An investigation of soil moisture associated with ephemeral streams, Wright Valley, Antarctica

• Main Author: Shanhun, Fiona L.
• Other Authors: Balks, Megan R., Campbell, David I.
• Format: Thesis
• Language: English
• Published: The University of Waikato 2019
• Subjects: Vanda; Wright Valley; Lake Vanda; Onyx River; Antarc*; Antarctica
• Online Access: https://hdl.handle.net/10289/12866

Ephemeral streams in Wright Valley, Antarctica, are fed by glacial melt and flow for between four and ten weeks annually. Hyporheic zones develop concomitantly with ephemeral stream channels. These zones are areas of saturated or moistened soil, depending on their proximity to the stream. The hyporheic zones are laterally extensive, and may represent a greater proportion of total meltwater than surface water in the stream channel, thus exacerbating the risk of accidental contamination of streams. The hydrological system in Wright Valley is closed, with streams flowing inland to Lake Vanda via the Onyx River. This study aimed to quantify the extent to which liquid moisture was present in soils associated with Goodspeed Stream, in order to better predict the vulnerability of stream margins to impacts of human activities. Soil samples were collected from transects across the Goodspeed lower alluvial fan and analysed for gravimetric moisture content, electrical conductivity, and particle size distribution. A pedotransfer function was used to estimate soil moisture potential in order to show the direction of water movement across the lower alluvial fan. Climate data including air temperature, soil temperature, and total solar radiation were measured; stream flow in Goodspeed Stream was estimated. The Goodspeed Stream near-stream and extended hyporheic zones were identified. Distal components of the hyporheic zone were also identified at distances of up to 7 4 m from Goodspeed Stream. Soil gravimetric moisture content increased with soil depth and proximity to Goodspeed Stream. Distal components of the hyporheic zone observed at distances of 21, 59 and 74 m from Goodspeed Stream had relatively high gravimetric moisture contents (up to 7%; 88 in visibly dry soils was 0.6%). The distal hyporheic zones have the potential to develop into flowing stream channels during periods of increased melt. Soil electrical conductivity ranged from 34 - 10520 μSiem. Salts precipitated at the soil surface were concentrated at the western-most edge of the extended hyporheic zone and on raised bar features across the fan, highlighting zones of movement and evaporation of soil moisture. The particle size distribution of the <2 mm fraction was relatively uniform across the fan, being dominated by medium sand (45%). Soil moisture potential decreased with distance from Goodspeed Stream, indicating that small spills occurring outside the extended hyporheic zone would be driven laterally across the fan, away from the stream. Spills within the extended hyporheic may be incorporated into Goodspeed Stream. Large spills anywhere on the Goodspeed lower alluvial fan would migrate downwards to ice cement before flowing down-slope under gravity towards the Onyx River. Areas vulnerable to accidental spills and physical disturbance were highlighted on oblique photographs. Three vulnerability zones were identified based predominantly on the observed extent and movement of soil moisture. Zone 1 designates stream channels or surface waters and near-stream hyporheic zones, Zone 2 encompasses extended hyporheic zones, while Zone 3 applies to soils of alluvial fans, including distal hyporheic zones. Recommendations were made as to the types of activities permissible in each of the three zones.