Ontogeny of Lakes
Successional Development
of Lake Ecosystems
Factors That Determine
Rates of Ontogeny
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Filling rates
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Inorganic material
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Basin morphometry
Drainage basin characteristics
Climatic factors
Organic material
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Autochthonous production
Allochthonous inputs
Decomposition rates
Ontogeny
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In late stages of ontogeny,
autochthonous productivity shifts from
planktonic dominance to littoral
dominance
Rates of ontogeny are greater in
shallow basins
Oligotrophic to Eutrophic
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Transition from unproductive to
productive has been conceptualized as
the transition from oligotrophic to
eutrophic
Oligotrophic to Eutrophic
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"Trophy" refers to the input of organic
matter per unit time
Eutrophe is German for "nutrient rich"
Oligotrophy and eutrophy were first
addressed in 1919 by Naumann and
1925 by Thienemann
Trophy is generally restricted in
definition to pelagic zones
Oligotrophic Lakes
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Oligotrophic lakes are generally
characterized by low rates of nutrient
input
Oligotrophic Lakes
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Large deep lakes usually remain oligotrophic
longer because of the greater dilution and
volume for biological activity and also
because of slower filling rates
Large, deep lakes do not develop anaerobic
hypolimnia as quickly and complexation and
formation of insoluble compounds is more
common in well-oxygenated water
Oligotrophic Lakes
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Sedimentation of nutrients reduce the
nutrient availability for biological activity
Loading rates of nutrients are extremely
critical determinants of rates of
eutrophication
Oligotrophic Lakes
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Precipitation reactions remove nutrients and
reduce autochthonous production in hard
water lakes and subsequently maintain low
concentrations of dissolved organic matter
Hard water lakes tend to resist eutrophication
and factors (such as acid rain in small
quantities) that reduce the buffering capacity
increase the rate of eutrophication
Dystrophic Lakes
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Dystrophy refers to high loading rates of
allochthonous organic matter
Bogs are fequently dystrophic but all
dystrophic lakes are not bogs and do
not contain bog flora
Allotrophy refers to the rate of input
from allochthonous sources
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Highly stained lakes with large inputs of
allochthonous organic matter have low
rates of phytoplankton production
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Abundance of refractory humic substances
and the low pH generally cause low rates of
microbial activity
Divalent cations are low in concentration
because of cation exchange and low inputs
from the drainage basin
Low pH and low nutrient availability restrict
phytoplankton production
Successional Development
in Shallow Lakes
Macrophytes
Ê
And Associated → Reed Swamps → Marshes
Microflora
and Fens Ì
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Moss
Vegetation
→
Bog
Systems
Terrestrial
Vegetation
All lakes do not become bogs before becoming
terrestrial
Bogs, Swamps, Marshes
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Development of bogs requires abundant
precipitation and high humidity
throughout the year
As the basin fills, littoral vegetation
advances toward the center of the lake
Bogs, Swamps, Marshes
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Swamp conditions are present when
standing water occurs among the
vegetation throughout the basin
Marsh conditions exist when there is no
standing water and sediments are
saturated throughout the year
Bogs, Swamps, Marshes
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Mosses can grow on the saturated
sediments and raise the elevation of
water in the mat above the original lake
level - a "raised bog"
The moat-like ring of water that
surrounds the central mat of moss and
vegetation is called the lagg zone
Bogs, Swamps, Marshes
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Quaking bogs form when rapid growth
of Sphagnum grows over an open water
area resulting in a floating mat
Think About It
Goodbye and
Good Luck