The Study On Seasonal/Spatial Variation Of Dissolved Organic Matter And Its Optical Properties And Their Application As Tracers Of Watermass Movement In Beibu Gulf

A comprehensive enviremental survey was conducted on four cruises over a two-year period from the summer of 2006 to the fall of 2007 in Beibu Bay. Performing both in situ measurement and laboratory analysis for Dissolved Organic Matter in surface,middle and bottom water.Using CDOM's optic character to research its source,distribution,transposition and seasonal change,analyse CDOM's spectral characteristic quantitatively and qualitatively.And the excitation-emission matrices especially.The data was statistically evaluated by cluster analysis to identify the source of CDOM,investigate major factor and biogeochemical process which control CDOM's distribution and variation.The main results are as follows:1.In BeiBu Bay water,significant seasonal variation was observed in both TOC and DOC,there is a correlation between TOC and DOC,which shows DOC composes major part of TOC in BeiBu Bay seawater.Vertical distribution of the concentrations of DOC and TOC also show seasonal difference,and their variations are similar.The negative correlation between TOC and salinity indicates that terrigenous freshwater input is the main sources of TOC in BeiBu Bay.Seasonal variation of CDOM in beibu bay is obvious,followed by winter＞spring＞autumn＞summer.The correlation between seasonal changes of S value and a355 was negative.The seasonal variations of S value show the highest average molecular weigh of CDOM in winter and lowest in summer,that may because of CDOM's photochemical reaction in summer.The concentration of a355 in surface waters are higher than in middle and bottom waters in spring and summer,and concentration distribution are relatively uniform in fall and winter.2.a355～S diagram shows that area I(Guangxi) affected by terrigenous sources, and a355 are decreasing with the increase of S values in areaⅢ(Southern Hainan Island ),that show CDOM in the area is marine-derived a355～S of CDOM distribution in areaⅡin Winter,spring and autumn show that it is the result of mixing of marine-derived CDOM from areaⅢand terrigenous CDOM from areaⅠ. Marine-derived CDOM is dominant in most areas in BeiBu Bay in summer,a good correlation between CDOM and salinity indicating that terrigenous input is principal sources of CDOM in coastal BeiBu Bay waters.No significant relevance was found between chlorophyll concentration and CDOM.3.We have identified four fluorescence components,including like-protein peaks C1 and C4 and humus-like peaks C2 and C3 by PRAAFAC in beibu bay water. Linear correlation was found between the absorption coefficient and three components(C2,C3 and C4),only like-tyrosine component different from other three components indicated its particular source and formation.Fluorescence components C2,C3,C4 negative correlated with salinity in spring and summer,and no correlation was observed between C1 and salinity,imply that terrigenous input is main source of organic matter in beibu bay.chlorophyll relatively correlate with C2～C4,but not with C1 show that the area is relatively less affected by the biological activity,microbial degradation and phytoplanktonis not a major source of CDOM in this area.4.By cluster analysis with CDOM absorption,S value,fluorescence,salinity, DOC and chlorophyll concentration,the whole beibu bay was divided into four areas, areaⅠmainly affect by coastal streams from southern GUANGXI,areaⅡeffect by westbound water from Qiongzhou Strait to beibu bay.AreaⅢeffect by anti-clockwise circulation in south-west Hainan Island,areaⅣeffect by coastal streams in southern Guangxi and water from Qiongzhou Strait flow into BeiBu Bay from south-west direction.Tracing water masses shows obvious corresponding relation between CDOM distribution and watermass movement,CDOM is a great tracer of water mass characteristic and water mass movement.