[Inorganic nitrogen and phosphate and potential eutrophication assessment in Liaodong bay]

On basis of field data measured during 4 cruises from June to September in 2002, variation feature of inorganic nitrogen and phosphate in Liaodong Bay was analyzed. Regression analyses of NH4+(-)N, NO3-(-)N, NO2-(-)N and PO4(3-)-P versus pH as well as inorganic nitrogen and phosphate versus salinity were also conducted. Finally, potential eutrophication of Liaodong Bay was assessed. It is shown that inorganic nitrogen and phosphate in Liaodong Bay vary with different months and different locations. In coast areas inorganic nitrogen and phosphate are mainly affected by rivers, while in central areas of the bay, they are subject to marine biochemical process. Ratio of inorganic nitrogen to phosphate rises to 60.6 from 52.5 in early June, then drops to 39, all far above Redfield value 16. Inorganic nitrogen and phosphate versus pH as well as salinity show different correlation. For example, the correlation coefficient of NO2(-)-N and pH even reaches 0.93. During 4 cruises in Liaodong Bay the total inorganic nitrogen is 212.0 microg/L, phosphate 10.1 microg/L, N/P 50.77. Potential eutrophication assessment indicates that during the survey period Liaodong Bay can be classified as a phosphate-limiting moderate-level nutrient area.