Abstract
Chlorophyll-a (Chl-a) concentration is an important indicator of phytoplankton bloom and water eutrophication. It is also a basic parameter of water quality. Remote sensing technology has been widely used for water quality monitoring in the past. In this study, the Chinese GF1 (Gaofen-1) WFV (Wide Field of View) images acquired on May 19th, 2016 were used to retrieve Chl-a concentration of central Bohai sea in order to assess the recovery condition of marine ecosystem which has been seriously polluted by the Penglai 19-3 platform oil spill accident in 2011. The remote sensing model of Chl-a concentration was developed using the linear regression method. The leave-one-out cross-validation (LOOCV) method showed that the average relative error and root mean square error (RMSE) between retrieved Chl-a concentration and in situ measurement was 11.67% and 0.1808, respectively. It indicated that the remote sensing model could correctly reflect the Chl-a concentration and its spatial distribution of the study area. The average Chl-a concentration in the buffer regions with the distance of 2km, 4km, 6km to the Penglai 19-3 platform was 0.32μg/L, 0.37μg/L and 0.40μg/L, respectively. They were in normal range and lower than that of the coastal waters. The spatial distribution of the result was similar to previous studies of Bohai sea in spring. These results indicated that Chl-a concentration of central Bohai sea was returned to normal after oil spill accident occurred for 5 years. The growth of phytoplankton in surface seawater has been returned to normal. The major causes for Chl-a concentration in the Bohai Sea was the land-sourced pollutant during the study period.
Highlights
The Bohai Sea is the only semi-enclosed inland sea of China, which has a low capacity of water exchanging, self-purification and dirt holding with the other ocean
The Chinese GF1 (Gaofen-1) wide field of view (WFV) (Wide Field of View) images acquired on May 19th, 2016 were used to retrieve Chl-a concentration of central Bohai sea in order to assess the recovery condition of marine ecosystem which has been seriously polluted by the Penglai 19-3 platform oil spill accident in 2011
These results indicated that Chl-a concentration of central Bohai sea was returned to normal after oil spill accident occurred for 5 years
Summary
The Bohai Sea is the only semi-enclosed inland sea of China, which has a low capacity of water exchanging, self-purification and dirt holding with the other ocean. Dissolved organic matter in the water increases due to the degradation of marine bacteria[5] All these will contribute to phytoplankton blooms in a short time, which causes significant increase of Chl-a concentration. On June 4th, 2011, the Penglai 19-3 platform located in central Bohai sea faced serious oil spill accident. It was the largest offshore oil spill accident along the Chinese coastline in recent decades. On July 5th, 2011, preliminary investigation report released by State Oceanic Administration showed that the average concentration of petroleum hydrocarbon around the platform was almost 40.5 times higher than historical observations. On June 12th, 2011, Chl-a concentration over an area of 800km about 56km northeast away from the platform was 13.66μg/L[7]. Another phytoplankton bloom was observed in June 2012 when the monthly Chl-a concentration reached to 6.40μg/L[8]
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