201
man-induced changes in the vegetation and
weathering processes (Likens et al. 1977 ). An
example of the effect of climate on weathering
was demonstrated in some endorheic lakes of
East Africa. Lakes in the humid areas may have
high weathering rates of the drainage basin. They
may receive greater inputs of silica and may be
largely HCO 3 -dominated.
Several attempts have been made to use chemical constituents of the sediments variously in
order to interpret rates of limnological activities
of lakes as well as changes in climate and alterations of the drainage basin. The analysis could be
based on the assumption that the chemical chronology could represent (at least on a long-term
basis) the composite changes in inputs to the lake
in metabolic transformations which had occurred
within the lake. For example, if we compare the
chemical composition of a number of elements
(which could be mostly biologically nonessential) in lake sediments, it could give an
effective evaluation of the chronology of the erosion and rates of leaching. Likewise, comparison
of rocks and soils could also yield similar results.
However, inputs of extremely inert conservative
elements, such as titanium, may allow an evaluation of erosion rates of the lake basins. Other elements may indicate disturbances of drainage
basins depending on the geology of the area. For
example, in Laguna de Petenxil, a small lake in
Guatemala, there had been increase in the sediment concentrations of calcium, strontium, potassium and, to some extent, sodium during periods
of active Mayan agricultural activities in the
drainage basin. Mn, Fe and P followed the fl uctuations of agriculturally determined alkalies and
alkaline earths in an analogous way (Deevey
et al. 1979 ).
Detailed studies had been done on the palaeolimnology of a small, closed lake of volcanic origin in Italy, namely, the Lake Lago di Monterosi.
The results had demonstrated the dramatic effects
of alterations to the catchment area by the construction of a road alongside the lake in early historical times (Hutchinson et al. 1970 ). The lake
was said to be quite productive shortly after its
formation. It had perhaps lasted for a period of
about 2,000 years. This was, probably, related to
easy leaching of materials initially. These materials
were said to be rich in potassium and also had
fairly high phosphorus content.
Notwithstanding the above, sedimentary
records of disturbances in the drainage basin are
quite common, e.g. the productivity of Grosser
Ploner See in Northern Germany was increased
markedly in the early thirteenth century by the
construction of a mill dam. This had raised the
depth of water by a few metres. This had also
fl ooded portions of the surrounding catchment
basin (Ohle 1979 ). In more recent times, in the
New World, there had been, perhaps, total clearance of forests over large portions of North
America. This had led to dramatic changes in productivity of lakes. These changes were recorded
in the chemical stratigraphy of sediments deposited during the last two centuries. Nevertheless,
increased leaching and nutrient loading often lead
to a marked acceleration of productivity. On the
contrary, when this increased leaching occurs in
calcareous regions, there could be high loading of
calcium and carbonates. This could lead to a negative effect on productivity due to carbonate interactions and sedimentation of essential inorganic
and organic nutrients (Wetzel 1970 ).
In addition to the above, the palaeolimnological conditions and productivity of an eutrophic
hard-water lake of southern Michigan were
re-constructed by combined analysis of the sedimentation of organic carbon, nutrients, fossil pigments, pollen and diatoms (Manny et al. 1978 ). It
is believed that algal productivity was low during
the late glacial period (14,075–10, 200 years BP)
under boreal conditions of low temperatures and
competition for nutrients, particularly phosphorus. Phosphorus was co-precipitated with CaCO 3 .
Subsequently, there followed a long period of
relatively constant but slowly increasing productivity from about 10,200 to 5,900 years BP. During
this period, as the climate had ameliorated, the
surrounding vegetation shifted from pine to oak
dominance. Later, from about 5,900 to 140 years
BP, several lines of evidence had indicated a gradual increase in areas suitable for the growth of
submerged littoral macrophytes. This had possibly
continued until littoral productivity had exceeded
with that of the phytoplankton.
