Fluvial Landscape Ecology: Addressing Uniqueness within the River Discontinuum. G.C. Poole. Freshwater Biology. 47(4): 641-660. 2002.
1. Since rivers and streams are patchy and strongly
hierarchical systems, a hierarchical patch dynamics paradigm can be
used as a framework for visualizing interactions between structure and
function in fluvial landscapes. The paradigm is useful for addressing
fundamental attributes of lotic ecosystems, such as heterogeneity,
hierarchy, directionality, and process feedback occurring across
spatial scales, and for illustrating spatio-temporal linkages between
disparate concepts in lotic system ecology such as the River Continuum
Concept, the Serial Discontinuity Concept, the Flood Pulse Concept, and
the Hyporheic Corridor Concept.
2. At coarse spatial scales, the
hierarchical patch dynamics paradigm describes each river network as a
unique, patchy discontinuum from headwaters to mouth. The discontinuum
is comprised of longitudinal series of alternating stream segments with
different geomorphic structures. Each confluence in the steam network
further punctuates the discontinuum since the sudden increase in stream
size can create a "gap" in the expected pattern of downstream
transitions. The discontinuum view recognizes general trends in habitat
characteristics along the longitudinal profile, but creates a framework
for studying and understanding the ecological importance of each
stream's individual pattern of habitat transitions along longitudinal,
lateral, or vertical vectors at any scale.
3. Object-oriented
modeling and programming techniques provide a means for developing
robust, quantitative simulation models that describe the dynamic
structure of patch hierarchies. Such models can simulate how the
structure and function of lotic ecosystems are influenced strongly by
landscape context (the ecological conditions within which the system is
set) and the metastructure (structural characteristics and
juxtaposition) of finer-scale patches comprising the system.
4.
A simple object-oriented, multi-scale, discontinuum model of solute
transformation and biological response along a stream channel
illustrates how changing the branching pattern of a stream and/or the
arrangement of its component patches along the downstream profile will
result in substantial changes in predicted patterns of solute
concentration and biotic community structure.
5. The importance
of context, structure, and metastructure in determining lotic ecosystem
function serves to underscore Hynes' (1975) concept that "every stream
is likely to be individual." Advancing the discipline of fluvial
landscape ecology provides an excellent opportunity to develop general
concepts and tools that address the individual character of each stream
network and integrate the concept of uniqueness within the river
discontinuum into our ecological understanding of rivers and streams.
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