Environmental Engineering Reference
In-Depth Information
Streambeds consisting of cobbles and boulders are very stable and provide the benthic macro-
invertebrates diversified living spaces. Therefore, cobbles and boulders are associated with high habitat
diversity. Stream flow over aquatic grasses has high velocity but the aquatic grasses generate a low velocity
canopy, moreover, the aquatic grasses themselves are also habitat for some species. Thus, streams with
aquatic grasses exhibit high habitat diversity. Some species may move and live within the fluid mud layer
and consume the organic materials in the mud layer. The interstices in a fine gravel bed are small but
sufficient for some species. A sand bed is compact and the interstices between sand particles are too
small for big benthic macro-invertebrates to move and live within them. If sand particles are moving as
bed load the bed provides no stable habitat for animals. Therefore, moving sand is the worst habitat for
benthic macroinvertebrates. Based on this discussion and field investigations of 16 streams, the D-values
for various substrates are listed in Table 10.7. It is well known that large woody debris can substantially
contribute to habitat quality in streams (Gippel, 1995; Abbe and Montgomery, 1996), and, thus, a more
generally applicable listing of D-values should also include a value for stream substrates with large woody
debris. However, large woody debris does not often occur in Chinese streams, therefore, a rating for large
woody debris has not been determined and is not listed in Table 10.7.
T able 10.7 Substrate diversity, D , values for different substrates (after Wang et al., 2009)
Boulders and
cobbles
(D>200 mm)
Aquatic
grass
Gravel
(2-200 mm)
Fluid clay mud
(D<0.02mm)
Silt (0.02
-0.2 mm)
Sand
(0.2-2 mm)
Unstable sand,
gravel, and silt
bed (0.02-20 mm)
Substrate
D
6
5
4
3
2
1
0
If a part of the streambed consists of one substrate and another part consists of the another substrate
and both parts have areas larger than one tenth of the stream surface, the two D-values for the two kinds of
substrates should be summed. However, if sand or silt fills the interstices of gravel the D-value should be
taken as for the substrate of sand or silt. If a streambed has three parts with different substrates: boulders
and cobbles, aquatic grasses, and fluid clay mud, and each of the three parts is larger than one tenth of
the total stream area, the sum of the D-values for the stream is
¦
D
65314
. If the streambed is
i
i
¦
covered by moving sand and gravel or the bed is very unstable,
.
D
0
i
i
Gorman and Karr (1978) also developed a Habitat Diversity Index combining the effects of substrate,
velocity, and depth. They showed that fish species diversity and richness were strongly related to a
combination of the effects of substrate, velocity, and depth. Their substrate classification is similar to that
proposed here with the main differences being in the divisions of sediment sizes into the various classes,
but a similar ordinal ranking is applied to the substrate material. They also developed class ranges for
velocity and depth throughout a reach determined by a weighting of point measurements. The index
applied here takes a simpler approach to considering the diversity of velocity and depth.
The biodiversity of streams depends not only on the physical conditions but also is affected by food
availability and water quality. Food availability is very different for different species and should be
studied separately. Generally speaking, water pollution reduces the number of species but may not reduce
the density of pollution-tolerant species. Water quality is not an inherent feature of a habitat and depends
on human disturbances. Therefore, water quality is not taken in the habitat diversity index. Water
temperature also is an important factor for stream ecology. However, the temperature does not vary much
in a reach of a stream unless a thermal discharge is present and it is not necessary to consider it in the
analysis of local habitat diversity. When habitat across different zones with great temperature differences
is studied, then temperature difference has to be considered in the analysis.
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