Environmental Engineering Reference
In-Depth Information
1
Introduction to Freshwater Algae
1.1 General introduction
photosynthetic - generating complex carbon com-
pounds from carbon dioxide and light energy. Some
algae have become secondarily heterotrophic, taking
up complex organic molecules by organotrophy or
heterotrophy (Tuchman, 1996), but still retaining fun-
damental genetic affinities with their photosynthetic
relatives (Pfandl et al., 2009).
The term 'algae' (singular alga) is not strictly a
taxonomic term but is used as an inclusive label
for a number of different phyla that fit the broad
description noted earlier. These organisms include
both prokaryotes (cells lacking a membrane-bound
nucleus; see Section 1.3) and eukaryotes (cells with
a nucleus plus typical membrane-bound organelles).
Humans have long made use of algal species, both
living and dead. Fossil algal diatomite deposits, for
example, in the form of light but strong rocks, have
been used as building materials and iltration media in
water purification and swimming pools. Some fossil
algae, for example Botryococcus , can give rise to oil-
rich deposits. Certain species of green algae are culti-
vated for the purpose of extracting key biochemicals
for use in medicine and cosmetics. Even blue-green
algae have beneficial uses. Particularly, Spirulina ,
which was harvested by the Aztecs of Mexico, is still
used by the people around Lake Chad as a dietary
supplement. Spirulina tablets may still be obtained in
some health food shops. Blue-green algae are, how-
ever, better known in the freshwater environment as
nuisance organisms, forming dense blooms. These
can have adverse effects in relation to toxin build-up
Algae are widely present in freshwater environments,
such as lakes and rivers, where they are typically
present as microorganisms - visible only with the aid
of a light microscope. Although relatively inconspic-
uous, they have a major importance in the freshwater
environment, both in terms of fundamental ecology
and in relation to human use of natural resources.
This topic considers the diversity of algae in fresh-
water environments and gives a general overview
of the major groups of these organisms (Chapter
1), methods of collection and enumeration (Chap-
ter 2) and keys to algal groups and major genera
(Chapter 4). Algae are considered as indicators of
environmental conditions (bioindicators) in terms of
individual species (Chapter 1) and as communities
(Chapter 3).
1.1.1 Algae - an overview
The word 'algae' originates from the Latin word for
seaweed and is now applied to a broad assemblage
of organisms that can be defined both in terms of
morphology and general physiology. They are simple
organisms, without differentiation into roots, stems
and leaves - and their sexual organs are not enclosed
within protective coverings. In terms of physiol-
ogy, they are fundamentally autotrophic (obtain-
ing all their materials from inorganic sources) and
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