ENVIRONMENTAL SYSTEMS Module Code: NG1028M

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ENVIRONMENTAL SYSTEMSModule Code NG1028M

• Dr Heidi Smith
• Lecture 1 part B Introduction to Systems

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Outline

• Characterising systems
• Systems and models
• Earth as a system
• Gaia
• Integration gradient
• Ocean crust interactions
• Ocean atmosphere interactions

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How might we characterise a system?

• We could base it on understanding of
  relationships among physical properties of
  elements (in the system)
• known as morphological systems

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Or we could base it on understanding of how
elements (in the system) are linked...

• known as cascading systems where output from
  one subsystem input to next
• flows represent processes
• process mode of operation by means of which
  matter or energy is transferred from one element
  (in the system) to another

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What are the elements in this system? What are
the links (processes) in this system?
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Systems and models

• integration of morphological and cascading
  systems is known as a
• process-response system
• share variables in two system types
• best depiction and explanation of the dynamics of
  environmental systems

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Systems and models

• Real world systems immensely complex - multitude
  of branching energy and material pathways and
  feedback links exist
• Systems approach helps to structure our
  investigations, it does nothing to really
  simplify the real world
• Models and modelling are the key
• Idealise the system and display or make clear its
  structure and how it works
• Integrated, systems approach can highlight
  relationships that could be obscured if a more
  conventional reductionist approach were adopted.

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Systems and models

• Rarely isomorphic (Greek - same/equal) where all
  elements, states, relationships and processes
  have corresponding component in the model
• Generally homomorphic models (Greek - similar)
  imperfect representations of reality
• or compartment models

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Models

• Static models
• At one point in time
• Dynamic models
• Changing conditions through time
• Simulations
• Numerical calculation of detailed response to new
  conditions

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Systems and models

• Compartments of these models treated as BLACK BOX
• Any unit whose function may be evaluated without
  specifying the contents (we dont know what
  happens inside the system!)
• At low resolutions models contain small number
  of relatively large black box components (or
  whole system may be treated as one black box)
• Progressively split into sub-compartments
  (treated as black boxes) as level of resolution
  increases

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Systems and models

• At intermediate levels of discrimination the
  model of whole system has become a partial view
  of the system, its structure, relationships and
  processes a GREY BOX model (we have partial
  understanding of what happens in the system)

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Systems and models

• As realism increases toward isomorphic model,
  this becomes a WHITE BOX model where elements,
  structure, relationships and processes are
  identified and incorporated (excellent but
  imperfect understanding)

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Systems and models

• Hierarchy of models of different levels of
  discrimination and complexity, appropriate to
  different scales of analysis
• Allows incorporation and coordination of
  specialist knowledge at appropriate level
• May be hardware models or a series of
  mathematical equations
• show the relationships between the changes that
  occur in the various components of a system under
  different conditions (e.g. increasing
  temperature, increasing rainfall or atmospheric
  acidity, or decreasing the number of predators in
  an environment by pesticide pollution)
• Last 50 years - construction of many complex
  mathematical models for entire biosphere (e.g.
  Club of Rome)
• highlight human impacts on environmental systems,
  and predicting future changes
• yielded interesting tentative conclusions, but
  have not been an entire success

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Systems and models

• Models are never going to be the complete answer
  to our understanding of the environment - because
  of staggering complexity of real environmental
  systems models approach the limits of analytical
  techniques
• Some models are deterministic, i.e. allow
  prediction of the outcome of some operation
  performed on the system

A systems approach ultimately must involve
reducing the description of the system and the
analysis of its organisation and behaviour to the
language and rigour of (quantitative) mathematics
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Systems and models ?

• Other models are stochastic, i.e. incorporate
  some element of randomness or uncertainty and are
  able to predict the probability of the outcome of
  an operation
• Recognise that some variables are truly random or
  are so complex that are best treated as random
• Modelling must retain continuous dialogue with
  reality
• Validation requires real data via field
  monitoring and measurement, description of
  spatial variation, laboratory experimentation,
  hardware modelling

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Problems limitations of models ?

• Understanding of the real world is imperfect and
  not uniform
• Inadequate understanding of processes
• Inadequate coverage of data in geologic past
• Poor spatial resolution
• Computational power limits chronologic resolution
  
• Most are primarily physical/chemical (biosphere?)
• Developed v developing world
• No guarantee that models developed using
  developed (European/North American) world
  mathematics based on empirical observations and
  the construction of inductive hypotheses can be
  extended to other areas, except in an abstract
  manner
• E.g. ecological or geomorphological models to
  the humid tropics
• So abstract mathematical models tend to obscure
  the rich geographical variety in real-world
  systems

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THE EARTH AS A SYSTEM
The atmosphere, the waters of the continents, the
oceans, and the surface of the crust are all
linked in a giant chemical system
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Earth as a system where did all this stuff come
from?

