Estimation of Fallen-leaf-derived Nutrient Load in Park Pond

Abstract

The pond in a park serves as a recreational waterside area; however, problems such as foul odors and landscape deterioration due to eutrophication persist. Despite these problems, quantitative evaluations of the impact of fallen leaves on water quality remain limited. Such evaluations are essential for developing effective tree planting and leaf litter management strategies. This study focused on Lake Nanko, a park pond in Shirakawa City, Fukushima Prefecture, in 2023. Fallen-leaf-derived nutrient loads were estimated through field surveys and laboratory experiments. The total nutrient load in Lake Nanko was determined by summing the fallen-leaf-derived nutrient load, river inflow, and nutrient elution from sediments. Annual leaf-derived nutrient loads entering the lake from the water surface were estimated at 9.51 kg-N (total nitrogen, T-N) and 0.480 kg-P (total phosphorus, T-P) , while riverine loads were 0.35 kg-N and 0.022 kg-P. The proportions of leaf-derived loads relative to the total nutrient load were 0.1% for T-N and 0.7% for T-P annually. Even during the leaf-fall season, the contributions were 0.1% for T-N and 2.6% for T-P. These findings indicate that nutrient loads from fallen leaves have only a limited impact on the overall water quality of Lake Nanko.