Long-term and High Temporal Resolution In-situ Monitoring of Potassium, Sodium, and Chloride in a Small Forested Catchment Using Flow Injection Potentiometry

Abstract

Long-term water quality data with high temporal resolution, together with hydrological data, are essential in developing hydrogeochemical and diffuse pollution modeling. An in situ flow injection potentiometry (FIP) system to monitor the stream water quality (chloride, sodium and potassium) every 15 minutes for two weeks was developed and tested in the laboratory and in a small forested catchment in Gozyo City, Nara Prefecture, Japan. The system resolves main hurdles that prevent long-term monitoring, except the problem of samples freezing in winter. Frequent calibration with three standards was adopted to compensate for the temperature dependency of ion-selective electrodes. The results of monitoring stream water quality in this catchment in 2004 showed clear differences in the concentration of the ions of chloride, potassium, and sodium depending on discharge: chloride showed the simple washout of accumulated atmospheric input, potassium implied the washout from the stock in the shallow soil layer, and sodium indicated the effect of ion exchange and chemical weathering.