A watershed is a basic unit of water and nutrient cycling with hierarchical structure, in which a variety of local communities are embedded. While nutrient imbalances cause environmental issues at the watershed level, at the community level there may be many urgent local issues such as aging and lack of successors. Our basic idea of watershed governance is that both local and watershed issues can be solved through cross-level interactions mediated by biodiversity, leading to enhancement of socialecological health of watershed systems (Fig. 1).

In the Yasu River sub-watershed of Lake Biwa, we found that local communities are revitalized through conservation of familiar nature, which provides ecosystem services in the social-cultural context. Style and stage of such community activities depend on social-historical background and ecosystem types. Some case studies revealed that these activities can have positive effects on biodiversity and nutrient cycling at the local level, and enhance community well-being. At least in this sub-watershed, our research suggests that biodiversity has the potential to facilitate cross-level interactions, though diffusion of such activities to the whole watershed remains a challenge.

In the Silang-Santa Rosa sub-watershed of Laguna de Bay, by contrast, biodiversity is critically endangered and most residents have lost interest in aquatic environments. Through interviews and stakeholder workshops, however, we found that groundwater can be a shared object of interest among diverse stakeholders in the watershed. Sharing knowledge on groundwater research directly related to familiar nature meaningful for local peoples’ lives and livelihoods facilitated active discussions in a watershed forum as a platform for watershed governance.

Using social and natural scientific approaches, such as action research and phosphate oxygen isotope analysis, to compare different watersheds, we summarized key socialecological characteristics affecting governance processes. Even when there is less explicit interest in biodiversity, as in the case of Silang-Santa Rosa sub-watershed, there is indication that stakeholder communication relevant to familiar nature can be facilitated if a boundary object, such as groundwater, is taken as a key focus point. Ultimately, since all lands around the planet can be seen as parts of diverse watersheds, we believe that our basic approach to watershed governance—adapted to individual social-ecological contexts—can address many global environmental issues.

As to social outcomes of our research project, in the Yasu River sub-watershed, knowledge and experience of community activities have been shared between up- and down-stream communities, enhancing discussion of watershed sustainability. In the Silang-Santa Rosa sub-watershed, a Memorandum of Agreement was concluded between the Laguna Lake Development Authority (national government) and Santa Rosa City (local government) in relation to installation of a water quality monitoring facility at the watershed level, while the women’s group was transformed from a mandatory “women’s desk” engagement to an environmentallyconscious group through conservation of sacred spring as familiar nature. A textbook on watershed governance will be published in FY2020, aiding the diffusion of transdisciplinary approaches developed by our project to diverse stakeholders in other watersheds.

Figure 1 A conceptual schema of adaptive watershed governance