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Life of a River - Biology
River Continuum Concept: Headwaters (pg 2 of 7)

Headwater streams typically have a steep gradient, with riffles, rapids, and falls. In forested areas, overhanging trees shade the channel, preventing the growth of many aquatic plants and minimizing the role of photosynthesis. Instead, most energy and nutrients enter the stream in the form of leaves and woody material (detritus).

This detritus is colonized by fungi and bacteria. Immature aquatic insects of various kinds, known as shredders, eat the fungi and bacteria. Common shredders in small streams are stonefly nymphs and cranefly larvae.

Other species of aquatic insects are collectors, gathering the particles expelled by the shredders. Among these are net-spinning caddisflies, which filter detritus and algae with silken nets, and blackflies, which collect drifting food on cephalic fans that resemble strainers.

A third group of insects in small streams is predators, such as the immature forms of some species of stoneflies, caddisflies, and dobsonflies (ferocious-looking hellgrammites).

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Introduction
Flow
Shape
Connections
Quality
Life
Description
Terrestrial plants
Terrestrial animals
Life cycles
Corridors
Refuges
Aquatic habitats
Adaptations
Continuum concept
Relationships
Consequences
Stories
Summary
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