ICA 8 NUTRIENT REGENERATION
1. Contrast intra- fluxes within an ecosystem
vs. inter-system cycling. fluxes between ecosystems
INTRASYSTEM CYCLING
2. Figure 1. 24.2 Trace an atom of phosphorus completing an intrasystem cycle; start
with it in soil. Soluble inorganic phosphates in water solution of soil  root uptake 
incorporation into organic compounds (e.g. ATP; nucleic acids) in plant tissues 
litterfall  dead organic matter  decomposition  mineralization  inorganic
phosphate in water solution of soil
3. What determines rate of nutrient regeneration in the soil? rate of ecosystem processes,
especially decomposition and mineralization
4. Explain how productivity depends on nutrient regeneration. Productivity depends on
elements (e.g. N) acquired via root uptake of soluble inorganic compounds that have
been regenerated in the soil.
5. Contrast decomposition: physical/chemical breakdown of dead organic matter
vs. mineralization: conversion of organic molecules to inorganic molecules in
decomposing matter; the final stage of nutrient regeneration
vs. weathering: physical/chemical breakdown of rock freeing soluble elements
6. Contrast the rate of weathering (very slow) and nutrient regeneration from litter (fast).
7. Outline the steps of nutrient regeneration from litter.
A. leaching of soluble substances
B. maceration by large detritus feeders
C. fungi breakdown cellulose/lignin  C,H,O
D.mineralization (organic inorganic) of P,N,S compounds by bacteria
8. Figure 2 24.9. What is depolymerization? breakdown of proteins, lignins, nucleic
acids, and other macromolecules in soil to produce small monomers that plants and
microbes can take up.
How does it regulate nutrient cycling? It is rate-limiting step in decomposition, and,
consequently, the limit on overall nutrient cycling (and indirectly productivity).
For what do plants and microbes compete in soil? small monomers, ammonia, and
nitrates; microbes immobilize inorganic compounds and remove them from the
available pool in the soil until they die, are decomposed or eaten by other consumers.
9. By what means does climate affect nutrient regeneration?
A. freeze/thaw cycles accelerate physical weathering; high temperatures and
adequate moisture accelerate chemical weathering
B. changes in soil properties affecting binding and solubility of nutrients
C. high temperatures and adequate moisture accelerate regeneration
10. Contrast
EUTROPHIC
OLIGOTROHPHIC SOILS
Level of nutrients
high
low
Geological activity active and recent
inactive
Age
young
old
How do high temperature and water availability affect rate of weathering? accelerate
Outline processes set in play when have high temperatures and abundant water.
1. high respiration  acid pH
2. removes cations (e.g. Ca++)
3. reduces storage capacity for nutrients (H+ have grabbed holding sites)
4. high leaching of cations
5. nutrient-poor soils
11. Many tropical soils are oligotrophic. Why can tropical forests be so productive?
A. rapid regeneration of nutrients from decaying matter
B. rapid uptake of nutrients (before leached)
C. efficient retention of nutrients
12. Figure 3 + 4. Compare 24.11
TEMPERATE
TROPICAL
Biomass
similar
similar
Nutrients in Soil/Biomass Ratio: K
1.2
0.5
P
23
0.1
N
11
2
Which differs more between biomes? nutrients in biomass or nutrients in soil?
What is the main conclusion? More nutrients are held in the biomass than soil in the
tropical forest compared to the temperate forest.
13. What is leaching? Downward movement in soil of soluble nutrients by water flow.
What may happen if the nutrients are not retained by the vegetation? leachedlost
What mechanisms aid in the vegetation retaining nutrients?
A. retain leaves for long time
B. withdraw nutrients form leaves before drop (reabsorption)
C. develop dense root mat near soil surface
D. grab nutrients quickly before leached away
E. store more nutrients in biomass, not soil
14. Go to Worksheet at back: Annual Circulation of N in a Deciduous Forest.
INTERSYSTEM CYCLING
15. What are inputs (gains) of nutrients on land?
A. Lithosphere: weathering of bedrock and soil
B. Atmosphere: wetfall (in rain); dryfall (dust particles)
C. Hydrosphere: runoff of water; floods
16. Figure 5. What are two generalizations about nutrient input from the atmosphere?
A. More input occurs from wetfall than dryfall (excluding vapors).
B. Specific nutrients differ greatly in amount of deposition.
17. What are outputs (losses) of nutrients on land?
A. Atmosphere: gaseous forms of nutrients that are blown to other ecosystems
B. Hydrosphere: runoff of water; erosion into water
Which cycle critically links flux between land and water ecosystems? hydrosphere
18. Balanced ecosystems are in equilibrium when inputs = outputs
What happens to nutrients when: inputs>outputs? nutrients accumulate; are stored
What happens to nutrients when:outputs>inputs?nutrients are lost to other ecosystem
Under which scenario is the ecosystem in non-equilibrium? inputs are not equal to
outputs (both I>O or O>I)
19. Figure 6. Hubbard Brook Watershed Study: What is the prediction? then amount of
dissolved substances in stream will be higher in devegetated than control watersheds.
Figure 7. Summarize the results. Net dissolved substances increased, then stabilized
from watershed with no trees, while they remained stable in control watershed with
trees.
Write the first sentence of your ‘discussion’ being written for this study. The results
support the hypothesis that vegetation increases soil stability and intrasystem
recycling of nutrients.
20. Figure 8. What is a general pattern? Gross output in streamflow increases as total
annual streamflow increases.
qualifying pattern? Amount of increase in output varies greatly among cations.
