199
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_12, © Springer India 2013
It had been a practice in the past to portray alterations
of aquatic ecosystems by changes brought about
in climatic conditions. However, today, the
changes which occur in the ecosystem are
refl ected by man’s activities. It may be noted here
that these alterations have been affecting the conditions of the basins of both lentic and lotic systems, water budgets, nutrient loadings and
budgets and, thereby, the resultant productivity of
the freshwaters. Remnants and records of these
changes are generally left in the sediments. The
sediments are relatively static derivatives of the
dynamic ecosystems. The prehistoric parameters
are usually dealt with by palaeolimnology.
Palaeolimnology is, thus, that branch of limnological science which mainly deals with the interpretation of sequences in the sediments. It also
focuses on diagenetic processes which can alter
that record. The fi nal aim is to gain insights into
waterbody’s conditions of the past, their productivity and the changes in the different regulatory
parameters which had led the lentic ecosystems
to succeed to a different state of productivity.
As it happens today, in the past too, biochemical substances were produced by organisms and
also resulted from their degradation. Thus, fossil
record of sediments includes the biochemical substances produced by organisms as well as morphological remnants of specifi c organisms (Frey 1974 ;
Korde 1966 ; Vallentyne 1960 ; Wetzel 1983 ).
The accumulated sediments in the lake basin
are derived from various sources. The composition of the sediments is greatly infl uenced by the
geomorphology of both the lentic and lotic basins.
It is believed that several lakes had originated
between the intervals of cyclic glaciation and
deglaciation. However, many lakes of earlier glacial periods might have been obliterated by succeeding glaciations, probably, due to fi lling up
with sedimentary materials or by draining. It is
here noteworthy that the recent retreat of the last
major glaciation phase could be the possible reason for the existence of so many lakes today. Most
of the lakes are very young (<20,000 years),
except some very ancient lakes, particularly in the
rift areas in Africa and Asia (Livingstone 1975 ).
Notwithstanding the above, the primary sedimented materials are supposed to be regulated by
regional geology and climate. They are, perhaps,
modifi ed by biological processes of both the
drainage basin of the lake and the lake itself.
Particulate matters are sorted according to their
size and density by water movements, such as
wave action and currents. This could result in the
formation of a general gradient from coarser particles near the shore to fi ner particles of sediments
in deeper waters. These gradients may often be
disturbed by different mechanisms which could
be related to the morphology of the lake basin.
12.1 Dating of Sediments
There are several methods to determine the age of
sedimented materials in lake deposits. In post-glacial
lakes, the most signifi cant method is, perhaps, to
12
Historical Records (Palaeolimnology)
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_12, © Springer India 2013
It had been a practice in the past to portray alterations
of aquatic ecosystems by changes brought about
in climatic conditions. However, today, the
changes which occur in the ecosystem are
refl ected by man’s activities. It may be noted here
that these alterations have been affecting the conditions of the basins of both lentic and lotic systems, water budgets, nutrient loadings and
budgets and, thereby, the resultant productivity of
the freshwaters. Remnants and records of these
changes are generally left in the sediments. The
sediments are relatively static derivatives of the
dynamic ecosystems. The prehistoric parameters
are usually dealt with by palaeolimnology.
Palaeolimnology is, thus, that branch of limnological science which mainly deals with the interpretation of sequences in the sediments. It also
focuses on diagenetic processes which can alter
that record. The fi nal aim is to gain insights into
waterbody’s conditions of the past, their productivity and the changes in the different regulatory
parameters which had led the lentic ecosystems
to succeed to a different state of productivity.
As it happens today, in the past too, biochemical substances were produced by organisms and
also resulted from their degradation. Thus, fossil
record of sediments includes the biochemical substances produced by organisms as well as morphological remnants of specifi c organisms (Frey 1974 ;
Korde 1966 ; Vallentyne 1960 ; Wetzel 1983 ).
The accumulated sediments in the lake basin
are derived from various sources. The composition of the sediments is greatly infl uenced by the
geomorphology of both the lentic and lotic basins.
It is believed that several lakes had originated
between the intervals of cyclic glaciation and
deglaciation. However, many lakes of earlier glacial periods might have been obliterated by succeeding glaciations, probably, due to fi lling up
with sedimentary materials or by draining. It is
here noteworthy that the recent retreat of the last
major glaciation phase could be the possible reason for the existence of so many lakes today. Most
of the lakes are very young (<20,000 years),
except some very ancient lakes, particularly in the
rift areas in Africa and Asia (Livingstone 1975 ).
Notwithstanding the above, the primary sedimented materials are supposed to be regulated by
regional geology and climate. They are, perhaps,
modifi ed by biological processes of both the
drainage basin of the lake and the lake itself.
Particulate matters are sorted according to their
size and density by water movements, such as
wave action and currents. This could result in the
formation of a general gradient from coarser particles near the shore to fi ner particles of sediments
in deeper waters. These gradients may often be
disturbed by different mechanisms which could
be related to the morphology of the lake basin.
12.1 Dating of Sediments
There are several methods to determine the age of
sedimented materials in lake deposits. In post-glacial
lakes, the most signifi cant method is, perhaps, to
12
Historical Records (Palaeolimnology)