8272

• UCREFRP Catalog Number: 8272
• Author: Wydoski, R. S. and E. J. Wick.
• Title: Flooding and Aquatic Ecosytems.
• USFW Year: 2000.
• USFW - Doc Type: 238-268, Chapter 9
• Copyright Material: YES

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Introduction

239

or riparian vegetation, and the ability of soil to absorb and retain water
(Baker et aI., 1988).
Periodic flooding of aquatic ecosystems is a natural phenomenon to
which native flora and fauna are adapted, although organisms can be ad-
versely affected by catastrophic events. Ecological functioning of many
wetlands depends on periodic flooding or recharge from groundwater.
The riparian zone around lakes can become flooded when water inflow
is greater than outflow, but this is generally of short duration without
serious effects to plants and animals. Tide fluctuations and flows from
streams and rivers cause dynamic natural changes in salinity, water tem-
perature, nutrient transfer, and sedimentation in estuaries. Catastrophic
flooding of seacoasts occurs from hurricanes and tidal waves (tsunamis)
caused by earthquakes or volcanic eruptions. Natural catastrophic flood-
ing in large rivers can occur from formation and failure of lava dams
deposited by volcanoes, as in the Grand Canyon of the Colorado River
in southwestern United States (Hamblin, 1990), or failure of ice dams
that occurred during the Pleistocene in the northwestern United States
(Baker. 1981). The power associated with such flooding can dramati-
cally change landscapes (Baker and Costa, 1987). For example, the fail-
ure of glacial Lake Missoula in the northwestern United States released
as much as 2000km3 of water with peak discharges of 15-17 million m3
S-l that were 30 thousand times greater than that produced by the largest
river on Earth, the Amazon River in South America (Baker and Bunker,
1985).
Flooding in small headwater streams is generally minor compared with
flooding in larger streams and rivers because drainage areas of the former
are smaller. Small streams are often found in forested landscapes where
soils can absorb and retain rainfall and meltwater. Flash flooding occurs
in small streams of arid regions when a sudden torrent of turbulent water
and sediment from summer thunderstorms in mountains causes erosion of
canyons, gulches, and arroyos. These streams are generally ephemeral so
aquatic ecosystems do not become permanently established and damage
is usually physical.
Generally, flooding of the piedmont reaches of large rivers is more com-
mon than in other aquatic systems because of the large volume of water
collected from an entire drainage basin. This water may cover a large area
of floodplain. Floods in large rivers can result in significant effects on
landscapes and aquatic systems.
Resiliency of most aquatic ecosystems damaged by flooding is often very
rapid. For example. catastrophic flooding of streams may result in the loss
ofa year-class of trout (Seegrist and Gard, 1972; Hanson and Waters. 1974;
Hoopes; 1975). However, Hanson and Waters (1974) documented the rapid
recovery in the standing crop and production rate of brook trout (Salvelinus
fontinalis) in a flood-damaged stream. In California. survival of O-age brook
trout fa fall spawner) was lowin years when fall floods occurred and high
in years after spring floods (Seegrist and Gard, 1972). Seegrist and Gard
reported that this pattern was reversed for spring-spawning rainbow trout,
Oncorhynchus mykiss. in the same stream.
This chapter discusses (1) the ecological importance of flooding to
aquatic ecosystems with an emphasis on large river systems, (2) effects
of human perturbations on aquatic ecosystems, (3) a case review of water