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Bacteria in Lakes. Decomposition. Bacteria responsible for most decomposition of particulate and dissolved organic matter in lakes Cannot keep pace with organic matter production. Two Types in Lakes. Pelagial bacteria Live within water column

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Bacteria in Lakes

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Bacteria in lakes

Bacteria in Lakes



  • Bacteria responsible for most decomposition of particulate and dissolved organic matter in lakes

  • Cannot keep pace with organic matter production

Two types in lakes

Two Types in Lakes

  • Pelagial bacteria

  • Live within water column

  • Act on dissolved and particulate organic matter in suspension

Two types in lakes1

Two Types in Lakes

  • Sediment bacteria

  • Live on or in the sediments

  • Act on materials that have settled out of the water

Two types in lakes2

Two Types in Lakes

  • Both groups important to organic matter recyling

  • Populations in sediments are several orders of magnitude greater than those in water column

Pelagial planktonic bacteria

Pelagial (Planktonic) Bacteria

  • Responsible for initial decomposition of organics in oxygenated waters

  • First to act on materials secreted by organisms, or washed in from watershed

Pelagial planktonic bacteria1

Pelagial (Planktonic) Bacteria

  • Numbers are substrate-limited

  • Correlation between photosynthetic activity and bacterial biomass

  • Highest in epilimnion, lowest in meta-, upper hypolimnion, increases near sediments (nutrient release)

Rate of decomposition

Rate of Decomposition

  • Dependent on:

  • Quality of organic matter

  • Simple vs. complex

  • N-containing vs. carbohydrate-based

  • Dissolved vs. particulate (>75% vs. 1-15%)

Rate of decomposition1

Rate of Decomposition

  • Dependent on:

  • Quantity of organic matter

  • Breakdown most efficient when bacteria not substrate-limited

Rate of decomposition2

Rate of Decomposition

  • Dependent on:

  • Temperature

  • Decomposition rate greater in warmer waters

Rate of decomposition3

Rate of Decomposition

  • Dependent on:

  • Oxygen

  • Most pelagial bacteria are aerobic forms - need O2 to live

Rate of decomposition4

Rate of Decomposition

  • Dependent on:

  • Stratification and basin morphometry

  • Affects decomposition of particulates

  • Decomposition more efficient in deep, less-productive lakes than shallow, productive systems

    • Particle settling distance, amount of organic matter

Sediment bacteria

Sediment Bacteria

  • Most abundant at water-sediment interface

  • Decrease rapidly with depth into sediments

Sediment bacteria1

Sediment Bacteria

  • Most are obligate or facultative anaerobes

  • Organic matter decomposed in absence of O2 to methane and CO2

Sediment bacteria2

Sediment Bacteria

  • 2-stage methane fermentation

  • Organic matter to organic acids (fac., obl. anaerobes)

  • Organic acids to CH4, CO2 (obl. anaerobes)

Sediment bacteria3

Sediment Bacteria

  • Methane production from sediments diffuses into water

  • CH4 oxidized to CO2 by aerobic bacteria in metalimnion during stratification

  • Little CH4 escapes into epilimnion

Sediment bacteria4

Sediment Bacteria

  • 95% of methane produced in sediments oxidized during fall turnover and beneath winter ice (may contribute to low O2)

Sediment bacteria5

Sediment Bacteria

  • In hypereutrophic lakes, CH4 may supersaturate hypolimnion during summer

  • Rise to surface as bubbles

  • Internal fertilization method - currents may carry nutrients back into epilimnion

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