A review of methods used to measure biomass and production of pelagic microbiota
in freshwaters and a study of the phytoplankton community in Lake Eckarfjärden.
By Danishta Dumur
Freshwater reservoirs can have several roles, the most common ones being the
supply of water for the generation of electrical power, the supply of water for drinking
and domestic use as well as recreation. The pre-requisite to carry out most of those roles
properly is the availability of ‘clean’ water, characterised by the absence of pollutants and
human dumpings. Frequent monitoring of such aquatic systems is an effective way to
prevent pollution.
Although pollution by the dumping in of garbage may be visible to the eye, the
effects of pollutants are hard to ‘see’ and thus, the monitoring system requires chemical
analysis of water parameters. Besides routine analyses of water chemistry, it is equally
important to monitor the rate and extent of ongoing biological processes within the
system. This is because productivity of a lake is better reflected by the biological quality
status rather than chemical data. One group of organisms targetted for monitoring the
health of aquatic systems is the free-floating microorganisms, which are commonly
known as plankton.
In freshwater lakes, it is very common to measure the abundance and production
of the phytoplankton (microscopic plants). There can be different species of
phytoplankton, which vary both in size and shape. Phytoplankton are important
biological indicators because they respond quickly to changes in water quality. They are
also a source of food for higher organisms including fish, such that a high biomass of
edible phytoplankton can contribute to a high abundance of fish in the same system.
However, the relationship among the organisms within ecosystems, as complex as
freshwaters, is not a simple one. The lake ecosystem is highly dynamic, where changes
are occuring fast and where the productivity of one particular organism depends on the
fate of another, such that studying all the inter-relationships would be impossible.
Bacterioplankton and phytoplankton constitute the basis of the pelagic food web upon
which all higher biota rely. Bacterioplankton are smaller organisms that have been shown
to be as equally important as phytoplankton in the lake system especially when it
concerns re-mineralisation of nutrients into a previously nutrient-deficient system.
In the determination of biomass and production of pelagic microbiota, different
methods have been applied. However, this review aimed at elaborating on only the most
common ones. Special emphasis has been laid on those methods that are thought to be
well-adapted in a system such as a tropical reservoir, which is expected to present
different chemical and biological characteristics in comparison to the north temperate
lakes, with respect to its geographical location. The performance of the methods in the
reservoirs is necessary, given the importance of reservoirs in the tropics. In order to
ensure a safe distribution to a population, the current monitoring system, requires to
include biological parameters too. The study provides a set of reliable and cost-effective
methods that can contribute to enhancing the monitoring system and thus improve water
quality standards.
Undergraduate thesis in Biology 10 p, autumn 2002
Department of Limnology, Uppsala University
Supervisors: Peter Blomqvist, Anna-Kristina Brunberg and Eva Nilsson