Characteristics of dissolved organic nitrogen (DON) in the surface water of Beijing Olympic Forest Park

The characteristics of dissolved organic nitrogen (DON) in surface water from Beijing Olympic Forest Park (BOFP) were investigated in this study. Nanofiltration (NF) pretreatment procedure using two NF membranes (NF90 and NF270) was applied to increase the accuracy and precision of DON measurements in surface water samples with high dissolved inorganic nitrogen/total dissolved nitrogen (DIN/TDN) ratios. Compared to NF90, NF270 showed better performance in lowering the DIN/TDN ratio and retaining DOC in both the synthetic water and raw water samples. DON concentrations ranged from 0.01 to 0.83 mg N L⁻¹ in water samples collected over four different months and showed a seasonal variation. The DON increased in summer due to the higher activity of decomposers on recent litterfall or because of a higher production of biomass in the surface water body. The molecular weight (MW) fractions of