Spatiotemporal Distribution Characteristics Of Chromophoric Dissolved Organic Matters(CDOM) In The Water Of Bohai Sea And Its Surrounding Rivers

UV spectral data and fluorescence excitation-emission matrix(EEM)was analyzed for the surface,middle,and bottom layer water samples of the Bohai Sea and its 36 surrounding rivers in December,2017 and April,August and November,2018.Distribution characteristics,seasonal variations and possible sources of CDOM in the study area had been investigated.Its dispersion,transformation,molecular characteristics and stability were also discussed.Fluorescence excitation-emission matrix(EEM)combined with parallel factor analysis(EEMs-PARAFAC)was applied to study the CDOM of Bohai Sea,and the traditional "peak finding method" was combined to identify the CDOM of rivers around the Bohai Sea.The main results are summarized as follows:1.The distribution of absorption coefficient(?355)were almost similar to fluorescence components in different seasons,and there was a positive correlation with the total fluorescence intensity.The salinity gradient gradually increases from the coastal waters to the offshore water while the ?355 decreases accordingly.The seasonal variation of a355 in the coastal waters of Bohai Sea is similar to that of surrounding rivers.2.The ?355 of CDOM in the study waters does not show a significant correlation with salinity,DOC and Chl-?.However,the seasonal variation characteristics of the absorption coefficients ?355 and DOC in the coastal waters of the Bohai Sea are similar to those in the surrounding rivers.The coastal waters of Bohai Sea are more affected by the input of terrestrial runoff.3.Fluorescence components of CDOM in the Bohai Sea were identified by EEMs-PARAFAC:there are one humic-like component,one tryptophan-like component and one lysine-like component in winter,two humic-like components and one tryptophan-like component in spring,three humic-like components and one tryptophan-like component in summer,three humic-like components and one lysine-like component in winter.The traditional "peak finding method" was used to identify five kinds of organic matter in rivers in different seasons,such as tyrosine-like,tryptophan-like,fulvic acid-like,humic-like components and microbial metabolites.4.The fluorescence components of CDOM as a whole show the same or similar seasonal variation pattern,and the fluorescence intensity gradually decreases from the nearshore to the offshore.In addition,the fluorescence intensity in the coastal waters is relatively high in different seasons.The above results show that the CDOM in the coastal waters of Bohai Sea is more obviously influenced by terrigenous input.5.The HIX value generally decreased gradually from nearshore to offshore in different seasons in the Bohai Sea,which was similar to the distribution of fluorescence intensity.The correlation between HIX value and humic-like components was stronger than that of protein-like components,indicating that humic-like components had higher degree of humification.It was found that FI,HIX and BIX values of CDOM in the coastal waters were similar to the rivers to a certain extent,and the fluorescence components were also significantly similar,which also indicated that the CDOM off the coast of the Bohai Sea was significantly affected by the terrestrial runoff input.6.The correlation of various humic-like components of CDOM in the Bohai Sea is obvious,indicating that they have similar sources and removal methods.There was a weak correlation between humic-like components and protein-like components in the Bohai Sea,indicating that humic-like components and protein-like components were less similar.7.Systematic analysis of the absorption coefficient a355,fluorescence intensity,salinity,DOC and Chl-a of M transect in the Bohai Sea in different seasons shows that the coastal rivers around the Yellow River estuary and Liaodong Bay have obvious input of CDOM at both ends of M transect,and meanwhile the phytoplankton contribute more to the central sea area of M transect.The characteristics,concentration and distribution of fluorescence components in the M transect have the same seasonal variation as that in the Bohai Sea as a whole.