7923

• UCREFRP Catalog Number: 7923
• Author: Carter, J. G. and V. A. Lamarra.
• Title: An Ecosystem Approach To Environmental Management, Chapter 17.
• USFW Year: n.d.
• USFW - Doc Type: 261-287
• Copyright Material: YES

light at the substrate (Figure 5).
easily quantified.

Such results are

Because most aquatic organisms are poikilothermic,
temperature is an essential parameter to be measured.
Wlosinski (1979) indicated in the validation of his Desert
Stream Ecosystem model (DSEM) that temperature was the
most important physical parameter affecting the community
metabolism. Experiments conducted in the White River
indicate that temperature is highly significant in
regulating decomposition (Figure 8).

40
Z
o
i= 30
en
o
Q. 20
:E
o
(.J
w
o
~

Y:4.74+0.0748x
R2: .91
N:52

o

100 200 300 400 500
DEGREE DAYS

Figure 8. Leaf decomposition rates as
percent weight loss. Studies conducted
in the White River (October, 1981-
April, 1982).

Fluvial Characteristics

The second major set of characteristics needed to
define the abiotic structure of the White River is the
fluvial characteristics (Table II). The chemical load of
the river is derived from atmospheric precipitation, from
mineral matter dissolved by the surface and ground waters,
and from atmospheric gases (previously described in Table
I, as external inputs).

Gibbs (1970) has distinguished three basic origins
for dissolved substances in surface waters. These are
atmospheric precipitation, rock weathering, and
evaporation-crystallization processes. The processes
affect the relative concentration of the maj~r
macro-elements found in freshwater (Na+, K+, ca+2, Mg+ ,

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