The substance, base, or nutrient on which, or the medium in which, a fixed organism is attached. Substrate types include soil, rocks, water, and leaf tissues.
(refers to the amount of silt within the substrate materials in the stream.)
Nearly all of the stream bottom is layered with a deep covering of silt.
Extensive coverings of silts, but with some areas of cleaner substrate.
Silt cover includes areas where silt is deposited in small amounts along the stream margin or is present as a "dusting" that appears to have little functional significance.
Substrates are exceptionally clean.