• All gases of atmosphere and all water on surface
  originated deep within the Earth at high pressure
  and temperature and escaped via volcanoes, hot
  springs and other zones of connection
• Volcanism has contributed enormous amounts of
  water, CO2 and other gases to the atmosphere and
  materials to the continents. Sunlight broke water
  molecules into its components H and O2.
  Photosynthesis by plants removed CO2 and added O2
  to the primitive atmosphere

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Gaia

• The positive and negative feedbacks that
  influence the operation of an environmental
  system, seem biological...
• Major impetus behind the Gaia hypothesis
• Gaia Mother Earth (Greek)

James Lovelock and Lynn Margulis
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Gaia

• "The biosphere is a self-regulating entity with
  the capacity to keep our planet healthy by
  controlling the chemical and physical
  environment.
• James Lovelock

Biosphere regulates the environment, instead of
just adapting to it
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Gaia

• "The Gaia hypothesis says that the temperature,
  oxidation state, acidity, and certain aspects of
  the rocks and waters are kept constant, and that
  this homeostasis is maintained by active feedback
  processes operated automatically and
  unconsciously by the biota.
• James Lovelock

Controversial as it is biotic (not abiotic)
components that play the major role in homeostasis
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The Gaia hypothesis

• The Earth is seen as a superecosystem (not really
  a superorganism as popularly stated since its
  development is not genetically controlled)
• Major systems are connected in intimate ways via
  many pathways
• Parts are so integrated that they are like cells
  in a living body

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• After outgassing, atmosphere evolved as a
  biological product
• Buildup of O2 and reduction in CO2
• Strong indirect evidence for hypothesis from
  comparison with other atmospheres
• Earths atmosphere is complete opposite of e.g.
  Venus and Mars
• Without critical buffering activities of early
  life forms and continued coordinated activities
  of plants and microbes that dampen fluctuations
  in physical factors, Earth would be similar to
  Venus, very hot, with no O2 in the atmosphere

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The Gaia hypothesis

• Life processes have greatly modified the
  atmosphere oceans
• By changes in CO2 concentration (temperature
  regulation)
• Maintained temperature between 10-20 C
• While the suns luminosity has increased 30
• Increased O2 (aerobic respiration)
• Atmospheric oxygen maintained between 10-30
• Built up O3 (shield UV radiation)
• Oceanic salinity has remained between 3-4

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From a systems perspective

• Symbiosis and cooperation more important than
  competition
• Survival is not important at the individual or
  species level
• Survival of the ecological system is important
• This can survive for eons

The Gaia hypothesis is one extreme of the debate
over degree of integration of systems
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Homeostasis v Homeorhesis

• According to Gaia the biosphere is highly
  integrated and self-organised cybernetic or
  controlled system.
• Control is not accomplished by external,
  goal-oriented, set-point controls like
  thermostats rather control is internal and
  diffuse involving hundreds of thousands of
  feedback loops and synergistic interactions in
  subsystems
• Homeostasis - physiological stability at organism
  level
• Homeorhesis - evolutionary and ecological
  stability
• maintaining the flow
• Above organism level control by feedback is less
  precise so there tends to be a pulsing rather
  than steady state
• Failure to recognise difference results in
  confusion about realities of balance of nature

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Cybernetics in the organism-ecosystem hierarchy
Compared with set point controls at organism
level and below, organisation and function at
ecosystem level are much less tightly regulated
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The Earth today can be thought of as

• A giant chemical reaction chamber made of 2
  sub-chambers
• HOT and COLD
• Conveyor belt between chambers is volcanism and
  tectonics

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The movements of solid lithosphere and magmas
combine to allow gases and water to separate from
rockmaking materials from interior and leak out
as rocks are pushed to surface in mountains,
mid-ocean ridges and volcanic island arcs
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Earth as a system

• Erosional processes take place at Earth surface
  all components come together again at lower
  temperature and pressure
• WEATHERING is the conversion of materials formed
  in hot chamber to materials stable in the cold
  one
• water and CO2 combine to form carbonic acid which
  weathers silicate minerals
• O2 (accumulated in the atmosphere as a by-product
  of photosynthesis that produces organic carbon)
  oxidises iron and other metals
• Chemical stabilities of minerals that can be
  formed by new components are so different at low
  temps and pressure, an entirely new set of
  minerals is formed (clays and carbonates instead
  of olivines and pyroxenes)
• Materials from chemical weathering eventually
  filter into the ground move to oceans via
  rivers

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Interactions of the solid, liquid and gaseous
earth

• Biosphere
• Interactions amongst surface regions are strongly
  influenced by the biosphere, which permeates all
  the other reservoirs
• Unlike all other reservoirs it is not a single
  connected volume

Biosphere animal, plants, fungi, protists,
prokaryotes
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Biospheric interactions

• Effects of organisms on the environment huge
• Through control of carbon cycle affects flow of
  CO2 and O2 through the Earth (ecosphere)
• Shells of organisms produce limestones, and
  contribute to storage of huge amounts of carbon
  (as CaCo3) in crust of earth incorporate trace
  elements such as strontium, providing a tracer
  for the oceans composition

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OCEAN-CRUST INTERACTIONS
The Solid and Liquid Earth
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Ocean-crust interactions

• Total ocean mass
• 1.4 x 1024 g
• Ocean contains
• 5.6 x 1020 g of Ca
• Entering from all rivers of world that transport
  Ca
• Derived from weathering of Ca minerals
• calcite, gypsum, calcium feldspars other
  calcium silicates
• Flux is sedimentation of calcium carbonate
• Also some precipitation of gypsum in evapourite
  deposits, other elements in various mineral
  forms
• Influx approx. Efflux
• i.e. oceans are close to a steady state

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Simple model of steady state ocean
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How long does an atom stay in the ocean?

