Ecological indication based on source, content, and structure characteristics of dissolved organic matter in surface sediment from Dagu River estuary, China

Dissolved organic matter (DOM) controls the fate of a variety of nutrients and trace metals in river estuary systems. The aim of our study is to explore the sources, structure characteristics of sediment DOM, and potential ecological release risk (heavy metal, N and P) under the environmental conditions of Dagu River estuary. The relative contribution of DOM source was calculated by carbon stable isotope (combining delta(13)C(DOM)and C/N ratios). The structural characteristics of sediment DOM in Dagu River estuary were determined by ultraviolet-visible spectroscopy (UV-vis) absorbance and fluorescence spectroscopy. The potential ecological risks of heavy metals and N and P release were also assessed. Results show that the relative contributions of rural area and aquaculture are high in Dagu River estuary. The humification degree of DOM in downstream river is higher than that in the estuary, and the sediment DOM in Dagu River estuary is influenced by both terrestrial input and biological metabolism. The potential risk of eutrophication in the estuary is high. Moreover, under the effect of aquaculture and rural area, there is higher potential ecological release risk of heavy metal in the estuary. And samples in the middle transect have the highest potential ecological risks of heavy metal. Therefore, a framework has been proposed to predict the ecological status of the estuary by analyzing the sources, content, and structural characteristics of sediment DOM. These results provide a new insight on ecological indication of DOM in Dagu River estuary.