I' Sources and Definitions:

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I. Sources and Definitions 1) detritus dead
OM and associated microflora (detritus has a
respiratory demand!) 2) heterotrophic energy
pathways food webs deriving energy from
non-living sources of OM 3) decomposers all
organisms involved in respiration, but
typically thought of as those organisms
utilizing detrital material 4) detritivores
consumers using detrital carbon substrates,
microbes like fungi and bacteria,
invertebrates like worms or various arthropods
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detritus and food quality food quality
measure of the value of OM as an energy source
to consumers

• Three major determinants of food quality
• size (e.g., monomeres vs polymers)
• bond type (aliphatic vs aeromatic,
  sterochemistry)
• nutrient content (CNP)

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Labile Organic Matter
Refractory Organic Matter
Labile unstable - biochemically high quality
Refractory resistant to treatment -
biochemically low quality
sugars
amino acids
tannins
lignin
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II. Size Fractioning of Organic Matter1) CPOM
coarse particulate organic matter (gt 1mm in size)
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2) FPOM fine particulate organic matter (0.4 ?m
1mm)
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3) DOM dissolved organic matter (lt 0.4 ?m
dissolved)
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III. CPOM Decomposition 1) leaf breakdown
vs decomposition Decomposition breakdown of
organic matter including physical reduction in
size and biotic oxidation of carbon - many will
argue that decomposition respiration Breakdown
loss of OM due to physical and biotic processes
that remove and redistribute mass
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2) log-linear decay model
(Peterson and Cummins 1974, Webster and Benfield
1986 )
Mo
dM/dt - k M - exponential decline - similar to
growth models where k r
Mt
0
time (days)
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3) decay continuum (Peterson and Cummins 1974)
processing continuum Peterson and Cummins
(1974) argued that variation in k ensured a
continuum of resources available to the benthic
biota (part of the RCCs temporal replacement
ideas)
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Aquatic Plants
Woody Vegetation
From review by Webster and Benfield (1986)
0.01
0.001
0.05
k, d-1
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4) The Fate of Autumn-shed Leaves that Fall into
Streams (Kaushik and Hynes 1971)

• stage I leaching
• - wetting and leaching of soluble compounds can
  be 50 of dry weight within 24 hours

