Distribution of Phosphorous-Containing Fine Colloids and Nanoparticles in Stream Water of a Forest Catchment

Natural fine colloids and nanoparticles have the potential to encapsulate and bind nutrients. Their size range and composition is therefore relevant to understand the transport of essential nutrients like phosphorus in an aquatic ecosystem. The aim of the study was to characterize fine colloidal and nanoparticulate bound phosphorus of distinct hydromorphological areas in stream water samples from a forested experimental test site in a small headwater catchment. Asymmetric Flow Field Flow Fractionation (AF4) coupled online to inductively coupled plasma mass-spectrometry (ICP-MS) was applied for size resolved detection of phosphorus (P), iron (Fe), and aluminum (Al) in the fractions. Additionally, the dissolved organic matter (DOM) content was derived from the online UV signal. Two distinct fractions were detected and characterized. For the first size fraction, variations in P concentrations strongly correlated to the course of Al variations; in addition, high Fe presence in both fractions was accompanied by high P concentrations. Moreover, DOM was detected with P in presence of Fe and Al. Possibly, Fe and Al containing particles are carriers of P compounds and associated with organic matter. The study enables for the first time to trace and conceptually define the inputs and source regions of fine colloidal and nanoparticulate fractions within a small river of a headwater catchment. The stream water investigations will be extended to additional test sites and a broader range of elements