7996

• UCREFRP Catalog Number: 7996
• Author: Wydoski, R. S. and E. D. Wick.
• Title: Ecological Value of Flooded Bottomland Habitats to Endangered Fishes in the Upper Colorado River Basin.
• USFW Year: 1996.
• USFW - Doc Type: \
• Copyright Material: NO

recently. The concepts of the river continuum (Vannote et al. 1980) and flood
pulse (Junk et al. 1989) apply to the Upper Colorado River Basin. The river
continuum concept applies to the headwaters and high gradient, restricted meander
canyon reaches while the flood pulse concept applies to low gradient,
unrestricted reaches that form floodplains in broad valley reaches. Lotic
systems not only transfer organic matter from upstream reaches in arid or semi-
arid regions (i.e., continuum concept) but also deposit this material in
floodplains where high productivity of invertebrates periodically enters the
river (i .e., flood pulse concept). Shallow floodplain habitats become much
warmer than the adjacent river, increasing the productivity for phytoplankton and
development of a food web (Welcomme 1979). Slow growth and higher mortality of
endangered Colorado River fishes has been attributed to lower water temperatures
in the Upper Colorado River Basin (Kaeding and Osmundson 1988). Floods and
fl oodp 1 a ins are now understood to be essent i a 1 components of ri ver systems
(Bayley 1991; Petts and Maddock 1994; Sedell et al. 1989). The energy dynamics
of large rivers is strongly influenced by floodplain habitats (Sedell et al.
1989) where productivity is higher than habitats in river channels (Hynes 1970;
Welcomme 1985; Welcomme 1989). The spawning strategies of fishes in many
tropical and some temperate areas are correlated with the flood pulse that is
associated with high productivity in shallow, flooded areas where organic matter
is retained (Junk et al. 1989). Welcomme (1985) stated that the shallow littoral
zone of floodplain habitats produce higher densities of zooplankton when compared
with the entire floodplain area.

IV. RELATION OF NUTRIENTS, SUNLIGHT PENETRATION, AND
WARM WATER TEMPERATURES IN PHYTOPLANKTON PRODUCTION

Phytoplankton productivity provides the basis for development of a food web.
Phytoplankton production and standing crops increase in concert with increases
in annual input of nutrients regardless of latitude. Carbon, nitrogen, and
phosphorus are key elements for phytoplankton production. Phosphorus is the most
limiting element in north temperate and subarctic waters (Schindler 1978).
Nitrogen is the most abundant element in the atmosphere and is generally not
limiting. Also, abundant carbon dioxide in the atmosphere provides the necessary
carbon. Therefore, phytoplankton production and standing crop in north temperate
freshwaters is generally proportional to the phosphorus input. Particulate
phosphorus, either chemically desorbed or actively mobilized by microbiota, is
not readily available in rivers with a high sediment load because most of the
phosphorus is bound to the sediments (Ell is and Stanford 1988). Watts and
Lamarra (1983) determined that between 21% and 49% of the total phosphorus in
Colorado River water at the bridge upstream from Moab, Utah in September and
October 1978 was bioavailable with most of the extractable element in the form
of calcium-bound phosphorus. Therefore, Watts and Lamarra (1983) concluded that
algae production was not nutrient limited in this reach of the Colorado River but
that primary production in this reach was inversely related to the turbidity of
the riverine environment.

Turbidity from suspended fine sediments in Upper Colorado River Basin rivers is
high and adversely affects primary and secondary production. Product i on of
phytoplankton and zooplankton (Tables 1 and 2) that form the basis for a food
pyramid are extremely low in the these rivers (Grabowski and Hiebert 1989; Cooper
and Severn 1994 a, b, c, and d; Mabey and Schiozawa 1993). High turbidity in the

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