Students will collect aquatic invertebrates in a shallow stream to study their diversity and relative abundance.  They will identify aquatic insects using a key and describe their structural adaptations for survival in the riffle zone.

TOPICS:  Insects, ecology, adaptation

LEVEL:  Middle and high school

TIME:  One class period for field work; one or more class periods for lab work.

ADVANCE PREPARATION:  Locate a small stream, which is ice free, rapidly flowing, and shallow with a rocky, erosional substrate.  Do not use a slow moving, deep water stream with a depositional substrate; it will have fewer aquatic insects and will be more dangerous to sample .

MATERIALS: Aquatic nets with rectangular or D-shaped frames are preferred .

PREDICTION: In class discussion, encourage creative, logical, and critical thinking. We recommend that you introduce the following ideas if they are not raised by students: Insects with flat streamlined bodies that fit tightly against the rocks are less likely to be swept away by the strong current in a riffle area .

SAFETY NOTE: Be sure students are dressed properly for winter weather.  Waterproof boots or waders are required for walking in the stream.  Rubber gloves are strongly recommended .

STEP A. The riffle zone is characterized by shallow fast moving water and turbulence as the water flows over rocks.  The water is typically clear and free of surface ice all winter.  Depending on temperature, the water may be slushy due to the presence of frazil ice; the bottom rocks may be blanketed with anchor ice under supercooled conditions.  The pool area has slow moving, deeper water, which may or may not be ice covered .

STEP B. The riffle zone substrate is made up of large rocks or pebbles typically smooth and rounded by erosion, and slippery to the touch due to attached algae and mosses.  The pool substrate is made up of finer sediment of sand, silt, clay and dark colored organic debris.  There is typically no rooted or attached vegetation.

QUESTIONS 7-11 require higher order thinking skills.  We recommend that you discuss these questions in class before having students write out their answers .

2. The water in the riffe zone is shallow fast flowing and turbulent.  The water in the pools is deep, sluggish, and calm .

3. The riffle zone has larger smooth rocks with moss or algae.  The pool substrate is muddy or sandy with organic debris and little vegetation .

4. Other aquatic invertebrates such as snails, leeches, worms (round, segmented, flatworms), crustaceans (pill bugs, scuds, crayfish) may be collected .

5. Answers will vary, but may include caddisflies, stoneflies, and mayflies .

6.

Insects	Adaptations
stoneflies, damselflies, dragonflies	hooks on appendages; flat streamlined bodies
mayflies, some beetles (waterpenny), Dobsonflies	flat, streamlined bodies
blackflies	sucker-like attachments
mothflies, soldierflies	sticky or slimy surfaces
caddisflies	cases or nets for attachment; hooks on appendaages

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7. The aquatic net is sufficient to collect the more mobile or burrowing insects.  Some of those attached more permanently to the substrate are very difficult to dislodge and are best observed directly by turning over rocks .

8. The water in the stream is probably well oxygenated as indicated by the diversity and abundance of aquatic insects collected, the cold temperature (cold water holds more oxygen) and the turbulence. Turbulent water picks up oxygen from the air by diffusion.  Ice cover or organic pollution (sewage discharge) would decrease the amount of oxygen in the water .

9. The faster current washes away the finer lighter particles (sand, clay, silt, and organic debris) and deposits the sediment in the slower moving water .

10. The substrate of riffle zones is called erosional because the fast flowing water erodes or flushes away the finer, lighter particles leaving the larger rocks .

11. The riffle zone is characterized by photosynthetic production.  Since sunlight easily penetrates the shallow water, attached mosses and algae are able grow.  (In contrast, the pool area contains organic matter that is decomposing.  The soft, shifting sediments of the pool may not allow for plant attachment even though light penetration may be sufficient for photosynthesis.  The pool area is characterized by bacterial decomposition.)