A hydrochemical basis for managing manganese in water supplies from upland basins

Manganese (Mn) concentrations exceeding the EC limit (0.05 mg 1^-1) occur in potable waters supplied from many UK upland basins. Mn removal from raw waters is costly so basin management strategies for Mn control are sought. Streamwater chemistry and discharge were monitored in two basins (HS4 and HS7) within a UK upland water-gathering ground. Cluster analysis, factor analysis and chemical mixing model techniques enabled the timing, sources and hydrological pathways of Mn to be deduced. Elevated Mn concentrations (>0.350 mg 1^-1) occur at HS4 in summer low flows arising from baseflow sources. At HS7, autumn storms contain maximum Mn, associated with flushing of soil stores. Chemical mixing models show that deep water accounts for 82% of Mn in runoff from HS4 but < 1% at HS7. Contrasting Mn behaviour in HS4 and HS7 demonstrates that basin management requires an extensive knowledge base due to the variability of hydrochemical processes.