Page 21 - Freshwater-Biology-and-Ecology-Handbook

In the past we have managed freshwater using only chemical assessments linked to pollution from
industrial and municipal discharges to the water environment.

Being able to assess water ecosystem health has been the result of significant research and
development over the past 100 years or so.

This was connected to progressive water environmental legislation, regulation and enforcement.

The fundamental principles and links between sewage Increasingly, we realise that chemical indicators alone are
pollution, water chemistry and biological impact are shown insufficient to understand ecosystem health. The damage
in Figure 3, from Hynes’ book The Biology of Polluted Waters that chemicals cause depends on the nature of the
(1960). The understanding of these interactions underlies ecosystem and its sensitivity. This varies according to the
(4)
all our current methodologies, and this figure remains highly nature of the water body and its geography. Untreated
relevant today. waste discharges may be a thing of the past but biological
systems do not fully recover. This is because all water
bodies are subject to combinations of other pressures that
were masked by the impacts of gross pollution. To achieve
true assessments of environmental health, biological and
ecological methods and targets are needed, complementing
chemical and hydrological assessments and targets.
These are used to set permit conditions and to help optimise
the management of discharges, abstractions and other
activities, to meet the ecosystem targets.

River flow and water level has significant impacts on
biological communities and is a key ecological component
of water management. Developing and enforcing minimum
flow conditions to our river systems is one of the most
crucial issues. Minimum flows are often neglected in
developing countries, and rivers that should naturally
have permanent flows may dry up for prolonged periods.
Historically, minimum flows have been set to optimise
and maintain potable, industrial and agricultural water
supply, but increasingly they are linked to biological needs,
expressed through ecological quality objectives.

The most straightforward examples are where flow
regimes are managed to allow migratory fish to move and
ensure connection to upriver spawning grounds. In some
cases, increased flow is maintained for a short time to
allow a ‘freshet’ to stimulate the migration of salmon. This
‘spate sparing’ is common in operating rules for reservoirs.
Increasingly, research into the needs of invertebrates for
amount and speed of water over the riverbed and seasonal
and other natural patterns of flow are enabling improved
outcomes to be achieved.
(a) Represents physical changes
(b) Represents chemical changes
(c) Represents changes in micro-organisms
(d) Represents changes in macro-invertebrates
Figure 3
Showing the effects of an organic effluent on a river and the
downstream changes to the chemistry, micro-organisms and the
invertebrates as the biota metabolises the waste and restores river
quality. Source: Hynes, Biology of Polluted Waters (1960) (4)

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