Properties,Spatiotemporal Distribution And Remote Sensing Retrieval Of DOC And CDOM In Poyang Lake

Dissolved organic carbon?DOC?is the largest organic carbon component in inland water system and plays an important role in carbon cycle process.DOC has tight relationship with chromophoric dissolved organic matter?CDOM?,which plays a critical role in water optical attenuation and in biogeochemical processing.This study focuses on the complexity of dynamic fluctuation and turbid water environment of the Poyang Lake to study the properties,temporal and spatial variation,transport and transformation,and environmental influence of DOC and CDOM.It had been selected different study areas as the testing sites,by controlled time and location sampling and measurements to study the temporal and spatial characterizes of DOC and CDOM and the environmental effects on DOC and CDOM;to study the optical properties of CDOM and the relationship between CDOM and DOC,in order to discuss the chemical composition and sources of CDOM and reveal the transport and transformation mechanism of CDOM and DOC in Poyang Lake;to establish inversion models by remote sensing for monitoring the dynamic variation of CDOM and DOC in Poyang Lake.The results demonstrated that:1.Concentrations of DOC were ranged from 1.34 to 7.22 mg/L with an average value of 2.27±0.82 mg/L.The absorption coefficients of CDOM at 355 nm?a_g?355??were ranged from 0.91 to 7.97 m^-1 with an average value of 2.77±0.97 m^-1.DOC concentrations and CDOM absorption coefficients in Poyang Lake presented a pattern of spatial and seasonal variation.DOC and CDOM were higher in wetland contributed waters than in open water areas.DOC and CDOM in spring and summer were higher than in autumn and winter.Hydrology,rainfall and land cover had a major impact on the spatial heterogeneity of DOC and CDOM in Poyang Lake.2.Concentrations of DOC and coefficients of CDOM absorption were significantly correlated at the range from 280 to 440 nm,especially at shorter wavelengths,which suggests that CDOM can be used as an effective DOC indicator in Poyang Lake.3.Spectral analysis with specific ultraviolet absorbance at 254 nm,absorption ratio between 250 and 365 nm and spectral slope indicated that CDOM in Poyang Lake was relatively high in molecule weight and aromaticity from terrestrial allochthonous inputs.Comparison of water samples revealed that CDOM in wetland contributed water had lower molecule weight and aromaticity influenced by autochthonous sources.4.The inversion models for estimating CDOM and DOC were performed well by distinguishing clean and turbid water based on different levels of turbidity.The band ratios of R?689?/R?497?and R?767?/R?826?were selected to establish models for retrieval of a_g?355?in clean water?TSM<10 mg/L?and turbid water?TSM?10mg/L?,respectively.The determination coefficients?r²?of calibration models for clean and turbid water were 0.70 and 0.73,respectively.The percentage root-mean-square errors?%RSME?of validation models for clean and turbid water were 13.2%and11.6%,respectively.5.The simulated Sentinel-2 and Landsat-8 bands based on reflectance spectra were used to examine potential capability for retrieving CDOM using these sensors.The results indicated that Sentinel-2 performed better than Landsat-8 for estimating a_g?355?.The Sentinel-2 band ratio of B4/B2 or B5/B2 and B7/B8 or B7/B8A are effective for retrieval of CDOM in clean and turbid water of Poyang Lake,respectively.This study has improved our understanding of DOC and CDOM in inland large turbid water lake,paved the foundation for understanding the spatial and temporal distribution and quantitative analysis of DOC and CDOM,improved the accuracy of estimating the amount of DOC and CDOM transported from rivers to large lakes,and enhance studies of carbon cycle and biogeochemical process in the inland water system.