Dissolved organic nitrogen (DON), a heterogeneous mixture of labile and refractory components, was long thought to reserved to bacterial degradation. Macrophytes are key species and provide the good ecological status in coastal waters, as it is claimed in the EU water framework directive. Uptake of DON via roots and shoots by macrophytes of the Darss-Zingster bodden chain was investigated using 15N tracer experiments. Over an annual cycle δ15N values of macrophytes and DON were analysed to examine DON as possible N source in field. DON concentrations were consistently high over the year and macrophytes take up DON from the water column and also the sediments. This give them a clear advantage over phytoplankton which can solely use the pool from the water column. DON was long disregarded and should integrated in N loading budgets for coastal waters in future.