Lecture 6.
Environment Cycles
Types of Environment Cycles
Environment cycles
Tectonic cycle
Hydrologic cycle
Biogeochemical cycle
Carbon Cycle
Nitrogen Cycle
Tectonic Cycle
• The tectonic cycle involves the creation and destruction of Earth’s solid
outer layer, the lithosphere.
• The lithosphere is about 100 km thick on average and is broken into
several large segments called plates which are moving relative to one
another.
• The slow movement of these large segments of Earth’s outermost rock
shell is referred to as plate tectonics.
• Plate tectonics has important environmental effects. Moving plates change
the location and size of continents, altering atmospheric and ocean
circulation and thereby altering climate.
https://pubs.usgs.gov/gip/dynamic/historical.html
Hydrological Cycle
The hydrologic cycle is the transfer of water from the oceans to
the atmosphere to the land and back to the oceans.
It includes evaporation of water from the oceans; precipitation on
land; evaporation from land; transpiration of water by plants; and
runoff from streams, rivers, and subsurface groundwater.
Of the total 1.3 billion km3 of water on Earth, about 97% is in
oceans and about 2% is in glaciers and ice caps; 0.76% is
shallow groundwater: 0.013% is in lakes and rivers; and only
0.001% is in the atmosphere.
Source: Figure 6.13 The hydrologic cycle
Component of Hydrological Cycle
• Surface run-off - when water flows directly overland to the river (sometimes called overland flow).
• Infiltration - when water passes through from the surface of the drainage basin into the soil layer.
• Percolation - the movement of water from the soil layer to the rock layer.
• Groundwater flow - the movement of water through the rock layer (sometimes called base flow)
towards the river channel.
• Evaporation - moisture loss into the atmosphere from water surfaces, soil due to the wind and sun’s.
• Transpiration – a biological process by which moisture is lost directly from a plant through pores in
its leaves.
• Evapotranspiration- Evapotranspiration (ET) is the sum of water evaporation and transpiration from a
surface area to the atmosphere.
Surface run-off
Google image
Infiltration & Percolation
https://nrcca.cals.cornell.edu/soil/CA6/CA0657.2.php
Biogeochemical Cycle
It’s the pathway that a chemical element follows through the Earth
system-from the atmosphere, waters, rock, or soils, to living organisms
and back to the atmosphere, ocean, soils, or to other organisms.
It’s chemical cycle because chemical elements are the form that we
consider.
It’s bio because these are the cycles that involve life.
It’s geo because these cycles include atmosphere, water, rocks, and
soils.
Biogeochemical Cycles and Life
All living things made up of chemical elements.
Macro-nutrients elements required in large amounts by all
life. Major macro-elements that form the fundamental building
blocks of life: Carbon, hydrogen, nitrogen, oxygen,
phosphorus, and sulfur.
Micro-nutrients elements required either small amounts by
life or moderate amounts for some forms of life and not others.
e.g. Iron, Cobalt, Chromium, Copper, Iodine, Manganese,
Zinc etc.
Carbon Cycles
• Carbon is the building block of life that anchors all
organic substances.
• The carbon cycle is the process that redistributes
carbon on earth.
• Plants use carbon dioxide, water and sunlight to make
their food, this process is called photosynthesis.
https://www.youtube.com/watch?v=BuV5GQFz0gg
Nitrogen Cycles
78% of the air in our atmosphere is made of Nitrogen.
Our body does not use the nitrogen that we inhale.
Our body gets nitrogen from food.
Nitrogen is essential to life because it is necessary for proteins including DNA.
Organisms cannot use or absorb nitrogen directly.
Some use N in an organic form and others (plants, algae, bacteria) can take up
N either as nitrate ions (NO3-), or the ammonium ion (NH4+)
https://www.youtube.com/watch?v=K5EOZenSSB8
Reading materials
• Chapter 6. Page 113-121
