Amino Sugars In Particulate Matters And Sediments Of The Yellow Sea And East China Sea And Their Indications Of Organic Matter Source And Degradation

Continental marginal seas are important regions for the production,transformation and burial of organic matters(OM),and they play an important role in the global carbon cycle.In this study,183 particulate matter samples and 84 surface sediment samples were collected from the Southern Yellow Sea(SYS),Yangtze River Estuary(YRE)and East China Sea(ECS),the amino sugars(AS)together with organic carbon,nitrogen,chlorophyll a,heterotrophic bacterial cell count and hydrological parameters were studied.The distribution and composition of amino sugars were firstly reported in the studying area,and the source,bioavailability and diagenetic states of the OM as well as their seasonal changes and influence factors were studied,and the bacterial OM contributions to organic carbon were estimated.The major results of this study are as followed:(1)Planktons and bacteria are important sources of particulate organic matters(POM)in the SYS and YRE,and their relative contributions varied in different sea areas and seasons.The level of primary production was a key influence factor of the source and bioavailability of POM.In the places that had high primary production,the higher ratios of glucosamine to galactosamine(GlcN/GalN)and C-and N-normalized yields of amino sugars(%AS-OC,%AS-N)indicated a feature of plankton source of POM,and the higher concentration of muramic acid(Mur)showed a higher concentration of fresh bacterial OM.The higher proportion of fresh plankton and bacterial OM indicated the POM had higher bioavailability.On the contrary,in the places where the primary production was low,the lower GlcN/GalN,%AS-OC and%AS-N implied a lower contribution of plankton(especially zooplankton)to POM,and the lower Mur concentration also indicated a lower contribution of fresh bacterial OM.The lower contribution of fresh OM indicated the POM was more degraded.Besides,the resuspension of surface sediments could significantly decrease the contents of particulate carbon and nitrogen(POC and PN)and had an effect on the source of POM.The contributions of relative fresh bacterial OM to particulate organic carbon(POC)were on average 29%in the studing area.The concentrations of particulate amino sugars(PAS)were 2.1?128.4 nmol/(mg dw)in the SYS.The PAS consisted of more than 95%of GlcN and GalN and less than 5%of mannosamine(ManN)and Mur.In 35°N section,the primary production was relatively high in spring,the GlcN/GalN was 8.1±3.7 on average and the%AS-OC and%AS-N were 11.0±6.2%and 10.2±6.0%on average,respectively,which clearly indicated a plankton source of POM.Then in autumn,when the primary production became lower,the GlcN/GalN decreased to 5.1±2.0,and the%AS-OC and%AS-N were 5.8±2.9%and 7.4±3.5%on average,respectively,indicating the contribution of plankton to POM decreased.The estimation based on Mur showed the contribution rate of fresh bacterial OM to POC were 33.8±18.4%and 28.1±18.9%in spring and autumn,respectively,demonstrating bacteria was an important source of POM in the SYS.As the primary production decreased from spring to autumn,the contribution of plankton and fresh bacterial OM to POM were both decreased,indicating the decrease of the labile part of POM and leading to a more degraded nature.The increase of C/N in autumn could also indicated the POM were more degraded than spring.The nearshore site had the highest primary production,however,the POC and GlcN/GalN were not very high.This might because the resuspension of surface sediments influenced the contents and sources of POM.In the YRE and adjacent sea area,the PAS concentrations were 1.2?107.0 nmol/(mg dw).The PAS consisted of more than 95%of GlcN and GalN and less than 5%of mannosamine(ManN)and Mur.In typical section of the YRE,the primary production was higher in spring and lower in autumn in nearshore area,meanwhile,the GlcN/GalN decreased from>3 to<3,and%AS-OC also decreased from spring to autumn,implying the source of POM transformed from plankton to bacteria.The higher%AS-N and lower DO concentrations in autumn than spring indicated the POM was more degraded in autumn.In offshore site(CJ-4),the primary production was higher in autumn than spirng,the GlcN/GalN increased from<3 in spring to>8 in autumn,the%AS-OC and%AS-N also increased from<3 in spring to>5 in autumn,indicating the source of POM transformed from bacteria to plankton.The estimation based on Mur showed the fresh bacterial OM contributed 10.8±3.7%and 40.5±19.1%of the POC in spring and autumn,respectively.In autumn,the contributions of plankton and fresh bacterial OM to POM both increased in offshore site,indicating a more labile nature than spirng.