Bacterial Metabolic Function Of Sediment And Its Indicative Role In The Division Of Ecological Function Units In River Basins

At present,studies on the division of aquatic ecological function mostly developed based on various aspects such as biodiversity conservation,water ecological resources conservation,and/or environmental factors,but these parameters often have some limitations.Also,there is a great debate about whether these parameters can fully or correctly reflect the functional attributes of different structural units of water ecosystems in the basin.In recent years,some metabolic pathways of bacterial communities have been used as one of the main tools for ecosystem health evaluation and monitoring,but there is no research precedent in the field of aquatic ecological function division.At the same time,it is unknown whether the diversity,structure and functional metabolic abundance of bacterial communities in sediments reflect the characteristics of ecological factors and functional expressions of regional unit in the study area.It is known that bacterial communities are very sensitive to the environment,but their metabolic functions may be convergent at similar ecological conditions.In this study,we take the catchment area of Duliujian River Basin and Yongding River Basin in Tianjin as the study area,the samplings of overlying water and sediment were collected,to study the diversity,structure,and functional metabolic abundance of bacteria in sediment from different continuous spatial units of main stream and tributaries,and to explore its feasibility as a key factor in the division of aquatic ecological function in the coastal river basins.The results showed as follows:(1)The variation characteristics of the water environmental factors at the river basin scale.The physicochemical properties of sediments in the Duliujian River Basin do not vary significantly among different spatial units,except for nitrate nitrogen.Also,the changes of physicochemical properties in different spatial units are not obvious.In Yonding River Basin,the organic matter of sediments differs significantly between the main stream and tributaries,but the water quality characteristics of the overlying water do not vary significantly.The reason for the lack of changes in physical and chemical properties of sediment and overlying water in the coastal river basins may be due to the exogenous input and endogenous variation of nitrogen,which cannot be accurately used as parameters in the division of aquatic ecological function.(2)The variation characteristics of bacterial flora at the river basin scale.In the sediments of the Duliujian River Basin,except for Shannon and Simpson indices,the rest of the diversity indices showed significant differences between different spatial units,which showed in an order of tributaries > main stream.Meanwhile,the physicochemical properties of sediments did not have significant effects on the diversity of bacterial communities.In the sediments of the Yongding River Basin,the bacterial community diversity was significantly influenced by p H,but it did not differ between tributaries and main stream.In addition,the metabolic abundance of the bacterial community in different spatial units showed an order of main stream >tributary,indicating that it can be used as a key indicator for the classification of river functional units to some extent.It was also found that the functional metabolism level of the bacterial community in the Duliujian River Basin was influenced by organic matter and total nitrogen content,while the functional metabolism of the bacterial community in the Yongding River Basin was influenced by moisture content and ammonium nitrogen content.Therefore,river water quantity and water quality(input of exogenous nitrogen)can affect the functional metabolism of bacterial communities.(3)Based on the functional metabolic level of the bacteria community in the sediments.The principal component analysis showed that the functional units of Duliujian River Basin and Yongding River Basin can not be classified well based on the variation of the physicochemical properties of sediments and overlying water,but the metabolic abundance of the bacterial community in sediment had obvious boundary characteristics between different spatial units of the two river basins,which can be classified into Level-1 and Level-2 clearly.In addition,the network co-occurrence analysis showed that the tributaries of the Duliujian River Basin and Yongding River Basin had more complex network topologies than the main streams.In this study,the division of ecological function cannot be properly performed based on the physicochemical properties of sediment and overlying water in coastal river basins.However,the functional metabolism of bacterial communities may be influenced by spatial variables,and different spatial units of the coastal river basin may show obvious boundary characteristics.Therefore,the metabolic abundance of bacterial community can be selected as a key indicator in the division of aquatic ecological function in coastal river basins.