382
Geomorphic Patterns, Processes, and Perspectives in Aquatic Assessment
are well recognized shorter-term climatic patterns
that influence hydrodynamics through regional
flood frequency relations (Webb and Betancourt,
1990). Extreme flood events are temporally clustered around ENSO events (Hirschboeck, 1987).
Periodicity of fire and associated erosion and patterns of sediment production also are driven by
ENSO events (Swetnam and Betancourt, 1990;
Meyer et al., 1995). Such semicyclic variability in
magnitude of precipitation, peak flow events, and
fire regimes results in alternating periods of quiescent erosion and clustering of mass wasting events,
creating a punctuated sediment delivery and transport regime (Benda et aI., 1998). Climatic induced
lake mixing also is responsible for temporal patterns of productivity and clarity in oligotrophic
lakes (Goldman et aI., 1989).
Assessments must also recognize that these climatic fluctuations and consequent processes, such
as streamflow dynamics, vary regionally and can
even produce opposite effects in different regions.
For example, regional differences in drought conditions are identified in the western United States
(Rogers and Armbruster, 1990), and in ENSOrelated streamflow variability for the entire United
States (Piechota and Dracup, 1996) and for the
western states (Redmond and Koch, 1991). Recognition of these geographic and temporal differences
is important for planning, interpretation, and comparison of interregional assessments. This is especially critical for assessments of large-scale watersheds that integrate regional differences of climatic
and hydrologic variability (Pultwarty and Redmond, 1997; Quigley and Arbelbide, 1997).
Seasonal climate development drives annual
variability in aquatic ecosystems. Lake dynamics
are characterized by seasonal patterns of thermocline stratification, water column stability, and mixing; the latter is considered the "master variable"
in seasonal development of biotic processes in deep
lakes (Sommer, 1985). Lake mixing and hydrodynamic character are key factors in lake classifications, which display regional distributional patterns
(Winter, 1977; Lewis, 1983). For streams, annual
variability and stability are characterized by the annual flow regime: the timing, stability, and persistence of base flows and the timing, variability, and
magnitude of high flows. This is illustrated by fish
distribution and habitat use variability along with
regional differences in flow development. For instance, in Pacific coastal streams, high water occurs in winter, and important overwintering areas
are areas of flow diversity or slower velocity, such
as off-channel habitats (backwaters and side channels). In colder climates with snow and ice cover,
there is a seasonal winter low flow, and juvenile
fish use ice-free areas and interstitial spaces in the
channel bed as refugia.
25.7 Conclusions
Any aquatic ecosystem assessment and restoration
strategy must be placed in the context of the multiscaled dynamics of the system and the geoclimatic
templates that constrain process dynamics, habitat
composition, and evolutionary life-history strategies. Coarse-scale geologic and climatic evolutionary processes enhance our understanding of
both patterns in the landscape and the distribution
and adaptation of biota relative to fluvial landscape
variability. Basin-level processes consist of delivery and routing of water and sediment (and other
materials) to the channel. Both sediment and hydrodynamics are interconnected and influenced by
climate, vegetation, watershed morphology, soils,
and geology. The geomorphic function of a watershed is to transport sediment and water delivered
to it by climatic and hillslope erosional processes.
In this sense, processes such as erosion and floods
are a natural function of the watershed. In a natural
setting, they create a balance between perturbation
and creation of habitat and are an important component of the disturbance regime or process dynamics of a watershed (Reeves et al., 1995; Benda
et al., 1998). Although the concept of disturbance
is becoming well established as a key to understanding both terrestrial and aquatic ecosystems,
disturbance has a negative connotation (Schroeder
and Savonen, 1997). Thus disturbance may be best
considered as the natural process dynamics of a system that organisms have adapted to in the context
of evolutionary life-history strategies. We can improve management through understanding the inherent variability of populations and their ecosystems in the context of process dynamics and the
strategies and diversity of life histories.
To understand ecosystem properties and management actions in the context of natural processes
and variability, we need to formalize the climatic
and geologic characteristics that influence thresholds, resiliency to disturbance, rates and pathways
of recovery, and complex process-response systems of watersheds. Formalized geoclimatic or biophysical settings in a hierarchical, integrated terrestrial-watershed classification framework will
greatly aid interpretation of landscape patterns and
processes. By providing a common framework for
communication, coordination, and information
management, classifications would increase effi-
Geomorphic Patterns, Processes, and Perspectives in Aquatic Assessment
are well recognized shorter-term climatic patterns
that influence hydrodynamics through regional
flood frequency relations (Webb and Betancourt,
1990). Extreme flood events are temporally clustered around ENSO events (Hirschboeck, 1987).
