2018 Volume 54 Issue 3 Pages 83-94
This study focused on the effect of leaf litter of different tree species on the water quality of ponds. Differences in the effects of substances eluted from dry leaves from a broad-leaved deciduous tree （Kunugi, Quercus acutissima） and an evergreen coniferous tree （Japanese cedar, Cryptomeria japonica） were examined using four outdoor experimental ponds. Each pond shape has a length 2.5 m, width 2.5 m and depth 1.0 m. Dry leaves were added to three of the ponds in ratios of 100% Kunugi, 100% Japanese cedar, and 50% of each species. The fourth pond was used as a control pond. The concentrations of CODMn, TP, TN, and potassium ions due to water－soluble substances from the dry Kunugi leaves were higher than those from Japanese cedar leaves; the elution rate was also faster for Kunugi leaves. Additionally, the concentration of chlorophyll-a （an indicator of phytoplankton） was greater in the “Kunugi pond” than in the “Japanese cedar pond.” Therefore, the influence of dry Kunugi leaves on water quality was greater than that of Japanese cedar leaves. However, dissolved oxygen, which is important in habitats for aquatic organisms, was observed in poor oxygen （dissolved oxygen: ＜2mg・L－1） inappropriate habitats in ponds treated with both Kunugi and Japanese cedar leaves, and these conditions continued for more than one week. In managing the water quality of ponds, it is possible to reduce the amount of elution by immediately removing fallen leaves from the water.
