Download Standing Water – lakes and ponds Lakes result from either barriers

Standing Water – lakes and ponds
Lakes result from either barriers to drainage or when
depressions (or excavations) form along a drainage
system
Majority of lakes are found in glaciated areas and
are formed by glacial action
Others are formed in river channels (oxbows), by
geological faulting, volcanic action, or sea level
changes
Beavers form ponds by blocking drainage and then excavating the basins and
seal the dam with the mud they dig up—lakes and man-made reservoirs are
formed in much the same way—excavation and impoundment.
Glacial lakes
Glaciers can form lakes in the following ways:
Ice can impound the flow in a drainage system
The flow can be blocked by glacial till or
moraines
Ice flow can scour or deepen a basin
The vast majority of lakes in the world occur in glaciated areas—74%
Ice blocks in till can melt out to form a “kettle” or
“pothole” which then fills up with seepage or
surface flow
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Moraine dams
tributary stream
Moraine
Mountain glacier
Moraine
Glacier
recedes
Glacier
recedes
•After the mountain glacier
recedes a large lake can fill
the scoured out valley.
•The moraine damming the
lake outflow maintains the
level
Moraine at the outlet of Upper Waterton lake
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Proglacial lakes
A Proglacial lake
A river is blocked by ice,
usually from a large
continental glacier
•the water flowing toward
the glacier forms a large
lake at the glacier margin
•Following the retreat of the last
glaciation most of the Canadian landscape
was covered by proglacial lakes
•Species tolerant of coldwater (salmonid
and coregonids) became very widespread.
•Opportunities for dispersal of
cool and warmwater species were much more limited
because these water bodies disappeared with the ice.
Proglacial lakes in southwestern Alberta and Montana (around 12,000 Bp)
western extent of the
continental glacier
Present Waterton lakes
Probable Waterton
glacial lake at the
height of the
Wisconsin glaciation
>12,000 yr bp.
This lake would have been
fed by the all of the
tributaries of the Oldman
system
This lake
probably served as a major
refugium from which fish and invertebrates
colonized the SSRB, after the ice age.
Genetic studies indicate that many lake trout
populations across western Canada came
from this glacial refugium
Eastern extent of the cordilleran glaciers
Waterton Lakes have a similar origin—Both Waterton and Memphremagog
have contain glacial relict animal species in their deep waters.
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Freshwater mysid shrimp are
important glacial relicts and have a
restricted range because of this.
They have been introduced to many
lakes because fisheries managers
thought that this would improve
fisheries yields
This has largely backfired because
Mysis tends to compete with
epilimnetic zooplanktivorous fish, and
because of their vertical migrations
are difficult for these fish to consume.
Most of the mysids for the
introductions to other western lakes
came from Upper Waterton Lake
Cirque lakes in the rockies
•Glaciers in headwater valleys tend to
scour out a bowl shaped basin and the
excavated material forms a moraine at
the lake outflow that maintains the lake
level after the glacier has receded.
•Drainage in Moraine lake was further
impeded by a large landslide across the
outflow
•Most cirque lakes are fishless unless
stocked
Pothole or kettle lake formed in glacial --usually small < 30 ha, but can be
quite deep--10-40 m. Watersheds are very small.
•Large blocks of ice left behind in moraines and till mounds as glaciers melt
and grow “stagnant”.
•As they gradually melt, they leave behind a depression in the till that fills
by seepage
•Many of the small pothole lakes in Alberta are kettle lakes.
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Another type of basin associated with ice melting.
Polygonal ponds
near the Lena
River, Russia
Most of the large and old lakes in the world are
Tectonic lakes
Many occupy ancient basins called grabens—formed by large geological faults
Rocks before faulting
Lake in a symmetrical graben
Polygon ponds form along the Arctic coastal lowlands.
Form in the summer as wedges of ice melt within the permafrost to form small
polygonal basins (around 50 m across) that fill up with surface water.
Lake in a tilted graben
See Fig. 6.2 in your text
Lake Baikal—one of the most famous tectonic lakes in the world, has existed for
over 20 million years
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Lake Baikal, or "Sacred Sea," is located in southeastern Siberia
Lake basins formed by tectonic
forces—warping, fracturing or other
deformation of the earth’s crust
• At 25-30 million years old, it is the oldest lake in the world and its fauna is mostly
endemic.
The Rift Valley lakes of East Africa
•It measures 636 km long by 80 km wide, and has 2100 km of coastline.
Rifts are cracks in the crust where the
continent is splitting up—two parts
heading in different directions.
•It's basin is made up of three underwater depressions, which together hold a
volume of 23,600 cubic km of water, 20% of the world's fresh surface water.
Large Valleys form in these splits
•Over three hundred rivers and streams flow into Baikal,
• Only the Angara River flows out of the lake.
•The deepest point in Lake Baikal is 1637 m, the average depth is 630 m,
Lake Albert
Lake Victoria
• it has an exceptional clarity which allows 40-50 m of visibility.
•Animals can live down to depths of over 600 m
•Storms can generate waves over 6m high.
•Lake Tanganyika is the longest lake in the world stretching 660 km north to south.
•It is also the second deepest freshwater lake in the world with a maximum depth of
1436 metres.
•The basin formed nearly 25 million years ago when a block of the Earth's crust
dropped down between blocks that rose on either side, creating the deep chasm in the
Western arm of Africa's Great Rift.
•Today it supports a thriving fishing industry sustaining an annual catch of close to
50,000 tonnes.
•The only river flowing out of Tanganyika is the Lukuga, a tributary of the Congo,
which eventually flows into the Atlantic Ocean.
Lake Tanganyika
Lake Malawi
A rich endemic fauna is found in the lake and supports the lucrative fishery
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African cichlids—endemic species have evolved in these ancient African lakes
Michael K. Oliver's "The Cichlid Fishes of Lake Malawi, Africa"
Few piscivorous
species have
evolved in these
lakes
Endemic cichlids
Are vulnerable to
Invading predators
Lates niloticus
The Nile Perch has invaded
Lake Victoria and many other east
African lakes , and has driven their
Native cichlid fauna almost to extinction
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