8142

• UCREFRP Catalog Number: 8142
• Author: Horn, M. J.
• Title: Nutritional Limitation of Recruitment in the Razorback Sucker ‎(
• USFW Year: 1996.
• Copyright Material: NO

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9

Based on correlations of tree-rings (Stockton and Jacoby 1976; Meko et al. 1995),

streamflow analyses of "fossil" flood deposits high above present stream beds and

changes in climate estimated by other means (Betancourt et al. 1990), the hydrologic

pattern in the Colorado River over millennia has been numerous years of low discharge

(drought conditions) alternating with shorter periods of high discharge (flood) (Leopold

1994). The heterogenous pattern of floodplain structures and riverine channels created a

constantly changing habitat template for organisms that comprised the riverine food web

(Southwood 1977; Stanford et al. 1995).

Although average primary productivity in such a system must have been

depressed by substrate instability and turbidity, local conditions in a given year were not

(Hynes 1972). The channel in valley reaches (often greater than 100 m in wide) was

broadly aggraded to less than 10 - 25 cm deep at baseflow, and much of the substrate was

coarse sand. Bedload stabilized quickly and waters cleared with decreased discharge.

Benthic algae and invertebrates with short life cycles (Gray 1981) became abundant in a

few days (Pearson 1967; Vanicek 1967; Seethaler 1978). As often as 2 to 5 years per

decade and sometimes more, low discharges lasted for greater than 6 months (July-

August to March-April) following 2- to 3-months of snowmelt runoff in April-July.

Extensive riverine fringes were also colonized rapidly and extensively (far more

frequently than the channel) by invertebrates and algae, thus providing a food source and

nursery to larval fishes (Stanford 1994).

Scour and elevated turbidity may have persisted throughout some years, but based

on available records, high discharges, occurred only 1 to 3 years per decade (Figure 2).