Detritus Food Chains and Biogeochemical Cycles Lecture 8 Chapters 21 and 22 - PowerPoint PPT Presentation

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Detritus Food Chains and Biogeochemical Cycles Lecture 8 Chapters 21 and 22

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Detritus Food Chains and Biogeochemical Cycles Lecture 8 Chapters 21 and 22 – PowerPoint PPT presentation

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Title: Detritus Food Chains and Biogeochemical Cycles Lecture 8 Chapters 21 and 22


1
Detritus Food Chains and Biogeochemical
Cycles Lecture 8 Chapters 21 and 22
2
  • 1. Much recycling of materials occurs within
    organisms
  • Example water/nutrients withdrawn from senescent
    leaf tissues of plants ? roots
  • Dead matter broken down via detritral food chain
  • Decomposition multistep process leading to
    mineralization
  • mineralization conversion of organic nutrients
    to mineral form
  • Terms
  • Fixation incorporation to organic molecule
  • Mineralization reduction of organic molecule
    returning component elements to inorganic
    associations

3
  • Life depends on recycling chemical elements
  • Nutrient circuits in ecosystems involve biotic
    and abiotic components and are often called
    biogeochemical cycles
  • Focus on
  • Each chemicals biological importance
  • Forms in which each chemical is available or used
    by organisms
  • Major reservoirs for each chemical
  • Key processes driving movement of each chemical
    through its cycle

4
Fixation
Mineralization
Exchange Pool
5
  • Two food chains
  • Grazing food chain
  • Herbivore ? carnivore
  • Detritus food chain
  • Dead matter and waste from grazing food chain and
    primary production
  • Provides input to grazing food chain

6
  • Detrivore food chain
  • heterotrophs feed on dead material
  • Provide prey in herbivore foodchain
  • Fragmentation
  • Microfauna and flora lt100um
  • Protozoans and nematodes
  • Mesofauna 100um? 2mm
  • Mites, potworms, springtails
  • Macrofauna
  • Millipedes, earthworms, snails, amphipods
    isoods
  • Decomposition
  • Bacteria and fungi produce extracellular
    enzymes

7
  • Fungi belong to a separate kingdom
  • several groups
  • produce long, thread-like strands (hyphae)
  • reproductive structures may be large and visible

8
(No Transcript)
9
  • Bacteria two distinct kingdoms
  • Single celled
  • Microscopic
  • Various shapes
  • Many may not be easily cultured
  • May develop populations quickly

10
  • Study of Decomposition Litterbag Studies
  • Weighed sample in mesh bag placed in soil
  • Withdrawn after time to determine remaining
    dry-weight
  • Dry weight estimate distorted by biomass of
    decomposer
  • Gives estimate of decomposition impacted by
  • Species
  • conditions

11
Other factors which may impact rate of
decomposition?
Decomposition of red maple leaves more rapid in
warmer, more humid climatesdde
12
  • Decomposition of different species and materials
    vary
  • Simple sugars ? bacteria and fungi
  • polymers (as cellulose) ? mainly fungi, some
    bacteria
  • Lignins ? only certain fungi

13
Lignin the stuff of wood, slow to degrade and
degredation rate levels off as it remains
Cellulose goes second, degraded by bacteria and
fungi
Proteins, solub. Carbohydrates easily degraded
14
Fig. 55-15
Ecosystem type
EXPERIMENT
Arctic
Subarctic
Boreal
Temperate
A
Grassland
Mountain
G
M
D
B,C
P
T
H,I
E,F
S
O
L
N
U
J
K
R
Q
RESULTS
80
70
U
60
R
O
Q
K
50
T
Percent of mass lost
J
P
40
S
D
N
F
30
I
C
M
L
20
H
A
B
E
G
10
0
15
10
5
0
5
10
15
Mean annual temperature (ºC)
15
  • The Rhizoshpere and Decomposition
  • 40 photosynthetic dry matter fuels microbial
    growth in rhizosphere
  • Fuels microbial growth which eventually releases
    nutrients ? increased availability to plants
    via mineralization
  • Soil Microbial Loop

16
Case Study Nutrient Cycling in the Hubbard Brook
Experimental Forest
  • Vegetation strongly regulates nutrient cycling
  • Research projects monitor ecosystem dynamics over
    long periods
  • The Hubbard Brook Experimental Forest has been
    used to study nutrient cycling in a forest
    ecosystem since 1963

17
Fig. 55-16a
(a) Concrete dam and weir
18
Fig. 55-16c
80
Deforested
60
40
20
Nitrate concentration in runoff (mg/L)
Completion of tree cutting
4
Control
3
2
1
0
1965
1966
1967
1968
(c) Nitrogen in runoff from watersheds
19
  • Decomposition in Aquatic systems
  • Impacted by environment
  • Photosynthetic processes at surface
  • Detritus falls to benthic zone
  • Low oxygen, cool temperatures
  • Stratification of water occurs through summer
  • spring/fall turnover events ? mixing of water
    column

