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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84

Nutrient Cycling (Spiraling)

The chemical elements necessary for life tend to ,:irculate from the
environment to organisms, and upon death and disintegration of the
organisms, are returned to the environment. Thus the term nutrient cycl ing
has been coined to describe the cyclic movement of inolrganic and orga<1ic
nutrients within ecosystems. Approximately 30 to 40 of the over 100
chemical elements are known to be required by living olrganisms. Both
essential and nonessential (mercury, lead, ,!tc.) organic and inorganic
nutrients cycle. Elements such as carbon, oxygen, hydrogen, and nitrogen
are required by organisms in large quantitiE!s, whereas only small amounts
are required of some trace metals such as copper, aluminum, etc.
Autotrophs and heterotrophs within stream ecosystems (as in other syste<:1s)
can survive only if the cycling process provides a full compliment of
essential elements.

The linear configuration of stream ecosystems from headwaters to
estuary changes the dynamics of cycling from the conventional "closed"
cycles to partially "open" cycles called nutrient spiraling (Webster 1975,
Wallace et al. 1977, Newbold et al. 1981, 1982, Elwood et al. 1983,
Minshall et al. 1983). The actual recycling of materials and nutrients in
stream ecosystems is controlled largely by biological activities related to
the biota, temperature, oxygen, and basic nutrient conditions. Spiraling
includes both physical and biological processes, but r'~cycling is primarily
a biotic process (Figure 6).

For convenience, atoms of nutrients may be design,ated as being
components of either a biological pool or a nonbiologi,cal pool. As
nutrient atoms are released from the biological pool tl,ey enter the
nonbiological pool (or flowing water medium) and may thereby be displaced
in a downstream direction. For example, a carbon atom within a dead and
disintegrating bacterial cell may be releas.!d to the flowing water. Its

displacement in a downstream direction will depend largely on water flow
and, in general, the greater the flow, the greater the distance between its
release point and the point where the atom is recycled or incorporated into
the biological pool. It is the "spacial" dimension or distance traveled
downstream that resembles a partially open cycle and which is described as
spiraling. The downstream movement (displacement) is primarily a function
of phYSical processes. The greater the wat"r flow, the greater the
distance between loops of the spiral.

The rate of nutrient spiraling may be fast or slow. Where biological
activities are high, recycling rates may be fast. Where biological
activities are low, recycling rates may be slow. The period between
nutrient release and its subsequent uptake is termed the turnover time.
The distance traveled during:, ~hfl turnover time may be 'lhort or long and is
~' referred to as the turnover length. Nutrient turnover distances (length)
and time are determined primarily by stream current velocity and the
presence and effectiveness of physical instream retention devices (Minshall
et al. 1983). A stream's response to dissolved and particulate inputs