Organic matter in estuaries

Organic carbon compounds in river waters occur in both particulate and dissolved forms. The definition is rather arbitrarily based on separation by a 0.45 gm filter pore size. More than 90 percent of the total organic carbon (TOC) occurs in the dissolved form. The bulk of dissolved organic carbon compounds consists of biopolymers (e.g. polypeptides, polysaccharides) and geopolymers (humic substances). Since the chemical structure of the geopolymers requires specialized, less common enzyme systems for breakdown, microbial attack introduces a strong bias favoring digestion of the biopolymers. As a result, the latter make up less than 10 percent of the dissolved carbon, especially in river water where primary productivity is low. Humic substances are therefore the main