Mor humus

Much of the Hgt pool was found in the upper part of the soil, which is rich in organic matter. This pattern is likely due to an elevated atmospheric deposition of Hgt over the extended period and immobilization of mercury by organic functional groups and accumulation of organic matter as part of the soil-forming process. The retention of mercury in the mor humus layer was almost complete due to the very strong association between Hgt and humic substances. 

Sjoberg, G., Knicker, H., Nilsson, S. I., and Berggren, D. (2004). Impact of long-term N fertilization on the structural composition of spruce litter and mor humus. Soil Biol. Biochem. 36, 609-618. 

Morphologically, two extreme humus forms can be distinguished " (a) mor, which is incompletely decomposed plant material, not incorporated into the lower, inorganic part of the soil, and (b) mull, namely, well decomposed material, thoroughly mixed with the inorganic part of the soil. 

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