| Samples of chromophoric dissolved organic matter (CDOM) that were collectedfrom the Yellow Sea and the East China Sea in spring and autumn were analyzed byexcitation–emission matrix spectroscopy (EEMs) in combination with parallel factoranalysis (PARAFAC), and we studied the components, origin, transposition andspatial and seasonal changes. This method identified three terrestrial humic-like (C1,C2and C3) and one protein-like (C4) substances. Based on horizontal distribution andvertical distribution of the four components on three special transects, the followingassignments were made. C1and C2have the similar horizontal distributions in spring,the distribution of C3has a bit of difference with them. The horizontal distributions inautumn and the vertical distributions of the three components in spring and autumnwere all similar. The distribution of C4was different from that of the threecomponents. The four components had different distributions in spring and autumn,and their fluorescence intensities were also different in the two seasons, this mightdue to the different influenced factors in the two seasons. Through analyzing therelationships between the four components and salinity, we can know that theterrestrial inputs had a far greater effect on CDOM in autumn than that in spring, theEast China Sea had a bigger terrestrial inputs than the Yellow Sea. The biologicalactivities were more active in spring than in autumn, and it also more active in theEast China Sea than that in the Yellow Sea. The path analysis of samples from themiddle and bottom layers in the East China Sea revealed that the causal effects on C1were-75.4%for salinity,6.3%for Chl-a, and-18.3%for apparent oxygen utilization(AOU); those causal effects on C2were-78.3%for salinity,13.7%for Chl-a, and-8.0%for AOU; those causal effects on C3were-67.6%for salinity,9.3%for Chl-a, and-23.1%for AOU; and those causal effects on C4were-2.0%for salinity,13.0%for Chl-a, and-85.0%for AOU. The path analysis of samples from the middle andbottom layers in the Yellow Sea revealed that the causal effects on C1were-61.9%for salinity,5.9%for Chl-a, and-32.2%for AOU; those causal effects on C2were-77.1%for salinity,4.8%for Chl-a, and-18.1%for AOU; those causal effects on C3were-64.8%for salinity,5.9%for Chl-a, and-29.5%for AOU; and those causaleffects on C4were-25.0%for salinity,25.0%for Chl-a, and-50.0%for AOU. Theseresults revealed that the components C1, C2and C3were mainly affected byterrestrial inputs, primary productivity of phytoplankton and microbial processes alsohad effect on them to some extent. The protein-like component C4was mainlyaffected by marine sources, and terrestrial inputs also had effect on it to some extent,microbial activities also played a key role to C4. The influenced factors also haddifferent effects on CDOM in the East China Sea and the Yellow Sea. The percentcontributions of intensities to total fluorescence of the four components were alsodifferent in different seasons and regions. The average contributions of C1(C2, C3and C4) in the surface, middle and bottom layers of spring were36.8%(13.6%,25.4%and24.2%),36.8%(13.9%,26.3%and23.1%),37.7%(13.7%,26.1%and22.7%) in the Yellow Sea. The average contributions of C1(C2, C3and C4) in thesurface, middle and bottom layers of autumn were37.8%(16.8%,27.9%and17.5%),38.2%(16.9%,27.6%and17.3%),40.8%(17.7%,26.7%and14.8%) in the YellowSea. The average contributions of C1(C2, C3and C4) in the surface, middle andbottom layers of spring were34.3%(12.3%,25.4%and28.0%),36.1%(12.9%,24.9%and26.1%),35.1%(12.5%,24.9%and27.5%) in the East China Sea. Theaverage contributions of C1(C2, C3and C4) in the surface, middle and bottom layersof autumn were33.6%(14.7%,27.1%and24.7%),34.1%(14.8%,26.8%and24.3%),40.3%(15.8%,26.1%and17.8%) in the East China Sea. These results revealed thatthe contributions of C1, C2and C3were higher in autumn than that in spring, and thecontribution of C4were higher in spring than that in autumn in both the East ChinaSea and the Yellow Sea. The contributions of C1, C2and C3were higher in theYellow Sea than that in the East China Sea, and the contribution of C4was higher in the East China Sea than that in the Yellow Sea. Through analyzing the relationshipsbetween the components, we can know that the components C1, C2and C3had thesame factors controlling their concentrations. Based on the vertical distributions of thefour components, we can conclude that the four components had differentdistributions, and their fluorescence intensities were also different in spring andautumn. On the transects of C and P, the terrestrial inputs had a greater effect onCDOM, and the terrestrial inputs was bigger in autumn that that in spring, thefluorescence intensities of C1, C2and C3were bigger in autumn. On the transect of D,the terrestrial inputs had a smaller effect on CDOM, the fluorescence intensities of C1,C2and C3were bigger in spring. The fluorescence intensity of C4was higher inspring on the all three transects. Through analyzing the horizontal and verticaldistributions of humification index (HIX) and fluorescence index (FI), we can knowthat the components C1and C2had the highest degree of humification and stayed thelongest time in the environment, and the terrestrial inputs had the greatest effect onthem. C4had the lowest degree of humification and the terrestrial inputs had thesmallest effect on it. The value of the HIX was smaller and CDOM in this area had alower degree of humification and briefly remained in the environment than theprevious studied area. CDOM in autumn had a higher degree of humification and wasmore stable. CDOM in the Yellow Sea had a higher degree of humification and wasmore stable than that in the East China Sea. |
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