Content and distribution characteristics of petroleum hydrocarbons in Daya Bay waters and sediments

We investigated the content and distribution characteristics of petroleum hydrocarbon in Daya Bay waters and sediments in spring, summer, autumn and winter of 2015. The mass concentrations of petroleum in surface waters ranged from 0.005 mg·L^–1 to 0.268 mg·L^–1 (average: 0.067 mg·L^–1). According to the National Seawater Standard, the water quality was at Grade Ⅲ. The average pollution index (P_i) was 1.34, indicating that the seawater had been polluted by petroleum hydrocarbons. The distribution of petroleum hydrocarbons in surface waters was mainly affected by the horizontal clockwise circulation. The petroleum hydrocarbons high value area was located in the eastern part in spring, southern part in summer, southwest in autumn and northern part in winter. The range of petroleum hydrocarbons mass fraction in surface sediments was 7−559 mg·kg^–1 (average:183.4 mg·kg^–1). The average P_i was 0.367, indicating that the surface sediments in Daya Bay were not polluted by petroleum hydrocarbon, except Station A9. Petroleum hydrocarbon was a point source in surface sediments, and the high value area was located in the central archipelagic region, northeastern Nan'ao Town and eastern Dalajia Island, and all of those areas were distributed in the petrochemical sewage area, near the channel and the petroleum terminal.