Abstract:Based on the investigation data from 21 sampling stations in the central region of the Bohai Sea in 2012, and by using Nemerow index, eutrophication index (EI), and potential eutrophication assessment model, an assessment was conducted on the environmental quality of water body in the Bohai Sea area. According to the Nemerow index assessment on the 12 indicators including pH, dissolved oxygen (DO), dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorous (DIP), chemical oxygen demand (COD), total petroleum hydrocarbons (TPHs), Cu, Zn, Pb, Cd, Hg, and As, 57.1% of the surface water quality was at slight pollution level or more serious pollution level, 33.3% of the ten meter water quality was at slight and moderate pollution level, 23.8% of the bottom water quality was at slight or more serious pollution level. TPHs was the most important factor in all the contamination factors. Among the 21 surface sea water samples, 12 (corresponding to 57.1%) were above the second marine water quality standards when evaluated with single factor index method. The standard-exceeding rates of ten-meter water and bottom water were 42.9% and 14.3% respectively. The polluted area was located in the southeast of survey area, next to the Bohai Bay and the Laizhou Bay. The horizontal distribution of sea water quality showed an increasing trend from the coastal area to the middle area. The sea water EI value of the central region of the Bohai Sea except 13 stations in the surface water was less than 1, the results showed that most of the seawater quality in the investigated area was at the poorly eutrophication level. The ratios of N/P in most of the sea water were much higher than Redfield ratios, and the situation of nitrogen limiting in the central Bohai Sea was gradually changing to that of relative lack of phosphate. The nutrients structure has changed into potential eutrophication of phosphorus limiting.
