Variability in N₂O emission controls among different ponds within a hilly watershed

While it is well established that small water bodies like ponds play a disproportionately large role in contributing to N₂O emissions, few studies have focused on lowland ponds in hilly watersheds. Here, we explored the characteristics of N₂O concentrations and emissions from various typical ponds (village, tea, forested, and aquaculture ponds) in a hilly watershed and examined the specific controls influencing N₂O production. Our findings revealed that tea ponds exhibited the highest N₂O flux (8.42 ± 8.23 μmol m^-2 d^-1), which was 2.8 to 3.3 times greater than other types of ponds. Remarkable seasonal variations were observed in tea and forested ponds due to the seasonality of nutrient-enriched runoff, whereas such variations were less pronounced in village and aquaculture ponds. Key factors such as nitrogen levels, temperature, and dissolved oxygen (DO) emerged as the primary controls of N₂O concentrations in ponds, heavily influenced by land use and human activities in their drainage areas. Specifically, N₂O production in tea and aquaculture ponds was driven by N inputs from fertilization and feed, respectively, while DO levels governed the process in village and forested ponds, influenced by abundant algae and forest vegetation. This study emphasizes that environmental factors predominantly drive N₂O production in ponds within hilly watersheds, but land use in the pond drainages acts as an indirect yet crucial influence. This highlights the need for future research to develop targeted emission reduction strategies based on land use to effectively mitigate N₂O emissions, promising a path toward more sustainable and climate-friendly watershed management.