SHORT-TERM VARIATIONS IN RAIN AND STREAM WATER CONDUCTIVITY AT A FORESTED SITE IN MID-WALES - IMPLICATIONS FOR WATER-MOVEMENT

Continuously monitored stream and rainfall conductivity data from a catchment in mid-Wales is presented. Using time series and end-member mixing techniques, it is shown that the conductivity of the stream is largely determined by the volume of water in the stream: the conductivity signal of the rainfall is damped out before it reaches the stream. The variations in stream conductivity are explained in terms of flow-dependent mixing of three chemically distinct water types. These comprise a well-buffered deep water or ground water source, an acidic soil water and a previously unidentified end-member with low conductivity.