SURFACE WATER DISSOLVED LOADS AND SOIL CHEMICAL WEATHERING RATES: RESULTS FROM THE SANTA CRUZ TERRACES
This study builds on an existing characterization of soil silicate weathering along a chronosequence of marine terraces near Santa Cruz (CA, USA). The Wilder Creek watershed drains these terraces, is underlain by a mixed bedrock lithology, and is subject to high rates of evapotranspiration. Soil water chemistry data and stream dissolved load based weathering rates from a series of nested watersheds in the Wilder basin indicate that basin-scale weathering rates are <20% of measured contemporary and long-term weathering rates determined for terrace soils. The soil data is representative of about 40% of the watershed area, with actively eroding, moderate to steep hillslopes making up the remainder. The discrepancy in basin and soil weathering fluxes suggests that additional factors need to be considered: saturation state inhibition of weathering within ground water, efflux during large periodic events associated with El Niño circulation patterns, the "flashiness" of the hydrograph, water residence times in different components of the system, and retention of weathering products within the soil/saprolite. Identifying the reasons for the discrepancy between soil and stream dissolved load weathering fluxes is needed for a full understanding of chemical weathering at landscape scales.