Spatial variation of multifunctionality among abandoned rice paddies and irrigation ponds: potential roles of hydrological and environmental factors

Introduction Historically, rice paddy fields and irrigation ponds in Asia have removed nitrogen from irrigation water, such as spring water from upland croplands, while simultaneously providing multiple ecosystem services and supporting biodiversity. However, abandonment has diminished their multifunctionality. Although some abandoned paddies/ponds function as natural wetlands, their hydrological/environmental characteristics are highly variable. Objectives We explored whether harnessing these abandoned sites as nature‐based solutions (NbS) can offer substantial opportunities for restoring ecosystem services and biodiversity, and identified key factors to enhance their multifunctionality. Methods We surveyed 61 abandoned paddies/ponds in the Lake Kasumigaura watershed, Japan, and quantified six ecosystem service and biodiversity indicators: water purification, water storage, methane (CH 4 ) regulation, damselfly richness, native fish richness, and resistance to invasive by exotic fishes. We examined tradeoffs/synergies among these indicators using principal component analysis. Results Principal component 1 revealed positive relationships among water purification, water storage, and damselfly richness. The strength of these synergies depended on the type of water flow: non‐channelized flow abandoned paddies/ponds exhibited higher synergies. Sites with stronger synergies tended to be less resistant to exotic fish invasion. Principal component 2 and principal component 3 represented CH 4 regulation and native fish richness, respectively, both of which were independent. CH 4 regulation decreased with lower dissolved oxygen concentrations, while native fish richness increased at sites with diverse vegetation types. Conclusions Our results highlighted the potential of abandoned paddies/ponds as multifunctional restoration tools in agricultural landscapes and suggested their effectiveness because NbS can be enhanced by managing hydrological/environmental factors.