Download Sediment Bacteria

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
 Act on dissolved and
particulate organic
matter in suspension
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 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

Responsible for initial
decomposition of
organics in
oxygenated waters
 First to act on
materials secreted by
organisms, or washed
in from watershed
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





Dependent on:
Quality of organic
matter
Simple vs. complex
N-containing vs.
carbohydrate-based
Dissolved vs.
particulate (>75% vs.
1-15%)
Rate of Decomposition

Dependent on:
 Quantity of organic
matter
 Breakdown most
efficient when
bacteria not
substrate-limited
Rate of Decomposition

Dependent on:
 Temperature
 Decomposition rate
greater in warmer
waters
Rate of Decomposition

Dependent on:
 Oxygen
 Most pelagial bacteria
are aerobic forms need O2 to live
Rate of Decomposition

Dependent on:
 Stratification and basin
morphometry
 Affects decomposition of
particulates
 Decomposition more
efficient in deep, lessproductive lakes than
shallow, productive
systems
 Particle settling
distance, amount of
organic matter
Sediment Bacteria
 Most
abundant at
water-sediment
interface
 Decrease rapidly
with depth into
sediments
Sediment Bacteria
 Most
are obligate
or facultative
anaerobes
 Organic matter
decomposed in
absence of O2 to
methane and CO2
Sediment Bacteria
 2-stage
methane
fermentation
 Organic matter to
organic acids (fac.,
obl. anaerobes)
 Organic acids to
CH4, CO2 (obl.
anaerobes)
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 Bacteria

95% of methane
produced in
sediments oxidized
during fall turnover
and beneath winter
ice (may contribute to
low O2)
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