For use in LRRs Q, U, V and Z.

A layer of muck with value of 3 or less and chroma of 1 or less, starting at a depth ≤15 cm (6 inches) from the soil surface.

User Notes: The presence of muck of any thickness at a depth of ≤15 cm (6 inches) is the only requirement. Normally, this expression of anaerobiosis is at the soil surface; however, it may occur at any depth ≤15 cm (6 inches). Muck is sapric soil material with a minimum content of organic carbon that ranges from 12 to 18 percent, depending on the content of clay. Organic soil material is called muck if virtually all of the material has undergone sufficient decomposition to prevent the identification of plant parts. Mucky peat (hemic material) and/or peat (fibric material) do not qualify. Generally, muck is black and has a “greasy” feel; sand grains should not be evident.