森林立地53(2), 61〜71 2011

Jpn J For Environ 53 (2), 61–71, 2011

 

Hydrochemistry and nutrient budgets in a natural forest　in a karst area of southwestern China

 

Xiaoqiang Lu¹, Hiroto Toda², Fangjun Ding³, Dongsu Choi² and Shengzuo Fang⁴

¹United Graduate School of Agriculture Science, Tokyo University of Agriculture and Technology

²Faculty of Agriculture, Tokyo University of Agriculture and Technology

³Guizhou Academy of Forestry Sciences, China

⁴College of Forest Resources and Environment, Nanjing Forestry University, China

 

Bulk precipitation, throughfall, stemflow, and stream water were collected and the concentrations of major ions were determined from samples collected from a subtropical natural evergreen and deciduous broadleaf mixed forest in Maolan, a karst area in southwest China, in order to quantify the input-output budgets of major dissolved nutrients and to examine changes in the chemical composition of precipitation after passing through the canopy. Calcium ion and Mg²⁺ derived predominantly from carbonate weathering were the major contributors to the hydrologic system’s compartments. Low ion concentrations and a high pH value characterized bulk precipitation quality that was influenced by natural rather than anthropogenic sources in Maolan. Calcium ion and Mg²⁺ had negative annual input-output budgets in contrast to K⁺, Na⁺, Cl^-, SO₄^2--S, and dissolved inorganic nitrogen (DIN) that had annual positive input-output budgets. We used a canopy budget model (Na⁺ tracer) to estimate amounts of dry deposition and canopy exchange of ions in throughfall. Calcium ion had the largest annual dry deposition, followed by SO₄^2- and NH₄⁺. Annual atmospheric deposition of DIN amounted to 12.3 kg ha^-1 yr^-1. Eighty-six percent of DIN input in the forest was retained in the plant-soil system, indicating effective immobilization by vegetation and/or soil microflora.

Key words : bulk precipitation, dry deposition, input-output budgets, karst, natural forest

 

盧暁強・戸田浩人・丁訪軍・崔東壽・方昇佐：中国南西部のカルスト地域における天然林を移動する水の水質及び養分収支．森林立地53：61-71，2011．

中国の南西部茂蘭のカルスト地域において，林外雨，林内雨，樹幹流及び渓流水を採取し，降水の樹冠通過前後の化学組成の変化を明らかにするとともに，主なイオンの収支を把握した。本調査地は，人為的攪乱のない亜熱帯常緑・落葉広葉樹が混交した天然林である。水循環におけるCa²⁺とMg²⁺の移動量が多く，カルストの炭酸塩岩の影響が示唆された。中国国内の他の地域に比べ，降雨のイオン濃度が低く，pHが高いという特徴は，人為的な影響よりもカルストの自然条件が大きいと考えられる。また，主なイオンの収支はCaとMgでマイナスとなり，K⁺，Na⁺，Cl^-，SO₄^2--S及び溶存無機態窒素（DIN）はプラスとなった。樹冠収支モデル（Na+トレーサー）を用い，林内雨中の乾性沈着とイオンの樹冠交換割合を推定した。年間乾性沈着量はCa²⁺が最も多く，ついでSO₄^2-，NH⁴⁺であった。森林に流入したDINは年間12.3 kg ha^-1で，そのうち86％は，植生―土壌生態系への保持が推察され，植生と土壌微生物に効果的に利用されていた。

キーワード：降水，乾性沈着，養分収支，カルスト，天然林

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