AbstractA reduction in precipitation and in a warming climate over recent years has caused many glaciers in Chilean Patagonia to retreat (Rivera et al., 2002; Rivera 2004; Bown, 2004; Masiokas et al., 2008). This changing precipitation also affects the discharge and water quality of many hydrological systems in South America (IPCC, 2014). However, despite these profound changes, little is known about meltwater, sediment, and solute export from remote glaciers in South America.
This study focused on two Patagonian river catchments (glaciated and de-glaciated). The glaciated Rio Huemules drained meltwater originating from the Steffen glacier, the most southerly glacier in the Northern Patagonian Icefield. The de-glaciated Rio Lloncochaigua was 580km further north. The catchments were 670 and 107 km2 respectively, and were chosen due to similarities in climate and bedrock lithology as well as being remote enough to avoid anthropogenic contamination. Data reported in this thesis were collected over 5 field seasons (2016- 2019).
Conductivity, temperature, depth, and turbidity were monitored in situ in both river catchments (Keller DTX-22, Turner Cyclops-7 and RBRTu sensors). Meteorological data were obtained from local weather stations. To enable the conversion of turbidity to suspended sediment (SS), manual samples of SS were also collected. Discharge records were generated for both study catchments following conversion of sensor depth to discharge, calibrated using Rhodamine dye tracing. Mean discharge was twice as high in the glaciated catchment (Rio Huemules: 106 m3s-1, σ: 156; Rio Lloncochaigua: 44.7 m3s-1, σ: 23.9). The water yield of the Rio Huemules (4.73m) was also higher than in the Lloncochaigua (0.885m), as glacial melt supplements rainfall collected within a larger catchment area. This melt created a steady discharge, on top of which the rainfall events had little effect. Discharge seasonality was also explored in both catchments, with the glaciated catchment typically showing peak flows in summer (1.6 times the winter background) whereas the non-glaciated catchment was almost unchanging.
Additionally, fluxes and yields of suspended sediment concentration from both rivers were studied. Annual sediment flux was five hundred times larger and the yield was almost ninety times larger in the Rio Huemules, reflecting the greater capacity of the glacier to erode its substrate.
|Date of Award||11 May 2021|
|Supervisor||Chris Yates (Supervisor) & Jemma L Wadham (Supervisor)|