『Abstract
Few studies of silicate mineral weathering have been conducted
in carbonate-bearing temperate forest soils. With climate and
vegetation held constant, we compared soil mineralogy and major
element chemistry of soil waters from a carbonate-free temperate
aspen forest site in the Cheboygan watershed, northern Michigan,
with that from carbonate-containing soils from experimental tree-growth
chambers (low- vs. high- fertility). All soils were well-drained
sands (quartz, Na-rich plagioclase, and K-feldspar) with minor
amounts of carbonate present only in the experimentally manipulated
soils. The Na+ concentrations in soil waters corrected
for atmospheric deposition (Na*) were used to compare
relative rates of plagioclase feldspar weathering across sites.
In natural soil water profiles, maximum concentrations of Na*,
Si, and dissolved organic carbon (DOC) were observed by a depth
of 15 cm, a soil zone free of carbonate minerals. Mean Na*
and DOC concentrations were different in the three soils, and
increased in the order natural soil＜low-fertility chambers＜high-fertility
chambers. while low pH environments are generally viewed as enhancing
weathering rates, here higher Na* appears to be related
to high DOC, which is consistent with observed increases in active
organic functional groups as pH increases. Our results suggest
that under a specific vegetative cover, the soil carbon environment
affects the weathering flux observed. Our study also suggests
that disturbed soils provide an enhanced physical and chemical
environment for weathering. generalized silicate weathering models
may benefit from including the enhancing effects of organic anions
at moderate pH in addition to precipitation and temperature.
Keywords: Chemical weathering; Michigan; Organic carbon; Plagioclase;
Soil; Soil water』
Introduction
Methods
Field area and sites
Soil solutions and gases
Analyses of soil mineralogy
Calculation of Na*
Results
Soil chemistry and mineralogy
Soil solution chemistry
Soil CO2
Discussion
Soil mineralogy and cation exchange
Carbon, soils, and driving mechanisms for mineral weathering
Weathering and carbon transformations
Summary and conclusions
Acknowledgments
References