ciclos da natureza
TRANSCRIPT
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EM 973
Desenvolvimento eMeio Ambiente
Arnaldo Walter
UNICAMP
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Ciclos na natureza e o meio
ambiente
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Objetivos e contexto
Ciclos da natureza so fundamentais para a manuteno da vida na
Terra. O ciclo da gua um exemplo claro, e no preciso
consideraes adicionais.
Ciclos de nutrientes (como Nitrognio e Fsforo) so essenciais
para as plantas e os animais.
Alteraes nos ciclos da natureza no esto associadas ao
deplecionamento dos reservatrios, mas sim alterao de
fluxos entres os reservatrios (e consequente variao das
condies fsico, qumicas e biolgicas), e poluio (alteraodas propriedades) dos sistemas da natureza (atmosfera, hidrosfera,
biosfera e litosfera).
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Princpios de Sustentabilidade (1)Miller and Spoolman. Living in the Environment : concepts, connections
and solutions.
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Princpios de Sustentabilidade (2)Miller and Spoolman. Living in the Environment : concepts, connections
and solutions.
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Natural cycles (1)http://www.learner.org/courses/envsci/unit/text.php?unit=8&secNum=2
Natural cycles are the processes by which all essential materials
flow through the living and the non-living parts of ecosystems.
Ecosystems receive materials as inputs and release them as
outputs. The cyclic path of material flow reuses the basic elements
over and over. Natural cycles supply ecosystems with nutrients, energy and
water.
Examples are the water, the carbon and the nitrogen cycles.
The smooth and steady functioning of cycles directly impactsecosystem stability. Conversely, disturbed cycles contribute
directly to ecosystem vulnerability.
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Natural cycles (2)CSU -http://www.colorado.edu/GeolSci/courses/GEOL1070/chap04/chapter4.html
Biogeochemical cycles are part of the larger cycles that describe
the functioning of the whole Earth. Biogeochemical cycles
correspond to the movement (or cycling) of matter through a
system.
The most important biogeochemical cycles affecting ecosystem
health are the water, carbon, nitrogen, and phosphorus cycles.
Biogeochemical cycles are cycles of materials or molecules
through the atmosphere, the hydrosphere, the lithosphere and the
biosphere.
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Biogeochemical
cycles (CSU)
Biologia + Geoqumica
= Biogeoqumica
Cincia que estuda o
ciclo do carbono (por
exemplo) e suasinterconexes com ciclos
de outros elementos
envolvidos no processo
da vida (principalmente
nitrognio, oxignio,
fsforo e enxofre).
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Nutrient cycles
CSUColorado State University.
http://www.colorado.edu/GeolSci/courses/
GEOL1070/chap04/chapter4.html
Movements through the
atmosphere are generally rapid,
while movements through the soils
are generally slow.
Increased transport by stream flow
severely disrupts the cycles of
elements without a gaseous phase.
Movements from terrestrial
biosphere to the ocean (via stream
flow, usually) must be replaced by
movements either through the
atmosphere (such as with nitrogen
and carbon) or by weathering (such
as with phosphorous or calcium).
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Water cycle (1)CSU -http://www.colorado.edu/GeolSci/courses/GEOL1070/chap04/chapter4.html
The most familiar of all
cycles is the water
cycle. The movement of
water is critical in all
cycles.
The water cycle helps to
demonstrate
connections between
local and globalecosystems.
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Water cycle (2)
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Water cycle (3)flows in km3/yearhttp://www.learner.org/courses/envsci/unit/text.php?unit=8&secNum=2
Water vapor
redistributes energy
from the sun around
the globe through
atmosphericcirculation.
Solar radiation drives
evaporation. This
process consumesnearly one-third of the
incoming solar energy
that reaches Earth's
surface.
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Water cycle (4)CSU
P: precipitation
Total 496,000 km3/yr (land 111,000
+ ocean 385,000)
E: evaporation
Total 496,000 km3
/yr (land 71,000+ ocean 425,000)
T: transpiration included in plant
evaporation
R: surface runoff26,000 km3/yr
SR: sub surface runoff(liquid12,000 + ice 2,000)
I: infiltration 14,000 km3/yr
S: springs 2,000 km3/yr
1 km3/yr = one trillion liters/year
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Water cycle (5)http://www.learner.org/courses/envsci/unit/text.php?unit=8&secNum=2
Estimate of the world water balance. Source: MIT OpenCourseWare.
Surface area
(million km2)
Volume
(million km3)Volume (%)
Equivalent depth
(m)Residence time
Oceans and seas 361 1,370 94 2,500 ~4,000 years
Lakes andreservoirs
1.55 0.13
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Carbon cycle (1)
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Carbon cycle (2)
CSUColorado State University.http://www.colorado.edu/GeolSci/courses/GE
OL1070/chap04/chapter4.html
One of the most
important to humans:
one of the primaryelements forming
human tissues;
and because it is
important to theclimate system;
carbon dioxide (CO2)
and methane (CH4) are
GHG.
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Carbon cycle (3)CSU
Fluxes to & from land: (GtC/year)
P: photosynthesis -120
PR: plant respiration - 60
SR: soil respiration - 60
SF: plants to soils - 60
FFF: fossil fuel formation - 0.0001FFB: fossil fuel burning - 6
DEF: deforestation - 2
Fluxes to & from ocean: (GtC/year)
D: dissolving - 107
E: exolving - 103CP: carbonate formation - 4
W: weathering - 0.6
Fluxes from volcanoes: (GtC/year)
V: 0.1
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Carbon cycle (4)IPCC (2003)
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Carbon cycles (5): carbon residence timeCSU
Some in fluxes are not balanced by out fluxes (e.g., the
atmosphere and fossil fuels). So residence time are slightly
different (and reservoirs are growing... or shrinking).
