Abstract:Based on environmental survey in March, May, August, October, 2011 and May, August, October from 1997 to 2010, the status of nitrogen and phosphorous pollution and its variations in shellfish culture areas of Jiaozhou Bay were analyzed and assessed. It was found that: (1) Nitrogen and phosphorus pollution in shellfish culture areas of Jiaozhou Bay was more serious in 2011. Concentrations of these nutrients met the national standard in March only, but were above the limit in all other months, when DIN concentrations were 11.11% to 100% and phosphate (PO4-P) concentrations were 33.33% to 66.67% higher above the limit. (2) DIN and PO4-P in survey areas showed obvious seasonal variations. The maximum and minimum values appeared in October and March, respectively. The mean pollution index (Pi) of DIN and PO4-P were 1.35 and 0.93 respectively, indicating more serious pollution by nitrogen. (3) Spatial variation was also found for DIN and PO4-P in Jiaozhou Bay, with much higher concentrations of nutrients in the western and eastern regions of shellfish culture area but lower in the central region. The ranking of monthly DIN and PO4-P eutrophication was August>March>May>October. (4) Relatively serious eutrophication was found in the survey areas, with 44.44%~100% sampling stations were in eutrophication. The ranking of average monthly eutrophication index values was August>October>May>March. (5) In the four months in 2011, the N/P ratio of most seawater samples was between 20.96 and 43.22, which was above the Redfield ratio, with only few exceptions in May, indicating that PO4-P may be the main limiting factor for phytoplankton growth. (6) Pollution index of nitrogen and phosphorus showed obvious interannual variation. Pi of DIN was the highest in 2008 and the lowest in 1997 and 2000, and Pi of PO4-P was the highest in 1997 and the lowest in 2011. (7) The causes of seawater eutrophication were very complex, but two main factors were identified in the aquaculture areas of Jiaozhou Bay. One was the large amounts of nitrogen, phosphorus and other nutrient inputs from the rivers, and the other was the shellfish aquaculture self pollution. In recent years, although the nitrogen and phosphorus pollution in shellfish culture areas of Jiaozhou Bay showed no obvious deterioration, eutrophication is still serious, which may contribute to more frequent algal blooms.
