Soil moisture measurement in the Ross Sea region of Antarctica using Hydra soil moisture probes

The objectives of this study were to determine the limitations of Hydra soil moisture probes (Stevens Water Monitoring Systems Inc., Oregon, U.S.A.) for use in Antarctica and to describe the soil moisture regimes of soils located at Scott Base, Marble Point and in the Wright Valley. Laboratory and field experiments were undertaken to compare Hydra probe soil moisture measurements with gravimetric soil moisture measurements. Once the limitations of the probes were determined Hydra probe data from three Antarctic sites over three years were analysed. Laboratory and field experiments showed that soil temperature, texture, and salinity all influenced the soil moisture results recorded by the Hydra probes. The interacting effects of soil texture, temperature and salinity were found to be generally within the ±3% limit of accuracy of the Hydra probe stated by the manufacturers. Up to five soil-moistening events were identified each summer at Scott Base and Marble Point, while in the Wright Valley soil-moistening was detected once, by one sensor, over three summers. Maximum volumetric liquid soil moisture contents of 23% at Scott Base, 32% at Marble Point, and 6% in the Wright Valley were recorded. At the 2 cm depth, the liquid soil moisture was >5% for a cumulative average of 860 hours each summer at Scott Base, 1 hour in the Wright Valley, and 310 hours at Marble Point. The drying period following soil-moistening for surface soils (2-5 cm depth) was about 6 days, which was extended to about 12 days when freeze-thaw cycles were occurring.