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 of 15 cm (6 inches) or less from the soil surface.

User Notes: The presence of muck of any thickness at a depth of 15 cm (6 inches) or less 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) or less. Muck is sapric soil material with a minimum content of 12 percent organic carbon. 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.