『Abstract
Constraining the range of chemical weathering rates in soils
is important because weathering can have a strong influence on
surface and ground water chemistry, soil nutrient release, neutralization
of acidity, and preparation of rock for physical erosion. Determination
of chemical weathering rates in soils developed from glacial till
can be advantageous relative to other soils, because soil ages
are more easily determined. To allow measurement of real differences
in weathering rates across sites, rigorous exclusion criteria
need to be applied to soil profiles to reduce uncertainty that
may arise from soil parent material heterogeneity and soil disturbance.
Soil profiles used for weathering rate calculations in this study
were required to have the following characteristics: a) an overall
decreasing concentration of the immobile element (Ti) with depth;
b) Ti concentrations of no more than 1 standard deviation lower
in the B horizon than in the C horizon; and c) at least three
mineral soil samples collected from above the C horizon. In the
White Mountains (New Hampshire), we applied these criteria to
data from 39 soil profiles developed in glacial till derived from
granitic and high grade metamorphic parent material. Soils were
excavated quantitatively, thus elinimating errors associated with
measurement of bulk density. The resulting long-term weathering
rates for individual soil pits range from 2 to 50 meq m-2
year-1. Average weathering rates for sites with two
or three profiles within 50 m of each other range from 10 to 30
meq m-2 year-1. Averaging weathering rates
from sites within 5 km of each other results in “local rates”
ranging from 13 to 22 meq m-2 year-1. An
inverse correlation is observed between site elevation and weathering
rate, which may reflect differences in temperature, precipitation
or vegetation type. Our best estimate of the regional average
long-term weathering rate for the White Mountains is 17 meq m-2
year-1, considerably lower than the 35 meq m-2
year-1 previously reported for a 12 ha catchment at
the nearby Hubbard Brook Experimental Forest. Weathering rates
determined from granitic glacial deposits of similar age elsewhere
in the world are of the same order of magnitude (2 to 62 meq m-2
year-1) as the rates determined in this study.
Keywords: Weathering; Soil; White Mountains; New Hampshire; Quantitative
soil pits』
1. Introduction
2. Study area
3. Sampling and analytical methods
4. Results
5. Discussion
5.1. Variability of chemical weathering rates
5.2. Comparison with other chemical weathering rates from soil
profiles
Acknowledgements
Appendix A. Supplementary data
References