Organic carbon source and burial during the past one hundred years in Jiaozhou Bay,North China

Organic carbon(OC),total nitrogen(TN),andPb in core sediment were measured to quantify the burial of organic carbon and the relative importance of allochthonous and autochthonous contributions during the past one hundred years in Jiaozhou Bay,North China.The core sediment was dated usingPb chronology,which is the most promising method for estimation of sedimentation rate on a time scale of 100-150 years.The variation of the burial flux of organic carbon in the past one hundred years can be divided into the following three stages:(1)relatively steady before 1980s;(2)increasing rapidly from the 1980s to a peak in the 1990s,and(3) decreasing from the 1990s to the present.The change is consistent with the amount of solid waste and sewage emptied into the bay. The OC:TN ratio was used to evaluate the source of organic carbon in the Jiaozhou Bay sediment.In the inner bay and bay mouth, the organic carbon was the main contributor from terrestrial sources,whereas only about half of organic carbon was contributed from terrestrial source in the outer bay.In the inner bay,the terrestrial source of organic carbon showed a steady change with an increase in the range of 69%-77% before 1990 to 93% in 2000,and then decreased from 2000 because of the decrease in the terrestrial input.In the bay mouth,the percentage of organic carbon from land reached the highest value with 94% in 1994.In the outer bay,the sediment source maintained steady for the past one hundred years.