Download biogeochemical cycles

BIOGEOCHEMICAL
CYCLES
BASICS
• Biogeochemical Cycle: The complete path a chemical takes
through the four major components, or reservoirs, of Earth’s
system (atmosphere, lithosphere, hydrosphere and biosphere)
• Atmosphere: Layer of gasses surrounding the Earth. Divided
into 4 layers (troposphere, stratosphere, mesosphere,
thermosphere)
• Lithosphere: The outer layer of the Earth, approx. 100km thick,
of which the plates that contain the ocean basin and
continents are composed
• Hydrosphere: The water portion of our planet consisting of
surface freshwater, oceans, glaciers, groundwater and
atmospheric water (clouds)
• Biosphere:
1.
2.
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That part of a planet where life exists
The planetary system that includes and sustains life
ENV 101: Introduction to
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BASICS
BIOGEOCHEMICAL
It is chemical
because it is
chemicals that are
cycled
It is bio because it
involves life
It is geo because the
cycle may include
the atmosphere,
hydrosphere, rocks
and soil
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ENV 101: Introduction to
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GENERAL CONCEPTS
1. Some chemical elements (e.g. O, N) cycle quickly and
are readily regenerated for biologic activity. Typically
these elements have a gas phase and are present in
the atmosphere and/or easily dissolved in water and
carried by the hydrologic cycle
2. Other chemicals are easily tied up in relatively
immobile forms and are returned slowly, by geologic
processes, to where they can be reused by life. They
typically lack a gas phase and are not found in
significant concentrations in the atmosphere. They are
also relatively insoluble in water (e.g. P)
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ENV 101: Introduction to
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GENERAL CONCEPTS
3. Most required nutrient elements have a light
atomic weight. The heaviest required
micronutrient is iodine
4. Since life evolved it has greatly altered
biogeochemical cycles and this alteration has
changed our planet in many ways
5. The continuation of processes that control
biogeochemical cycles is essential to the long
term maintenance of life on Earth
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ENV 101: Introduction to
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GENERAL CONCEPTS
• All living things are made up of chemicals (24 out of the
more than 103 known chemicals are required for life)
• Macronutrients: Elements required in large amounts by
living things. Include the big 6 (C, H, O, N, P, S)
• Micronutrients: Chemical elements required in very small
amounts by at least some forms of life. (e.g. B, Cu, Mo)
• Limiting Factor: The single requirement for growth
available in the least supply in comparison to the need
of the organism
• Some elements can be toxic even at low concentrations
(e.g. Hg) while other elements that are essential in small
concentrations can be toxic at higher concentrations
(e.g. Cu)
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ENV 101: Introduction to
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PERIODIC TABLE OF THE ELEMENTS
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ENV 101: Introduction to
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SIMPLIFIED BIOGEOCHEMICAL CYCLE
• Source: Refers to a compartment that donates to another compartment
• Sink: Refers to a compartment the receives materials (e.g. a chemical
element)
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ENV 101: Introduction to
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GEOLOGICAL CYCLE
• Geologic Cycle: The processes responsible for the
formation and change of Earth materials
• Encompassing term for:
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•
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Tectonic cycle
Rock Cycle
Hydrologic Cycle
Biogeochemical cycle
ENV 101: Introduction to
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TECTONIC CYCLE
• It involves the creation/destruction of the Earth’s outer layer
(lithosphere)
• The lithosphere is broken into large plates that move relative to
each other (plate tectonics) at a rate of 2 -15cm per year
• Process driven by heat from the interior (which rises) while at
the same time cooler denser slabs sink bank into the Earth’s
crust setting the plates in motion
• Impacts:
• Changes the position, size and shape of continents
• Can change ocean and atmospheric circulation patterns leading to
environmental change
• Can also create ecological islands, leading to the development of
new species
• Boundaries are geologically active areas (earthquakes and
volcanoes)
• Types of plate boundary: Convergent, divergent, transform
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TYPES OF PLATE BOUNDARIES
• Convergent boundaries
• Plates move into each other
• Leads to the destruction of lithosphere
• Types:
• Continental crust and oceanic crust
• Continental crust less dense than oceanic crust
• Therefore oceanic crust gets subducted while the continental crust “floats” on
top
• Can lead to extensive volcanism
• e.g. The Andes mountains of South America
• Continental crust and Continental Crust
• Both crusts of equal density
• Leads to buckling, fracturing and deformation of the crust
• e.g. The Himalaya’s
• Oceanic Crust and Oceanic Crust
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One is thrust underneath another
Leads to extensive volcanism
Can lead to the formation of volcanic island arcs
e.g. Mariana islands
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TYPES OF PLATE BOUNDARIES
• Divergent boundaries
• Plates are moving apart, leads to the production of new
lithosphere
• Typically occurs at mid-ocean ridges (seafloor spreading)
• e.g. The Atlantic Ocean
• Transform boundaries
