『Abstract
The spatial variability of long-term chemical weathering in a
small watershed was examined to determine the effect of landscape
position and vegetation. We sampled soils from forty-five soil
pits within an 11.8-hectare watershed at the Hubbard Brook Experimental
Forest, New Hampshire. The soil parent material is a relatively
homogeneous glacial till deposited 〜14,000 years ago and is derived
predominantly from granodiorite and pelitic schist. Conifers are
abundant in the upper third of the watershed while the remaining
portion is dominated by hardwoods. The average long-term chemical
weathering rate in the watershed, calculated by the loss of base
cations integrated over the soil profile, is 35 meq m-2
yr-1−similar to rates in order 〜10 to 15 ka old soils
developed on granitic till in temperate climates. The present-day
loss of base cations from the watershed, calculated by watershed
mass balance, exceeds the long-term weathering rate, suggesting
that the pool of exchangeable base cations in the soil is being
diminished. Despite the homogeneity of the soil parent material
in the watershed, long-term weathering rates decrease by a factor
of two over a 260 m decrease in elevation. Estimated weathering
rates of plagioclase, potassium feldspar and apatite are greater
in the upper part of the watershed where conifers are abundant
and glacial till is thin. The intra-watershed variability across
this small area demonstrates the need for extensive sampling to
obtain accurate watershed-wide estimates of long-term weathering
rates.』
1. Introduction
2. Setting
3. Sampling and analytical methods
4. Results
4.1. Physical and chemical properties of soils
4.2. Estimates of chemical weathering
4.2.1. Titanium variability
4.2.2. Elemental depletion factors
4.2.3. Long-term weathering rates
5. Discussion
5.1. Weathering variability with depth and landscape position
5.2. Long-term weathering rates
5.3. Present-day weathering rates and cation losses
5.4. Mineral weathering rates
5.4.1. Plagioclase
5.4.2. Apatite
5.4.3. Biotite
5.4.4. Potassium feldspar
5.5. Spatial variation of weathering
6. Conclusions
Acknowledgments
References