Ecology
PART III
Recycling Matter
Lesson Objectives
• Define biogeochemical cycles.
• Describe the water cycle and its processes.
• Give an overview of the carbon cycle and the oxygen
cycle.
• Outline the steps of the nitrogen cycle.
BIOGEOCHEMICAL CYCLES
bio- biotic components
geo- geological and abiotic components
WATER CYCLE
Evaporation, Sublimation, and
Transpiration
Sun drives the water cycle.
Heats oceans, lakes, and other bodies of
water.
Heated water evaporates.
Evaporation
Heats ice and snow.
Heated ice and snow turns into water vapor.
Sublimation
Heat causes plants to release water through their
stomata (pores in leaves)
Transpiration
Condensation and Precipitation
Rising air currents carry water
from evaporation, sublimation,
and transpiration into the
atmosphere….eventually
forming CLOUDS
Groundwater and Runoff
Rain falls on land and soaks
into ground infiltrating and
becomes groundwater
Or rain falls on land and flows
over it
Runoff ends up in bodies
of water
CARBON CYCLE
Carbon in rocks is dissolved by water and ends up in
oceans
Other carbon from burned fossil fuels or their byproducts ends up in the atmosphere or biosphere
Note: fossil fuels are
formed from the
remains of dead
organisms
Carbon in the Atmosphere
• Living organisms release carbon dioxide as a byproduct
of cellular respiration.
• Carbon dioxide is given off when dead organisms and
other organic materials decompose.
• Burning organic material, such as fossil fuels, releases
carbon dioxide.
• When volcanoes erupt, they give off carbon dioxide that
is stored in the mantle.
• Carbon dioxide is released when limestone is heated
during the production of cement.
• Ocean water releases dissolved carbon dioxide into the
atmosphere when water temperature rises.
• From methane gases released from landfills
Carbon in the Ocean Water
Most comes from atmospheric carbon
dioxide that dissolves in ocean water thus
forming carbonic acid. (in cooler water)
– The process is reversible in warmer water
changing carbonic acid to bicarbonate ions
– Bicarbonate ions are also deposited into
oceans from runoff
Carbonic acid H2CO3
Bicarbonate ions  HCO3-
Carbon in the Biosphere organic pathway
• Photosynthetic algae and bacteria take up bicarbonate ions in
the ocean use it to synthesize organic compounds
• Terrestrial autotrophs remove carbon dioxide from the
atmosphere to synthesize organic compounds
• Both recycle it back through a process called cellular respiration
• Decomposers release carbon dioxide when they consume dead
organisms
• They rates of exchange are about equal
Carbon in Rocks and Sediments
(geological pathway)
• Long, slow process through rock
formation, subduction, and volcanism
• In oceans begins as sedimentary rock;
pressure of additional layers forms the
rock
Oxygen Cycle
• Movement of oxygen through the
atmosphere, biosphere, and the lithosphere.
Oxygen and the Hydrosphere
• Failures in this type of
movement = development of
hypoxic (low oxygen) zones
or dead zones
• Cause: excessive nutrient
pollution from human
activities that lead to
depletion of oxygen required
to sustain marine life
Oxygen and the
Biosphere/Atmosphere
• Free oxygen in the biosphere (0.01%) and
atmosphere (0.36%).
• The main source of atmospheric free
oxygen is photosynthesis.
Photosynthesizing organisms include the
plant life of the land areas as well as the
oceans.
• Additional source of atmospheric free
oxygen comes from photolysis
Oxygen and the Lithosphere
• Largest reservoir of Earth's oxygen is
within the silicate and oxide minerals of
the crust and mantle (99.5%).
NITROGEN CYCLE
• Most nitrogen is stored in the atmosphere (78%
nitrogen gas)
• Nitrogen moves through abiotic and biotic
components of ecosystems
Absorption of Nitrogen
• Plants and producers make nitrogencontaining organic compounds
(chlorophyll, proteins, nucleic acids)
• Plants absorb nitrogen from
the soil through their root hairs
in the from of nitrate ions
– Nitrogen is changed in the soil
through nitrogen fixation into
nitrate ions
Nitrate ions  NO3-
Nitrogen Fixation
Nitrogen-fixing bacteria
live in soil or in the root
nodules of legumes
In aquatic system, some
cyanobacteria fix
nitrogen
Nitrogen gas in the atmosphere can also be fixed by
lightning
Some nitrogen is converted into fertilizer by humans
Ammonification and Nitrification
• Decomposers break down organic remains and
release nitrogen in the form of ammonium ions
– Ammonification
• Certain soil bacteria convert the ammonium ions into
nitrites. Others convert the nitrites into nitrates that
plants can absorb
– Nitrification
Ammonium ions NH4Nitrites  NO2Nitrates  NO3
Denitrification and the Anammox
Reaction
• Denitrifying bacteria in soil convert some
nitrates back to nitrogen gas  NO2
– Denitrification
• In aquatic systems, bacteria in the water
convert ammonium and
nitrite ions to water
and nitrogen gas
- Anammox Reaction
Lesson Summary
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Chemical elements and water are recycled through biogeochemical cycles. The
cycles include both biotic and abiotic parts of ecosystems.
The water cycle takes place on, above, and below Earth’s surface. In the cycle,
water occurs as water vapor, liquid water, and ice. Many processes are involved
as water changes state in the cycle. The atmosphere is an exchange pool for
water. Ice masses, aquifers, and the deep ocean are water reservoirs.
In the carbon cycle, carbon passes among sedimentary rocks, fossil fuel deposits,
the ocean, the atmosphere, and living things. Carbon cycles quickly between
organisms and the atmosphere. It cycles far more slowly through geological
processes.
The oxygen cycle produces most available oxygen through photosynthesis by
plants on land and phytoplankton on the ocean’s surface. Some oxygen is made in
the atmosphere when sunlight breaks down atmospheric water. Oxygen is used
by both biotic and abiotic factors in ecosystems: plants, animals, bacteria,
decomposition, fire, and oxidizing agents
The nitrogen cycle moves nitrogen back and forth between the atmosphere and
organisms. Bacteria change nitrogen gas from the atmosphere to nitrogen
compounds that plants can absorb. Other bacteria change nitrogen compounds
back to nitrogen gas, which re-enters the atmosphere.