The RT of carbon in the air (mostly CO, but some CH4) is long
enough that the air is well mixed (mixes in about 1 year).
The RT of soils: some parts cycle very slowly (1,000's of years),
some parts very rapidly (a few weeks to monthse.g., leaves)
The RT of fossil fuels reflects all fuels suspected to exist: coal:
~ 350 years; oil: ~ 40 years; natural gas: ~ 60 years.
The RT of ocean: the surface water (short RT, few months to
years) and deep water (long RT, 200 to 400 years). Ocean RT
reflects the circulation of the ocean (deep water formation).
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Carbon cycles (6): silicatesCSU
Long term cycle of the carbon cycle, tied with the rock (silicate) cycle. The time
scale for this cycle is millions to hundreds of millions of years.
On this time scale, carbon cycling by plants, oceans and the atmosphere is
thought to be in balance (steady state orequilibrium) ... so carbon dioxide levels
in the atmosphere are thought to be controlled by weathering rates and rates of
volcanic eruptions.
Weathering rates are thought to be controlled by rate of tectonic uplift: more
uplift, more weathering and less atmospheric carbon dioxide. This may explain
the slow decline in atmospheric carbon dioxide from levels of several thousand
ppm about 100 million years ago, to 280 ppm in the pre-industrial time: during
this time, the Tibetan Plateau and Rocky Mountain Plateau were raised by
tectonic activity.
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Nitrogen cycle (2)
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Nitrogen cycle (3): chemical cycles and
reservoirs (CSU)
F = fixation;
D = denitrification ;
O = oxidation .
Atmosphere: 4,000,000 Gt
Land Plants: 3.5
Soils: 9.5 Gt
Oceans: 23,000 Gt
Sediments and rocks:
200,000,000 Gt
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Nitrogen cycle (4):
fluxes (CSU)
Fluxes: (in Mtyear )
LF: Land Fixation 140
LD: Land denitrification 130
OF: Oceanic Fixation 50
OD: Oceanic denitrification 110
I: Industrial dixation 100FFB: Fossil fuel burning 20
BB: biomass burning 10
L: Lightning 20
D: Decay 1200
G: Growth 1200L-O: Land-to-Ocean 48 (rivers
36; dust 6; NOx 6)
O-L: Ocean-to-Land 15 (sea
spray)
Burial: 10
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Nitrogen cycles (5)CSU
Industrial fixation is used to make fertilizers to provide usable
nitrogen for crops. This flux is comparable to natural fixation.
Specialized bacteria and lightning are the only natural ways that
nitrogen is fixed.
How did agriculture survive before fertilizers? Early civilizations
had to rely on natural regeneration of fixed nitrogen:
Annual floods bring fresh sediments (e.g., Nile Valley);
Slash/burn agriculture: once the soil nutrients are depleted,
move on to a new place;Crop rotation: certain crops (e.g. soybeans) are good at fixing
nitrogen, others (e.g. corn) use it up; plant on alternate years.
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Nitrogen cycles (6): residence timesCSU
Nitrogen in the atmosphere: 14 million years; land plants: ~ 3 years; oceans: ~
20,000 years; soils: ~ 9 years
As pollutants: NOx ~ 4 days and as N2O ~ 120 years.
In reservoirs where N2 is the dominant form (of nitrogen) (e.g., atmosphere,
ocean), the residence times is long.
In reservoirs where fixed nitrogen is dominant (e.g., soils, plants), the residence
times is short.
N2 is very stable, but fixed nitrogen compounds are very reactive (that's why
plants can utilize them).
Eutrophication corresponds to increasing the nutrients in a body of water.Runoff carrying excess nitrate fertilizers enriches these bodies of water;
algae respond to this first and excess algae implies depletion of O2 in the water.
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Phosphorus cycle (1)
Importance: phosphorus is a necessary, limiting nutient and
Phosphate runoff causes eutrophication.
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Phosphorus cycle (2)
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Phophorus cycle (3): reservoirsCSU
Earth's Crust: 20,000,000,000 Mt
( recoverable : ~20,000) (most of
the phosphorus is in rocks).
Ocean: 100,000 Mt; Freshwater:
~100 Mt; Land Plants: ~3,000 Mt;
Soils: ~100,000 Mt.
Main fluxes (Mt/year)
M: Mining - 50 (humans)
F: Fertilization - 50 (humans)
W: Weathering -10
R: Runoff - 20
B: Burial - 13
D: Decay - 200
G: Growth - 200
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Phosphorus cycles (5): fluxesCSU
Ocean deposits: 5,000 years (with respect to input). Availability to
marine organisms is limited by the fact that most P is in the deep
ocean.
Land deposits: for phosphate rocks, 44 years.
Longer if less concentrated deposits are mined (~ 175 years).
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Ciclos na natureza (2)(Klee e Graedel, 2004))
A mobilizao antropognica deCarbono, Nitrognio e Fsforo.
O problema est em que tais
mobilizaes alteram ciclos vitais
no planeta.
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MobilizaoAntropognica [Gg/ano]
MobilizaoNatural [Gg/ano]
Minerao ________ Decaimentono oceano
4.860 Mobilizao
total
[Gg/ano]
118.450.281
Fsseis 7.013.630 Oceano p/atmosfera
9.991 Antropognica/Natural
10,37%
Biomassa 4.110.800 Produode plantas
107.311.000 Antropognica/Total
9,39%
Total 11.124.430 Total 107.325.851
Ciclo de CarbonoKlee e Graedel (2004)
Gg = 1.000 t