20
  • Export of resources ? loss of nutrients
  • Example 1. logging
  • Logs nutrients removed from forest
  • Increased nutrient water flow ? nutrient loss via
    streams
  • Stream salmon fishery
  • Salmon represent nutrient transfer mechanism from
    sea to terrestrial ecosystem
  • Fire
  • Alters mineralization rate/processes
  • Subsequent leaching/runoff ? nutrient loss

21
  • Import of nutrients/alteration of normal cycling
  • Possible sources
  • Runoff from adjacent ecosystems
  • Agricultural
  • Municipal/industrial
  • Impacts
  • Toxins some may accumulate higher levels food
    chain via bio-accumulation or bio-magnification
  • Eutrophication nutrient enrichment in lake/pond
    ? biological activity ? stimulation of detrital
    food chain ? anoxia
  • Global/environmental C,N and global climate

22
  • Two types of biogeochemical cycles based input
    source to ecosystems
  • Sedimentary
  • Rock and salt solution phases
  • Include S, P
  • Gaseous
  • Global
  • Include C, N, O
  • Many cycles hybrid
  • Exchange pool
  • Reservoir

23
  • Carbon cycle
  • Closely tied to energy flux
  • Major exchange pool atm CO2 (at 0.03 )
  • Uptake via photosynthesis
  • Immobilized in carbonates of shells, fossil fuels
  • Subject to daily seasonal flux

24
  • The Phosphorus Cycle
  • Phosphorus is a major constituent of nucleic
    acids, phospholipids, and ATP
  • Phosphate (PO43) is the most important inorganic
    form of phosphorus
  • The largest reservoirs are sedimentary rocks of
    marine origin, the oceans, and organisms
  • Phosphate binds with soil particles, and movement
    is often localized

25
Fig. 55-14d
Precipitation
Geologic uplift
Weathering of rocks
Runoff
Consumption
Decomposition
Plant uptake of PO43
Plankton
Dissolved PO43
Soil
Uptake
Leaching
Sedimentation
26
  • Nitrogen cycle
  • N essential to life amino acids, nucleic acids
  • Atm. N2 stable, difficult bond to break
  • Fixation largely biological (ca 90)
    agricultural use requires fossil fuel input

27
  • Fixation of N N
  • Free living aerobics as Azotobacter, certain
    cyanobacter
  • Lichen symbionants
  • Mutualists associated with certain plant groups
  • N2 N N (NH3)2
    NH4
  • H energy


  • NO3

Ammonium form available to plants
Ammonia (gas)
Nitrate produced by soil bacteria from ammonium
may also be taken up by plants or mineralized to
N2
Under acidic conditions converts to ammonium but
may be lost to atmosphere
28
  • Organic nitrogen is decomposed to NH4 by
    ammonification, and NH4 is decomposed to NO3 by
    nitrification
  • Denitrification converts NO3 back to N2

29
Fig. 55-14c
N2 in atmosphere
Assimilation
Denitrifying bacteria
NO3

Nitrogen-fixing bacteria
Decomposers
Nitrifying bacteria
Ammonification
Nitrification
NH3
NH4
NO2


Nitrogen-fixing soil bacteria
Nitrifying bacteria
30
Human activities now dominate most chemical
cycles on Earth
  • As the human population has grown, our activities
    have disrupted the trophic structure, energy
    flow, and chemical cycling of many ecosystems

31
Nutrient Enrichment
  • In addition to transporting nutrients from one
    location to another, humans have added new
    materials, some of them toxins, to ecosystems

32
Agriculture and Nitrogen Cycling
  • The quality of soil varies with the amount of
    organic material it contains
  • Agriculture removes from ecosystems nutrients
    that would ordinarily be cycled back into the
    soil
  • Nitrogen is the main nutrient lost through
    agriculture thus, agriculture greatly affects
    the nitrogen cycle
  • Industrially produced fertilizer is typically
    used to replace lost nitrogen, but effects on an
    ecosystem can be harmful

33
Fig. 55-17
34
Contamination of Aquatic Ecosystems
  • Critical load for a nutrient is the amount that
    plants can absorb without damaging the ecosystem
  • When excess nutrients are added to an ecosystem,
    the critical load is exceeded
  • Remaining nutrients can contaminate groundwater
    as well as freshwater and marine ecosystems
  • Sewage runoff causes cultural eutrophication,
    excessive algal growth that can greatly harm
    freshwater ecosystems

35
Fig. 55-18
Winter
Summer
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