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Biogeochemical Cycles
Nutrient Cycles
What are nutrients?

Nutrients are chemicals that organisms must take in from their environment

Macronutrients are required by organisms in large amounts and include water,
carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, and calcium

Micronutrients are required in trace amounts and include zinc, molybdenum, iron,
selenium, and iodine
Why do we need to understand
nutrient cycles?

Nutrients do not flow down onto Earth in a steady stream from above (like
energy)

describe the pathways nutrients follow between communities and the
nonliving portions of ecosystems

Reservoirs are sources and storage sites of nutrients


Major reservoirs are usually in the abiotic environment (rocks, water, atmosphere)
Processes are the changes that occur to move nutrients

May involve changes of state or chemical form
Hydrologic (water) cycle
 Water is essential for all terrestrial communities because other nutrients must be
dissolved in it before they can be used

major reservoir in the oceans

travels through the atmosphere, to reservoirs in freshwater lakes, rivers, and
groundwater, and then back again to the oceans

The oceans contain more than 97% of Earth’s water

Solar energy evaporates water, and it comes back to Earth as precipitation
The Hydrologic Cycle
reservoirs
processes
water vapor in
the atmosphere
precipitation
over land
precipitation
over the ocean
evaporation
from land and
transpiration
from plants
evaporation
from the
ocean
evaporation from
lakes and rivers
lakes and rivers
seepage into soil
groundwater,
including
aquifers
runoff
from rivers
and land
extraction for
agriculture
water in
the ocean
carbon cycle
 Chains of carbon atoms form the framework of all organic molecules, the building blocks
of life

major reservoirs in the atmosphere and oceans

Moves through producers and into the bodies of consumers and detritus
feeders, and then back to its reservoirs
The Carbon Cycle
reservoirs
CO2 in the
atmosphere
processes
trophic levels
burning
fossil fuels
CO2 dissolved
in the ocean
respiration
fire
photosynthesis
producers
consumers
detritus feeders
and decomposers
decomposition
fossil fuels
(coal, oil, natural gas)
nitrogen cycle
 Nitrogen is a crucial component of proteins, many vitamins, nucleotides (such as
ATP), and nucleic acids

major reservoir in the atmosphere

reservoirs of ammonia and nitrate in the soil and water, through producers and
into consumers and detritus feeders, and then back again to its reservoirs

nitrogen gas (N2) makes up 78% of the atmosphere, this form of nitrogen
cannot be utilized by plants
 Plants
utilize nitrate (NO3–) or ammonia (NH3) as
their nitrogen source
 N2 is converted to ammonia by specific bacteria
during a process called nitrogen fixation
 Denitrifying bacteria break down nitrate,
releasing N2 back to the atmosphere
The Nitrogen Cycle
reservoirs
processes
trophic levels
N2 in the
atmosphere
burning
fossil fuels
lightning
application of
manufactured fertilizer
consumers
ammonia and
nitrates in water
producers
uptake by
producers
detritus feeders
and decomposers
nitrogen-fixing
bacteria in soil
and legume roots
decomposition
denitrifying
bacteria
ammonia
and nitrates
in soil
phosphorus cycle
 Phosphorus is a crucial component of ATP and NADP, nucleic acids, and phospholipids of
cell membranes; it is also a major component of vertebrate teeth and bones

major reservoir in rock bound to oxygen as phosphate

moves from phosphate-rich rocks to reservoirs of phosphate in soil and water,
through producers and into consumers and detritus feeders, and then back to its
reservoirs
The Phosphorus Cycle
reservoirs
processes
trophic levels
phosphate
in rock
geological
uplift
application of
manufactured
fertilizer
runoff
from rivers
consumers
producers
detritus feeders
and decomposers
decomposition
runoff from
fertilized
fields
uptake by
producers
phosphate
in water
phosphate
in soil
phosphate
in sediment
formation of
phosphate-containing
rock
Human Disruption

Many of the environmental problems that plague modern society are caused by human
disruption of biogeochemical cycles.

industrial processes transfer toxic substances such as lead, arsenic, mercury, uranium, and oil
into the environment

bioaccumulation

addition of herbicides and pesticides to lawns and shrubs

farm fields, gardens, and suburban lawns, ammonia, nitrate, and phosphate are supplied by
chemical fertilizers


combustion of fossil fuels releases sulfur dioxide and nitrogen oxides into the atmosphere


eutrophication – adding nutrients to water
acid rain
Carbon emmisions release CO2
 Enhanced global warming