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

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S04 ,Cl, HC03 ' C03 ). Because of the sources and
mechanisms of weathering, the air-water-terrestrial
interface is critical in the movement and translocation of
chemical constituents into the White River. For example,
a decrease in the pH of rainfall to 5 or 6 from a normal 7
to 8 can result in soil nutrient leaching. At lower pH
values rainfall can leach 10-15 thousand years of
accumulated exchangeable soil nutrients in periods as
short as 30 to 100 years. These soil nutrients,
dominantly monovalent and divalent cations, could move
into the river system, increasing the concentration of
dissolved solids and the potentially growth limiting
nutrients, nitrogen and phosphorus. During 1981, diurnal
variations of 200-300% in orthophosphate and nitrate were
documented for the White River during a single storm
event.

BIOTIC FACTORS

The purpose of the following discussion is to
describe dominant biotic processes of stream communities
which may be important to document for the White River.
The present state of knowledge concerning the biological
structure and function of stream ecosystems is based on
four factors: (1) the dependence of consumer organisms
for a large portion of their energy supply on
allochthonous organic material from the terrestrial system
watershed; (2) the utilization of organic input during the
fall-winter period of lowest temperatures (prior to spring
runoff); (3) the dominance of some stream segments by
primary producers and (4) the relationship between the
allochthonous and autochthonous organic inputs to the
system.

One technique for characterizing the White River
ecosystem is to determine the input, processing, and
export rates of particulate detritus. A brief summary of
the processing that occurs for "particulate organic
material" (POM) is as follows. After a piece of coarse
particulate organic material (CPOM) enters the stream
(twigs, branches, leaves, etc.), two processes occur
rapidly (Cummins, 1973). First, the soluble fractions are
leached from the coarse material. This leaching occurs
within the first 24 hours and can account for a 5-30%
weight loss. The second process is the colonization of
the coarse particles by microorganisms. The major groups
are: cells and spores of bacteria, aquatic hyphomycete
fungi, and protozoans. The large colonized particles are
reduced to smaller sizes (FPOM - fine particulate organic
matter) by abrasion (current and turbulence), animal
feeding, and microbial assimilation. The

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