『Abstract
A knowledge of the processes involved in streamflow generation
are critical to an understanding of solute transport and weathering
rates in upland catchments. The determination of specific flow
pathways and the formulation of process-based models have proved
difficult in such terrains, largely due to the heterogeneous nature
of catchments and the necessary limitations of bulked parameter
models. Natural geochemical tracers have proved invaluable in
developing conceptual models of catchment functioning and for
constraining weathering processes and geochemical cycling. Strontium
isotopes have been used as a natural tracer to calculate weathering
rates for Sr and Ca, and to constrain the dominant flow pathways
in two upland forested sub-catchments (Afon Hafren and Afon Hore)
of the River Severn at Plynlimon in Central Wales. The dominant
source of Sr in the catchments is considered to be from the weathering
of silicate minerals. weathering rates for Sr and Ca in the Afon
Hafren, calculated using Sr isotopes, were similar to those derived
from mass balance studies. The rates for the Afon Hore were similar
for Ca, but significantly different for Sr. The reason for the
difference is unclear, but may be due to additional sources (calcite)
in the catchment. Strontium isotope ratios for different input
sources and compartments within the catchment were characterised
and helped to identify potential flow pathways. The data suggest
an important role for groundwater inputs in contrast to previous
models which indicated a dominant role for soil waters.
Keywords: 87Sr/86Sr; Catchment; Plynlimon;
Weathering; Flowpath』
1. Introduction
1.1. Background
1.2. Chemical weathering
1.3. Isotopes in catchment studies
2. The Plynlimon catchments
2.1. Study site
2.2. Sampling and analytical techniques
3. Results
3.1. Bedrock samples
3.2. Rainfall
3.3. Soil samples
3.4. Stream waters
3.5. Groundwaters
4. 87Sr/86Sr as an indicator of weathering
phases and weathering rates in the catchment
5. 87Sr/86Sr as an indicator of flow paths
in the catchment
5.1. The soil zone
5.2. Surface water and groundwater
5.3. Flow processes and mixing in the catchment
6. Summary and conclusions
Acknowledgements
References