Periodicity of fire and associated erosion and patterns of sediment production also are driven by
ENSO events (Swetnam and Betancourt, 1990;
Meyer et al., 1995). Such semicyclic variability in
magnitude of precipitation, peak flow events, and
fire regimes results in alternating periods of quiescent erosion and clustering of mass wasting events,
creating a punctuated sediment delivery and transport regime (Benda et aI., 1998). Climatic induced
lake mixing also is responsible for temporal patterns of productivity and clarity in oligotrophic
lakes (Goldman et aI., 1989).
Assessments must also recognize that these climatic fluctuations and consequent processes, such
as streamflow dynamics, vary regionally and can
even produce opposite effects in different regions.
For example, regional differences in drought conditions are identified in the western United States
(Rogers and Armbruster, 1990), and in ENSOrelated streamflow variability for the entire United
States (Piechota and Dracup, 1996) and for the
western states (Redmond and Koch, 1991). Recognition of these geographic and temporal differences
is important for planning, interpretation, and comparison of interregional assessments. This is especially critical for assessments of large-scale watersheds that integrate regional differences of climatic
and hydrologic variability (Pultwarty and Redmond, 1997; Quigley and Arbelbide, 1997).
Seasonal climate development drives annual
variability in aquatic ecosystems. Lake dynamics
are characterized by seasonal patterns of thermocline stratification, water column stability, and mixing; the latter is considered the "master variable"
in seasonal development of biotic processes in deep
lakes (Sommer, 1985). Lake mixing and hydrodynamic character are key factors in lake classifications, which display regional distributional patterns
(Winter, 1977; Lewis, 1983). For streams, annual
variability and stability are characterized by the annual flow regime: the timing, stability, and persistence of base flows and the timing, variability, and
magnitude of high flows. This is illustrated by fish
distribution and habitat use variability along with
regional differences in flow development. For instance, in Pacific coastal streams, high water occurs in winter, and important overwintering areas
are areas of flow diversity or slower velocity, such
as off-channel habitats (backwaters and side channels). In colder climates with snow and ice cover,
there is a seasonal winter low flow, and juvenile
fish use ice-free areas and interstitial spaces in the
channel bed as refugia.
25.7 Conclusions
Any aquatic ecosystem assessment and restoration
strategy must be placed in the context of the multiscaled dynamics of the system and the geoclimatic
templates that constrain process dynamics, habitat
composition, and evolutionary life-history strategies. Coarse-scale geologic and climatic evolutionary processes enhance our understanding of
both patterns in the landscape and the distribution
and adaptation of biota relative to fluvial landscape
variability. Basin-level processes consist of delivery and routing of water and sediment (and other
materials) to the channel. Both sediment and hydrodynamics are interconnected and influenced by
climate, vegetation, watershed morphology, soils,
and geology. The geomorphic function of a watershed is to transport sediment and water delivered
to it by climatic and hillslope erosional processes.
In this sense, processes such as erosion and floods
are a natural function of the watershed. In a natural
setting, they create a balance between perturbation
and creation of habitat and are an important component of the disturbance regime or process dynamics of a watershed (Reeves et al., 1995; Benda
et al., 1998). Although the concept of disturbance
is becoming well established as a key to understanding both terrestrial and aquatic ecosystems,
disturbance has a negative connotation (Schroeder
and Savonen, 1997). Thus disturbance may be best
considered as the natural process dynamics of a system that organisms have adapted to in the context
of evolutionary life-history strategies. We can improve management through understanding the inherent variability of populations and their ecosystems in the context of process dynamics and the
strategies and diversity of life histories.
To understand ecosystem properties and management actions in the context of natural processes
and variability, we need to formalize the climatic
and geologic characteristics that influence thresholds, resiliency to disturbance, rates and pathways
of recovery, and complex process-response systems of watersheds. Formalized geoclimatic or biophysical settings in a hierarchical, integrated terrestrial-watershed classification framework will
greatly aid interpretation of landscape patterns and
processes. By providing a common framework for
communication, coordination, and information
management, classifications would increase effi-