Sampling of dissolved inorganic (DIP) and organic phosphorus (DOP) compounds in natural water by Diffusive Gradients in Thinfilms (DGT)

Summary

This report presents results from the work package 1 (WP1) of the EUTROPIA project, funded by the Research Council of Norway (RCN). The goal of WP1 was to improve the fractionation methods for phosphorus (P) compounds in water based on new auto-analytical techniques and passive samplers using Diffusive Gradient in Thin films (DGTs). Special focus was given to the Dissolved Inorganic and Dissolved Organic Phosphorus fractions (DIP and DOP) in water, as these contain the most bioavailable phosphorus compounds. The DGT adsorbents ferrihydrite (Fe-DGT) and the new titanium dioxide based (Metsorb™) adsorbent (Me-DGT) were compared. Both DGT adsorbents are known to collect the DIP fraction (orthophosphate). We wanted to study if the DOP fraction in water also could be collected by these adsorbents by using two low molecular weight model compounds adenosine monophosphate ( AMP) and inositol hexakisphosphate (phytic acid, IP6). High collection efficiency and satisfactory extraction efficiency was achieved. A field study was performed in the Morsa-Vansjø catchment in stream water draining a forested, a mixed agriculture/forest and agricultural area. The results for the DGT-DIP fraction were comparable to the corresponding DIP fraction in stream water, while the DGT-DOP fractions showed some promising features. The results from the laboratory study and the field study is presented and discussed in the report.