168
initially growing in shallower water. Ruttner had
also noted Hydrilla verticillata, Potamogeton
malayanus, Najas falciculata and Myriophyllum
spicatum in Lake Toba. All these AM have been
found to reach a depth of 5 m. However, Chara
sporadically occurred down to 12 m. In Lake
Tahoe, vascular plants had not been much
recorded, but, wherever recorded, generally not
beyond 6.5 m. However, Chara virgata was
found to extend even up to a depth of 75.5 m
(Frantz and Cordone 1967 ). In Lake Vrana,
angiosperms were not recorded at <7.7 m.
Conversely, Myriophyllum spicatum and Nitella
opaca could grow up to a depth of >38 m and
Spirogyra could penetrate up to 50–52 m (Golubic
1963 ). Further, in Crystal Lake, Wisconsin,
angiosperms and Isoetes macrospore were
reported to occur in the top 4 m. Then, there
occurred a sterile zone from 4 to 15 m. Below
this, mosses had covered the bottom to the maximum depth of 20 m (Fassett 1930 ).
Angiospermic AM are apparently unable to
grow normally when under pressures of 2 atm,
corresponding to 1 atm of air at sea level and the
pressure of 10 m of water. Some inhibition may
occur at total pressures of 1.5 atm, corresponding
to 5 m of water, in certain species.
8.2
Zonation, Depth Distribution
Mechanical action of the wind and water movements are possibly the most important environmental factors at the margin of the lake. On the
other hand, in deeper water, illumination is
clearly not the only factor of importance, though
it may be of paramount importance. Finally,
edaphic differences in the sediments, in which
most of the AM are rooted, may be almost as
important as variation in illumination.
Under the above background, most large
lakes, receive the full force of wind and waves at
least on the shores. Thus, they lack any visible
higher plants. On the other hand, small lakes
may have much vegetation along equally
exposed and similarly directed coastlines. This
may be explained by the relationship of wave
height to the fetch of the wind. Further, very
shallow areas of considerable size may also be
fringed with emergent vegetation even though
parallel but more fl at parts of the shoreline lack
such vegetation. However, the waves may
become translatory losing energy to the bottom
in very shallow water.
Incidentally, in Poland, the margins of lakes
have been classifi ed into three zones, namely, (a)
litholittoral or rocky, (b) psammolittoral or sandy
and (c) phytolittoral or with much vegetation.
These terms may usefully be used for other
regions also.
8.3
Growth Forms and Depth
Distribution
Spence ( 1964 ) studied the depth distributions of
plants in the Scottish lochs. He had examined the
vertical frequency of different growth forms classifi ed by him as emergent, fl oating leaved, broad
leaved and submerged. The emergent and fl oating AM generally tend to occur in shallower
waters than do the others. The uniform occurrence of rosulate or isoetid forms, independent of
depth, is the most interesting feature of the distribution of AM. This may indicate that the form is
not primarily an adaptation to distribution but,
rather, to the oligotrophic nature of the waters in
which such plants are commonest, with dependence on the sediments rather than the water as a
source of nutrients.
8.3.1 Growth Forms
8.3.1.1 Emergent AM
They are junciform, except in most protected
bays. However, the herbiform emergent AM, e.g.
the larger Alismataceae, are, primarily, AM of
ponds. It may be apt to be much better developed
on the sheltered side of the lake upwind than on
the exposed opposite shore where emergent AM
exist and are not confi ned to particularly sheltered
inlets. This phenomenon appears to be in vogue
and often conspicuous in regions where SW wind
is strongly prevalent, e.g. Sweden ( Thunmark
1937 ), Denmark (Boye Peterson 1917 ) and North
8 Aquatic Macrophytes in Lakes
initially growing in shallower water. Ruttner had
also noted Hydrilla verticillata, Potamogeton
malayanus, Najas falciculata and Myriophyllum
spicatum in Lake Toba. All these AM have been
found to reach a depth of 5 m. However, Chara
sporadically occurred down to 12 m. In Lake
Tahoe, vascular plants had not been much
recorded, but, wherever recorded, generally not
beyond 6.5 m. However, Chara virgata was
found to extend even up to a depth of 75.5 m
(Frantz and Cordone 1967 ). In Lake Vrana,
angiosperms were not recorded at <7.7 m.
Conversely, Myriophyllum spicatum and Nitella
opaca could grow up to a depth of >38 m and
Spirogyra could penetrate up to 50–52 m (Golubic
1963 ). Further, in Crystal Lake, Wisconsin,
angiosperms and Isoetes macrospore were
reported to occur in the top 4 m. Then, there
occurred a sterile zone from 4 to 15 m. Below
this, mosses had covered the bottom to the maximum depth of 20 m (Fassett 1930 ).
Angiospermic AM are apparently unable to
grow normally when under pressures of 2 atm,
corresponding to 1 atm of air at sea level and the
pressure of 10 m of water. Some inhibition may
occur at total pressures of 1.5 atm, corresponding
to 5 m of water, in certain species.
8.2
Zonation, Depth Distribution
Mechanical action of the wind and water movements are possibly the most important environmental factors at the margin of the lake. On the
other hand, in deeper water, illumination is
clearly not the only factor of importance, though
it may be of paramount importance. Finally,
edaphic differences in the sediments, in which
most of the AM are rooted, may be almost as
important as variation in illumination.
Under the above background, most large
lakes, receive the full force of wind and waves at
least on the shores. Thus, they lack any visible
higher plants. On the other hand, small lakes
may have much vegetation along equally
exposed and similarly directed coastlines. This
may be explained by the relationship of wave
height to the fetch of the wind. Further, very
shallow areas of considerable size may also be
fringed with emergent vegetation even though
parallel but more fl at parts of the shoreline lack
such vegetation. However, the waves may
become translatory losing energy to the bottom
in very shallow water.
Incidentally, in Poland, the margins of lakes
have been classifi ed into three zones, namely, (a)
litholittoral or rocky, (b) psammolittoral or sandy
and (c) phytolittoral or with much vegetation.
These terms may usefully be used for other
regions also.
8.3
Growth Forms and Depth
Distribution
Spence ( 1964 ) studied the depth distributions of
plants in the Scottish lochs. He had examined the
vertical frequency of different growth forms classifi ed by him as emergent, fl oating leaved, broad
leaved and submerged. The emergent and fl oating AM generally tend to occur in shallower
waters than do the others. The uniform occurrence of rosulate or isoetid forms, independent of
depth, is the most interesting feature of the distribution of AM. This may indicate that the form is
not primarily an adaptation to distribution but,
rather, to the oligotrophic nature of the waters in
which such plants are commonest, with dependence on the sediments rather than the water as a
source of nutrients.
8.3.1 Growth Forms
8.3.1.1 Emergent AM
They are junciform, except in most protected
bays. However, the herbiform emergent AM, e.g.
the larger Alismataceae, are, primarily, AM of
ponds. It may be apt to be much better developed
on the sheltered side of the lake upwind than on
the exposed opposite shore where emergent AM
exist and are not confi ned to particularly sheltered
inlets. This phenomenon appears to be in vogue
and often conspicuous in regions where SW wind
is strongly prevalent, e.g. Sweden ( Thunmark
1937 ), Denmark (Boye Peterson 1917 ) and North
8 Aquatic Macrophytes in Lakes