Study On Ecosystem Health Assessment And Blue-Green Infrastructure Optimal Allocation Of Urban Watershed

The increasing impervious surfaces resulting from urbanization development and intensifying precipitation extremes with climate change pose significant urban area challenges.These conditions significantly modify the watershed hydrological and geomorphological processes and have brought a series of resource and environmental problems,such as the degradation of river network structure,soil erosion,and water pollution,placing mounting pressure on urban biodiversity,ecosystem services,and resilience.Ecosystem health assessment and ecological management zoning are prerequisites for ecological restoration and urban watershed sustainability.As an important component of ecological space,blue-green infrastructure provides multiple benefits,such as flood risk reduction,biodiversity maintenance,and heat island effect mitigation.It plays a significant role in urban watershed ecosystem quality enhancement and ecosystem management.Taking the Yangmei River Basin in Guangzhou City as the study area and integrating the multidisciplinary knowledge of landscape architecture,landscape ecology,hydrology,and geography,this study analyzed the direction and contribution of landscape composition and configuration to runoff changes based on the storm water management model(SWMM)and landscape dynamic analysis,and constructed the ecosystem health assessment framework of urban watersheds from two dimensions of ecological integrity and ecosystem services.In addition,the corresponding optimization strategy was proposed by combining the multi-functional benefits of blue-green infrastructures to improve the ecological health of urban watersheds.The main works are as follow:(1)The SWMM model,with strong applicability in an urban watershed,can better provide water quantity and quality information.In this study,the SWMM model of the Yangmei River basin was constructed.The SWMM parameters of the Yangmei River Basin referred to model parameters of the Tianhe Smart City community,with sufficient data and a calibrated and verified model.These parameters were calibrated and verified through the comprehensive runoff coefficient method.The sensitivity analysis results of the SWMM model parameters revealed that Dstore-imperv,Mix Rate,and Pct Zero were moderately sensitive.At the same time,Decay Constant,Max Rate,Dstore-perv,N-perv,and N-imperv exhibited a decreasing sensitivity.Drying Time does not affect the runoff coefficient.(2)To study the relationship between landscape changes and runoff,the SWMM model,landscape metrics,correlation analysis,and the random forest importance measure were integrated to analyze the direction and contribution of landscape composition and configuration to runoff changes.Results indicated that woodland could reduce runoff,while farmland and water bodies positively impacted runoff changes.The higher fragmented landscape pattern was likely to have altered the runoff,while landscape patterns of a larger size,higher concentrations,and a declining richness typically reduced runoff.The random forest importance evaluation demonstrated the significant contributions of Patch Density,Shannon’s Diversity Index,and Large Path Index to runoff.(3)In terms of ecological integrity and ecosystem services,the ecosystem health assessment framework of urban watersheds was constructed in this study.In addition,urban watershed ecosystem health assessment was obtained on a grid scale by introducing landscape pattern models,hydrological models,and ecosystem service models.The results showed that the watershed ecosystem health changed drastically in the western mountains and the southeastern living area from 1999 to 2013.During 2013-2019,the watershed ecosystem services value increased,and the deterioration of the watershed ecosystem health slowed down.From 1999 to 2019,the overall watershed ecological health has improved,but the regional differences have widened.Five ecological management zones were obtained based on the dynamic changes in the watershed ecological health in the past 20 years,aiming to provide a theoretical basis for the follow-up watershed management and ecological environment improvement.(4)As an effective tool for rainwater management,blue-green infrastructure can promote natural infiltration and evapotranspiration processes and reduce flood damage to the watershed’s ecological environment.In this paper,the response surface method was selected to optimize the allocation of four selected green infrastructures.The runoff total control rate,pollutant removal percentage,and comprehensive economic cost were quantified by SWMM model simulation and life cycle cost analysis.The results showed that the optimal layout proportions of green roof,permeable pavement,vegetated swale,and bioretention cell were34.818%,49.838%,29.999%,and 20.000%,respectively.Based on the optimal green infrastructure layout scheme,seven blue infrastructures in the Yangmei River basin were reconstructed to meet the demand of the total storage volume in the study area.(5)As one of the best practices for stormwater runoff control,green roofs can also be used as habitats or stepping stones to participate in the construction of blue-green infrastructure networks to maintain biodiversity.To alleviate the contradiction between the blue-green infrastructure construction and the land shortage,integrating the potential green roofs and their landscape connectivity,a blue-green infrastructure network optimization method was proposed based on morphological spatial pattern analysis,landscape connectivity assessment,and minimum cumulative resistance model.The results showed that compared with the scenario without potential green roofs,there were more paths for species dispersal and exchange occurring among ecological patches in the blue-green infrastructure network with integrated potential green roofs,and the movement of individuals,populations,and species within construction land increased.