Dissolved organic matter (DOM) in aquatic ecosystems has gained wide concern because of its influence on the light attenuation, nutrient availability and contaminant transport. Human activities strongly influence the DOM of rivers in different ways, including increased agricultural activities and industrial and domestic emissions. However, recent socio-economic development with rapid urban development has significantly enhanced the discharge of sewage, and has caused high loads of DOM, which in turn pose a great risk to aquatic ecosystems. To effectively guide water management for protecting aquatic ecosystem health, it is very critical to investigate the distribution and source of dissolved organic matter in urban rivers. In this study, the distribution and source analysis of DOM in Beiyun River were evaluated, where covers the most populated area with a population of 14 million, representing the most urbanized watershed of Beijing. Since the main receiving source of the river is treated and untreated wastewater in Beijing City, the water quality is highly polluted by anthropogenic inputs. However, information on DOM of Beiyun river has not been reported. Therefore, this study can not only reveal the biogeochemistry of DOM in Beiyu River, but also provide useful implications of pollution control for similar urban rivers. The fingerprint features were extracted from the Excitation-Emission Matrix Spectrum of fluorescent dissolved organic matter (FDOM) in 23 sampling sites of Beiyun river during November 2013. Three separate fluorescent components were identified by Parallel factor analysis (PARAFAC) model, including two humic-like components (C1: 240, 300/385 nm; C2: 255, 350/400 nm) and one protein-like component (C3: 230, 280/340 nm). The results indicated that humic-like materials were generally the dominated component of FDOM, accounting for 76.18% of the average total fluorescence intensity. Positive relationships were found between the fluorescence intensity and the concentrations of some water quality indicators, such as total nitrogen, ammonia nitrogen and total phosphorus, indicating the same sources of these components. Thus, the migration and transformation of nitrogen & phosphorus could also influence the level of FDOM. The distribution of total fluorescence intensity showed a distinctly different spatial pattern. The fluorescence intensity decreased firstly along the upstream to midstream continuum, and then increased from the midstream to downstream. The FDOM in the upstream could be attributed to the industrial effluent and agricultural runoff inputs. Among the upstream to downstream continuum, the content of FDOM in the midstream was the lowest. Limited domestic pollution was suggested as the major source. In the downstream, the sources of FDOM could be interpreted as industrial, agricultural wastewater and livestock wastewater discharge. The relative abundance of protein-like materials was markedly increased in this area, indicating the sources of DOM was highly impacted by human activities. In addition, our study also concluded that the removal efficiency of DOM in wastewater plants is not very desirable, which implied that stronger support for DOM removal in sewage system is needed to alleviate DOM pollution and improve water quality.
Keywords: Beiyun River; excitation-emission matrix spectrum; fluorescent dissolved organic matter (FDOM); parallel factor analysis(PARAFAC); pollution source; spatial distribution.