Degradation of Dissolved Organic Matter in Humic Waters by Bacteria

Abstract

The standing stock of dissolved organic matter (DOM) in surface waters depends on import, washout, indigenous primary production and processes of internal loss, including abiotic mineralization (particularly photooxidation), microbial mineralization and flocculation followed by sedimentation. The DOM in such waters is a complex mixture of different compounds. Some of these, such as free and combined amino acids and carbohydrates, have in many cases been identified and quantified. Although the bulk of the DOM has not been described in detail, a major constituent of it is generally humic matter. The composition of the fraction of the DOM that is utilized and mineralized by bacteria, however, is poorly known. This chapter concerns both the importance of microbial utilization for the dynamics of DOM, and the importance of recalcitrant DOM as a substrate for microbial growth in humic waters. The impact of such factors as flocculation and photochemical processes upon the microbial degradation will also be discussed. The further consequences which the production of bacterial biomass can have on the structure and function of the ecosystem through the consumption of DOM will be considered as well, but is elucidated in greater detail in Chapter 11.