(2)Comaring with those in POM,the source indicators based on AS such as GlcN/Mur,%AS-OC and%AS-N were more easily affected by degradation process,indicating the bioavailability of SOM was lower than that of POM.But as the AS was a kind of semi-labile biomolecules and temporarily enriched during the degradation in SOM,it is speculated that the degradation state of SOM in the inner shelf of SYS and ECS was at early or medium stage.Bacterial OM was an important source of sediment organic matters(SOM)in the inner shelf of the SYS and ECS,and the contributions of relative fresh bacterial OM to sediment organic carbon were on average 21.5%in the studing area.The sedimentation of particulate matters from upper water column had a certain of influence on the source and diagenetic states of the SOM,especially in nearshore area where the water was shallow.Comparing with sand area,the mud area contained more organic matters in sediments,but the particle size could not decide the source and diagenetic states of SOM.In the ECS,the sediments of nearshore mud area contained more chitin material than offshore area and had higher bioavailability.While in the mud area of the SYS,the sediments contained higher proportions of degraded bacterial OM and the SOM was more degraded than those in non-mud area.In SYS and YRE,the concentrations of AS in the surface sediments were 0.18?8.25 nmol/(mg dw),and the AS consisted of on average 95%of GlcN and GalN and less than 5%of ManN and Mur.In the 35°N section of the SYS,GlcN/GalN ratios were<2 in all sites and both seasons and indicated a major bacterial source.In the offshore mud area,the contents of organic carbon and nitrogen were higher than those in nearshore area.The Mur(nmol/mg dw)was also higher in mud area,but the Mur(nmol/(mg C))was lower,indicating the higher contents of OM in mud area was not mainly contributed by fresh bacterial OM.The relatively high%AS-OC and%AS-N implied that the OM in SYS surface sediments had undergone degradation,but as the AS were semi-labile biomolecules and temporarily enriched during the degradation process,it is speculated that the degradation state of SOM in SYS was at early or medium stage.At the meantime,the higher ratios of GlcN/Mur in mud area demonstrated that the SOM was more degraded in mud area than that in sand area.The low GlcN/GalN in sediments implied that the high contents in organic carbon and nitrogen in mud area could be contributed by degraded bacterial OM.The estimation based on Mur showed the fresh bacterial OM contributed 28.2±8.6%and 21.7±8.7%of the sediment organic carbon in spring and autumn,respectively.In the inner shelf of the ECS,the concentrations of AS in surface sediments were 0.48?7.23 nmol/(mg dw).The AS consisted of on average 95%of GlcN and GalN and less than 5%of ManN and Mur.GlcN/GalN ratios were<2 in all sites and both seasons and indicated a major bacterial OM source.Comparing with offshore sand area,the contents of OM,GlcN/GalN ratios and Mur concentrations were all higher in nearshore mud area,indicating the surface sediments in nearshore mud area contained more OM and the SOM contained more chitin material and fresh bacterial OM than those in offshore area.Although the low GlcN/GalN indicated a major bacterial OM source,the%AS-OC and%AS-N were higher than those in bacteria OM,which implied that the SOM had undergone degradation,and the degradation was at early or medium stage.In the meantime,the GlcN/Mur ratios were lower in nearshore mud area than those in offshore area,indicating the SOM in mud area was fresher.The Chl-a in surface water,the SOM contents and GlcN/GalN ratios in surface sediments were lower,and the Mur concentrations were higher in autumn than summer,indicating the settling particles in surface sediments in summer were degraded and converted to bacterial OM in autumn.these seasonal changes were more obvious in nearshore area,where the primary production was relatively high and water depth was shallow,indicating the settling of POM had important influence on the source of SOM in nearshore.In summer,the Chl-a in seawater had positive correlations with Mur in surface sediments,however in autumn,the correlations disappeared as the Chl-a contents decreased,which further indicated that the settling of POM had important influence on the source of POM.The estimation based on Mur showed the fresh bacterial OM contributed 13.1±6.4%and 28.5±17.9%of the sediment organic matters in the inner shelf of the ECS in spring and autumn,respectively.The contribution was higher in autumn than summer and also higher in nearshore mud area than offshore sand area.The AS parameters showed obvious differences of source and diagenetic states between POM and SOM.The lower GlcN/GalN ratios in SOM showed the higher contribution of bacterial OM,while the higher GlcN/GalN ratios in POM indicated the higher contribution of plankton OM.Comparing with those in POM,the source indicators such as GlcN/Mur,%AS-OC and%AS-N in SOM could be obviously elevated by degradation process,leading to a conflict result with GlcN/GalN,which indicated that the SOM was more degraded than POM.