Nutrient%20cycling%20

1
Nutrient cycling Ecosystem Health

• READINGS for this lecture series
• KREBS chap 27. Ecosystem Metabolism III
  Nutrient Cycles
• KREBS chap 28. Ecosystem Health
• Human Impacts Pp 590 600
• WEB Downloads

2
NUTRIENT CYCLING

• Energy 1-way flow
• - eventually gets lost
• Nutrients cycle

mineralization
Inorganic (rocks, air, water)
Organic (living organisms)
assimilation
3
Human activity
4
Three main types of cycles

• 1. Biochemical cycles
• Redistribution within/between organisms
• This really is r- and K-selection from first
  term
•  
• 2. Biogeochemical cycles
• Exchange within an ecosystem
• N, P - rapid exchange
• Ca - long if stored in long-lived tree tissue
•  
• 3. Geochemical cycles
• Exchange of chemicals between ecosystems
• Nutrients and dust
• CO2, SO2, NOx

5
Three main types of cycles

• 1. Biochemical cycles
• Redistribution within/between organisms
• This really is r- and K-selection from first
  term
•  
• 2. Biogeochemical cycles
• Exchange within an ecosystem
• N, P - rapid exchange
• Ca - long if stored in long-lived tree tissue
•  
• 3. Geochemical cycles
• Exchange of chemicals between ecosystems
• Nutrients and dust
• CO2, SO2, NOx

6
Three main types of cycles

• 1. Biochemical cycles
• Redistribution within/between organisms
• This really is r- and K-selection from first
  term
•  
• 2. Biogeochemical cycles
• Exchange within an ecosystem
• N, P - rapid exchange
• Ca - long if stored in long-lived tree tissue
•  
• 3. Geochemical cycles
• Exchange of chemicals between ecosystems
• Nutrients and dust
• CO2, SO2, NOx

7
Krebs Fig. 27.12 p573
SULPHUR CYCLE
8
Krebs Fig. 28.8 p591
CARBON CYCLE
9
Krebs Fig. 27.17 p579
NITROGEN CYCLE
10
78 of air is N2
11

• These figures have
• All sorts of rates of transfer
• We can compare between systems

• More interesting
• What influences the rates?
• What are the impacts of altering the rates?

12

• These figures have
• All sorts of rates of transfer
• We can compare between systems

• More interesting
• What influences the rates?
• e.g. forms of nutrients, types of organisms
• What are the impacts of altering the rates?
• e.g. disturbance, pollution, etc.

13
Compartment Models

• Quantitative descriptions of storage and
  movement of nutrients among different
  compartments of an ecosystem
• Coarse few broad compartments
• e.g. plants, herbivores
• Fine many detailed compartments
• e.g. separate species

14
Compartment Models

• POOL the quantity of a particular nutrient in
  a compartment
• FLUX the quantity moving from one pool to
  another per unit time
• TURNOVER TIME the time required for movement
  of an amount of nutrient equal to the quantity
  in the pool (POOL/FLUX)

15
Krebs Fig. 27.2 p562
Phosphorus cycle in a lake (simplified)
Turnover time (water) 9.5 (pool) /152 (flux)
0.06 day
16
NUTRIENT PUMP

• Any biotic or abiotic mechanism responsible for
  continuous flux of nutrients through an ecosystem

• Biotic tree roots, sea birds,
• Pacific salmon
• Abiotic lake overturn, ocean upwelling

17
Nutrient pump (Terrestrial)
18
Mycorrhizae
19
Mycorrhizae
20
Nutrient pump (temperate lake turnover)
21
Marine ecosystem
22
Nutrient pumps (Marine)
23

• BIOGEOCHEMICAL CYCLES
• A few general points (terrestrial systems)
•  
• Nutrient cycling is never perfect i.e. always
  losses from system

Inputs
Outputs
Precipitation Runoff stream flow
Particle fallout from atmosphere Wind loss
Weathering of substrate Leaching
Fertilizer pollution Harvesting
24
terrestrial systems contd

• Inputs and outputs are small in comparison
• to amounts held in biomass and recycled

(i.e. relatively tight cycling is the norm)
3. Disturbances (e.g. deforestation) often
uncouple cycling
4. Gradient in rates of decomposition and
nutrient cycling from poles to tropics
25
HUBBARD BROOK FOREST

• Experiments done to
• Describe nutrient budget of intact forest
• Assess effects of logging on nutrient cycles

