25.4 Hydrological Processes
can link evolutionary attributes of organisms, such
as life-history adaptation, to processes and the dynamic nature of aquatic systems (Southwood, 1977;
Poff and Ward, 1990). In this respect, persistence,
stability, and predictability are important concepts
that can link life-history and habitat attributes with
processes of hydrodynamics and sediment transport. A major contribution in our understanding of
coarse-scale ecosystem dynamics is how geomorphic perspectives of landscape evolution and behavior lend an essential time perspective to landscape patterns and processes (Swanson, 1979;
Thomes, 1983). Although often overlooked in assessments, behavior is considered an important dynamic property of ecosystems (Allen and Starr,
1982). In aquatic systems, behavior is the dynamic
result of the collective, interactive operation of climatic, hydrological, and erosional processes.
25.3 Geologic Processes
Analysis of aquatic landscape patterns must focus
on more than surface processes and vegetation dynamics and is best considered in context of landscape origin and development. Large-scale climatic
and geologic processes form the landscape patterns
on which contemporary processes operate. To better understand landscape variability and the controlling factors on aquatic ecosystem composition
and dynamics, we must recognize and formalize
these geologic patterns as geomorphic or geoclimatic templates. Geologic processes, primarily tectonics and vulcanism, act as endogenous energy inputs, which are reflected in patterns of channel
networks and landform relief (Tricart, 1974). In
tum, landform relief influences potential energy of
aquatic systems as expressed in watershed morphology and stream profile relief (Morisawa,
1985). Regional landform developmental processes
and resultant properties impart a particular character to regions (Coates, 1974; Hack, 1982). Such
processes and features include tectonic uplift and
faulting, isostatic release and pluton development,
lithology, stratigraphy and structural deformation,
and Pleistocene glacial processes. Our knowledge
of these processes provides predictive and explanatory power of the spatial distribution and compositional properties of watershed, stream, and biotic patterns. For example, Pleistocene glacial
processes form different landscapes with variable
hydrologic and habitat conditions, which explains
corresponding distribution of salmonids (Benda et
aI., 1992) and bivalves (mussels) (Strayer, 1983).
We also need to consider coarse-scale fish distri369
bution in the evolutionary context of geologic
processes such as tectonics and watershed evolution (Minckley et aI., 1986).
We cannot adequately interpret aquatic patterns
without considering that watersheds have evolved
with and adjusted to different geologic processes
and erosional regimes. In this respect, both basin
and channel patterns reflect climate and landform
evolution since the Quaternary period (Petts and
Foster, 1985). Differences in bedrock and surficial
lithology, in the context of basin and channel evolution, help frame explanation of within-region differences in watershed properties (Cunha et aI.,
1975; Kowall, 1976; Miller and Ritter, 1990) and
contemporary variation in channel characteristics
(Hack, 1965; Benda et aI., 1992). For example,
processes such as tectonic uplift and landform tilting influence spatial variation in valley entrenchment and stream profile characteristics in mountainous areas (Merritts and Vincent, 1989; Rhea,
1993). In lowland alluvial rivers, areas of slow tectonic activity affect channel patterns, channel direction, and sediment transport (Ouichi, 1985;
Marple and Talwani, 1993). Because bedrock composition and structural arrangement are static representations of geologic processes, they are fundamental in the analysis and interpretation of basin
and channel patterns (Morisawa, 1985). Because
the longitudinal stream profile reflects historical
geologic processes and properties of watersheds
(Hack, 1957; Wheeler, 1979), we can use the profile for preliminary assessment and interpretation
of basin and stream characteristics and even for
stream segment stratification (Hack, 1973; Shepherd, 1985; Bisson and Montgomery, 1996). Also,
patterns of basin morphology related to geologic
properties and processes can be identified by multivariate analysis, an underutilized tool in aquatic
assessments (Mather and Doornkap, 1970; Miller
and Ritter, 1990).
