『Abstract
To evaluate whether rates of weathering of primary minerals are
underestimated in watershed mass-balance studies that fail to
include products of weathering accumulating in plants and in developing
soil, changes in the calcium and magnesium content of vegetation
and soil fractions were measured in large, monitored lysimeters
(sandbox ecosystems) at Hubbard Brook Experimental Forest, New
Hampshire. Weathering was evaluated over 4-8 yr in sandboxes planted
with red pine (Pinus resinosa Ait.) and kept mostly free
of vegetation (nonvegetated). Three mass-balance equations were
used that cumulatively include (a) Ca and Mg in precipitation
inputs and drainage outputs, (b) accumulation of Ca and Mg in
vegetation, and (c) changes in products of weathering in soils.
Soil products were evaluated with an extraction process designed
to avoid removing ions from primary minerals. Relative to the
input-output equation, the estimated rate of weathering increased
2.4 (Ca) and 1.8 (Mg) times when accumulation of Ca and Mg in
pine biomass was accounted for, and 8 (Ca) and 23 (Mg) times when
changes in soil products were also included. Weathering estimates
that included accumulation in vegetation and soil products were
261 (Ca) and 92 (Mg) kg ha-1 yr-1 in the
pine sandbox. These rates were 10 (Ca) and 18 (Mg) times higher
than the rates in the nonvegetated sandbox, which were not significantly
greater than zero. This study raises the possibility that weathering
can play a significant role in the release of nutrients available
to plants over short periods. Faster rates like this become extremely
important where managers are trying to balance nutrients available
to plants from precipitation and weathering release with outputs
including harvest removals.
Keywords: cations; denudation; ecosystems; nutrient availability;
sustainability; weathering』
『要旨
植物および発達する土壌に蓄積される風化産物を計算に入れていない流域質量バランス研究で、一次鉱物の風化速度が過小に見積もられていないかどうかを評価するために、植生および土壌画分のカルシウムとマグネシウム含有量がニューハンプシャー州のHubbard
Brook実験林において大規模のモニターされたライシメーター（浸漏計）（砂箱生態系）で測定された。風化作用は４〜８年間にわたりアカマツ（Pinus
resinosa Ait.）を植えた砂箱およびほとんど植生のない（無植生）砂箱で評価された。（a）降水インプットと排水アウトプット中のCaとMg、（b）植生中のCaとMgの蓄積、および（c）土壌における風化産物の変化を、累積的に含む３つの質量バランス式が使われた。土壌産物は一次鉱物から取り去られるイオンを避けるように工夫された抽出過程で評価された。インプット−アウトプット式に比べて、見積もられた風化速度は、マツ・バイオマスへのCaとMgの蓄積を考慮したときの1.4倍（Ca）と1.8倍（Mg）増加し、土壌産物の変化も含めたときの8倍（Ca）と23倍（Mg）増加した。植生の蓄積と土壌産物を含んだ風化の見積りは、マツ砂箱で
261（Ca）と 92（Mg）kg/ha/年だった。これらの速度は、０よりも意味があるほど大きくなかった非植生砂箱での速度より、10
（Ca）倍と18（Mg）倍大きかった。風化は短期間に植物に利用できる栄養分を放出するという重要な役割を演じる可能性を、本研究は提示している。伐採除去を含むアウトプットで降水と風化からの放出から植物に対して利用できる栄養分のつりあいを管理者がとっている場合に、このような速い速度は非常に重要になる。』
Introduction
Methods
Mineralogy
Net drainage loss
Drainage
Precipitation
Accumulation in vegetation and litter
Change in weathering products left in soils
Statistical analyses
Results
Mineralogy
Light minerals
Heavy minerals
Minerals in the clay fraction
Compositions of the weathering equations
Drainage losses (drainage)
Bulk precipitation inputs (precipitation)
Accumulation of Ca and Mg in plants and litter (Δvegetation)
Changes in products of weathering in soil (Δproducts)
Rates of primary mineral weathering
Equation 5 (weathering = drainage - precipitation)
Equation 6 (weathering = drainage - precipitation + Δvegetation)
Equation 7 (weathering = drainage - precipitation + Δvegetation
+ Δproducts)
Discussion
Weathering in aggrading ecosystems
Weathering contributions to plant-available pools
Weathering in ecosystems
Weathering and ecosystem sustainability
Acknowledgements
References