Using factor analysis and end-member mixing techniques to infer sources of runoff generation

Factor analysis and (two-component) end member mixing analysis
(EMMA) were applied to high resolution stream chemistry data from three
catchments to infer sources of iron- and manganese-rich runoff in the
catchment area and to evaluate their temporal and spatial influence on the
stream water quality. Two Fe and Mn sources were identified: (a) an organic
soilwater source, associated with Fe and Mn accumulation in the organic-rich
upper soil horizons and (b) a deep soilwater/groundwater source arising from
reduced metal mobilisation in the deeper soils. While (a) provides the
dominant Fe and Mn inputs during storm events, (b) becomes important just
before peak flow when riparian groundwater is displaced into the stream,
giving rise to high Fe and Mn concentrations. The timing of such high Fe and
Mn loadings in the stream runoff has important implications for the water
supply management of the catchment.