Assessing the impact of physical distance and substitute distance on stated preferences: a choice experiment case from a Chinese bay

Spatial distance is a crucial factor influencing the public's willingness to pay (WTP) for ecosystem services improvements, and clarifying its impact on preferences and WTP is essential for enhancing the validity of value assessments. Based on this, Jiaozhou Bay in China was taken as a case study, with spatial distance divided into two categories: the physical distance from respondents' residences to Jiaozhou Bay and the substitute distance to the nearest alternative bay. Research data from a survey of 568 members of the public were collected using a choice experiment (CE), and a random parameter logit (RPL) model was employed to analyze the impact of these two distance variables on public preferences and WTP. The results show that: (1) public preferences and WTP for bay landscape function and green tide scale exhibit a significant physical distance decay effect, with a clearly defined spatial boundary; (2) substitute distance has a positive effect on preferences and WTP for bay water clarity, landscape function, and green tide scale, indicating a compensatory preference mechanism when substitute resources are less accessible; and (3) spatial distance effects are heterogeneous across social groups, with female and highly educated respondents showing more stable WTP in response to distance variation. These findings confirm the critical role of spatial distance in shaping environmental preferences and offer policy implications for better integrating spatial dimensions into the design of environmental interventions.