FLOOD00235

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Title: Stream, Riparian, and Wetland Ecology - Class material, Volume 1 of 2
• Date: 9/1/1987
• Prepared For: Students
• Prepared By: Professor Windell
• Floodplain - Doc Type: Educational/Technical/Reference Information

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processing rates. For example, loss rates of less than 0.5 percent per day
are characteristic of .slow. leaf litter such as hemlock and oak, whereas
ash and alder leaves may be converted at greater than 1.5 percent per day
(Peterson and Cummins 1974, Sedell et al. 1975).

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The River Continuum Concept

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The River Continuum Concept proposes that natural stream ecosystems
may be characterized as extending from theIr headwater beginnings (i.e.,
first order tributaries) to mouth or estuary and that these ecosystems
provide a continuous gradient of physical conditions >rhich affect organic
matter storage and transport and the response of biotIc communitiE!s
(Vannote et at. 1980). The stream order system, although not perfect,
provides a convenient structural framework upon which community structure
and function can be related to stream width and length. A hypothetical
drainage system is used to illustrate biotIc communit)r structure and
function in a downstream direction along a longitudinally linked twelfth
order stream system. The stream system provides a gradient of ch,mging
physical, chemical, and biological conditions (Figure 2). Longitudinally,
the stream system is divided into three major ecological zones based on
small headwater feeder streams (orders 1, 2, 3), medium-size streams
(orders 4, 5, 6), and large streams (orders 7 to 12). The boundaries
between the three zones are not intended to be rigidl)r fixed and may vary
from drainage to drainage by shifting the "ones upstrE!am or downsl:ream
depending on a number of factors including climate, longitude, lal:itude,
altitude, geomorphology, number of inflowing tributarIes and the "ature of
the riparian zone. These factors are superimposed on the overall tendency
for the physical conditions to change progressively and predictably with
increasing stream size. Significant differences in the downstream gradient
of changing physical conditions (abiotic component) is related to
significant changes in the biotic components such as producers,
microconsumers, and macroconsumers. Thus the coalesc:lng network of
within a drainage basin represents a longitudinally LLnked gradient
physical habitat conditions that support a continuum ()f communities
ecosystem material processes.

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Headwater Feeding Streams

Headwater feeder streams constitute a massive feeder network within
watersheds that collect and channel materials from the landscape to
downstream reaches. When evaluated on the basis of stream length, first
and second order streams collectively exceed 75 percent of the total length
of U.S. streams. Addition of the third order segments increases the
collective length to 85 percent of the total national stream milage. The
first, second and third order streams form critically important links
between themselves, the surrounding landscape and downstream reaches
(Figure 2).

The most distinctive characteristics of headwater feeder streams
include smallness, narrowness, a gradient (i.e., decreasing slope) greater