Aquatic Habitats In Sustainable Urban Water Management

Aquatic habitat rehabilitation: Goals, constraints and techniques 73
TYPE I ERROR (a)
Indicator variance
metric indicates
impact when no
impact occurs
moderate error
TYPE II ERROR (b)
metric indicates
impact when it
occurs
Phytoplankton
Zooplankton
Macroinvertebrates
Macrophytes
power to detect change
Fish
Figure 5.1 Bioassessment: A conceptual model presenting errors assessment for different indicator
groups
Sources: Lapińska, 2004; Johnson 2001.
A type I error (α) is made in testing an hypothesis when it is concluded that a result is positive when it really is not,
while a type II error (β), when it is concluded that something is negative when it really is positive.
that some groups are effective as early indicators, while others are effective as late-warning
indicators, and their effectiveness depends on the type of stressor. Thus the selection of
complementary early- and late-warning indicator groups increases the probability of
detecting an impact if it occurs, and hence has become a common practice. For example,
macrophytes, which have low seasonal variability but exhibit slow changes in the community
structure, are useless as an early warning indicator. But, for the same reason, when
change is detected in the macrophyte species composition, then the probability of no
impact occurrence is low (Johnson, 2001). A highly variable phytoplankton community
and the periphyton group are excellent indicators of nutrient enrichment, as they tend to
respond very rapidly to changes in the water trophic state. Response from macro invertebrates
is not that rapid, but they are more sensitive to habitat characteristics (also more
habitat-bound) and to long-term trophic changes. Statistically, the most accurate fish indicators
are not useful in the case of nutrient enrichment incidents, but they are the most
appropriate if the ecosystem stressor is temperature or chemical contaminant.
There are three main methodological approaches used for riverine quality
bioassessment:
●
A single metric approach based on a single parameter from an indicator group; for
example, species richness, density of individuals, similarity or diversity of communities
(Saprobic index, Trent Biotic Index, the Danish Stream Fauna Index, the
Belgian Biotic Index, the Extended Biotic Index)