Optical Properties Of Riverine CDOM And Their Reponse To Key Eco-Environmental Factors

CDOM?chromophoric dissolved organic matter?,as the colored compound of dissolved organic matter?DOM?in the aquatic environment,is the important optical absorption substance in ultraviolet-visible wavelength.The concentration and composition of CDOM could change the underwater light field,and affect the aquatic ecosystem.Due to the different sources of CDOM,e.g.,autochthonous?plankton metabolism?and allochthonous?runoff?,the concentrations and composition of CDOM generally showed different optical characteristics over different regions.Rivers,as an important link between land and sea,attracted extensive attentions on the study of CDOM in inland waters.In view of the previous studies on CDOM were focused on the ocean and bay,few studies were conduct on the riverine CDOM optical characteristic and their response to eco-environmental characteristics.Based on the riverine samples from the Tibetan Plateau,the Northeast Plains and city rivers in the Changbai Mountains,this study first revealed the characteristics,sources,temporal-spatial,composition of the riverine CDOM in the regions,then analyzed the likely environmental influences on the CDOM.This study aimed to provide supports for comprehensively understanding the CDOM in inland waters,and development and reference of the water resources management and ecosystem protection.Compared with water quality parameters from other regions,the dissolved organic carbon?DOC?concentration of riverine samples were 2.89 mg L^-1 in Tibet Plateau?7.77 mg L^-1 in Northeast Plains and 16.49 mg L^-1 in urban rivers,respectively.The riverine DOC level on the Tibet Plateau showed a lower level than reported in Northeast Plains and urban rivers.Compared with water quality parameters from other regions,the riverine samples from the Tibetan Plateau showed a relatively higher total nitrogen?TN?level,a lower total phosphorus?TP?level and a higher electrical conductivity?EC?level.In addition,the concentrations of norfloxacin and enrofloxacin from the Northeast Plains were 25.60 ng L^-1 and 3.23 ng L^-1 respectively,relating to the terrestrial inputs.The CDOM absorption parameters,e.g.,a?350?,SUVA₂₅₄,S_275-295 and Sr,in Tibetan Plateau,Northeast Plains and urban rivers showed significant difference.For CDOM absorption a?350?,riverine samples from Tibetan Plateau exhibited a lower level with the higher level were found in plains and urban rivers.For E_250:365,the riverine samples from Tibet Plateau exhibited higher value 7.90 than that in Northeast Plain 7.24 and Urban river-section 6.54.For SUVA₂₅₄,the value in Tibet Plateau,Northeast Plain and Urban river-section were 3.32 L mg C^-1 m^-1,4.05 L mg C^-1 m^-1and 1.61 L mg C^-1 respectively,with the lower level could be found in urban rivers.For S_275-295,the averaged value in Tibet Plateau was 0.0202 nm^-1,0.0182 nm^-1 in Northeast Plains and 0.017 nm^-1 in urban rivers.These results indicated that small molecules dominated the CDOM in rivers of the Tibetan Plateau,while DOC?CDOM?in the mountain rivers was mainly higher molecules.CDOM optical absorption parameters of rivers generally showed significant seasonal difference,relating to the influence of environmental factors in the watersheds.The appropriate number of CDOM fluorescence components in rivers of the Tibetan Plateau,the Northeast Plains and urban area of the Changbai Mountains were determined by parallel factor analysis model,i.e.,one protein-like fluorescence component C1?Ex=230 nm and Em=360 nm?,one humic-like fluorescence component C2?Ex=245 nm and Em=450 nm?and one soil fulvic-acid fluorescence peak C3?Ex=240 nm and Em=480 nm?,respectively.Riverine samples from the urban rivers showed a highest C1 fluorescence intensity 27.76 nm^-1 than that in the Tibetan Plateau and Northeast Plains.Then the riverine samples from Northeast Plains exhibited a higher C2 fluorescence intensity 18.57 nm^-1 than that in Tibetan Plateau and urban rivers.In addition,the riverine samples from the urban area exhibited a higher C3 fluorescence intensity 53.89 nm^-1 than that in the Tibetan Plateau and the Northeast Plains.These results from the riverine CDOM demonstrated that the low CDOM unit absorption and fluorescence intensity in the Tibetan Plateau.This process could in link with the more solar radiation could limit the phytoplankton photosynthesis and be harm to the aquatic environments.The results of fluorescence index FI₃₇₀ indicated that most of CDOM in the rivers of the Tibetan Plateau and the Northeast Plains were of the allochthonous inputs.Then CDOM of riverine were derived from both microbial degradation and terrestrial inputs.The results of fluorescence index FI₃₁₀ indicated that biological activities in rivers of the Tibetan Plateau and the Northeast Plains contributed less to autochthonal inputs than those in the urban rivers.Based on multi-source remote sensing data,the influence of environmental and anthropic factors on CDOM optical properties and water quality was analyzed.The results showed the water quality parameters from rivers of the Tibetan Plateau explained 84%of the CDOM variations,and 95%of the CDOM variations in rivers of the Northeast Plains,and 96.2%of the CDOM variations in the urban rivers.Riverine samples were divided by elevations,CDOM level a?350?generally showed an increasing tendency with the abating elevations.Then the tryptophan-like fluorescence component C2 exhibited an increasing tendency with elevation in.The annual total sunshine hours and a?350?exhibited a correlation due to the photochemical bleaching.The correlation between monthly average temperature and DOC,and between C3 fluorescence component intensity and DOC was medium,which could also be found in the results of monthly average precipitation.Correlations between the total population,GDP and CDOM optical parameters were poor.Spatial variations in land cover contribution to the obvious difference of CDOM optical characteristics,indicating highly diverse chemical composition and transformation history.Built-up lands presented relatively higher a?350?,C1 and C3,and also lower FI₃₇₀ and FI₃₁₀.Lower a?350?values and fluorescence parameters were found in grasslands and unexploited lands.The fluorescence components C1 and C3derived from parallel factor analysis model were moderately correlated with sulfamethoxazole and metronidazole.Above all,different optical properties of CDOM in regional rivers are both affected by natural and anthropic factors.