202
That lakes progress from states of oligotrophy
to eutrophy is an old concept. It is not necessarily universal (Hutchinson 1973 ). Lake productivity is believed to respond to changing nutrient
incomes, climate and morphometry. This has
been demonstrated from chemical analyses of
sediment stratigraphy, coupled with other indices of past productivity. It is also believed that
accumulation rates of N, P and organic matter in
sediments were commonly high in early postglacial time, which was supposed to be a period of
rich availability of nutrients. Increases or
decreases in lake productivity today are usually
directly related to interferences caused by activities of man.
12.3 Organic Constituents
The problem of origin of sedimentary organic
constituents may be addressed with regard to
their chemical analyses. It may be ascertained
whether the organic compounds had originated
inside or outside of the lake basin. Moreover,
many organic compounds undergo degradation
both during and after sedimentation. It is said
that total amino acid, carbohydrate and chlorophyllous and fl avonoid pigment residues in
lake and bog sediments usually increase towards
the surface. Further, carotenoid pigments also
generally increase upwards in more recent lake
sediments. They, however, decrease markedly
in the developmental transition from a lake to
a bog.
Concomitant to above, much information
is available on organic compounds and their
distribution in sediments (Cranwell 1976 ;
Philp et al. 1976 ). Today, there has been a
shift from simple measurements, such as the
amount and distribution of total organic matter, C or N, to molecular characterisation of
individual compounds. For example, analyses of carbon-chain lengths of n -alkanes
derived from plant lipids indicated that sediment could be characterised by the type of
humic material from which it had been
derived.
12.4 Pigments
The fossil pigments have by far been, perhaps,
the most promising organic constituents of sedimentary stratigraphy which have been investigated in detail. Vallentyne ( 1960 ) did extensive
works in this fi eld. The photosynthetic pigments
undergo molecular transformations upon plant
senescence, in which ions (e.g. Mg ion of chlorophylls) and side groups are lost progressively
during physical or biological degradation. There
is, in fact, a tendency for the degradation products to increase in stability.
In sediments, large number of pigments are
found. However, non-degraded chlorophylls are
rare. Concomitantly, degradation products of
other pigments like pheophytins, chlorophyllides, pheophorbides and bacteriochlorophyll
have been identifi ed and quantifi ed.
Vallentyne ( 1956 , 1960 ) had done pioneering
studies on fossil pigments of sediments of many
different lake systems. These data allow interpretation of the ecological records of the various
lakes when correlated with the stratigraphy of
microfossils of organisms. Analyses of Bethany
Bog in Connecticut, USA, exemplify the potential information that pigments can provide with
critical interpretation (Vallentyne 1956 ).
A general correlation between sedimentary
pigments and productivity had been demonstrated
by a number of analyses on several different types
of lakes. Most of the studies had indicated maximum concentrations of pigments during early
postglacial period after a period of Tundra conditions associated with retreating glaciation.
Notwithstanding the above, the rapid eutrophication of many recent lakes, often within the
last century, is, generally, refl ected by large
increases in the pigment concentrations of recent
sediments. This recent increase often coincides
with renewed leaching of nutrients because the
land could have been deforested for agriculture.
Concomitantly, the inverse relationship between
CaCO 3 and pigment stratigraphy had been demonstrated in a number of hard-water lakes (Wetzel
1970 ; Manny et al. 1978 ).
12 Historical Records (Palaeolimnology)
That lakes progress from states of oligotrophy
to eutrophy is an old concept. It is not necessarily universal (Hutchinson 1973 ). Lake productivity is believed to respond to changing nutrient
incomes, climate and morphometry. This has
been demonstrated from chemical analyses of
sediment stratigraphy, coupled with other indices of past productivity. It is also believed that
accumulation rates of N, P and organic matter in
sediments were commonly high in early postglacial time, which was supposed to be a period of
rich availability of nutrients. Increases or
decreases in lake productivity today are usually
directly related to interferences caused by activities of man.
12.3 Organic Constituents
The problem of origin of sedimentary organic
constituents may be addressed with regard to
their chemical analyses. It may be ascertained
whether the organic compounds had originated
inside or outside of the lake basin. Moreover,
many organic compounds undergo degradation
both during and after sedimentation. It is said
that total amino acid, carbohydrate and chlorophyllous and fl avonoid pigment residues in
lake and bog sediments usually increase towards
the surface. Further, carotenoid pigments also
generally increase upwards in more recent lake
sediments. They, however, decrease markedly
in the developmental transition from a lake to
a bog.
Concomitant to above, much information
is available on organic compounds and their
distribution in sediments (Cranwell 1976 ;
Philp et al. 1976 ). Today, there has been a
shift from simple measurements, such as the
amount and distribution of total organic matter, C or N, to molecular characterisation of
individual compounds. For example, analyses of carbon-chain lengths of n -alkanes
derived from plant lipids indicated that sediment could be characterised by the type of
humic material from which it had been
derived.
12.4 Pigments
The fossil pigments have by far been, perhaps,
the most promising organic constituents of sedimentary stratigraphy which have been investigated in detail. Vallentyne ( 1960 ) did extensive
works in this fi eld. The photosynthetic pigments
undergo molecular transformations upon plant
senescence, in which ions (e.g. Mg ion of chlorophylls) and side groups are lost progressively
during physical or biological degradation. There
is, in fact, a tendency for the degradation products to increase in stability.
In sediments, large number of pigments are
found. However, non-degraded chlorophylls are
rare. Concomitantly, degradation products of
other pigments like pheophytins, chlorophyllides, pheophorbides and bacteriochlorophyll
have been identifi ed and quantifi ed.
Vallentyne ( 1956 , 1960 ) had done pioneering
studies on fossil pigments of sediments of many
different lake systems. These data allow interpretation of the ecological records of the various
lakes when correlated with the stratigraphy of
microfossils of organisms. Analyses of Bethany
Bog in Connecticut, USA, exemplify the potential information that pigments can provide with
critical interpretation (Vallentyne 1956 ).
A general correlation between sedimentary
pigments and productivity had been demonstrated
by a number of analyses on several different types
of lakes. Most of the studies had indicated maximum concentrations of pigments during early
postglacial period after a period of Tundra conditions associated with retreating glaciation.
Notwithstanding the above, the rapid eutrophication of many recent lakes, often within the
last century, is, generally, refl ected by large
increases in the pigment concentrations of recent
sediments. This recent increase often coincides
with renewed leaching of nutrients because the
land could have been deforested for agriculture.
Concomitantly, the inverse relationship between
CaCO 3 and pigment stratigraphy had been demonstrated in a number of hard-water lakes (Wetzel
1970 ; Manny et al. 1978 ).
12 Historical Records (Palaeolimnology)