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 CYCLESbio- biotic components

geo- geological and abiotic components

WATER CYCLE

Evaporation, Sublimation, and Transpiration

Sun drives the water cycle.

Heats oceans, lakes, and other bodies ofwater.Heated water evaporates. EvaporationHeats ice and snow.Heated ice and snow turns into water vapor. SublimationHeat 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 CYCLECarbon in rocks is dissolved by water and ends up in

oceansOther carbon from burned fossil fuels or their by-

products ends up in the atmosphere or biosphere

Note: fossil fuels are formed from theremains of deadorganisms

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 nitrogen-

containing 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 NH4-

Nitrites NO2-

Nitrates 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• 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.