森林内外の降水中の養分量について (III) : 流亡水中の養分量について

Abstract

1. 第1・第2報において, 林外降水・林内降水・樹幹流に含まれる養分濃度・量・その季節的変化・1年間合計量などを測定した結果を報告した。2. 第3報は, 林外降水・林内降水・樹幹流とともに, 地表流・地申流・渓流流出水に含まれる養分濃度・量を測定し, (ただし, 地中流は養分濃度のみ, 渓流流出水に関するデータは広葉樹林についてのみ), 森林生態系における水溶性養分の動態を考察した結果の報告である。分析した養分は第1・2報と同じくカリウム・カルシウム・マグネシウム・リン・硝酸態チッ素・アンモニア態チッ素である。3. 渓流流出水の養分濃度は林内降水+樹幹流の濃度に較べてひくく, かつ季節的な動きもすくなかった。渓流流出水に含まれる養分量も林内雨+樹幹流に較べてちいさかった。渓流の養分量を規制する最大の因子は林外降水量と一次の関係をもつ渓流流出量であった。渓流の養分量と林外降水量はほぼ一次の関係をもっていた。4. 秋・冬期には降水量がすくない上に, 溶脱をうけやすい新鮮な落葉があるので, 地表流・地中流の濃度がたかくなる傾向があり, とくに広葉樹林地表流にこの傾向が著しかった。一般にカリウム・カルシウム・マグネシウムでは地中流の濃度が地表流よりたかいことが多く, リン・硝酸態チッ素・アンモニア態チッ素では, その逆のばあいがおおかった。5. 林外雨から渓流にいたるまで, 森林生態系の各部分を通過するときの降水の流水に含まれる各養分の年平均濃度値を求め, 垂直的な変化を考察した。リンを除いて, 各養分濃度は林床に達したときにはそうとうたかくなった。カリウム・カルシウム・マグネシウムは地表流・地中流とその濃度をたかめ, 逆にリン・硝酸態-・アンモニア態-チッ素は濃度が低くなる傾向があった。地中流から渓流にいたるあいだに広葉樹林における各養分濃度はひじょうにちいさくなった。林外降水の濃度と渓流の濃度を比較すると, カリウム・カルシウム・マグネシウムでは, 林外降水より渓流の濃度がたかく, 逆に他の三養分では林外降水のほうがたかかった。6. 森林生態系にとって収入である林外雨の養分量と, 支出である渓流流出水の養分量を広葉樹林について比較すると, カリウム85％, カルシウム57％, マグネシウム180％, リン26％, 硝酸態チッ素18％, アンモニア態チッ素8％で, マグネシウム以外は収入が支出よりおおきかった。

1) The results of the studies carried out at the Hinoki (Chamaecyparis obtusa) and the broadleaved forest in the Kyoto University Kamigamo Experimental Forest Station, on the following items have been already submitted in a first and second report. The items consisted of the nutrient concentration and the amount contained in open rain fall, through-fall, and stem-flow in two forests, their seasonal fluctuations, and the total amount of nutrients per ha annum. 2) In the the present report an investigation on the movement of water soluble nutrients in the forest ecosytems was carried out, by examining the nutrient contents in surface-, undeground- (-10cm depth) and stream-runoff as well as in open rain, through-fall and stem-flow. Because the Hinoki stand was not in the watershed of the stream, no data was available for stream runoff in this case. The nutrients analysed and studied were of following: potassium, calcium, magnesium, phosphorus, nitrate- and ammonia-nitrogen which are the same as in the first and second reports. 3) The six nutrient concentrations in stream dischage were much smaller than those in the through-fall plus stem-flow (net-precipitation), and their seasonal fluctuations were smaller as well. (Fig. 4) The most efficient factor for the amount of nutrients in stream dischage was the amount of stream discharge itself, concequently the nutrient amounts in stream discharge were almost proportional to the amounts of stream discharge and the gross precipitation (open rain fall). (Fig. 6) 4) In autum and winter, the surface- and underground- runoff water in most cases increased their nutrient concentrations because of low precitation and the existence of new litter fall from which nutrients could be leached easily. The increase was especialy remarkable in the case of potassium contained in the broadleaved forest. In most months, the nutrient concentrations of potassium, calcium, and magnesium contained in underground runoff were higher than those in surface runoff, and those of phosphorus, nitrate- and ammonia-nitrogen contained there, were smaller. (Fig. 9) 5) The water passes through the each layer of the forest ecosystem, i.e. the net precipitation, surface-, underground-runoff, and then into a stream. The nutrient concentrations contained in the waters of successive layers were analysed and their fluctuations studied verticaly. Upon reaching the forest floor as net precipitation, the nutrient concentrations increased with one exception of phosphorus. In the surface and the underground layer, nutrient concentrations changed as mentioned above. In the flow from the underground layer to the stream, the water decreased its nutrient concentrations remarkably. In the case of potassium, calcium, and magnesium, the nutrient concentrations in the stream discharge were higher than in the open rain water and it was lower in the cases of phosphorus, nitrogen. (Fig. 11) 6) The nutrient amount in gross precipitation is the income and that in the stream discharge is the output for the forest ecosystem. The budget of the amounts of water soluble nutrients of the broadleaved forest ecosystem were estimated. (Figs. 12, 14) The percentages of potassium, calcium, magnesium, phosphorus, nitrate- and ammonia- nitrogen of the output to the income were 85, 57, 180, 26, 18 and 8% respectively. It can be said that the forest ecosystem accumulates water soluble nutrients except for maguesium. (Fig. 15, Table 3)