P1252428438QgojZ

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Dissolved Particulate
Inorganic DIC CO2, H2CO3, HCO3-, CO32- CaCO3
Organic Diss. organic carbon (DOC) Large refractory compounds Small, reactive compounds Living organisms Dead particulate organic material
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Riverine Input
CO2
DOC
hn
POC
River, GW DIC
DIC
DOC
POC
Other Heterotrophs
Autotrophs
PIC
animals
Sediments
PIC
POC
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Lakes as Carbon Sources
Mirror Lake, NH
Direct measurements Autumn Spring/Summer/Fa
ll Summer Tropical lakes
Cole, 1994 1650 lakes 50 directly measured 1600
CO2 calculations
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DOC gtgt POC HMW DOC gt LMW DOC
Cotner, 2001
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Allocthonous Delivery of OC

• Terrestrial DOC HMW DOC
• Plant taxa, soil anoxia
• Nutrient-poor (High C/N, C/chl a)

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Internal Loading of DOC

• Secretion/decomposition major source of LMW,
  nutrient rich DOC
• Trophic state affects DOC, DOCPOC
• Rivers low DOCPOC

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POC Size reactivity effects

• Large POC colonized by microbes, fungi,
  progressively decomposed to CO2, DOC
• Terrestrial POC more recalcitrant than aquatic
  POC,DOC

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DOC degradation

• Degradation rates of DOC
• Humic, fulvic phenolics, lignin long-lived
• Sugars short-lived
• Most sediments dominated by fine-grained POC and
  terrestrial HMW compounds

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Photolysis

• Degradation of DOC by light (especially UV)
• Complete oxidation to CO2, Incomplete to
  reactive LMW OC

• Rapid, dependent on climate, latitude, ozone
• Rates typically low (10-20 of DOC metabolism),
  but important for recalcitrant OC

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Detrital Chain Or Microbial Loop
Grazer Chain

• Most respiration occurs in microbial loop
• Microbe/algal competition for nutrients

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(No Transcript)
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Biomass
Net Ecosystem Autotrophy vs. Heterotrophy
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English channel
(g/m
)
Herbivores
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Herbivores
Plants
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PP
The inverted pyramid
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• High bacterial growth efficiency in eutrophic
  lakes
• Bacterial dominance of oligotrophic lakes
• Bacterial/algal competition for N, P
• Net ecosystem heterotrophy vs. autotrophy

BGE bacterial growth efficiency BR bacterial
respiration PR plankton respiration
Biddanda, B.et al. 2001
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mgC/m2 or mgC/m2/day
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Buildup of CO2 in Hypolimnia
- Microbial respiration of DOC/POC
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• All sediments are anoxic

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Rates of methanogenesis
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Conclusions

• Lakes receive large inputs of recalcitrant DOC
  and POC from land
• Watershed vegetation, soils, and climate
  influence the type, quality, and quantity of
  terrigenous OC
• Autochthonous OC inputs largely a function of
  lake trophic state
• Bacteria metabolize aquatic and terrestrial DOC
  and POC as part of microbial loop,
• Photolysis further degrades DOC
• Most OM decomposition is in the sediments where
  methanogenesis is a very important process of OM
  decomposition