Chemistry of Natural Organic Matter—The Next Step: Commentary on a Humic Substances Debate

Natural organic matter (NOM) is ubiquitous on the Earth surface and influences every biogeochemical reaction wherever it is present, and its impact on reactions varies with its abundance, structure, and chemistry. Because of decades of field and laboratory studies conducted on NOM in different environments, we are moving away from treating it as a black box to developing molecular structure–based approaches in investigations of soil, sediment, and aquatic systems and are beginning to make major advances in the detailed understanding of the molecular and structural characteristics of NOM, which in turn are helping in deciphering the biochemical processes involved in its evolution in the environment. Yet, many questions remain: How does NOM exist in different soil and aquatic environments? How should we obtain NOM from a sample, and does the isolated NOM represent the NOM in a sample? Do the geochemical reactions explored with extracted NOM represent the reality? How can we study NOM in situ? Here I present a synopsis of critical perspectives on the state of NOM research and a commentary on the reviews and debate presented in this special section on the NOM nomenclature, extraction procedures, and studies involving NOM in different environmental processes.