River Ecology and Restoration - River Dynamics and Integrated River Management - page 681

The complexity of these methods varies along a number of important dimensions, including prediction
of habitat suitability versus population numbers, analysis for a single place and single time versus a
temporal sequence of spatially complex requirements, and analysis for a single target species versus a set
of target species involving tradeoffs. Each of these dimensions must be carefully considered in selecting
an analysis procedure appropriate to the problem at hand.

10.3.4 Habitat Evaluation and Modeling

10.3.4.1 Habitat Diversity
Habitat evaluation is an important aspect of bioassessment. Habitat has a definable carrying capacity, or
suitability, to support or produce wildlife populations (Fretwell and Lucas, 1970). The capacity depends,
to a great extent, on the habitat diversity. A habitat diversity index is needed to represent this characteristic.
The physical conditions of stream habitat are mainly (1) the substrate; (2) water depth; and (3) flow
velocity (Gorman and Karr, 1978). Different physical conditions support different bio-communities and
diversified physical conditions may support diversified bio-communities. A habitat diversity index, H D , is
proposed as follows (Wang et al., 2009):

¦

HNN D (10.12)

D hv i

i

where N h and N v are numbers for water depth diversity and velocity diversity, and D is the substrate
diversity, which is different for different substrates. For water depth less than 0.1 m the habitat is
colonized by species that like high concentrations of dissolved oxygen and plenty of light. For water
depth larger than 0.5 m the habitat is colonized by species that like low light and dissolved oxygen. Many
species may live in water with depths between 0.1-0.5 m. If a stream has three water areas: (1) shallow
water, in which the water depth is in the range of 0-0.1 m; (2) mid depth water, in which the water depth
is in the range of 0.1-0.5 m; and (3) deep water, in which water depth is larger than 0.5 m, and each of the
three areas is larger than 10% of the stream water surface area, N h 3. If a stream has only shallow water
and mid-depth water, and each of them is larger than 10% of the stream water surface area, N h 2. The
value of N h for other cases can be analogously obtained. For flow velocity less than 0.3 m/s the habitat is
colonized by species that swim slowly. For velocity higher than 1 m/s the habitat is colonized by species
that like high velocities. Many species live in the current between 0.3-1 m/s. If a stream has three water
areas: (1) lentic area, in which the flow velocity is smaller than 0.3 m/s; (2) mid-velocity area, in which the
flow velocity is in the range of 0.3-1 m/s; and (3) lotic area, in which the velocity is larger than 1 m/s,
and each of the three areas is larger than 10% of the stream water surface area, N v 3. If a stream has only
lentic and mid-velocity areas, and each of them is larger than 10% of stream water, N v 2. The value of
N v for other cases can be analogously obtained.
The selection of the critical values of water depth and velocity are determined by studying the habits
of species, mainly of macro-invertebrates. It is found from field investigations that in the Yangtze River
basin some species in the water depth between 0.1-0.5 m are different from those in shallower or deeper
water. Similarly, some species living in the current range of 0.3-1 m/s are different from those in currents
lower than 0.3 m/s or higher than 1 m/s. Beauger et al. (2006) reported that the highest species richness
and density were found in various substrates where the velocity ranged between 0.3 and 1.2 m/s, and
depths ranged from 0.16 to 0.5 m. Below 0.3 m/s the riverbed tends to be filled and not very productive,
whereas above 1.2 m/s the current velocity acts as a constraint for most living material. Undoubtedly, at
lower depths, vegetation and animals are disturbed by light, conversely at higher depths in which the
primary productivity decreases, the bio-community is disturbed due to light attenuation. At lower and
higher depths and velocities, only those species tolerant to the constraints may colonize the habitat.