Objective Large-scale waterfront green spaces serve both as valuable resources for biodiversity and as significant recreational facilities for urban residents. Residents face a severe mental health crisis, especially in high-density built environments. This research intends to explore the influence mechanism of biodiversity level in waterfront green space on mental restoration, in hope of enhancing residents’ mental health and providing a theoretical basis for building a healthy city.

Methods This research takes the “100-mile Yangtze River Ecological Corridor: Urban Section” in the central urban area of Wuhan as an example, and selects 18 relatively enclosed small sites in 5 waterfront green spaces as sample sites. A total of 447 questionnaires (437 valid ones) are distributed in 7:00-9:00 a.m. and 16:00-18:00 p.m. on weekdays to obtain residents’ perception of plant diversity and bird diversity, as well as their perceived restorativeness and mental restoration level. Then the influence mechanism of perceived biodiversity on residents’ mental restoration, as well as the mediating effect of perceived restorativeness are explored by constructing a structural equation model (SEM).

Results Perceived biodiversity can significantly promote residents’ mental restoration, and perceived restorativeness serves as a mediator in the linkage between perceived biodiversity and mental restoration. Specifically, perceived plant diversity may directly promote mental restoration and indirectly enhance perceived restorativeness by influencing perceived restorativeness. In addition, there are differences in the contribution of “plant species diversity”, “plant color diversity” and “plant odor diversity” to mental restoration (0.820, 0.780 and 0.694 respectively). Besides, there is also a significant positive correlation between perceived bird diversity and perceived restorativeness (p < 0.05), but there is no significant correlation between perceived bird diversity and mental restoration, and perceived bird diversity can only indirectly contribute to mental restoration through the mediator element of perceived restorativeness. The three dimensions of “bird species diversity” and “bird sound diversity” and “bird color diversity” have similar capabilities to promote mental restoration by restoring attention (0.842, 0.839 and 0.820 respectively). That is, perceived plant diversity, which significantly influences mental restoration, mainly focuses on the visual dimension, whereas the perceived bird diversity takes both visual and auditory dimensions into account. In addition, the farther away from riverbank, the stronger the positive effect of perceived bird diversity on perceived restorativeness. In contrast, personal attributes such as gender, age, education, income, and frequency of contact with nature show no significant influence on residents’ health benefits.

Conclusion This research concludes that perceived biodiversity has a positive effect on mental health among residents in large urban waterfront spaces. There are a number of measures that can be taken in the future to enhance the benefits that waterfront green spaces can provide for improving the mental health of residents: 1) It is important to mix a variety of land covers throughout the overall layout to create a sense of rich landscape heterogeneity, and special sidewalk and cycle track should be set in green spaces to mitigate the influence of noise, especially the noise from motor vehicles. 2) Plant configuration and mixing can be improved by increasing the number of plant species and enhancing the color richness, and the proportion of native plants can also be increased since native plants are easier to recognize than other plant species. Food source plants and vegetation with high heights can be selected to attract birds to a particular area. 3) For waterfront facility and green space management, there is a need to add waterfront elements with restorative benefits (water-friendly platforms, e.g.) on the riverbanks and to enhance waterfront safety management. Firstly, the existing stone embankment may be replaced by interplanting vegetation layers, which can maintain the buffering effect against flooding while further attracting birds to stay. Secondly, graded stepped barges can be used to provide viewing points at different heights to create a comfortable viewing environment. This may facilitate shoreline waterfowl observation and increase water surface visibility. Additionally, a temporary railing should also be included in the design of the water-friendly platform to ensure safer interaction with the water body. 4) It is also important to set up science popularization and education facilities for biodiversity to, through regular public outreach, promote biodiversity science popularization activities in green spaces, and thus improve residents’ perception of biodiversity. The purpose of this research is to offer an innovative perspective on improving the quality of waterfront green space in high-density built environments. This is also significant for contributing to urban residents’ health and well-being. In the future, the aim is to optimize experiment design so that experimental conditions can be controlled and more indicator organisms (e.g., insects) can be selected. Moreover, in the future, there will be a focus on how to analyze the influence mechanism of biodiversity on mental health at multiple spatial and temporal scales.