chapter  1
36 Pages

Issue of Organic Matter

Since organic matter is the ultimate source and origin of humic matter, it is perhaps necessary to start this book on issues of humic matter with some detailed studies, examining first what organic matter entails and what its relation is to humus and humic matter in the environment. At first recognized only in the lithosphere, and particularly in the pedosphere as one of the four major soil constituents, today organic matter is also considered in the hydrosphere as an important component for the continuation of life. Next to the terrestrial concept of organic matter as represented by soil organic matter (SOM), a new concept has emerged lately to accommodate the issues of organic matter in streams, lakes, and the oceans, called aquatic organic matter. It is not exactly a truly new concept but rather an extension of an older idea used in the 1950s or before by limnologists in their studies on biological life and its activity in natural waters. When by the end of the last century, biogeochemists and especially hydrologists at the U.S. Geological Survey became attracted to humic acid research, they also turned their attention to aquatic organic matter and its dissolved fraction that they called DOM. Although aquatic organic matter-assigned here by the author, for convenience, the acronym AOM-is still closely related with SOM, several major differences stand out that make it different from SOM, requiring the two-AOM and SOM-to be treated as separate entities. For example, grass, shrubs, and trees are the major sources of terrestrial organic matter, whereas algae and plankton are the origin of AOM, creating great differences in

quality and chemical composition between the two groups of organic materials. Recognizing AOM as a group of substances, important for biological life and in formation of humic substances in natural waters, has also changed the perception of many other people regarding these substances in water. Regarded by the general public at first as contaminants discoloring stream and lake waters, making them unfit for drinking or other human applications, AOM is now believed by many to be essential for sustaining the health of the ecosystem. In other words, it can be stated that “what was considered dirt is now a valuable material.”