The distribution characteristics and seasonal variation of total dissolved nitrogen and phosphorus in the surface of Qinzhou bay

Four voyage investigations were done between 2015 and 2016 in order to study the distribution characteristics and seasonal variation total dissolved nitrogen(TDN), total dissolved phosphorus(TDP), dissolved organic nitrogen(DON) and dissolved organic phosphorus(DOP) in Qinzhou bay, Guangxi. It was shown that the TDN concentrations range from 9.37 to 77.52 μmol/L in this water, and TDP concentrations range from 0.20 to 4.08 μmol/L. Influenced by river runoff, the spatial distribution characteristics of TDN and TDP in Qinzhou bay were presented diminishing from inner bay to outer bay. The average concentrations of DON in August, November and March, DOP in August and March were higer than inorganic nitrogen and phosphorus respectively. The average ratio of DON and TDN reached 72.0%±19.7% in August, While DOP/TDP is 58.4%±20.1% in the same month. DON and DOP is an important part of dissolved nitrogen and phosphorus, and they may provide nutrition conditions for the growth of phytoplankton.