The Response Of Orgnic Carbon Of Sediments To Basin Change Over Changjiangestuary And Its Adjacent Waters

Sediments and hydrodynamic environment over Changjiang drainage basin and Changjiang subaqeous delta have changed due to human activities.According to water and sediment model,grain size,mineral,organic carbon,and alkane,we had a good understanding on the response of Changjiang subaqueous delta to basin change.However,it is not clear that how the relationship between Changjiang subaqueous delta and Zhe-Min inner shelf deposition change.We collected 118 surficial sediments and 2 cores during 2013?2014 in the range of 28?32°N east to 125°E.In order to explore the response of sediments to natural mechanism and human activities,Grain size,organic carbon,n-alkanes and ²¹⁰Pb activity were analyzed.Two regions are identified within the study,which are Changjiang subaqueous delta and the north of Zhe-Min inner shelf deposition.The data are as follows.The content of total organic carbon?TOC?,total nitrogen?TN?,stable carbon isotope(?¹³C),stable nitrogen isotope(?¹⁵N)and C/N in surficial sediments were respectively?0.33±0.11?%,?0.04±0.01?%,?-23.51±0.76?‰,?8.98±2.29?‰ and 8.78±1.69.Nalkanes are bimodal and the former has a bigger proportion.The average size and sorting coefficient of Core H6 were respectively 7.28 ?m and 1.64,whose mass deposition rate was 1.93 g/cm² a.Sensitive grain components were 0.24?11.48?m,11.48?239.88?m and 239.88⁹54.99?m.TOC,?¹³C,TN,?¹⁵N and C/N in core H6 were respectively?0.39±0.1?%,?-23.94±-0.29?‰,?0.04±0.01?%,?6.76±1.29?‰ and?8.71±1.67?%.Core H17 had different mass deposition rate in varying depth,0.60 g/cm².a between 0?12cm and 0.49g/cm².a below 12cm.The average grain size was 6.61?m and sorting coefficient was 1.38.Sensitive grain components were 0.32?6.61?m and 6.61?316.23 ?m.TOC,?¹³C,TN,?¹⁵N and C/N in core H6 were respectively?0.54±0.18?%,?-23.54±-0.48?‰,?0.06±0.01?%,?6.43±1.14?‰ and?8.90±2.59?%.The results showed that horizontal distribution of surficial sediments was related to hydrodynamics.In the junction of various dominating hydrodynamic factors,fine particulate deposited,TOC and TN were higher.Terrigenous organic matter had a weak influence offshore.The San-Men Bay and the Jiaojiang Estuary might polluted by petroleum.The sensitive coarse grain can indicate flood,typhoon and human activities in the Changjiang subaqueous delta.In the north of Zhe-Min inner shelf deposition,the sensitive coarse grain were affected by East Asian Winter Monsoon and typhoon,the fine grain were related with flood or human activities.Since the 1950s,China's entered into the socialist construction period,aggravated watershed activities,industrial and agricultural pollution,domestic waste emissions increasing and engineering constructions have had influences on material transported from river to sea.In 1970s to 1980s,the effect of mankind on the watershed and the coastal area was more obvious.The suspended sediment concentration decreasing and the intensified hydrodynamics in the Changjiang estuary resulted in fine-grained sediments transiting to the south.The temporal variation and spatial distribution of the sediments in the study area mainly controlled by the change of the river basin,including natural change and human activities.A more clear understanding of "source" to "sink" between Changjiang subaqueous delta and Zhe-Min inner shelf deposition had been obtained.It is significant to perceive the impact of human activities on the coastal marine environment.