Fish in Lakes

Lake Succession
Change in Lakes
 Lakes
not static - always changing
 Change
is not random, but directional
Change in Lakes
 In
general, lakes proceed from a stage in
which productivity is low, to a stage of high
productivity
Change in Lakes
 Concurrent
with change in productivity, the
lake gradually fills in with organic matter
and inorganic sediments
Change in Lakes

Filling in and increasing productivity together
produce lake aging or eutrophication
 Gradual process that takes 100s or 1000s of
years
The Process
 Start
with a newly
formed lake glaciated region
 Oligotrophic
- low
productivity severely limited by
cold climate
The Process
 Leeching
from
basin, runoff from
watershed carries
low amount of
nutrients
 Produces low
productivity,
primarily from
phytoplankton
The Process

Low productivity
maintained by
continued low inputs
of inorganic nutrients
from outside basin

Low productivity ->
low levels of organic
matter -> low rates of
decomposition
The Process
 High
dissolved O2
in hypolimnion
results in low
release of nutrients
from sediments
Low Productivity Cycle
“Oligotrophic”
Medium Productivity Cycle
“Mesotrophic”
Med.
Med.
Med.
Med.
Med.
Med.
Med.
Med.
Med.
High Productivity Cycle
“Eutrophic”
High
High
High
High
High
High
High
Low
High
Early Succession









High O2
Low CO2
Inorganic soil
Sparse vegetation
Sparse food (chiefly pelagic)
High transparency
Low fertility
Usually alkaline
“Coldwater” fishes
Late Succession









Low O2
High CO2
Organic soil
Abundant vegetation
Abundant food
Low transparency
High fertility
Increasing acidity
“Warmwater” fishes
Human-caused Lake Aging
Cultural eutrophication
 Slow
turnover
Accumulation
of nutrients,
excessive plant
growth, algae
blooms
Case Study: The Great Lakes
Littoral Encroachment
Littoral Encroachment

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