substrate (marine biology)

Stream substrate (sediment) is the material that rests at the bottom of a stream. There are several classification guides. One is:Mud – Comprised of silt and clay.Sand – Particles between 0.06 and 2 mm in diameter.Granule – Between 2 and 4 mm in diameter.Pebble – Between 4 – 64 mm in diameter.Cobble – between 6.4 and 25.6 cm in diameterBoulder – more than 25.6 cm in diameter.
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