is surface water
• 0.01% of total water is accessible for human use.
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Interrelations in Nature
• Nature comprises of different systems
• They are all interconnected and influence
each other.
• E.g. The hydrologic cycle affects Earth’s
temperature and climate.
• E.g. The biosphere (plants and animals)
affect the hydrologic cycle.
• No system can be studied in isolation of the
others.
Sat, July 19, 2008 AM220 Lecture 3
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Hydrological Cycle & Earth’s Albedo
• Evaporation—cloud formation
• Increased albedo or reflection coefficient is a measure of the ‘whiteness’ of the earth when viewed through space.
• Greater the albedo→lower is the solar radiation absorbed by the earth→lower is the temperature of the globe (Greater cooling).
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Albedo and Tree Cover
• Trees tend to have a low albedo• Deciduous trees: 0.15-0.18 (15-18%)
• coniferous trees 0.09-0.15 (9-15%)
• Hence, removing forests → increases albedo →localized
climate cooling.
• However, trees also provide local evaporative cooling and
carbon sequestration; loss of trees reduces these cooling
effects.
• Cloud feedbacks and snow cover further complicate the issue.
• Studies of new forests indicate: • A net cooling effect in tropical and mid-latitude areas
• A net neutral or slightly warming effect in high latitudes (e.g. Siberia)
• Betts, Richard A. (2000). "Offset of the potential carbon sink from boreal forestation by decreases in surface albedo". Nature 408 (6809): 187–
190. doi:10.1038/35041545.PMID 11089969.
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Phytoplankton, Clouds, Albedo
• Phytoplankton produce dimethylsulfoniopropionate (DMSP)
• Converted to Dimethyl sulfide (DMS) in ocean
• Escapes to atmosphere, oxidizes to SO2 and nucleates clouds.
• This is an example of how the biosphere (plankton) regulates the hydosphere (global precipitation), earth’s albedo and global temperature.
• CLAW Hypothesis: negative feedback; regulation of global temperature.
• Anti-CLAW Hypothesis: positive feedback; escalation of global warming.
Sat, July 19, 2008 AM220 Lecture 3
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CLAW Hypothesis
• warm oceans→more phytoplankton → more DMS → More clouds → cooling (negative feedback; regulation)
• A schematic diagram of the CLAW hypothesis of Charlson et al. (1986; Nature 326, 655-661).
Sat, July 19, 2008 AM220 Lecture 3
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Anti-CLAW Hypothesis:
• warm oceans → stalling of thermohaline ocean currents→ocean stratification → less nutrients from ocean bottom in euphotic zone → less phytoplankton → less DMS → less clouds → more heating (positive feedback; escalation)http://upload.wikimedia.org/wikipedia/en/thumb/c/cc/CLAW_hypothesis_graphic_2_AYool.png/200px-CLAW_hypothesis_graphic_2_AYool.png
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Sat, July 19, 2008 AM220 Lecture 3
Global Conveyer Belt
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Plants: Significance in Water Cycle
• Taproots go upto 100x deeper than canopy
• Short-circuit pathways for soil water
redistribution
• In dry spells, water from below brought to
surface, to increase nutrient extraction,
photosysnthesis and transpiration.
• In wet spells, promote percolation
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Plants: Significance in Water Cycle
• Plants pump huge quantities of water from soil to air.• 100s to 1000s L/day
• Regulate T and humidity. In a clearing in Nigeria, soil T upto 5°C higher; humidity reduced by 50% compared to adjacent forest.
• Evapo-transpiration of trees—nature’s pump and cooler
• Drop in Amazon’s temperature in June/July is due to transpiration.
• Transpiration: 40% of Amazonian rain is from transpiration
• Afforestation efforts: appropriate types and density.• /http://www.i-sis.org.uk/LOG4.php
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Importance of Rainforests
• 25% of rain never reaches the ground.; wets canopy and evaporates
• 25% of total—runoff
• 50% of total pumped up and transpired by plants.
• 75% of rainwater is returned to the atmosphere; new clouds, new rain,
• Colossal heat pump—energy of six million atom bombs/day; redistributes energy to higher latitudes
• Up to 80% incident solar energy carried by hot, humid air;• rises rapidly and develops into thunder clouds that
simultaneously
• water areas further downwind
• Releases latent heat
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Importance of Rainforests
• Absorb 2 billion tonnes of CO2/yr; about 20-30% of fossil C emissions
• Destruction of the Amazon:• May stall the heat pump
• Accelerate drought and desertification (positive feedback)
• Loss of CO2 sink; accelerate global warming.
• Reforestation cannot replace natural stands. Loss of soil carbon.
Sources:
Prof. Eneas Salati from the University of São Paulo, Piracicaba – Brasil http://www.fgaia.org.br/texts/e-rainforests.html
http://www.hydrogen.co.uk/h2_now/journal/articles/1_global_warming.htm
http://www.hydrogen.co.uk/h2_now/journal/articles/2_global_warming.htm
http://www.greendiary.com/entry/increasing-global-warming-decreases-forests-co2-absorption-capacity
http://www.i-sis.org.uk/LOG4.php
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Human Impacts on Water Cycle
• Depletion of groundwater resources
• Pollution of ground and surface freshwater
• Desertification—loss of soil moisture
• Global Warming: Warmer oceans—more
algae—more DMS in atmosphere—More
cloud formation—increased albedo—lower
temperature?...Contrary ice core evidence.
