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Limnological studies of dystrophic waters

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Bowling, LC (1988) Limnological studies of dystrophic waters. PhD thesis, University of Tasmania.

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Abstract

A number of aspects of the limnology of dystrophic lentic
freshwaters are covered in this thesis. Initially, studies covering
a wide range of heterogeneous lakes and reservoirs from several
different areas are reported, to give an overall perspective of many
of the roles dissolved humic substances play in various limnological
processes. More detailed case studies of a number of dystrophic lakes
and reservoirs are then outlined, to demonstrate how dissolved humic
substances actively influence the limnology of these individual waters.
Investigations of the underwater light climates of fifty lakes
and reservoirs fr om Tasmania, thirty-seven from north-east New South Wales, and of twenty-six coastal dune lakes in south-east Queensland
showed that dissolved humic substances were the major attenuators of
light in all three areas. Increasing gilvin concentrations led to
the rapid extinction of light at shallow depths, and to changes in
its underwater spectral distribution from green-yellow in the
clearest waters, to red in the most humic. Turbidity and phytoplankton
were important contributors to attenuation in only a few of the waters
studied. Results from Tasmania allowed the construction of a
predictive model for use in estimating the underwater light climates
of the many remote lakes of the island where in situ measurements are
impossible, from simple laboratory measurements of small water samples.
The rapid attenuation of light in humic waters also strongly affects
thermal stratification, leading to strong thermal gradients, shallow
thermoclines, and lengthy periods of stratification.
Chemical aspects were also examined. Strong negative correlations
were found between the concentration of dissolved humic substances and
pH in coastal dune lake waters from south-east Queensland, King and
Fl inders I s l and s , and we s tern and south-wes t Tasmania.In contrast,
there was no correlation between these two parameters in north-east
New South Wales waters, probably due to lower humic concentrations
and buffering by higher bicarbonate levels . Calcium and bicarbonate
levels were also some times low in acidic, dystrophic lakes.
A wide range of photo synthetic organisms were present in the sites
investigated from New South Wales, Queensland, and coastal lakes of
south-west Tasmania. Phytoplankton came both from the Chlorophyceae
and from other algal divisions, and desmids and dinoflagellates were e specially common. Proportions of green algae decreased relative
to those with accessory photosynthetic pigments, as humic concentration
increased, in the highly humic western and south-west Tasmanian lagoons,
but this was not apparent in the less dystrophic waters of the other
two areas. However, high humic concentrations reduced the number of
phytoplankton genera present from all groups. Chrysophytes dominated
the phytoplankton communities of polyhumic Lake Chisholm.
Studies of Lake Chisholm, the reservoirs of the Pieman River
Power Development, and the meronictic lakes of the lower Gordon River,
all in Tasmania, showed humic materials played an important role in
their limnology. The rapid attenuation of light, and subsequent
strong thermal stratification for much of the year lead to sluggish
circulation, all owing near-meromictic conditions in Lake Chisholm,
and the protection and resultant slowing of the demise of ectogenic
meromixis in the Gordon River lakes. These features, along with
enhancing the solubility of iron and manganese in the reducing,
sulphide laden bottom waters of the Pieman River reservoirs, enabled
their chemical stratification. However, other factors, such as basin
morphometry and shelter, are also of importance in the limnology of
these lakes and reservoirs.

Item Type: Thesis (PhD)
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Date Deposited: 19 May 2014 05:27
Last Modified: 15 Sep 2017 01:06
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