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4) The Fate of Autumn-shed Leaves that Fall into
Streams (Kaushik and Hynes 1971)
B) stage II microbial processing - leaf
conditioning associated with microbial influences
on OM substrate, seen as key in terrestrial
environments
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4) The Fate of Autumn-shed Leaves that Fall into
Streams (Kaushik and Hynes 1971)
C) stage III fragmentation by both mechanical
and invertebrate activity
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5) features influencing breakdown stages A)
leaching i) prior exposure - rain or
floodplain exposure ii) constituent loss -
differential loss of soluble compounds,
polyphenols iii) species variation - species
differ in their propensity to loose these sorts
of compounds alder 4, maple and elm 16,
cottonwood 50 iv) macrobiota - little role for
biota (microbes not important either, same
rates in oxic and anoxic environments
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B) microbial colonization and processing i)
nutrient content
Gessner and Chauvet (1994)
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B) microbial colonization and processing i)
nutrient content
Suberkropp and Chauvet 1995)
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B) microbial colonization and processing i)
nutrient content
Rosemond and Pringle
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B) microbial colonization and processing ii)
lignin content
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iii) chemical toxicity - potential for 2?
compounds to be influential (e.g.,
eucalyptus) iv) changing leaf chemistry a)
nitrogen - N (and some other elements )
increase as and total mass
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iv) changing leaf chemistry a) nitrogen - other
elements are lost
b) non-soluble compounds - rapid loss of
lipids, - cellulose and hemicellulose loss is
slower - lignin is slowest
v) importance of microbes fungi alone can cause
75 loss of amss within 6 weeks
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C) detritivore influence - 3rd stage is
primarily due to detritivore activity i) role
in size fractionation - important in size
class transformation ii) correlative and
experimental evidence - leaves tethered to
bricks vs. bags - mesh size - experimental
streams w/o detritivores show 25 loss by
macroinverts - nutrient release may be important
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IV. Processing of other CPOM 1)
Macrophytes - similar course, but rates are
generally faster - not really true for emergent
forms where support tissue is a large portion
of biomass 2) Woody Debris - slow
decomposition due to high lignin, cellulose and
low surface area low ability to
penetrate Alder ½ life 7 months spruce 17
years
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V. Fine Particulate Organic Matter (FPOM) 1)
Sources A) macroinvertebrates and leaf
decomposition - fragmentation by eating
(orts) - loss due to fecal production (frass,
01. 1.0 mm) - coprophagy is suggested -
peritrophic membrane B) fungal FPOM
production during leaf decomposition -
maceration of CPOM by fungi alone can be
substantial (5 weeks _at_ 10C 41-51 loss to
FPOM) - results in FPOM of lower toughness
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V. Fine Particulate Organic Matter (FPOM) 1)
Sources C) other sources i) DOM
flocculation - colloidal forms that border on
particualte ii) forest soils - transport
from banks and soils iii) periphyton - algal
cells in transport or deposited pools 2)
Techniques to study origin and composition of
FPOM A) light microscopy B) lignin
content C) lignin oxidation products D)
stable carbon isotopes E) CN ratio
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2) Techniques to study origin and composition of
FPOM A) light microscopy - direct
observation of particles, composition and
abundance B) lignin content - algae and
bacteria lack lignin, denotes vascular plant
origin C) lignin oxidation products -
breakdown of lignin produces specific products
that relate to the degree of preservation,
type and origin of plant source D) stable
carbon isotopes - grasses act differently (C4),
elevation, other influences E) CN ratio -
atomic ration, highest in unaltered plant
detritus ( 20), soil OM (10-12), microbial
biomass (6-7)
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3) Relative magnitude of FPOM sources A)
origins of FPOM in the Amazon (Hedges et al.
(1986) - FPOM from the Amazon basin, most is
soil OM B) large river surveys C) mass
balance in headwater streams D) sorbed OM and
mineral surfaces
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3) Relative magnitude of FPOM sources A)
Amazon FPOM B) large river surveys - over
a range of large rivers the CN ratio
derived from suspended POC and PON was
8.5 soil OM
CN ratios of particulate material in the worlds
largest rivers (from Meybek 1982)
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3) Relative magnitude of FPOM sources A)
origins of FPOM in the Amazon (Hedges et al.
(1986) B) large river surveys C) mass
balance in headwater streams - Ward and Aumen
(1986) leaves not a major source of FPOM in
Pacific NW streams (wood and soils) - Wallace
et al. (1982) loss of leaf shredders changed
FPOM output in streams
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3) Relative magnitude of FPOM sources A)
origins of FPOM in the Amazon (Hedges et al.
(1986) B) large river surveys C) mass
balance in headwater streams -Wallace et al.
(1999) experimental exclusion of leaf inputs
- experimental exclusion of leaf inputs? (Meyer
et al. 1998)
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3) Relative magnitude of FPOM sources A)
origins of FPOM in the Amazon (Hedges et al.
(1986) B) large river surveys C) mass
balance in headwater streams D) sorbed OM on
mineral surfaces - flotation techniques can
separate particles by density - analysis shows
that most OM was present as DOM sorbed to
mineral surfaces vs. plant fragments - role of
small iron particles to selectively retain
DOM landscape chromatography sensu Aufdenkampe
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4) Transport of FPOM A) transport distances
for wood similar distances for small wood and
leaves ( 10m) before being retained, 100m under
high flow conditions B) FPOM transport
distances 100s of meters based on corn
pollen, dyed yeast - radio-labeled particles
200m in 2nd order and 800m in Salmon River
headwaters (Cushing et al. 1993) C) filter
feeding influence despite high density of
filter- feeders (e.g., lake outlet) they have
little or no influence on transport or
deposition
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VI. Dissolved Organic Matter (DOM) 1)
Sources A) leaf leachate B) extracellular
release (leaky joints) C) soils and
groundwater 2) DOM quality and composition -
typically low, refractory humic and fulvic
material - composition (10-25 know structure
like carbs, fats, proteins) - else
categorical Id with 50-75 (as much as 90
in blackwater) humic or fulvic
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VI. Dissolved Organic Matter (DOM) 3)
Concentrations and sources A) soils
quantitatively important, concentration in soil
waters vary from 2-30 mg/L, DOC changes along
flow paths - Meyer and Tate (1983) rooting
zone 2-12 ppm, seeps 0.2-0.7 ppm B)
groundwater low DOC due to biological and
chemical OM degradation, long residence times,
1-2 ppm C) precipitation concentration
evolves above canopy 1-2 ppm throughfall 2-3
ppm (may be as high as 25 ppm), average values
for Bear Brook, NH 18 ppm (Fisher and
Likens 1973)
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VI. Dissolved Organic Matter (DOM) 4) In-stream
transformations of DOC A) primary biotic
processes uptake by microorganisms B)
abiotic processes floculation, precipitation,
sorption C) autumnal DOC pulse - may be
high (42 of total fall input to a New England
stream) but not seen as increased DOC - leachate
lost from stream quickly (48-72 hrs) - sediments
responsible 85 over 9 days vs. 25 over 4
days for water column processes - abiotic uptake
chelating to Al and Fe
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5) Microbial uptake and biofilms A) biofilm
composition gelatinous polysaccharide
matrix, algae, bacteria, fungi, extracellular
enzymes, exudates, detrital particles B)
biofilm function - role of the matrix C)
microbial production i) cell density and
biomass ii) metabolic activity iii)
determinants iv) fates
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5) Microbial uptake and biofilms B) biofilm
function - role of the matrix i) reduces
diffusion rates ii) enhances DOC
transformation iii) active exoenzymes iv) ion
exchange
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5) Microbial uptake and biofilms C) microbial
production i) cell density and
biomass - epifluorescence microscopy, ATP
anlysis, SEM ii) metabolic activity -
3H-thymidine, respiration iii)
determinants - OM quantity and quality
iv) fates - consumption and export