25.4 Hydrological Processes
25.4.1 Climate and Hydrology
Climate controls exogenous energy inputs to
ecosystems as precipitation and radiation and thus
is the driving force behind geomorphic and hydrologic processes and aquatic ecosystem temporal
variability. This section focuses on how climatic
processes regulate the dynamic variability of regional hydrology. Climatic factors control the character of the hydrologic regime through the timing,
duration, and intensity of rainfall and by how the
can link evolutionary attributes of organisms, such
as life-history adaptation, to processes and the dynamic nature of aquatic systems (Southwood, 1977;
Poff and Ward, 1990). In this respect, persistence,
stability, and predictability are important concepts
that can link life-history and habitat attributes with
processes of hydrodynamics and sediment transport. A major contribution in our understanding of
coarse-scale ecosystem dynamics is how geomorphic perspectives of landscape evolution and behavior lend an essential time perspective to landscape patterns and processes (Swanson, 1979;
Thomes, 1983). Although often overlooked in assessments, behavior is considered an important dynamic property of ecosystems (Allen and Starr,
1982). In aquatic systems, behavior is the dynamic
result of the collective, interactive operation of climatic, hydrological, and erosional processes.
25.3 Geologic Processes
Analysis of aquatic landscape patterns must focus
on more than surface processes and vegetation dynamics and is best considered in context of landscape origin and development. Large-scale climatic
and geologic processes form the landscape patterns
on which contemporary processes operate. To better understand landscape variability and the controlling factors on aquatic ecosystem composition
and dynamics, we must recognize and formalize
these geologic patterns as geomorphic or geoclimatic templates. Geologic processes, primarily tectonics and vulcanism, act as endogenous energy inputs, which are reflected in patterns of channel
networks and landform relief (Tricart, 1974). In
tum, landform relief influences potential energy of
aquatic systems as expressed in watershed morphology and stream profile relief (Morisawa,
1985). Regional landform developmental processes
and resultant properties impart a particular character to regions (Coates, 1974; Hack, 1982). Such
processes and features include tectonic uplift and
faulting, isostatic release and pluton development,
lithology, stratigraphy and structural deformation,
and Pleistocene glacial processes. Our knowledge
of these processes provides predictive and explanatory power of the spatial distribution and compositional properties of watershed, stream, and biotic patterns. For example, Pleistocene glacial
processes form different landscapes with variable
hydrologic and habitat conditions, which explains
corresponding distribution of salmonids (Benda et
aI., 1992) and bivalves (mussels) (Strayer, 1983).
We also need to consider coarse-scale fish distri369
bution in the evolutionary context of geologic
processes such as tectonics and watershed evolution (Minckley et aI., 1986).
We cannot adequately interpret aquatic patterns
without considering that watersheds have evolved
with and adjusted to different geologic processes
and erosional regimes. In this respect, both basin
and channel patterns reflect climate and landform
evolution since the Quaternary period (Petts and
Foster, 1985). Differences in bedrock and surficial
lithology, in the context of basin and channel evolution, help frame explanation of within-region differences in watershed properties (Cunha et aI.,
1975; Kowall, 1976; Miller and Ritter, 1990) and
contemporary variation in channel characteristics
(Hack, 1965; Benda et aI., 1992). For example,
processes such as tectonic uplift and landform tilting influence spatial variation in valley entrenchment and stream profile characteristics in mountainous areas (Merritts and Vincent, 1989; Rhea,
1993). In lowland alluvial rivers, areas of slow tectonic activity affect channel patterns, channel direction, and sediment transport (Ouichi, 1985;
Marple and Talwani, 1993). Because bedrock composition and structural arrangement are static representations of geologic processes, they are fundamental in the analysis and interpretation of basin
and channel patterns (Morisawa, 1985). Because
the longitudinal stream profile reflects historical
geologic processes and properties of watersheds
(Hack, 1957; Wheeler, 1979), we can use the profile for preliminary assessment and interpretation
of basin and stream characteristics and even for
stream segment stratification (Hack, 1973; Shepherd, 1985; Bisson and Montgomery, 1996). Also,
patterns of basin morphology related to geologic
properties and processes can be identified by multivariate analysis, an underutilized tool in aquatic
assessments (Mather and Doornkap, 1970; Miller
and Ritter, 1990).
25.4 Hydrological Processes
25.4.1 Climate and Hydrology
Climate controls exogenous energy inputs to
ecosystems as precipitation and radiation and thus
is the driving force behind geomorphic and hydrologic processes and aquatic ecosystem temporal
variability. This section focuses on how climatic
processes regulate the dynamic variability of regional hydrology. Climatic factors control the character of the hydrologic regime through the timing,
duration, and intensity of rainfall and by how the