ABSTRACT
Natural organic matter, in its broadest sense, refers to the complex and chemically and physically diverse substances that result directly or indirectly from the photosynthetic activity of plants. In the geosciences, the authors typically limit the use of this term, however, to substances derived from the partial decay of detrital materials originating from terrestrial and aqueous plants. This definition includes everything along the diagenetic pathway from living plants to fossil fuels such as coal and petroleum. The incomplete turnover of plant litter in most of the world’s ecosystems results in the accumulation of soil organic matter. The fractions of humus from soil or aquatic environments called fulvic and humic acids differ primarily in their hydrophobicity and solubility characteristics, with concomitant differences in average molecular size and mass.
