25.6 Variability and Ecosystem Dynamics in Assessments
corporated with multivariate spatial analysis of
channel morphometry. We should realize that channel classifications based primarily on morphology
are limited because the relations to processes are
not clearly defined. This impedes our need to understand particular process relations as they pertain
to channel change or evolution, particularly in the
context of local and upstream constraints. More
evolutionary, process-based models of channel
change have been developed for specific regional
conditions (Simon, 1994; Downs, 1995). These
specific process-based types of classifications
would be a natural extension for regional assessments and recovery plans. The concept of sensitivity to disturbance, recovery, and types and direction of channel change can be incorporated into
classifications by including the factors discussed
previously that constrain channel morphology and
dynamics, such as climate, bedrock, bank materials, and valley-floodplain morphology (Downs and
Gregory, 1993; see Figure 25.5).
Classic channel developmental models in alluvial lowland streams emphasize planform development from straight to more stable meandering
forms (Keller, 1972). In steeper upland streams, energy dissipation and channel adjustment is often
in a vertical dimension, which is well summarized
by Montgomery and Buffington (1993). Beschta
(1981) presents a model of channel response to increased sediment load for gravel streams of less
than 5% slope, which results in increased width and
reduction of pools as exemplified in streams in California (Lisle, 1982). Various land-use practices in
the stream corridor affect processes and channel
degradation (Galay, 1983). Multivariate techniques
are useful to elucidate the complexity of these various land-use impacts on streams and threshold response of channel change. (Touysinhthiphonexaym
and Gardner, 1984; Wood-Smith and Buffington,
1996).
The processes and features that influence aquatic
systems and channel form and dynamics vary with
position within the landscape and stream network
and with watershed, lake, or channel size. Methods, models, and interpretation in assessments must
account for these spatial changes. For example,
progressive change in a downstream direction is a
dimension of variability unique to stream systems
that confounds within- and between-stream comparisons and the influence of terrestrial impacts on
the stream. To account for this functional change
with increasing size, stream assessments need to be
scaled to watershed size or discharge (Hughes and
Omernick, 1983) and by stratifying stream segments by position both within the basin and the
381
landscape (geoclimatic setting) (Maxwell et aI.,
1995).
The generalized, coarse-level resolution of
downstream change in channel size, morphology,
discharge, sediment characteristics, longitudinal
profile shape, and physical and biotic processes is
reflected in various conceptual models. Schumm
(1977) simplifies the function of watershed processes as three zones of sediment supply, transport,
and deposition. This watershed zonation is also
linked with channel processes and channel classification (Montgomery and Buffington, 1997) and
the river continuum concept of downstream change
in stream-riparian connection, retention, and biotic
composition and processes (Vannote et al., 1980;
Petts and Foster, 1985). We also need to scale the
relative function and effect of landscape features
and processes to watershed size. For example, the
influence and function of wood boles (Bilby and
Ward, 1989; Ralph et aI., 1994) and the persistence
and impact of hillslope processes (Swanson et aI.,
1985) are related to stream discharge and stream
power. Channel features that affect habitat formation are often scaled to the size of the channel
(Lisle, 1986), as are channel patterns such as pool
spacing and meander wavelengths. Likewise, geomorphic "reach" dimensions used in assessments
can be scaled by channel widths (length-channel
width, valley width-channel width).
25.6.1 Climate and Ecosystem Dynamics
Because hydrodynamics are a major driving force
in aquatic systems (Legendre and Demers, 1984),
it is imperative that we place ecological assessments and restoration strategies in both geographic
and temporal contexts of multiscaled climate
change and ecosystem dynamics. Climatic fluctuations drive various aspects of ecosystem dynamics, such as semicyclic patterns of drought and variation of streamflow, fire and erosion cycles, and
temperature regimes (Currie, 1984; Ebbesmeyer et
aI., 1991). Scientists have recently recognized interdecadal climate change (20- to 30-year cycles)
that is a coarse-scale driver of ecosystem dynamics. This scale provides an illumination of how lifehistory strategies and regional fish productivity are
related to long-term fluctuations in climate and
ocean conditions (Hare et aI., 1999). Various climatic fluctuations also affect fish production by
controlling storm events and bed scour, streamflow
timing, and volume, which in tum affect survival,
rearing, and both upstream and downstream migration of fish (Pultwarty and Redmond, 1997).
