リターフォールによる金属元素の林地への還元

Abstract

森林生態系での金属元素の挙動を知るため, 樹冠通過雨や樹幹流とともに, 林地への金属元素の流入媒体となるリターフォールについて, その季節変動とそれに含まれる各種金属元素をアカマツ, クロマツ, ヒノキを主とする山地林分で2年間にわたって調査した。リターフォールは10月から12月にかけて顕著に高い季節変化を示し, また年平均のリターフォールは5. 03t/haであった。熱中性子放射化分析法によって全てのリターフォール試料について検出できた金属元素は, 濃度の高い方から, Ca, Mn, Al, Fe, Na, Zn, Rb, La, Ce, Sm, とScで, 一部のリターフォールについてはVも定量された。最も高いCaの平均濃度は1. 24％, もっとも低いScは0. 1ppmであった。リターフォールによって林地に還元される金属元素は, Ca 30. 1, Mn 3. 27, Al 2. 12, Fe 0. 91, Na 0. 40, Zn 0. 17 (kg/ha・yr) などが比較的多く, 以下, Rb 19. 5, La 6. 93, Ca 4. 27, V 1. 76, Sm 1. 62, およびSc 0. 24 (g/ha・yr) であった。

The behavior of nutrient elements such as N, P, K, Ca, and Mg in a forest ecosystem have been reported. Most of these reports have been mainly focused on the amounts of nutrient elements and the circulation in a forest. However, many metal elements beside above mentioned elements returned to forest soil with throughfall, stemflow, dust, and litterfall. In this paper, the behavior of metal elements returned to a forest soil with litterfall was investigated at Kiryu experimental site, southeast part of Shiga prefecture, where the stand of this site mainly comprises of Hinoki (Chamaecyparis obtusa Endl.), Akamatsu (Pinus densiflora Sieb. et Zucc), and Kuromatsu (Pinus Thunbergii Parl). Litterfall was collected over two years (from Nov., 1985 to Oct., 1987). Litterfall increased from October to December, and the annual average was 5.03 kg/ha･yr. The metal elements in litterfall were measured using instrumental neutron activation analysis. The metal elements such as Ca, Mn, Al, Fe, Na, Zn, Rb, La, Ce, Sm, and Sc were detected in all samples, but V was detected in only a part of samples. The amounts of metal elements returned to the forest soil with litterfall were as follows ; Ca 30.1, Mn 3.27, Al 2.12, Fe 0.91, Na 0.40, Zn 0.17 (in kg/ha･yr) and Rb 19.5, La 6.93, Ce 4.27, V 1.76, Sm 1.62, Sc 0.24 (in g/ha･yr).