What statistical test generated those lines? Regression analysis
21. Figure 9. What contributes in input? atmospheric (rain and dust)
What contributes to output? soil erosion, runoff, ground water percolation to
water table
What are two main conclusions about net change?
A. Some cations have a positive, while other have a negative net change;
No cation is in equilibrium.
B. The cause of non-equilibrium differs among cations; some have I>O, while
others have O>I.
22. Figure 10. What are the primary sources to meet nutrient requirements?
Intersystem input: atmospheric (rain and dust) and rock weathering
Intrasystem transfers: reabsorption and detritus turnover
Are most nutrient requirements met from intra- or inter-system cycling? Intra
Are any cations in excess of requirements? Yes, e.g. N because 100% of requirement
is met by intrasystem transfers, yet much intersystem input also occurs
What happens to the excess? It accumulates and is stored with unstated
consequences for other parts of the intrasystem cycle.
23. Figure 11. Summarize the pattern. NPP increases as total P inflow increases.
What causes variation in input? Amount of rainfall and extent of floods.
NUTRIENTS and AQUATIC PRODUCTIVITY (Please IGNORE 24-35; you are NOT
responsible for those concepts.)
24. Figure 12. 24.16 In oceans, where is highest level of NPP? Over continental shelves
with shallow water and in areas of upwelling from the depths of the ocean. Why?
Great proximity to nutrients in shallow water and get fresh input of nutrients from
upwelling.
Lowest amount of NPP? Open ocean Why? Low nutrients (especially Fe + Si)
25. What maintains NPP of aquatic systems?
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
A. transport of nutrients from bottom
B. sediments to surface (in shallow water or upwelling)
C. import of nutrients from other ecosystems
Figure 13. What drives seasonal cycles in temperate lakes? temperature profiles +
wind
What is stratification? establishment of distinct layers of temperature in a lake
Figure 14. 24.17 What is a thermocline? Depth in water at which temperature
changes abruptly between an upper lower of warm and a lower layer of cold water.
Do all lakes have one? No; stratification and a thermocline are common in
temperate lakes.
Figure 15. 24.18 Which profile is for a deep (a) vs. shallow-water system? (c)
Within the temperature profile, where is productivity greatest? at the thermocline
Why? Regenerated nutrients occur below this level
What is the positive effect of stratification on production? increases production by
retaining phytoplankton in photic zone
What is its negative effect? decreases production when sedimentation carries
nutrients below photic zone
Describe the annual cycle in temperate lakes of nutrient availability:
Summer: with time, stratification occurs and no new nutrients are available;
existing nutrients are depleted as dead organims fall to the bottom. Productivity
declines and becomes low.
Spring and Fall: Winds break up temperature stratification and the water is mixed,
bringing up nutrients to the photic zone. Productivity is high.
How does this cycle in nutrient availability affect the seasonal cycle in NPP?
NPP is high in spring and fall, low in summer, and non-existent in winter with ice.
What causes an oligotrophic lake? Low nutrient input from adjacent land; rocks are
old and weathered – or nutrients in them tied up and not soluble.
What causes a eutrophic lake? Runoff bringing input of nutrients; shallow lake
with rich nutrient source
Which will have greater NPP? eutrophic lake
Figure 16. 24.20 What controls trophic structure and productivity of lakes?
Lakes are P limited; adding P changes trophic structure (enhances
blue-green algae) and increases productivity.
Why do estuaries and salt marshes have such high NPP?
1. Rapid local regeneration of nutrients
2. External input of added nutrients from upstream.
How do they affect nutrients and energy levels in oceans? They are a net exporter
and energy and nutrients to the oceans.
Figure 17. 24.22 Roughly, what is photosynthetic efficiency? (152/2500)100
What is GPP? 152,000
Roughly, what is ecological efficiency? 10% from plant to herbivore;
5% from herbivore to carnivore
What is % of NPP going into decomposition food chain? (33/118)100
What absolute amount of NPP is exported from this salt marsh? 15,359
Where does it go? ocean
Draw a map (land next to ocean). Add labeled fluxes for: intrasystem and
intersystem cycling of P. Include flux between multiple pools.
ANNUAL CIRCULATION OF N IN A DECIDUOUS FOREST:
IS THE FOREST IN EQUILIBRIUM?
Annual requirement (kg/ha/hr)
Leaf production
Wood growth in:
Branches
Trunks
Roots
Total growth
Leaching
Throughfall
Stemflow
Total
Total annual requirement
Annual uptake (kg/ha/hr)
Woody increment
Returns
Leaching
Litterfall
Total
85.7
2.1
4.1
13.2
19.4
8.3
0.4
9.2
114.3
19.4
9.2
63.5
72.7
Total annual uptake
92.1
Reabsorption (kg/ha/yr)
22.2
1. What three components of the annual requirement account for the total requirement
(114.3)?
Leaf production + Wood growth + Leaching
Show your math as well here: 85.7 + 19.4 + 9.2 = 114.3
2. What two processes bring resources to meet the total requirement (114.3)?
Annual uptake + reabsorption
Show your math as well here: 92.1 + 22.2 = 114.3
3. What three components of annual uptake account for total uptake (92.1)?
Woody increment and Leaching and Litterfall
Show your math as well here 19.4 + 9.2 + 63.5 = 92.1
4. Is the forest in equilibrium? YES yes or no. Explain your reasoning.
Annual requirement is fully met by annual uptake + reabsorption
114.3 = 92.1 + 22.2