A telemetering system for monitoring aqueous polythionates in an active crater lake

We have developed an in-situ monitoring system for aqueous polythionates in the Yugama crater lake at Kusatsu-Shirane volcano. A commercially available nitrate-selective electrode has a Nernstian response to the concentration of polythionates in solution in the range of pH 2.5–11. However, many active crater lakes contain highly acidic water (pH ranges from 0.2 to 2). The monitoring system reduces the acidity of the lake water to pH 4 without changing the concentration of polythionates using a high efficiency cation-exchange membrane technique. The monitoring system was placed in a submersed station, because the Yugama surface lake water freezes in mid-winter. The system is described and preliminary data are reported.