Organic Matter Research Laboratory

What is organic matter?

 

 Close-up of a wetland, showing multiple sources of DOM

 Close-up of a wetland, showing multiple sources of  dissolved organic matter (DOM)

Dissolved organic matter (DOM) is found in every water body, both marine and freshwater. It is a heterogeneous mixture derived primarily from the decomposition products of plant material, bacteria and algae. The character of aquatic DOM varies according to precursor material, which falls broadly into two categories: allochthonous, which is terrestrially-derived and autochthonous, which means it is derived from within the aquatic ecosystem.

DOM amount and composition is important because it is one of the most significant sources of bioavailable organic carbon in aquatic ecosystems. It is a complex soluble organic compound that varies in its reactivity and ecological role and plays a critical role in nutrient transport and aquatic food web dynamics. Due to its interaction with light, DOM can have a significant effect on the biological activity in aquatic systems since it diminishes light as it penetrates the water column, which protects organisms from harmful irradiation. In contrast, from a drinking water standpoint DOM is considered a constituent of concern since a fraction of this material reacts during disinfection to form by-products that in high concentrations can negatively affect human health.

The chemical composition of DOM is determined by its source (e.g. plant, soil, algae, wastewater) and environmental processing (e.g. biodegradation and photodegradation). Optical properties such as absorbance and fluorescence are used to gain insight into DOM composition - these techniques are relatively rapid and inexpensive and allow for the comprehensive tracking of DOM dynamics in watersheds.

Identifying changes in DOM composition is of great importance because it will provide insight into DOM persistence, fate and reactivity (e.g. bioavailability, propensity to form disinfection by-products, mercury methylation) in aquatic ecosystems.