In general, the public perceives wetlands to be beneficial for physical and mental health, which is consistent with the conclusion of previous studies that urban green space and blue-green space are beneficial to people's physical and mental health (see Sect. 1.2.2). A possible reason for the lowest perceived health benefits during the Peak could be the higher risk of infection. Limited access to WPs during the Peak could also contribute to the low perception of health benefits. The increase in perceived health benefits after the Peak shows that inaccessibility to WPs for a period of time may improve perceived health benefits from WPs.
On the city level, the moderate epidemic risk is associated with greater physical and mental health benefits for those who visited the park during the Peak. In contrast, very high risks have a negative impact on perceived physical health benefits, and lower risks are not conducive to perceived mental health benefits. Surprisingly, for respondents who live in the most severely affected cities during the Peak, the expected psychological healing effect of visiting WPs after the epidemic was lower than those living in other regions.
On the community level, unexpectedly, the perceived level of physical and mental health benefits after the Peak is negatively associated with the lockdown degree of the community, suggesting that quarantine did not lead to an increase in health-related motivation for visiting WPs.
In terms of WPs level, habitat services were considered to be the most important ecosystem services that promote the perceived health benefits. The possible reasons are: (1) self-reported happiness is positively correlated with the perceived species richness of birds, butterflies, and plants (Dallimer et al. 2012); (2) the biologically diverse natural environment can improve health by exposure to a pleasant environment or encouraging health promotion behaviours (Lovell et al. 2014); (3) there is a strong positive correlation between vegetation cover and personal well-being. The relationship between human well-being and nature is weakly correlated with changes in species richness, bird abundance, and plant density (Luck et al. 2011). However, habitat services were regarded as indirect health-related ES that affect human health through another service, and the mechanism of their effect on health is still unclear. The importance of habitat, air purification and recreation services align with the motivation for visiting WPs (e.g. being close to nature and wildlife habitat, enjoying fresh air and going out for exercises).
On the individual level, this study has found that men perceive higher health benefits than women when visiting urban blue-green spaces during the Peak. There is no significant gender difference before and after the epidemic. This is different from the result of a previous study based on two of Canada's blue-green spaces that women usually perceive higher health well-being than men from visiting nature reserves (Lemieux et al. 2012). The phenomenon that housewives and the elderly are more dependent on the local environment and therefore are more susceptible to the local environment(de Vries et al. 2003) could be a possible explanation to our result that the temporarily unemployed (e.g. housewives) and retirees (e.g. the elderly) perceived higher mental health benefits than the other two groups after the Peak. In addition, health experts' perception of mental health benefits before the epidemic and that of physical and mental health after the Peak were significantly lower than other professional groups, which indicate that lay people may have overestimated or health experts may have underestimated the health benefits of visiting WPs. Besides, health experts believe that the health benefits after the peak of the epidemic are slightly lower than before the outbreak, while other people have the opposite view. This may be because health experts believe that travel after the peak of the epidemic poses a higher risk.
This study is based on a large number of subjective responses regarding the perceived health effects of WPs. It does not objectively measure the health effects of WPs. Ecosystem disservices could negatively affect the perception of health benefits. For conducting the questionnaire, it was the assumption that there is little risk of infection by COVID-19 when visiting wetland parks after the Peak, which naturally excludes the effect of some infectious disease-related ecosystem disservices on health perception. Moreover, factors such as the quality, area, and degree of nature of the WPs may affect health (Ekkel and de Vries 2017), and perceived health benefits. This study is a general analysis based on national sampling. It does not provide a detailed analysis of specific WPs, including their quality, area, and degree of nature. To control the number of questions and response time, this study did not use more detailed assessment scales (e.g. EQ-5D (Leidl 2009), General Health Questionnaire (White et al. 2013)) to assess health status. This could have an influence on the respondents' self-reported health status. Most participants had a high level of education, suggesting that they understand the contents of the questionnaire well. Due to the nature of the epidemic, and the restrictions in face-to-face research, this study has to rely on the Internet, thus making it difficult to involve the elderly and non-Internet users.