27
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_2, © Springer India 2013
2.1
The Total Aquatic System
We usually refer to fi xation of solar energy during
photosynthesis and its transfer through food webs
when we talk about energy fl ow in ecology.
However, there is a much greater fl ow of energy
in physical processes which is absolutely critical
to the functioning of aquatic ecosystems. Stated
briefl y, it is the energy required to carry plant
nutrients from deeper waters (where they tend to
accumulate) to surface waters where they could
be used in photosynthesis. This represents biological production as a fl ux solar energy in a conceptual model. The gate of valve which controls
the fl ow of energy is operated by the quantum of
plant nutrients. However, plant productivity is
generally limited by the supply of plant nutrients.
The greater the depth of water, the greater is the
energy required to bring up the nutrients. Hence,
the shallow bodies of water are generally more
productive.
It may be noted here that energy for upwelling
is obtained primarily from four mechanisms,
namely , convective cooling, wind-induced
currents, river run-off and tidal currents. Of
these, the fi rst three are driven by solar energy,
while the last one by the gravitational pull of the
moon. We may, however, consider them as
physical energy subsidies which assist the
biological processes.
Atmospheric cooling results in increasing
density in the upper layers and a tendency for
surface waters to sink. Further, wind over water
causes a surface current in the same direction.
Friction between the moving water and the stationary lower layer generates vertical turbulent
mixing, thus, bringing some of the deeper water
to the surface. Wind-induced mixing and upwelling complement convective cooling as a way of
mixing temperate lakes after summer stratifi cation. On a global scale, wind-induced currents
cause huge circulation patterns in the world’s
oceans. Concomitant to above, at places, where
rivers discharge to the sea, a layer of freshwater
moves across the denser salt water. However, in
the shallow bays and estuaries, where the rise
and fall of the tides are considerable in relation
to the volume of the basin, tidal currents may be
suffi cient to keep the waters well mixed at all
times. Nutrients regenerated from the benthos
are then continually made available to primary
producers.
2.2
Aquatic Systems as Integral
Part of the Biosphere
The biosphere is that portion of the earth which
supports life. It extends a few millimetres into
the sediments of the abyssal depths of the oceans
and to the tops of the earth’s highest mountains.
However, the modern biosphere is not only the
product of evolutionary processes operating
over at least three of the earth’s 4.5-billion-year
history but is today maintained in a surprising
degree by the intricate processes of life in
2
The Limnology of Lentic System
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_2, © Springer India 2013
2.1
The Total Aquatic System
We usually refer to fi xation of solar energy during
photosynthesis and its transfer through food webs
when we talk about energy fl ow in ecology.
However, there is a much greater fl ow of energy
in physical processes which is absolutely critical
to the functioning of aquatic ecosystems. Stated
briefl y, it is the energy required to carry plant
nutrients from deeper waters (where they tend to
accumulate) to surface waters where they could
be used in photosynthesis. This represents biological production as a fl ux solar energy in a conceptual model. The gate of valve which controls
the fl ow of energy is operated by the quantum of
plant nutrients. However, plant productivity is
generally limited by the supply of plant nutrients.
The greater the depth of water, the greater is the
energy required to bring up the nutrients. Hence,
the shallow bodies of water are generally more
productive.
It may be noted here that energy for upwelling
is obtained primarily from four mechanisms,
namely , convective cooling, wind-induced
currents, river run-off and tidal currents. Of
these, the fi rst three are driven by solar energy,
while the last one by the gravitational pull of the
moon. We may, however, consider them as
physical energy subsidies which assist the
biological processes.
Atmospheric cooling results in increasing
density in the upper layers and a tendency for
surface waters to sink. Further, wind over water
causes a surface current in the same direction.
Friction between the moving water and the stationary lower layer generates vertical turbulent
mixing, thus, bringing some of the deeper water
to the surface. Wind-induced mixing and upwelling complement convective cooling as a way of
mixing temperate lakes after summer stratifi cation. On a global scale, wind-induced currents
cause huge circulation patterns in the world’s
oceans. Concomitant to above, at places, where
rivers discharge to the sea, a layer of freshwater
moves across the denser salt water. However, in
the shallow bays and estuaries, where the rise
and fall of the tides are considerable in relation
to the volume of the basin, tidal currents may be
suffi cient to keep the waters well mixed at all
times. Nutrients regenerated from the benthos
are then continually made available to primary
producers.
2.2
Aquatic Systems as Integral
Part of the Biosphere
The biosphere is that portion of the earth which
supports life. It extends a few millimetres into
the sediments of the abyssal depths of the oceans
and to the tops of the earth’s highest mountains.
However, the modern biosphere is not only the
product of evolutionary processes operating
over at least three of the earth’s 4.5-billion-year
history but is today maintained in a surprising
degree by the intricate processes of life in
2
The Limnology of Lentic System