Assessment of water environmental quality of mariculture areas in Liusha Bay in 2012-2013

Based on the quarterly investigation data from 2012 to 2013，the basic physical and chemical indexes of water quality of mariculture areas in Liusha Bay were analyzed，and the water environmental quality was assessed by the methods of organic pollution index（A），eutrophication index（E）and nutrient quality index（NQI）. The results showed that the general concentration of inorganic phosphorus（DIP）was lower than 0.05 mg/L，while that of inorganic nitrogen（DIN）was relatively high，especially in spring and summer（0.692-3.067 mg/L and 0.521-0.979 mg/L，respectively），indicating a phosphorus limitation in mariculture areas in Liusha Bay. Comparatively higher concentration of COD was found in spring（4.62-5.81 mg/L）and summer（2.87-3.65 mg/L）. The concentration of Chl-a of inner harbor was at the range of 4.85-8.79 μg/L in summer and autumn，indicating a moderate eutrophication of water body. With a concentration of Chl-a exceed 10 μg/L in summer，station 1 and station 3 of outer harbor presented obvious eutrophication. Serious eutrophication state was characterized by higher values of E（more than 1 from summer to winter）and NQI（surpass 3 every quarter）. Serious in spring and summer（value of A exceed 4），the organic pollution was improved in autumn and winter（value of A lower than 4）. In contrast with previous data，sharp increased concentration of DIN and heavier eutrophication were witnessed.