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Outline
• Segments of the Environment
• Gaia Theory
• Biogeochemical Cycles
• Hydrologic Cycle
• Nitrogen Cycle
• Carbon Cycle
• Phosphorous Cycle
• Sulphur Cycle
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Nitrogen Cycle
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Nitrogen Reservoir
N is an essential component of proteins, nucleic acids and other cellular constituents.
• Reservoirs – 79% of the atmosphere is N2
gas.
• The N=N triple bond is relatively difficult to break, requires special conditions. As a result most ecosystems are N-limited.
• N2 dissolves in water, cycles through air, water and living tissue.
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Nitrogen Fixation
• Nitrogen Fixation
• Abiotic: lightning (very high T and P) 107 metric tons yr-1 ~ 5-8% of total annual N fixation. (weathering of rocks is insignificant)
• Biotic: Nitrogen fixation by microbes, 1.75 x108
metric tons yr-1 (symbiotic bacteria: azobacter or rhizobium- legumes
• Industrial: The Haber-Bosch process (1909) 5x107 metric tons yr-1 – high P & T, Fe catalyst to convert N2 to NH3;& NH4NO3
• Combustion Side Effect: 2x107 metric tons yr-1.
High T and P oxidizes N2 to NOx
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Nitrification-Denitrification
• Nitrification by chemoautotrophs
• Bacteria of the genus Nitrosomonas
oxidize NH3 to NO2-
• Bacteria of the genus Nitrobacter oxidize
the nitrites to NO3-
• Denitrication Anaerobic respiration of
NO3- to dinitrogen gas by several species of
Pseudomonas, Alkaligenes, and Bacillus
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Fate of N
• Sources of anthropogenic N loads: Fertilizers, Legume Crops, Combustion and forest burning, livestock.
• In most terrestrial and freshwater ecosystems N is a limiting nutrient, gets cycled efficiently.
• What happens when plants have enough N (i.e. greater 16:1 N:P ratio)?
• When N saturation of ecosystem occurs, excess N tends to leave the system in the form of nitrate.
• Flushing/erosion – dissolved and particulate matter in streamwater, (DIN, DON, TN, Org N)
• Leaching to groundwater – NO3- poor sorption to clays,
highly water soluble.
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Effects of Increased N loading
Since 1940s amount of N available for uptake has more than doubled. Anthropogenic N inputs are now equal to biological fixation.
• Eutrophication in aquatic systems, coastal algal blooms and “Dead Zone”, fish kills, increased turbidity,
• Selective pressures in terrestrial systems favoring species-poor grasslands and forests
• Nitrate MCL – 10 mg/L …
• Nitric oxide – precursor of acid rain and smog
• Nitrous oxide – long lived greenhouse gas that can trap 200 times as much heat as CO2
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Fertilizer use
Adapted from the Food and Agriculture Organization of the United Nations (FAO), FAOSTAT Statistical Database (FAO, Rome, 1997).
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Outline
• Segments of the Environment
• Gaia Theory
• Biogeochemical Cycles
• Hydrologic Cycle
• Nitrogen Cycle
• Carbon Cycle
• Phosphorous Cycle
• Sulphur Cycle
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Availability of Carbon
• Earth’s C content = 0.19% (0.032% in
lithosphere)
• Atmospheric CO2 is the main utilizable
reservoir
• 18% in biomass
• Main reservoirs air, rocks (carbonates),
oceans.
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Carbon Cycle
CO2
Fossil FuelsCaCO3Ocean
Corals,
shells
Plants Animals
Dead Organic Matter
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Human Impacts on Carbon Cycle
• Fossil fuel burning, land use (clearing,
agriculture and degradation)
• Increase in atmospheric green house gasses
such as CO2, methane, SOX, NOX, etc.
• Greenhouse effect, global warming and
climate change.
• Detailed study later…
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Potential contributors to climate
change
• Complex interactions in the climate puzzle
• Feedback mechanisms
• Some interesting twists
• Increasing temp. reduces CO2 solubility
(reduced C-sink capacity of the ocean)
• Ocean Acidification reduces C-sequestration in
the form of CaCO3
• 740ppm CO2 in water by 2100. Reduction in
population of mussels by 25% and oysters by 10%
• At 1800ppm, shells will dissolve
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Outline
• Segments of the Environment
• Gaia Theory
• Biogeochemical Cycles
• Hydrologic Cycle
• Nitrogen Cycle
• Carbon Cycle
• Phosphorous Cycle
• Sulphur Cycle
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Phosphorous Cycle
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P-cycle and Human Impacts
• One of the longest cycles
• Essential nutrient; DNA, ATP, ADP, fat,
cell membranes
• P-containing detergents
• Mining phosphate rock
• P-containing fertilizer use
• P in water leads to eutrophication
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Outline
• Segments of the Environment
• Gaia Theory
• Biogeochemical Cycles
• Hydrologic Cycle
• Nitrogen Cycle
• Carbon Cycle
• Phosphorous Cycle
• Sulphur Cycle
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AM220 Lecture 7
Sulphur Cycle
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S-Cycle and Human Impacts
Essential steps:
• Oxidation (combustion or biological) of sulfide and elemental S to sulfate (SO4
2– )
• Reduction of sulfate to sulfide.
• Utilization of sulfates by plants and animals
• Deposition and mineralization of organic S to sulfides
Human Impacts
• SO2 from industry and combustion (e.g. coal, petrol).
• SO2 oxidized to H2SO4 in the atmosphere—acid rain.
• SO2 can deposit onto surfaces and be oxidized to sulfate in the soil
• SOx global warming
• Sulfates are toxic to some plants