The Content And Fluorescent Components Of Dissolved Organic Matter And Its Source Identification In Dagu River-Jiaozhou Bay Estuary

Identification of allochthonous sources of dissolved organic matter?DOM?plays a significant role in biogeochemical cycles and regional management in estuarine areas.In this study,samples of sediments and potential sources including farmland,forest,aquaculture,industrial and rural area were collected.Carbon stable isotope(?¹³C_DOM)were used to evaluate the relative contribution of DOM of the terrestrial and marine sources.Meanwhile,carbon stable isotope(combing?¹³C_DOM and C/N ratios)and fluorescence spectroscopy were applied to calculate the relative contribution of each DOM source in Dagu estuary.Furthermore,their capabilities for the source apportionment were compared.This study provides a useful insight for carbon cycling and the interaction of terrestrial and marine biogeochemical processes.Results showed that:?1?Among the main potential sources,DOM content,C/N ratio and?¹³C value showed significant spatial differences.The high DOM content of forest and aquaculture pond was related to the high humification degree of forest and the high density bait of aquaculture pond,respectively.The high C/N ratio of forest soil was closely related to the high carbon content of vegetation litter.The low C/N ratio of other land types was mainly affected by its high anthropogenic nitrogen fertilizers.The?¹³C of rural and industrial areas was more negative,which was related to domestic and industrial waste.?2?In the sediments of the Dagu River estuary,the DOM content reached the highest value at R6 site.The variation of DOM content among other sample sites was not obvious.This was related to river transport,tidal action,soil salinity,the land use types and human activities around different sample sites.The range of C/N varied from 5.15 to 10.01,indicating that the marine and terrestrial materials were the main sources of DOM.The higher C/N values meant the greater terrestrial materials input.The value of?¹³C was between-25‰^-21‰.And the closer to the sea,the greater the impact of marine sources.The value of?¹³C at R5 suddenly became negative,which was related to the large amount of domestic and industrial sewage input around the site.?3?Tyrosine-like,tryptophan-like and fulvic-like fluorescent components had a high ratio among the five fluorescent components of DOM in Dagu river estuary.?4?The sources of DOM in the estuarine areas contained terrestrial and marine material.The dominant sources were different at different sites.Overall,the terrestrial contribution decreased gradually from inland to offshore coast,while the marine material increased gradually.Land use types,surface runoff and tide were important factors affecting the spatial distribution of relative contribution.?5?The input sources of DOM obtained with isotope ratios contained most of the land uses in Dagu estuary.Farmland,aquaculture and industry were the dominant sources.By contrast,the source obtained with fluorescence spectroscopy was mainly aquaculture.Furthermore,we discussed the spatial variability of source contributions in different locations along the river?from internal to seaward areas?based on isotope ratio analysis.These results indicated that:1)In general,the allochthonous input of DOM derived from multiple sources.In different sediment sites,the contributions of land use were different.2)among the potential sources,aquaculture and industrial areas were the dominated sources.And the contributions derived from aquaculture pond showed a seaward increase characteristic.