The Distribution And Application Of GDGTs In The Jiulong River-estuary System,Southeastern China

In the past two decades,Glycerol Dialkyl Glycerol Tetraethers,GDGTs in breviation,have shown its great potential in in tracing organic matter and reconstructing environmental parameters in different environments.Previously,the application of GDGTs in river-estuary systems was mainly concentrated in large river-estuaries.However,due to the complexity of organic matter sources and hydrological environment in large river-estuaries,results have showne the complexity of different river-estuary systems.Therefore,the sources of organic matter and reconstruction environment parameters by GDGTs were affected by complex factors and were difficult to be clarified.In contrast,the complexity of organic matter sources and hydrological environment in small river-estuary systems can be relatively less complex,and GDGTs may perform better in the research of organic matter sources exploration and environmental parameter reconstruction.Under these circumstances,we focused on a small sub-tropical river-estuary system(the Jiulong River-Estuary System,JRES),and examined the GDGTs behaviors in this system,to answer the following two main scientific questions:(1)Application of GDGTs as an organic source indicator;(2)Application of GDGTs for the reconstruction of environment parameters.Based on the research results,the following main conclusions are obtained:In the JRES,the abundance of iGDGTs and cren,as well as the iGDGTs/bGDGTs ratio increased from the riverbank soil to the estuarine surface sediments,which indicated the overall increasing input of marine organic matter.In the estuarine surface sediments,the decreasing BIT value indicated an overall trend of decreasing input of terrestrial organic matter from the upper estuary to the lower estuary.At the same time,the abnormally high BIT values in the estuary indicated the hydrodynamic conditions and special geographical locations can affect the preservation of terrestrial organic matter.In addition,combined with the results of nalkanes,organic carbon and nitrogen isotopes,and particle size,the estuarine organic matter was comprehensively to be affected by seasonal changes and higher plant inputs.The Monte Carlo Simulation strategy based on organic carbon isotopes and carbon/nitrogen ratios has well verified the accuracy of BIT in the estuary.Abnormally high values of GDGT-O/cren(9.67±11.33)and abundance of bGDGTs(4.40±3.16?g/g)in the riverbed surface sediments,indicated changes in river water quality caused by human activities resulted in changes in microbial communities.This is supported by the abnormally high BIT value(0.87±0.10)in riverbed surface sediments.The iGDGT-derived estuarine water-surface temperature(TEX86H)was obviously lower than the measured values,thus,more local calibration should be carried out in future research.The iGDGT-derived river water-surface temperature(TEX86H)was close to the measured values,although the influence of soil inputs and archaeal community changes might need further justification as suggested by previous studies.The CBT-pH showed good correlation with the measured soil pH.While MBT/CBT-MAAT only in soil samples was close to measured values,we suggested they were applicable to soils of JRES,while in river and estuary,local calibration are required in future work.To explore the correlation between bGDGTs based proxies and environmental parameters,we have separated 5-and 6-methyl bGDGTs,but found that in the soil of the Jiulong River watershed,the bGDGTs based proxies were not clearly related to the measured environmental parameters after separating 5-and 6-methyl bGDGTs.We believed that the insufficient number of samples may be the major reason for the poor correlation statistically.