Solute contributions from precipitation to the compositions of soil waters in a marine terrace chronosequence
Abstract
Solute loading of soil waters by rainfall together with evapo-transpiration can increase the concentrations of various dissolved constituents. This process complicates the modeling of saturation states for the different mineral phases in the soil profile that are products of the weathering of primary minerals found in the original granitic source material. The estimation of true rates of regolith weathering due to CO2 drawdown at temperate hydrogeological sites requires having soil pore water solute concentration data which have been corrected for solute inputs from precipitation before proceeding with chemical weathering calculations. As part of a chemical weathering study of a coastal marine terrace chronosequence located in the vicinity of Wilder Ranch State Park, Santa Cruz County, CA, bulk samplers and automatic precipitation-event samplers installed at a range of sites enabled us to determine elemental concentrations and isotopic compositions of rainfall solutes which influence the overall compositions of the pore waters. Variations in rain sample chemistry (mole-ratio data using Na, Mg, Ca, Cl and SO4) correlated with precipitation intensity result from solute inputs contributed by marine and terrestrial aerosols. Higher strontium-isotope ratios (87Sr/86Sr), which point to radiogenic dust sources, occur in rain water collected in the fall at the beginning of the rainy season while lower ratio values indicating marine aerosol sources appear in winter and spring samples. Use of the NOAA HYSPLIT particle-tracking program for computing the chronological progression of storm tracks during precipitation events could show the development of solute levels in rain. Subsequently, the installation of wind sensors along with the automatic rain collectors afforded the capability of correlating high resolution wind-speed and wind-direction data with changing compositions of rain samples collected at fixed-time intervals during storm events. Wind data show that wind directions during periods of rainfall generally deviate from those that prevail from the northwest during dry periods.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H53B1036V
- Keywords:
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- 1836 HYDROLOGY / Hydrological cycles and budgets;
- 1843 HYDROLOGY / Land/atmosphere interactions;
- 1854 HYDROLOGY / Precipitation;
- 1886 HYDROLOGY / Weathering