El Nino-La Nina (ENSO, 2- to 7-year cycles)
corporated with multivariate spatial analysis of
channel morphometry. We should realize that channel classifications based primarily on morphology
are limited because the relations to processes are
not clearly defined. This impedes our need to understand particular process relations as they pertain
to channel change or evolution, particularly in the
context of local and upstream constraints. More
evolutionary, process-based models of channel
change have been developed for specific regional
conditions (Simon, 1994; Downs, 1995). These
specific process-based types of classifications
would be a natural extension for regional assessments and recovery plans. The concept of sensitivity to disturbance, recovery, and types and direction of channel change can be incorporated into
classifications by including the factors discussed
previously that constrain channel morphology and
dynamics, such as climate, bedrock, bank materials, and valley-floodplain morphology (Downs and
Gregory, 1993; see Figure 25.5).
Classic channel developmental models in alluvial lowland streams emphasize planform development from straight to more stable meandering
forms (Keller, 1972). In steeper upland streams, energy dissipation and channel adjustment is often
in a vertical dimension, which is well summarized
by Montgomery and Buffington (1993). Beschta
(1981) presents a model of channel response to increased sediment load for gravel streams of less
than 5% slope, which results in increased width and
reduction of pools as exemplified in streams in California (Lisle, 1982). Various land-use practices in
the stream corridor affect processes and channel
degradation (Galay, 1983). Multivariate techniques
are useful to elucidate the complexity of these various land-use impacts on streams and threshold response of channel change. (Touysinhthiphonexaym
and Gardner, 1984; Wood-Smith and Buffington,
1996).
The processes and features that influence aquatic
systems and channel form and dynamics vary with
position within the landscape and stream network
and with watershed, lake, or channel size. Methods, models, and interpretation in assessments must
account for these spatial changes. For example,
progressive change in a downstream direction is a
dimension of variability unique to stream systems
that confounds within- and between-stream comparisons and the influence of terrestrial impacts on
the stream. To account for this functional change
with increasing size, stream assessments need to be
scaled to watershed size or discharge (Hughes and
Omernick, 1983) and by stratifying stream segments by position both within the basin and the
381
landscape (geoclimatic setting) (Maxwell et aI.,
1995).
The generalized, coarse-level resolution of
downstream change in channel size, morphology,
discharge, sediment characteristics, longitudinal
profile shape, and physical and biotic processes is
reflected in various conceptual models. Schumm
(1977) simplifies the function of watershed processes as three zones of sediment supply, transport,
and deposition. This watershed zonation is also
linked with channel processes and channel classification (Montgomery and Buffington, 1997) and
the river continuum concept of downstream change
in stream-riparian connection, retention, and biotic
composition and processes (Vannote et al., 1980;
Petts and Foster, 1985). We also need to scale the
relative function and effect of landscape features
and processes to watershed size. For example, the
influence and function of wood boles (Bilby and
Ward, 1989; Ralph et aI., 1994) and the persistence
and impact of hillslope processes (Swanson et aI.,
1985) are related to stream discharge and stream
power. Channel features that affect habitat formation are often scaled to the size of the channel
(Lisle, 1986), as are channel patterns such as pool
spacing and meander wavelengths. Likewise, geomorphic "reach" dimensions used in assessments
can be scaled by channel widths (length-channel
width, valley width-channel width).
25.6.1 Climate and Ecosystem Dynamics
Because hydrodynamics are a major driving force
in aquatic systems (Legendre and Demers, 1984),
it is imperative that we place ecological assessments and restoration strategies in both geographic
and temporal contexts of multiscaled climate
change and ecosystem dynamics. Climatic fluctuations drive various aspects of ecosystem dynamics, such as semicyclic patterns of drought and variation of streamflow, fire and erosion cycles, and
temperature regimes (Currie, 1984; Ebbesmeyer et
aI., 1991). Scientists have recently recognized interdecadal climate change (20- to 30-year cycles)
that is a coarse-scale driver of ecosystem dynamics. This scale provides an illumination of how lifehistory strategies and regional fish productivity are
related to long-term fluctuations in climate and
ocean conditions (Hare et aI., 1999). Various climatic fluctuations also affect fish production by
controlling storm events and bed scour, streamflow
timing, and volume, which in tum affect survival,
rearing, and both upstream and downstream migration of fish (Pultwarty and Redmond, 1997).
El Nino-La Nina (ENSO, 2- to 7-year cycles)