• Occurs where plates grind past each other
• Lithosphere is not being created or destroyed
• e.g. San Andreas Fault
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MAJOR GLOBAL TECTONIC PLATES
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ENV 101: Introduction to
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THE HYDROLOGIC CYCLE
• The transfer of water from the oceans, to the
atmosphere, to the land and then eventually back
to the oceans
• Has the following components
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Evaporation from the ocean
Precipitation on land
Evaporation from land
Transpiration by vegetation
Surface runoff (streams, rivers)
Subsurface flow
Storage on land (lakes, dams, glaciers)
Evaporation from lakes and dams
ENV 101: Introduction to
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THE HYDROLOGIC CYCLE
• Process driven by solar energy
• Distribution of water:
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Oceans: 97%
Glaciers and ice caps: 2%
Shallow ground water: 0.8%
Lakes and rivers: 0.01%
Atmosphere: 0.001%
• The rate of transfer of water from the land to the ocean
is relatively low
• The land and ocean somewhat isolated from the
hydrologic cycle
• Most of the rainfall in the ocean came from water evaporated
from the ocean and likewise for land
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THE HYDROLOGIC CYCLE
Units:
thousands
of km3/yr
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• Approx. 60% of the
water that
precipitates on land
evaporates back to
the atmosphere,
while 40% flows
back to the ocean
• Water is not evenly
distributed on land
as this has
environmental
implications
ENV 101: Introduction to
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THE ROCK CYCLE
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ENV 101: Introduction to
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A group of processes that
produce igneous, sedimentary
and metamorphic rocks
The rock cycle can serve as a
sink for carbon (formation of
coal or anthracite)
Additional elements can also
be incorporated into rock
such as limestone (a sink for
Ca)
Additionally certain gasses
can be released into the
atmosphere during the
formation of igneous rocks
(the extrusive variety)
Rocks, through the process of
weathering, can be a source
of a variety of chemical
elements into the environment
THE CARBON CYCLE
• Atmosphere:
• Exists in a gaseous state (CO2, CH4)
• Removed from atmosphere by:
• Photosynthesis
• Diffusion with ocean
• Introduced into atmosphere by:
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Respiration
Wildfires
Burning of fossil fuels
Decomposition of organic materials
Diffusion with ocean
Volcanic eruptions
ENV 101: Introduction to
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THE CARBON CYCLE
• Hydrosphere
• Exists as dissolved CO2, or as CO3-2, HCO3• Removed from ocean by:
• Photosynthesis of algae and photosynthetic organisms
• Diffusion with atmosphere
• Formation of CaCO3 in sea shells
• Introduced into ocean by:
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Respiration of marine organisms
Diffusion with atmosphere
Rivers (dissolved CO2, organic particles)
Wind
ENV 101: Introduction to
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THE CARBON CYCLE
• Biosphere
• Plants take up C during the process of photosynthesis
• Higher trophic levels obtain their C by feeding on the lower
trophic levels
• Decomposition of material is decomposed into organic
compounds as well as CO2
• In areas where there is not enough oxygen or the
temperature is too low, the rate of decomposition slows
down and organic material accumulates
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THE CARBON CYCLE
• Lithosphere
• Very small constituent of crust (0.035% by weight)
• The accumulated organic material in land systems can over
time become compressed by geologic forces
• This compression squeezes out O and H (contained within
the organic material) increasing the carbon content
leading to the formation of coal
• In marine systems the compression of organic material
(mostly phytoplankton) leads to the formation of oil and
natural gas
• The formation of limestone (CaCO3) in marine environments
is also a sink for carbon
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ENV 101: Introduction to
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THE CARBON CYCLE
Units: billions
of metric
tonnes
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THE PHOSPHOROUS CYCLE
• Atmosphere:
• P does not have a gaseous phase on Earth
• Found in the atmosphere only in small particles of dust
• Hydrosphere:
• P tends to form compounds that are relatively insoluble in
water
• Transported by rivers to the oceans in soluble form or as
suspended particles
• Runoff of industrial and agricultural wastes can introduce
phosphates into water systems. (can lead to environmental
degradation - Eutrophication)
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ENV 101: Introduction to
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THE PHOSPHOROUS CYCLE
• Biosphere
• Enters biota through uptake of phosphate by plants, algae
and photosynthetic bacteria
• Can be returned to land by pelagic birds that feed on fish
which in turn feed on plankton which take up P
• These birds nest on off shore islands and their P rich excrement
accumulates (guano).
• These accumulations can be up to 40m thick
• Lithosphere
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Occurs in an oxidised state (phosphate)
Combines with Ca, Mg, K, Fe to form minerals
Rate of transfer slow compared to that of C or N
Recycled in marine sediments to become part of the rock
cycle
ENV 101: Introduction to
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THE PHOSPHOROUS CYCLE
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ENV 101: Introduction to
Environmental Science