Study on Temporal and Spatial Variation of Nutrients and Evaluation on Eutrophication in the Seawater of the Bohai Sea in Winter and Spring of 2014

Abstract:

In this study we evaluated the level and distribution of nutrients in the Bohai Sea based on the survey in the spring and winter of 2014. We found that compared to winter of 2014, the level of inorganic nitrogen was higher in the spring, and the average contents of NO2- -N and NH+4-N were 1.94 and 3.49 times higher in the spring respectively. However, the average content of PO43--P in spring was about 80% of that in winter. According to the seawater quality standard, in winter the inorganic nitrogen content was lower than the first-level seawater standard, and the active phosphate content was slightly higher than the standard; in spring the inorganic nitrogen content was lower than the standard, and the active phosphate content was lower too. In terms of horizontal distribution, the coast area had higher DIN but lower PO43--P than the central area. Due to the effects of runoff river estuary the isolines of DIN and PO43--P were dense in the Laizhou Bay. In winter of 2014 the N/P ratio was slightly lower than Redfield ratio, but in spring the former was higher than the latter and there was a relative lack of inorganic phosphorus. According to the potential eutrophication assessment model, the nutrition level was poor in both winter and spring of 2014. In winter the organic pollution index A value was 0.66 and the organic pollution level was 1, indicating good water quality. In spring the organic pollution index A value was 1.05 and the organic pollution grade was 2, which meant the water body started to be polluted.