高齢化したスギ・ヒノキ人工林小流域の斜面下部伐採が土壌および渓流の水質に及ぼす影響  [in Japanese] Effects of Forest Cutting in a Lower Slope on Soil Water and Stream Water Chemistry in a Watershed of Old Japanese Cedar and Cypress Stands.  [in Japanese]

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Author(s)

    • 浦川 梨恵子 Urakawa R.
    • 東京農工大学大学院連合農学研究科 United School of Agricultural Science, Tokyo University of Agriculture and Technology
    • 戸田 浩人 Toda H.
    • 東京農工大学大学院共生科学技術研究所 Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology
    • 生原 喜久雄 Haibara K.
    • 東京農工大学大学院共生科学技術研究所 Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology

Abstract

高齢のスギ•ヒノキ人工林小流域(99年生)における流域面積の約20%の斜面下部の伐採が,養分動態に与える影響を明らかにするため,伐採の前後で渓流水量および土壌水分量の測定,土壌水,湧水および渓流水の水質分析を行った。伐採後,表層土壌(0~10cm)では土壌水分が減少し,下層(30~60cm)は湿潤状態にあった。また,渓流からの流出水量は年間約100mm増加した。表層土壌水(5cm)のNO<SUB>3</SUB><SUP>-</SUP>, Ca<SUP>2+</SUP>, Mg<SUP>2+</SUP>およびK+濃度は伐採1,2年目の夏季に3~7倍に上昇したが,3年目には伐採前の水準に戻った。渓流水でも夏季にNO<SUB>3</SUB><SUP>-</SUP>, Ca<SUP>2+</SUP>およびMg<SUP>2+</SUP>濃度が,伐採前同時期の約1.5倍に上昇し,分析を行ったすべてのイオンで濃度の季節変動が大きくなった。伐採後の土壌水中のNO<SUB>3</SUB><SUP>-</SUP>-N量は,30 cm以深における増加が顕著で,伐採3年目でも伐採前の4倍以上を維持していた。伐採後,NO<SUB>3</SUB><SUP>-</SUP>-N流出量は4.0~5.Okg ha<SUP>-1</SUP> yr<SUP>-1</SUP>増加したが,土壌水中のNO<SUB>3</SUB><SUP>-</SUP>-Nの増加量と比較すると少ないことから,土壌中で生成した無機態窒素のすべてが渓流へ流出するわけではなく,土壌中での窒素の蓄積および消費が示唆された。

The effects of forest cutting on nutrient dynamics, soil water content and chemistry, and stream water discharge rates and chemistry were examined for three years after the partial (lower slope ; 20% of total area) forest cutting of a watershed composed of artificial stands of old (99 years) Japanese cedar and cypress in Gunma prefecture, Japan. After the forest cutting, the soil water content in the surface soil layer (010 cm) decreased, although it increased in a deeper layer (3060 cm). The annual stream water discharge increased by about 100 mm after forest cutting. Compared to the period before cutting, the concentrations of NO<SUB>3</SUB><SUP>-</SUP>, Ca<SUP>2+</SUP>, Mg<SUP>2+</SUP>, and K<SUP>+</SUP> in surface soil water (5 cm) also increased during the summers of the first two years by about 37 times. However, three years after forest cutting, the concentrations decreased to the same levels as those in the period before cutting. Similarly, the stream water concentrations of NO<SUB>3</SUB><SUP>-</SUP>, Ca<SUP>2+</SUP>, and Mg<SUP>2+</SUP> increased 1.5 times. Seasonal changes in the concentrations of all analyzed ions in stream water increased in comparison with those before cutting. After forest cutting, the amount of NO<SUB>3</SUB><SUP>-</SUP>-N in the 3060 cm layer increased by four times the amount before cutting. Furthermore, this large amount persisted during the three consecutive years after the forest cutting. The NO<SUB>3</SUB><SUP>-</SUP>-N export to stream water increased up to 4.05.0 kg ha<SUP>-1</SUP> yr<SUP>-1</SUP> after cutting. However, the increase in the amount of NO<SUB>3</SUB><SUP>-</SUP>-N leaching to stream was smaller than that in soil water; this indicates the great potential of soil as a medium for NO<SUB>3</SUB><SUP>-</SUP>-N export. A higher amount of NO<SUB>3</SUB><SUP>-</SUP>-N in deeper soil (>30 cm) suggests retention and/or consumption of this ion in the soil even after the forest cutting.

Journal

  • Journal of the Japanese Forest Society

    Journal of the Japanese Forest Society 87(6), 471-478, 2005

    THE JAPANESE FORESTRY SOCIETY

Codes

  • NII Article ID (NAID)
    130003580647
  • Text Lang
    JPN
  • ISSN
    1349-8509
  • Data Source
    J-STAGE 
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