24
Ecological Classification and
Mapping of Aquatic Systems
Mark E. Jensen, Iris A. Goodman, Christopher A. Frissell, C. Kenneth Brewer, and
Patrick S. Bourgeron
24.1 Introduction
Ecological classifications group similar items to
provide a framework for organizing our knowledge
about ecosystems (Driscoll et al., 1984; Jensen et
aI., 1991). Examples of such classification schemes
include soil taxonomy (USDA-SCS, 1975), potential vegetation types (Driscoll et aI., 1984), channel units (Hawkins et al., 1993), stream types (Rosgen, 1994), valley bottom types (USDA, 1978), and
watershed types (Jensen et al., 1997). These classifications can be given a spatial component by describing their composition within ecological mapping units (Cleland et aI., 1997).
Ecological mapping units are commonly delineated based on different criteria than those used in
ecological classification; that is, ecological unit
maps are often based on coarser-scale differentia
designed to predict repeatable patterns of the finerscale classifications they are assumed to constrain.
For example, ecological unit maps at the landtype
scale are commonly delineated based on landform
and geologic criteria (Cleland et aI., 1997). The
classification components they are assumed to constrain include soil families and plant associations;
the former are usually identified based on soil texture, climate, and mineralogy and the latter on presence of upper- and lower-layer indicator plant
species. This approach to mapping (moving up one
scale and predicting the patterns of interest) is extremely cost effective because survey costs commonly increase exponentially with increased resolution. Furthermore, this approach is appropriate
from an ecological, as well as an economic, standpoint because many ecosystem patterns are hierarchically organized.
In this chapter, we present a hierarchical framework for the ecological classification and mapping
352
of freshwater aquatic systems (i.e., riverine, lacustrine, and groundwater systems). We begin our discussion by reviewing basic concepts important to
the classification and mapping of aquatic systems
and follow by describing selected classification and
mapping systems commonly used in aquatic
ecosystem characterization. This discussion focuses primarily on classification systems for
streams, lakes, groundwater, hyporheic zones, and
wetlands. Finally, we present general recommendations on the use of terrestrial ecological units in
aquatic ecosystem characterization and the appropriateness of aquatic ecological units to multiscale
descriptions of ecosystem patterns and processes.
24.2 Basic Concepts
24.2.1 Scaled Relations of
Aquatic Systems
Ecological systems are groups of interacting, interdependent parts (e.g., species, habitats) linked to
each other by the exchange of energy, matter, and
information. These systems are considered complex because they are characterized by strong interactions among components, complex feedback
loops, discontinuities, thresholds, and limits (Constanza et al., 1993). Such attributes make it difficult to separate cause and effect relations and to
use knowledge of ecosystem behavior at fine scales
to predict behavior at coarser scales. Accordingly,
descriptions and classifications of ecosystems must
acknowledge the nested characteristics of terrestrial
and aquatic systems at multiple spatial scales
(Bourgeron and Jensen, 1994).
Complex ecosystem patterns and the multitude
of processes that form them exist within a hierar-
Ecological Classification and
Mapping of Aquatic Systems
Mark E. Jensen, Iris A. Goodman, Christopher A. Frissell, C. Kenneth Brewer, and
Patrick S. Bourgeron
24.1 Introduction
Ecological classifications group similar items to
provide a framework for organizing our knowledge
about ecosystems (Driscoll et al., 1984; Jensen et
aI., 1991). Examples of such classification schemes
include soil taxonomy (USDA-SCS, 1975), potential vegetation types (Driscoll et aI., 1984), channel units (Hawkins et al., 1993), stream types (Rosgen, 1994), valley bottom types (USDA, 1978), and
watershed types (Jensen et al., 1997). These classifications can be given a spatial component by describing their composition within ecological mapping units (Cleland et aI., 1997).
Ecological mapping units are commonly delineated based on different criteria than those used in
ecological classification; that is, ecological unit
maps are often based on coarser-scale differentia
designed to predict repeatable patterns of the finerscale classifications they are assumed to constrain.
For example, ecological unit maps at the landtype
scale are commonly delineated based on landform
and geologic criteria (Cleland et aI., 1997). The
classification components they are assumed to constrain include soil families and plant associations;
the former are usually identified based on soil texture, climate, and mineralogy and the latter on presence of upper- and lower-layer indicator plant
species. This approach to mapping (moving up one
scale and predicting the patterns of interest) is extremely cost effective because survey costs commonly increase exponentially with increased resolution. Furthermore, this approach is appropriate
from an ecological, as well as an economic, standpoint because many ecosystem patterns are hierarchically organized.
In this chapter, we present a hierarchical framework for the ecological classification and mapping
352
of freshwater aquatic systems (i.e., riverine, lacustrine, and groundwater systems). We begin our discussion by reviewing basic concepts important to
the classification and mapping of aquatic systems
and follow by describing selected classification and
mapping systems commonly used in aquatic
ecosystem characterization. This discussion focuses primarily on classification systems for
streams, lakes, groundwater, hyporheic zones, and
wetlands. Finally, we present general recommendations on the use of terrestrial ecological units in
aquatic ecosystem characterization and the appropriateness of aquatic ecological units to multiscale
descriptions of ecosystem patterns and processes.
24.2 Basic Concepts
24.2.1 Scaled Relations of
Aquatic Systems
Ecological systems are groups of interacting, interdependent parts (e.g., species, habitats) linked to
each other by the exchange of energy, matter, and
information. These systems are considered complex because they are characterized by strong interactions among components, complex feedback
loops, discontinuities, thresholds, and limits (Constanza et al., 1993). Such attributes make it difficult to separate cause and effect relations and to
use knowledge of ecosystem behavior at fine scales
to predict behavior at coarser scales. Accordingly,
descriptions and classifications of ecosystems must
acknowledge the nested characteristics of terrestrial
and aquatic systems at multiple spatial scales
(Bourgeron and Jensen, 1994).
Complex ecosystem patterns and the multitude
of processes that form them exist within a hierar-