26
CEC Cation Exchange Capacity
27
Annual Nitrogen budget for the undisturbed
Hubbard Brook Experimental Forest. Values are
Kg, or Kg/ha/yr
28

• Deforestation is a major change in community
  structure, with a consequent
• loss of nutrients (Krebs Fig 27.7 p567)
• x20-30 normal loss of NO3 in Hubbard Brook
• reduction in leaf area
• 40 more runoff (would have transpired)
• more leaching
• more erosion and soil loss
• decouples within-system cycling of decomposition
  and plant uptake processes
• all the activities (and products) of spring
  decomposition get washed away

29
Logging causes decoupling of nutrient cycles and
losses of nitrogen as nitrates and nitrites
30
Calcium
Concentrations of ions in streamwater from
experimentally deforested, and control,
catchments at Hubbard Brook.
Potassium
Nitrate-N
31
Uncoupling of N-cycle
1) Logging causes increased nitrification
2) H displace nutrient cations from soil micelles
H gtCagtMggtKgtNa
32
4. Gradient from poles to tropics
POLAR TROPICS
Decomposition Slow Rapid
Proportion nutrients in living biomass Low (mostly in dead organic matter) High
Cycling Slow Rapid

33
(No Transcript)
34
Relative proportion of Nitrogen in organic matter
components
ROOTS
35
Relative proportion of Nitrogen in organic matter
components
SHOOTS
36
DECOMPOSITION

• IF TOO SLOW
• Nutrients removed from circulation for long
  periods
• Productivity reduced
• Excessive accumulations of organic matter (e.g.
  bogs)

• IF TOO FAST
• Nutrient depletion
• Poor chemistry and physics of soil (e.g.
  decreased soil fertility, soil moisture and
  resistance to erosion) (e.g. tropical laterites)

37

• WHAT DETERMINES DECOMPOSITION RATES IN FORESTS?
• moisture and temperature
• pH of litter and the forest floor
• more acid promotes fungi, less bacteria
• species of plant producing the litter
• chemical composition of the litter
• C/N ratio - high gives poor decomposition
• microbes need N to use C
• N often complexed with nasties (e.g. tannin)
• optimum is 251
• Douglas fir wood 5481
• Douglas fir needles 581
• alfalfa hay 181
• activities of soil fauna e.g. earthworms

38

• Decomposition Rates influenced by
• temperature
• moisture
• pH, O2
• quality of litter
• soil type
• soil animals (size)
• type of fauna / flora
• rapid if bacterial
• slow if fungal

39

• RATE OF DECOMPOSITION
• humid tropical forests about 2 - 3 weeks
• temperate hardwood forests 1 - 3 years
• temperate / boreal forests 4 - 30 yr
• arctic/alpine / dryland forests gt40 years
• generally, rate of decomposition increases
  with increased amount of litterfall

Residence time the time required for the
complete breakdown of one years litter fall
40
Residence times (years)
41
Residence times (years)
42

• Decomposition Rates influenced by
• temperature
• moisture
• pH, O2
• quality of litter
• soil type
• soil animals (size)
• type of fauna / flora
• rapid if bacterial
• slow if fungal

(mineral content, C/N ratio)
43
Litter accumulation in forest floor
44
Relationship between rate of litter decomposition
and litter quality (C/N ratio)
Plant species weight loss in 1 year C/N ratio bacterial colonies fungal colonies Bact / Fungi ratio
Mulberry 90 25
Redbud 70 26
White Oak 55 34
Loblolly pine 40 43
Faster decomposition at lower C/N ratios
45

• Decomposition Rates influenced by
• temperature
• moisture
• pH, O2
• quality of litter
• soil type (influences bugs)
• soil animals (size)
• type of fauna / flora
• rapid if bacterial
• slow if fungal

46
100 90 80 70 60 50 40 30 20 10 0
0.5 mm mesh bags
leaf litter remaining
7.0 mm mesh bags
(J) J A S O N D J F M A
47
Litter decomposers
48

• Decomposition Rates influenced by
• temperature
• moisture
• pH, O2
• quality of litter
• soil type (influences bugs)
• soil animals (size)
• type of fauna / flora
• rapid if bacterial
• slow if fungal

49
Relationship between rate of litter decomposition
and the balance between bacteria and fungi
Plant species weight loss in 1 year C/N ratio bacterial colonies fungal colonies Bact / Fungi ratio
Mulberry 90 25 698 2650 264
Redbud 70 26 286 1870 148
White Oak 55 34 32 1880 17
Loblolly pine 40 43 15 360 42
Faster decomposition at higher bact/fungi ratios