Biogeochemical Cycles
Biology, Geology and Chemistry
Cycle
Nutrients through the Ecosystem
I. General Information
 A.
Biogeochemical cycles =
materials cycle between the living and
physical parts of an ecosystem
B. Types of cycles
1. Water
2. Carbon
3. Nitrogen
II. Water Cycle
II. Water Cycle
A.
Driven by
the Sun
B. Steps of Water Cycle
1. Evaporation –
a. Sun heats Earth
b. H2O evaporates
c. H2O goes into atmosphere as
H2O vapor
II. Water Cycle
2. Condensation
H2O condenses
(goes from gas to liquid)
to form
clouds
II. Water Cycle
3. Precipitation
H2O leaves clouds, falls on Earth
E.g. rain, snow, sleet, hail
4. Percolation / Infiltration
H2O enters soil, becomes groundwater
II. Water Cycle
5. Run–off
Some H2O moves on surface to rivers,
lakes & oceans
6. Transpiration
H2O released from plant leaves,
returns to atmosphere
II. Water Cycle
C. Where is the H2O on Earth?
1. Oceans
97.2%
2. Glaciers
2.15%
3. Lakes
0.009%
4. Soil
0.005%
5. Atmosphere
0.001%
6. Streams
II. Water Cycle
III. Carbon Cycle
III. Carbon Cycle
A.
How does carbon enter the
living part of the cycle?
1. Photosynthesis
Plants, algae, & cyanobacteria
use CO2 to make
organic compounds (sugars)
2. Nutrients move C through trophic levels
Consumers move organic compounds
III. Carbon Cycle
B. How does carbon get back into the physical
part of the cycle?
1. Respiration
O2 used
to break down sugars,
CO2 released
III. Carbon Cycle
2. Combustion

Fossil fuels & wood burned
CO (carbon monoxide) released to
atmosphere

Factory & Auto emissions release CO to
atmosphere
III. Carbon Cycle
3. Erosion
 CaCO2
from shells
returned to system
as sediment
 Shelled organisms die
 Sediment returns C to ecosystem by erosion
(wind & water)
III. Carbon Cycle
5. Decomposition of waste and dead materials
 Some dead organisms become fossil fuels
 Some
dead organisms and waste decay,
returning nutrients to the soil
III. Carbon Cycle
IV. Nitrogen Cycle
IV. Nitrogen Cycle
A.
General information
1. N needed to make proteins
Proteins = large molecules that
perform almost all of living
organisms’ vital f(x)s
(functions)
IV. Nitrogen Cycle
2. N hard to convert into a form
usable by plants
3. Most steps of N cycle occur in the soil
4. Bacteria very important to the N cycle
IV. Nitrogen Cycle
B. Steps of the N cycle
1. Nitrogen fixation
Bacteria work with
legumes
(peas, beans, peanuts)
to take N2 from atmosphere,
put it into the soil
IV. Nitrogen Cycle
2.Ammonification
 Animals
& plants
deposit
nitrogenous
waste
 Decomposers
 (bacteria & fungi)
convert
organic N
(proteins) to
ammonia (NH3)
IV. Nitrogen Cycle
3. Nitrification
Another kind of bacteria convert
ammonia (NH3) → to ammonium
to nitrites (NO2-) & nitrates (NO3-)
NH3 → NH4 + →
NO2- + NO3-
IV. Nitrogen Cycle
4. Denitrification
Another kind of bacteria
convert nitrites and nitrates
to nitrogen gas
NO2- + NO3- → N2
IV. Nitrogen Cycle