sapropel noun. 
['saprǝpɛl] E20.[German, formed as SAPRO- + Greek pēlos mud, earth, clay.]An unconsolidated nitrogen-rich sludge of decomposing aquatic micro-organisms that accumulates in anaerobic environments on the bottoms of lakes and seas.
 ■   sapro'pelic adjective E20.  [TahlilGaran] English Dictionary ▲