Ecosystem service value of Fenhe River based on Manning formula
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Abstract:
The value of river ecosystem services was a crucial factor in determining the necessary ecological flow of river courses and ensuring the success of ecological water supplement projects. The primary course of the Fenhe River served as a case study to improve the traditional method of calculating river ecosystem service values by incorporating the Manning formula. Six hydrological stations, including Fenhe Reservoir Station, Yitang Station, and Hejin Station, were analyzed for their complex cross-sectional configurations and hydraulic parameters such as longitudinal gradient ratio and river roughness. This comprehensive approach was essential in understanding the diverse and variable nature of river ecosystem service values. A detailed analysis was conducted to explore the variability of river ecosystem service values. The results indicated a clear increase in river ecosystem service values with rising flow levels, although this increase exhibited diminishing marginal returns. The ecological and economic value of a single cubic meter of river water showed a gradual decrease as flow levels increased, indicating a progressively slower rate of decline. This phenomenon underscored the importance of optimizing flow levels to maximize both ecological and economic benefits without overburdening the river system. The relationship between flow and river water ecological value, combined with the actual situation of the study area, suggested that there was a range of flow rates that could both maintain a healthy river ecosystem and maximize socio-economic development. Significant insights were revealed when the Fenhe River introduced six hundred million cubic meters of Yellow River water, ensuring an ecological water supplement of at least fifteen cubic meters per second during the dry season. Under these conditions, the ecological economic value of a single cubic meter of water in the main stream of the Fenhe River was determined to be 8.74 yuan. Consequently, the annual ecological value of the river was calculated to be 4.131 billion yuan. These figures highlighted the substantial economic contributions of maintaining adequate ecological flows in river systems. The shape of the river channel cross-section affected the relationship between flow and water surface width, thus altering the relationship between flow and river water surface area. The total value of river ecological services increased with flow, but the rate of increase slowed down, consistent with the law of diminishing marginal returns. Several conclusions were derived from this study: First, based on the relationship between flow rates and river water ecological value found in this study, and considering the actual situation of the study area, it was determined that there is a range of flow rates that can maintain a healthy river ecosystem while maximizing socio-economic development. The shape of the river channel cross-section affected the relationship between flow and water surface width, thus altering the relationship between flow and river water surface area. Second, the total value of river ecological services increased with flow, but the rate of increase slowed down, consistent with the law of diminishing marginal returns. The relationship between river water ecological value and flow followed the theory of diminishing marginal returns, showing a negative correlation. As flow increased, the ecological value per cubic meter of river water decreased exponentially. Whatever, when six hundred million cubic meters of Yellow River water were introduced into the Fenhe River, with an ecological water supplement of no less than fifteen cubic meters per second during the dry season, an annual ecological value of 52.44 billion yuan was generated. Over sixteen years, the total ecological value reached 839.04 billion yuan, approximately eight times the investment of 10.41 billion yuan for the Fenhe ecological water replenishment and supply project. This has significant implications for maintaining the ecological flow of the Fenhe River. Finally, constructing a dynamic model of river ecosystem service value that accounts for spatiotemporal variations remains a key focus for future research. This approach will help provide a more accurate assessment and management strategy for river ecosystems, ensuring their sustainability and the long-term benefits they provide to both the environment and society.
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