• Residence time RT
• capacity/rate of influx
• Average length of time that elapses between entry
  of atom into the sea its removal by
  sedimentation

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Significance of residence times

• Seawater has constant relative chemical
  composition
• Total salinity may change via evaporation,
  relative amounts of elements remains same
• Oceans circulate mix over time scale of c. 1000
  yrs
• ? If RT longer than 1000 yrs it will be
  well-mixed everywhere in ocean, if less than
  1000 yrs any particular atom will leave ocean by
  sedimentation before it can be homogenised

Knowing RT important for

• Working out general dynamics of ocean-crust
  system
• Predicting behaviour of toxic/radioactive
  elements in ocean
• Predicting behaviour of (excess) CO2 in ocean

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Calculating residence times e.g. Ca

• RT ratio of total quantity, A, of a substance
  in a reservoir to the influx rate ?A/?t where ?A
  denotes the amount added in a given time ?t
• RT A
• ?A/?t
• Total quantity, A, of Ca in ocean calculated from
  its average conc. in seawater x mass of oceans
• A 0.4g/kg x 1.4 x 1021 kg 5.6 x 1020 g
• Influx rate calculated from conc. of Ca in
  average river water x flux of river water to
  ocean per yr
• ?A/?t 0.015g/kg x 4.6 x 1016 kg/yr 6.9 x
  1014 g/yr

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Calculating residence times e.g. Ca

• Dividing total quantity by influx
• A 5.6 x 1020 g 0.8 x 10 6
  years
• ?A/?t 6.9 x 1014 g/yr
• 800 000 years is a little lower than most other
  major elements weathering and sedimentation
  rates of calcium-rich rocks are fast compared to
  rates for other elements - Iron (Fe) has RT 100
  yrs
• Ca from weathering of limestone has high influx
  readily taken up by organisms that build shells
  composed of CaCO3

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Average concentration residence times of some
major elements in the oceans
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OCEAN-ATMOSPHERE INTERACTIONS

• The Liquid and Breathing Earth

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Ocean-atmosphere interactions

• Atmosphere interacts with oceans and land along
  the thin layer of air immediately overlying
  surface
• Main role is medium of exchange between
  crust/oceans over long time scale of geologic
  processes
• Over short term (human time scales) it can be
  considered a reservoir
• Top layers of water evaporate precipitation
  enters the ocean
• Gas molecules escape from dissolved state in
  water dissolution of gas molecules from air to
  water, speeded by evaporation of sea spray

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Ocean-atmosphere interactions

• RT of gases in atmosphere much shorter than in
  oceans, mix on a timescale of about 1 year
• Reflects size of reservoir
• 1/60th of CO2 in oceans
• Ca - At conc. of 345 ppm RT of 10 yrs (includes
  cycling through biosphere and atmosphere)
• N 400 000 000 yrs most is nitrogen gas (N2)
  stored in atmosphere and efflux to sediments is v
  small
• Sulphur dioxide (SO2) RT of hours-weeks, v little
  stored in atmosphere

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Average concentrations and residence times of
some gases in the atmosphere
cycled through combined atmosphere
biosphere cycled through combined atmosphere
sediments
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Compared to the oceans, the atmosphere

• Is more heterogeneous in temperature gas
  composition
• Has faster reactions between gas molecules,
  strongly affected by sun
• e.g. Ozone is formed in significant amounts only
  in certain layers of the atmosphere where
  radiation from the sun makes O2 molecules react
  with each other and with other gases
• Reflects the activities of the biological world
  to a greater extent
• e.g. sulphur gases, methane, 02 contributed
  largely by organisms

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Variation of temperature with height in the
atmosphere. Atmospheric pressure decreases
from 1 at sea level to 0.01 at c. 30 km and to
lt0.00001 at c. 120 km
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Physical connections

• Winds of atmosphere responsible for waves of
  ocean and major current systems which transport
  heat and mix chemically
• Through evapouration and transport by current
  systems the interaction determines salinity of
  surface waters
• On land wind form dunes

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Physical connections

• Heat exchange affects heat transfer from equator
  to poles in both reservoirs
• Nearly half heat absorbed by atmosphere comes
  from condensation of water vapour, producing
  precipitation
• Most important aspect of heat exchange between
  oceans, atmosphere and land may be the warming of
  atmosphere by radiation absorption by certain
  gases

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The major reservoirs fluxes of the
mantle-crust-oceans-atmosphere systems. In
this steady-state box model all fluxes balance so
any substance remains constant with time