Complementarity between two metrics which use invertebrates to assess riparian conditions of rivers.
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Date
2005
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Abstract
Conservation of streams involves an understanding of their physical , chemical and
biological entities. SASS5 is a biomonitoring method developed to monitor the habitat
quality of a water body. It is based on differential scores attributed to various
macroinvertebrate families with varying degrees of sensitivity to anthropogenic impact.
This method , however, does not assess impacts on particular species.
Odonata are good candidates for study at the species level as they are well researched and
males are easily identified . As adults, they are known to be sensitive indicators of both
riparian and river conditions. Yet Odonata cannot be an umbrella taxon for all other taxa .
Therefore, the main aim of this study is to determine the complementarity of the two
metrics (Odonata assemblages and SASS5), establishing whether Odonata assemblages
offer additional information on, or insight into, riverine habitat quality as portrayed by
SASS5.
To accomplish this, certain objectives were addressed . 1) The variation of SASS5 scores
and 2) Odonata assemblages between river systems, structural habitat types (open or
closed canopies) and compositional habitat types (indigenous or alien vegetation). 3)
Whether SASS5 scores vary to the same extent, and, 4) on the same spatial scale (river
system and point localities) as Odonata abundance and species richness .
The relationship between these two metrics was determined along three rivers in the
Pietermaritzburg basin. Sampling units (SUs) with extremes in vegetation structure
(sunlight and shaded SUs) and vegetation composition (alien or indigenous) were
selected. Using this range of environmental conditions placed environmental extremes
on the macroinvertebrate populations at point localities and having three different river
systems added the dimension of variation over a broader scale, thus stretching the two
metrics to investigate whether both responded similarly or in different ways.
Results indicated that both metrics provide a similar portrait of overall river conditions.
At the smaller spatial scale, the Odonata assemblage, unlike SASS, was highly sensitive
to the riparian vegetation. Odonata species were less sensitive to vegetation composition
but differentially sensitive to vegetation structure. However, landscape context is also
important, with point localities being affected by the neighboring dominant habitat type.
Larval Odonata alone did not provide this information. Overall, aquatic
macroinvertebrates and adult Odonata provide a highly complementary pair of metrics
that together provide large spatial scale (river system) and small spatial scale (point
localities) information on the level of impact of stressors such as riparian invasive alien
trees.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
Keywords
Riparian ecology--KwaZulu-Natal., Odonata--Habitat., Stream ecology--KwaZulu-Natal., Invertebrates--KwaZulu-Natal--Ecology., Theses--Zoology.