[Potential Bioavailability of Dissolved Organic Nitrogen in the Discharge Outlets of Sewage Treatment Plants Around the Jiaozhou Bay].

Dissolved organic nitrogen (DON) is an important portion of total dissolved nitrogen (TDN) transported to the coastal from land-based sources and its bioavailable moieties of DON are regarded as potentially important nitrogen sources for eutrophication in coastal environments. Based on the four field observations conducted in July, November 2012 and in March, May 2013 at the four sewage treatment plants (STPs) around the Jiaozhou Bay (JZB), the concentrations and compositions of total dissolved nitrogen (TDN) as well as total dissolved amino acids (TDAA) were analyzed, and the ratio of dissolved organic carbon (DOC) to DON and the composition and abundance of amino acids were regarded as indexes to evaluate the bioavailability of DON in STPs around JZB. The concentrations of TDN ranged from 413.10 µmol L⁻¹ to 3,580.65 µmol · L⁻¹ and showed a seasonal variation tendency, which were higher in March and November and lower in May and July, and the percentages of DON to TDN varied from 2.14% to 88.75%. In the discharge outlets of STPs around JZB, the values of DOC/DON were low and ranged from 0.2 mol · mol⁻¹ to 26.2 mol · mol⁻¹ with an average of (5.05 ± 6.39) mol · mol⁻¹, while the values of TDAA/DOC were high and ranged from 0.33% to 3.02% with an average of 1.54% ± 0.78%. Based on TDAA/DOC, the bioavailable proportion of the dissolved organic matter was estimated, which accounted for 0.44% to 46.97%. In conclusion, DON in the discharge outlets of STPs around JZB possessed high bioavailability and might contribute to the eutrophication of coastal water in JZB.