Quantifying 'humics' in freshwaters: purpose and methods

Natural organic matter (NOM) plays an important role in many environmentally relevant processes. NOM includes many different types of compounds, not all of which behave similarly. Much effort has gone into characterising some fractions of NOM (e.g. humic substances) in the different environmental compartments, in finding tracers to ascertain their origin, etc. However, few methods exist for quantifying the different types of NOM and, as a result, field studies have limited themselves to measuring only total or dissolved organic carbon. In this article, the few existing methods for humic substance quantification are reviewed, and the implications of the current lack of simple measurement methods are discussed in relation to two fields of high environmental relevance: trace element speciation modelling and natural colloid and engineered nanoparticle fate.