Identification of source apportionment and its spatial variability of dissolved organic matter in Dagu River-Jiaozhou Bay estuary based on the isotope and fluorescence spectroscopy analysis

Identification of allochthonous sources of dissolved organic matter (DOM) plays a significant role in biogeo-chemical 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 (combing delta C-13(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. Results suggested that the input sources of DOM obtained with isotope ratios contained most of the land uses in Dagu estuary. And 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 (3.4%-66.1%) expect for G22 areas (91.7%). This study provides a useful insight for carbon cycling and the interaction of terrestrial and marine biogeochemical processes.