The colloidal state of “dissolved” organic matter and its significance for recalcitrance

Dissolved organic matter (DOM) is the major pool of organic matter in the water column of almost every aquatic ecosystem. It represents substantial global pools and fluxes of carbon.

Hence, the dynamics of DOM, including its role as a source of greenhouse gases and as a long-term carbon sink are a central interest in biogeochemistry.

Operationally defined as the organic matter not retained by filtration, using filters with sub-micrometer pores (commonly 0.2 µm), all of it is not dissolved in the strict sense, but it also includes molecular aggregates and colloids.

The significance of the colloidal state of DOM for the persistence and degradation of DOM has received surprisingly limited attention.

In preliminary studies, we have found that the colloidal fraction is recalcitrant to microbial degradation, while the labile material is in the truly dissolved fraction of DOM. Building on this finding, we hypothesize that the colloidal state of DOM is a major reason for its recalcitrance.

Across various wet ecosystems, we will characterize the contribution of colloids to the DOM pool, the role of colloids for resistance to bacterial degradation, and the precursor molecules for colloid formation.

We expect to present the first general synthesis of how the colloidal state of DOM influences its degradation and persistence.