167
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_8, © Springer India 2013
8.1
The Distribution of Aquatic
Macrophytes in Lakes
A discourse of aquatic macrophytes (AM) forms
one of the central themes of the study of wetlands
and lakes.
8.1.1 The Vertical Extent
of the Vegetation
The vertical gradients in any environmental variable are much steeper in a lake than on a hillside,
so that a descent of 10–15 m into the water may
lead to a drop of summer temperatures to 5–6 °C,
almost total extinction of the light fl ux, and
increase in pressure by 1–1.5 atmosphere (atm).
In general, tracheophytes are not known to occur
at <11.5-m depth. However, there could be an
exception. Potamogeton strictus may reach a
depth of just over 11.5 m, Chara spp. to 14 m and
the moss Hygrohypnum to 29 m only in Lake
Titicaca. This lake is also unique in recording the
deepest well-established occurrence of an angiosperm at an altitude of 3,815 m MSL (Tutin
1940 ). The usual lower limit appears to be about
9 m or, possibly, a little less. However, the bryophytes and Charophyceae extend to much greater
depths than do the tracheophytes in clear lakes. In
extreme cases, they may reach of depth of
>100 m. Further, there is least doubt that the
lower limit of macroscopic vegetation of some
sort is set by the illumination. The AM tend to
disappear when the irradiance on the bottom is
between 1 and 2 % of the surface value. In very
clear lakes, the plants going deepest are the
mosses, liverworts and Characeae. In less clear
lakes, they may be fl owering plants of members
of the genus Isoetes . Moreover, certain species of
angiosperms clearly more often penetrate to low
light intensities than do others within the range in
which angiosperms may occur. Potamogeton
praelongus, Ceratophyllum demersum , etc. may
extend to depths where the illumination is no
>2% of its value at the surface. Notably, some of
these species owe some of their effi ciency in deep
water to their low respiratory rate, so that net
photosynthesis differs less from gross than would
be the case in other plants, which live habitually
near the surface.
Concomitant to above, a brief account of the
distribution of different AM in different lentic
bodies is given below.
In the L’ac d’Annecy in the French Alps, no
angiosperms are known to grow in depths >11 m;
except, Najas marina and Elodea canadensis
have been recorded possibly from depth ranges
of 12–15 m and 10–12 m, respectively (Dangeard
1925 ). However, in nearly all lakes, the AM do
not generally extend to >9.0 m. Hill ( 1969 ) had
recorded Lagarosiphon major almost to 10 m in
Lake Aratiatia, Auckland, in New Zealand.
Further, Ruttner had found Ceratophyllum
demersum at a depth range of 8–9 m in Lake
Ranau in Sumatra, which could almost certainly
be due to the drift and sinking of specimens
8
Aquatic Macrophytes in Lakes
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_8, © Springer India 2013
8.1
The Distribution of Aquatic
Macrophytes in Lakes
A discourse of aquatic macrophytes (AM) forms
one of the central themes of the study of wetlands
and lakes.
8.1.1 The Vertical Extent
of the Vegetation
The vertical gradients in any environmental variable are much steeper in a lake than on a hillside,
so that a descent of 10–15 m into the water may
lead to a drop of summer temperatures to 5–6 °C,
almost total extinction of the light fl ux, and
increase in pressure by 1–1.5 atmosphere (atm).
In general, tracheophytes are not known to occur
at <11.5-m depth. However, there could be an
exception. Potamogeton strictus may reach a
depth of just over 11.5 m, Chara spp. to 14 m and
the moss Hygrohypnum to 29 m only in Lake
Titicaca. This lake is also unique in recording the
deepest well-established occurrence of an angiosperm at an altitude of 3,815 m MSL (Tutin
1940 ). The usual lower limit appears to be about
9 m or, possibly, a little less. However, the bryophytes and Charophyceae extend to much greater
depths than do the tracheophytes in clear lakes. In
extreme cases, they may reach of depth of
>100 m. Further, there is least doubt that the
lower limit of macroscopic vegetation of some
sort is set by the illumination. The AM tend to
disappear when the irradiance on the bottom is
between 1 and 2 % of the surface value. In very
clear lakes, the plants going deepest are the
mosses, liverworts and Characeae. In less clear
lakes, they may be fl owering plants of members
of the genus Isoetes . Moreover, certain species of
angiosperms clearly more often penetrate to low
light intensities than do others within the range in
which angiosperms may occur. Potamogeton
praelongus, Ceratophyllum demersum , etc. may
extend to depths where the illumination is no
>2% of its value at the surface. Notably, some of
these species owe some of their effi ciency in deep
water to their low respiratory rate, so that net
photosynthesis differs less from gross than would
be the case in other plants, which live habitually
near the surface.
Concomitant to above, a brief account of the
distribution of different AM in different lentic
bodies is given below.
In the L’ac d’Annecy in the French Alps, no
angiosperms are known to grow in depths >11 m;
except, Najas marina and Elodea canadensis
have been recorded possibly from depth ranges
of 12–15 m and 10–12 m, respectively (Dangeard
1925 ). However, in nearly all lakes, the AM do
not generally extend to >9.0 m. Hill ( 1969 ) had
recorded Lagarosiphon major almost to 10 m in
Lake Aratiatia, Auckland, in New Zealand.
Further, Ruttner had found Ceratophyllum
demersum at a depth range of 8–9 m in Lake
Ranau in Sumatra, which could almost certainly
be due to the drift and sinking of specimens
8
Aquatic Macrophytes in Lakes