Articles | Volume 1, issue 3
Hydrol. Earth Syst. Sci., 1, 653–660, 1997
https://doi.org/10.5194/hess-1-653-1997
Hydrol. Earth Syst. Sci., 1, 653–660, 1997
https://doi.org/10.5194/hess-1-653-1997

  30 Sep 1997

30 Sep 1997

Continuous pH, electrical conductivity and temperature measurement at Plynlimon: towards an integrated, reliable and low maintenance instrument system

P. Hodgson* and J. G. Evans P. Hodgson and J. G. Evans
  • Institute of Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, OX10 8BB, UK.
  • *Present address: BIRAL, PO Box 2, 1 Beach Road West, Portishead, Bristol, BS20 7JB, UK.

Abstract. Water quality data for the Nant Tanilwyth stream, Plynlimon (an acidic upland stream, the waters of which are of such low ionic strength that measurement is difficult), has been recorded using a new integrated field instrument system. The negligible drift of the pH electrode allows the system to operate for extended periods (months) without re-calibration, whilst maintaining a standard deviation of 0.19 pH units between its readings and laboratory reference measurements. Conductivity measurements, although within the sensor manufacturer's specification, did not provide meaningful readings at conductivities below 50 μS cm-1. Using the pH data as a surrogate tracer, a high temporal resolution estimate of the stream dynamics, in terms of the contributions of groundwater and soil-water is presented; the dependence of these relative proportions on instantaneous flow and antecedent conditions is shown. It is concluded that, whilst improvements in instrumentation have been made, greater accuracy is still desirable for some scientific applications and ways forward are described.