Variation of dissolve inorganic nitrogen and its relationship with environmental factors in Beihai bay in a 10 year period
北海湾近10 年来溶解无机氮含量变化及其与环境因子的关系

Based on the surveying data in eight cruises in Beihai bay from 1995 to 2004, variation of dissolve inorganic nitrogen and its relationship with environmental factors were analysed. It was found that the DIN content was high in spprings and summers, butlow in falls and winters, revealing the important contribution of the runoff of Nanliu river. In all cruises, the content of NO3 was the highest, the content of NH4+ the second, and NO2- the lowest. The percentage of NO3 in DIN was more than 63.38% except for the Fall of 2004, which was the main existing form of DIN in the bay. By analyzing the data of different terms, we found that the content of DIN significantly ascended in springs and falls but descended in Winter and Summer. More and more culture discharge effluents was the main effect reaction. The correlation analysis indicated that, regarding the dependence between DIN and the environmental factors, salinity was the predominant factor. The dependence between DIN and COD was at the second place. The dependence between DIN and other environment factors were in the order of pH > DO > Chl.a, being most closely related to NO3 and NO2, as indicated by the strong positive correlations in seven cruises. Strong positive correlation with NH4+ was only present in the fall and winter when runoff had less effects.