Biogeochemical Cycles
(Nutrient Cycles)
❧
❧In terms of matter, Earth is a
closed system
❧Nothing enters or leaves, just recycled
❧This is the Law of Conservation of
Matter!
❧ Matter is neither created nor destroyed,
but recycled and reused
❧Important cycles: carbon, oxygen,
nitrogen, phosphorus, water
Carbon Cycle = process where C is cycled
b/w atmosphere, land, water, & organisms
(during photosynthesis & cellular
respiration)
❧ Steps:
How Humans Affect the Carbon
Cycle
❧ Burn fossil fuels → releases CO2 into atmosphere
❧ More CO2 in atmosphere causes global warming
through greenhouse effect
How You Can Reduce Your
Carbon Impact:
❧Use gas-efficient
cars
❧Carpool/ use public
transportation
❧Walk or ride bike
when possible
❧Eat locally-grown
food
❧Use less plastics &
disposable products
Oxygen Cycle = process where oxygen is
cycled b/w atmosphere, ocean, & organisms
❧ All organisms need Oxygen
1. Producers release O2 during photosynthesis
❧CO2 + H2O + sun → C6H12O6 + O2
2. Organisms use O2 during cellular respiration
❧ C6H12O6 + O2 → CO2 + H2O + energy
3. O2 is stored:
❧Dissolved in oceans
❧Oxygen in the atmosphere:
❧ O2 is 21% of lower atmosphere
❧ Ozone (O3) in upper atmosphere protects us from
UV rays
Nitrogen Cycle = process where nitrogen (N)
is cycled b/w atmosphere, bacteria, & other
organisms
❧ All organisms need N for proteins & nucleic acids
(DNA)
1. N2 gas must be changed by nitrogen-fixing
bacteria:
❧ They convert N2 into nitrates (NO3)
2. Plants get NO3 from soil → animals eat plants
3. Plants & animal waste puts N back into soil in form
of ammonia (NH4)
4. Other bacteria convert ammonia into nitrites (NO2)
& nitrates
Nitrogen Cycle
How Humans Affect the
Nitrogen Cycle
❧Have doubled
amount of N on land
due to use of
fertilizers & burning
fossil fuels
❧Problems of too
much N:
❧ Rivers & lakes
becoming acidic
❧ Global warming
Hydrologic (Water) Cycle = path of
H2O through environment
❧ Most H2O is stored in oceans
❧ Ocean H2O is turned to vapor (gas) by evaporation
& winds push vapor around globe
❧ H2O vapor turns to liquid in atmosphere =
condensation
❧ Liquid falls as precipitation (rain, snow, etc.)
❧ Living organisms use H2O, then return it to
environment through:
❧ Breathing & sweating
❧ Waste
❧ Transpiration from leaves (plants) (leaves sweating)
❧ Water Cycle
❧
How Humans affect the Water
Cycle:
❧
❧Remove H2O faster than nature can
replace it
❧Drain wetlands → increases flooding
❧Pollution
Phosphorus Cycle = movement of
phosphorus (P) between environment &
organisms
❧P is important in DNA and ATP
Steps:
1.Rocks erode, putting phosphate into soil and water
2. P is taken up by plants & converted to organic
molecules
3. Animals eat plants
4. Decomposing plants & animals & waste return P
to environment
❧How humans affect P cycle:
❧ Excess phosphate from fertilizers can cause too
much algal growth in water → kills fish & other
organisms
Phosphorus
Cycle
❧
Excess P due
to fertilizers!