Study On The Distribution Of Dissolved Organic Matter And Photodegradation In The Pearl River Estuary

Dissolved Organic Matter(DOM)is the largest carbon pool in the ocean and plays an important role in the global carbon cycling.However,the research of carbon cycling on the estuary is relative weak,this paper studied the spatial and seasonal variations of DOM in the Pearl River Estuary(PRE).And also,the photochemical process was explored to provide the basic data for the model of carbon cycling in estuaries.The PARAFAC analysis technology was employed for the fluorescence excitation-emission matrix.There are five fluorescence components were identified in the PRE,which was protein-like components C1 and C5,the marine derived humic-like component C3 and terrigenous humic-like components C2 and C4,and significant linear correlations between each component.The study found that the DOM in the PRE was mainly autochthonous origin again.The horizontal distribution of DOM with salinity was no-conservative and affected by autochthonous and fluvial transportation in pearl river.The concentration of DOM shows that the upstream of the estuary are greater than the downstream.The west transaction of the estuary is greater than the east transaction of the estuary,and the surface is slightly larger than bottom.The seasonal variation of CDOM and FDOM is shown as summer>autumn>winter,and DOC is shown as spring>winter>summer>autumn.This study also found significant linear correlations between a(330)and DOC,FDOM and DOC.So the future research can take advantage of CDOM and FDOM absorbance characteristics using in the water color remote sensing to investigate DOC concentration.This study estimated the annual DOC flux from the PRE was 0.29 Tg/a,and the annual CDOM flux was 0.38 Tm2/a.The experiment photochemical degradation of different salinity gradient in August and January,the results show that the photochemical degradation can cause the DOM molecules change of the internal structure and composition.Such as the decreases of DOM aromaticity and the relative molecular weight.The photobleaching rate of the fresh water end-member is greater than that of the seawater end-member.And the mixing zone of the estuary is the maximum of the photobleaching rate.DOC photooxidation rate is relatively complex,the DOC photooxidation rate of the fresh water end-member is much faster than other stations,the mixing zone M07 photooxidation rate in August was about 3 times January.In this study,the DIC photoproduction rate was also roughly estimated,and the rate of DIC photoproduction in the upstream of the estuary was much higher than that other stations.