12.2 Inorganic Chemistry
man-induced changes in the vegetation and
weathering processes (Likens et al. 1977 ). An
example of the effect of climate on weathering
was demonstrated in some endorheic lakes of
East Africa. Lakes in the humid areas may have
high weathering rates of the drainage basin. They
may receive greater inputs of silica and may be
largely HCO 3 -dominated.
Several attempts have been made to use chemical constituents of the sediments variously in
order to interpret rates of limnological activities
of lakes as well as changes in climate and alterations of the drainage basin. The analysis could be
based on the assumption that the chemical chronology could represent (at least on a long-term
basis) the composite changes in inputs to the lake
in metabolic transformations which had occurred
within the lake. For example, if we compare the
chemical composition of a number of elements
(which could be mostly biologically nonessential) in lake sediments, it could give an
effective evaluation of the chronology of the erosion and rates of leaching. Likewise, comparison
of rocks and soils could also yield similar results.
However, inputs of extremely inert conservative
elements, such as titanium, may allow an evaluation of erosion rates of the lake basins. Other elements may indicate disturbances of drainage
basins depending on the geology of the area. For
example, in Laguna de Petenxil, a small lake in
Guatemala, there had been increase in the sediment concentrations of calcium, strontium, potassium and, to some extent, sodium during periods
of active Mayan agricultural activities in the
drainage basin. Mn, Fe and P followed the fl uctuations of agriculturally determined alkalies and
alkaline earths in an analogous way (Deevey
et al. 1979 ).
Detailed studies had been done on the palaeolimnology of a small, closed lake of volcanic origin in Italy, namely, the Lake Lago di Monterosi.
The results had demonstrated the dramatic effects
of alterations to the catchment area by the construction of a road alongside the lake in early historical times (Hutchinson et al. 1970 ). The lake
was said to be quite productive shortly after its
formation. It had perhaps lasted for a period of
about 2,000 years. This was, probably, related to
easy leaching of materials initially. These materials
were said to be rich in potassium and also had
fairly high phosphorus content.
Notwithstanding the above, sedimentary
records of disturbances in the drainage basin are
quite common, e.g. the productivity of Grosser
Ploner See in Northern Germany was increased
markedly in the early thirteenth century by the
construction of a mill dam. This had raised the
depth of water by a few metres. This had also
fl ooded portions of the surrounding catchment
basin (Ohle 1979 ). In more recent times, in the
New World, there had been, perhaps, total clearance of forests over large portions of North
America. This had led to dramatic changes in productivity of lakes. These changes were recorded
in the chemical stratigraphy of sediments deposited during the last two centuries. Nevertheless,
increased leaching and nutrient loading often lead
to a marked acceleration of productivity. On the
contrary, when this increased leaching occurs in
calcareous regions, there could be high loading of
calcium and carbonates. This could lead to a negative effect on productivity due to carbonate interactions and sedimentation of essential inorganic
and organic nutrients (Wetzel 1970 ).
In addition to the above, the palaeolimnological conditions and productivity of an eutrophic
hard-water lake of southern Michigan were
re-constructed by combined analysis of the sedimentation of organic carbon, nutrients, fossil pigments, pollen and diatoms (Manny et al. 1978 ). It
is believed that algal productivity was low during
the late glacial period (14,075–10, 200 years BP)
under boreal conditions of low temperatures and
competition for nutrients, particularly phosphorus. Phosphorus was co-precipitated with CaCO 3 .
Subsequently, there followed a long period of
relatively constant but slowly increasing productivity from about 10,200 to 5,900 years BP. During
this period, as the climate had ameliorated, the
surrounding vegetation shifted from pine to oak
dominance. Later, from about 5,900 to 140 years
BP, several lines of evidence had indicated a gradual increase in areas suitable for the growth of
submerged littoral macrophytes. This had possibly
continued until littoral productivity had exceeded
with that of the phytoplankton.
12.2 Inorganic Chemistry