Abstract

The thesis investigates the solute concentration of water samples collected at various points along the hydrological pathway from the atmosphere to the stream. Adoption of the pathway approach facilitated study of the effects of vegetation and granite weathering on the solute chemistry. The experiment was conducted in a small (4.75 km²) drainage basin on Dartmoor and the experimental design was based on three hillslope transects through different vegetation types, namely acid grassland, and grassland invaded by bracken and sitka spruce forest. Water samples of precipitation, throughfall, litterflow, interflow, springs and the stream were collected regularly and analysed. From this the solute chemistry at each monitoring point was characterised. Spatial differences at points within each transect were due to their discharge and position on the slope; those between transects were the result of vegetation differences. Temporal variations in solute concentration were examined and related to sources of the chemicals, hydrometeorological conditions, season and catchment characteristics. Principal components analysis was employed to summarize solute variation s of the major flow points through time. Precipitation was dilute, weakly acidic and dominated by sodium and chloride derived from marine sources. Vegetation type exerted a major influence on the incidence of litterflow and interflow as well as on the solute chemistry, concentrations being greatest in the forest and least in the grassland. This effect was also recorded at the springs. In addition, the solute chemistry of the stream was affected by the forest, in particular by aerosol entrapment. Sodium and chloride still dominated the chemical composition but silica, derived from granite weathering, was also important. A geochemical balance was calculated from the atmospheric input s and losses in the stream; the mineral sources and their alteration products were investigated. The chemical denudation rate for the catchment was computed and weathering was found to be still active and highly localised. The implications of this, result for granite landforms is discussed.

Document Type

Thesis

Publication Date

1983

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