Energy Flow in Ecosystems (Section 5.3)
Representation by Effect (Section 2.5.4)
Biochemical Oxygen Demand (Section 5.4)
Energy Flow in Ecosystems
Energy Flow in Ecosystems
Energy fixation
Organic matter
Autotrophs
Heterotrophs
Aerobic respiration
Energy Flow in Ecosystems
Anaerobic respiration
Nitrate removal
Mercury cycling
Drinking water
Sludge digestion
Energy Flow in Ecosystems
Biomass
Production
Autotrophs
Primary producers
Algae
Phytoplankton
Heterotrophs
Secondary producers
Primary Consumers
Herbivores
Zooplankton
Heterotrophs
Secondary consumers
Planktivores
Heterotrophs
Tertiary consumers
Piscivores
Carnivores (also omnivores)
Energy Flow in Ecosystems
Food chain
Food web
Energy Flow in Ecosystems
Energy Flow in Ecosystems
Energy Flow in Ecosystems
Microbial loop
(sustainable?)
Other types of units: representation by effect.
Other types of units: representation by effect.
Other types of units: representation by effect.
Organic Matter.
CO2  H2
… what’s in here?
Organic Matter.
Proteins
(polymers of amino acids)
Carbohydrates
(sugar and the polymers starch and cellulose)
CO2  H2
Fats (
Fats
(formed from glycerol and fatty acids)
Organic Matter.
Photosynthesis
CO2  H2O  C( H2O)  O2
Respiration
C( H2O)  O2  CO2  H2O
also …mineralization
oxidation
stabilization
Representation by Effect - Organic Matter.
Respiration
CO2  H2
C( H2O)  O2  CO2  H2O
When organic matter is used as a substrate for respiration,
… when it is oxidized
… when it is mineralized
… when it is stabilized
it exerts a “biochemical oxygen demand” or BOD.
BOD - Representation by Effect.
… impacts on lakes and rivers?
Biochemical Oxygen Demand
BOD: the amount of dissolved oxygen (mg/L) required to
oxidize the organic matter in water.
CBOD: BOD exerted through oxidation of carbonaceous
material.
C( H2O)  O2  CO2  H 2O  
NBOD: BOD exerted through oxidation of ammonia.
NH4  2HCO3  2O2  NO3  2CO2  3H2O  
Biochemical Oxygen Demand
NBOD is simple stoichiometry,
NH4  2HCO3  2O2  NO3  2CO2  3H2O  
Stoichiometry does not work for CBOD because not all of the
organic matter present is biodegradable.
C( H2O)  O2  CO2  H 2O  
Thus the CBOD is never greater and almost always less than
the theoretical BOD (ThBOD).
C6 H12O6  6O2  6CO2  6H2O  
but for wastewater, not so much!
Biochemical Oxygen Demand
Concentration
L0
dL
 kL  L
dt
Lt  L0  expkL t
Distance or TimeTime (yr)
Biochemical Oxygen Demand
BOD Remaining (L)
Lt  L0  expkL t
BOD Exerted (y)
yt  L0  Lt
yt  L0  L0  expkL t
yt  L0  (1  expkL t )
Biochemical Oxygen Demand
BOD Exerted
BOD Remaining
Biochemical Oxygen Demand
5-day BOD and Ultimate BOD
yt
L0 
1  exp  kL t
5-day BOD is a laboratory measurement.
Ultimate BOD is for field aplications.