Identifying spatial and temporal dynamics of proglacial groundwater–surface-water exchange using combined temperature-tracing methods

Abstract

The effect of proglacial groundwater systems on surface hydrology and ecology in cold regions often is neglected when assessing the ecohydrological implications of climate change. We present a novel approach in which we combined 2 temperature-tracing techniques to assess the spatial patterns and short-term temporal dynamics of groundwater-surface-water exchange in the proglacial zone of Skaftafellsjökull, a retreating glacier in southeastern Iceland. Our study focuses on localized groundwater discharge to a surface-water environment, where high temporal-and spatial-resolution mapping of sediment surface and subsurface temperatures (10-15 cm depth) were obtained by Fiber-Optic Distributed Temperature Sensing (FO-DTS). The FO-DTS survey identified temporally consistent locations of temperature anomalies at the sediment-water interface, indicating distinct zones of cooler groundwater upwelling. The high-resolution FO-DTS surveys were combined with calculations of 1-dimensional groundwater seepage fluxes based on 3 vertical sediment temperature profiles, covering depths of 10, 25, and 40 cm below the lake bed. The calculated groundwater seepage rates ranged between 1.02 to 6.10 m/d. We used the combined techniques successfully to identify substantial temporal and spatial heterogeneities in groundwater-surface exchange fluxes that have relevance for the ecohydrological functioning of the investigated system and its potential resilience to environmental change.

Groundwater–surface-water interactions: current research directions

“…tuaries, ocean beaches and wetlands. Tristram et al (2015) used FO-DTS surveys to map groundwater discharge through the bed of an internally drained proglacial lake in Iceland. They combined the surveys with vertical temperature profiles at 3 locations, which were used to calculate rates of groundwater flow through the lake bed.…”

Combined use of thermal methods and seepage meters to efficiently locate, quantify, and monitor focused groundwater discharge to a sand‐bed stream

“…Tristram et al . [] used an interesting but time‐consuming approach of comparing bed‐surface and buried (10 cm depth) cables in the near‐shore margin of a lake; strong anomalies detected by the buried cables were often greatly subdued in bed‐surface data, even in this lentic system. Briggs et al .…”

“…However, that study was conducted in a small lake with minimal currents and waves that might otherwise dilute a thermal signal at or near the sediment bed. Tristram et al [2015] used an interesting but time-consuming approach of comparing bed-surface and buried (10 cm depth) cables in the near-shore margin of a lake; strong anomalies detected by the buried cables were often greatly subdued in bed-surface data, even in this lentic system. Briggs et al [2012] deployed a cable along the sediment-water interface of a large, fast-flowing stream and were able to observe a discrete cold anomaly that coincided with focused groundwater gain to the stream.…”

Mesocosm experiments identifying hotspots of groundwater upwelling in a water column by fibre optic distributed temperature sensing

“…FO‐DTS has been used to detect GW discharge at the sediment–water interface in lakes (Blume et al, ; Liu et al, ; Tristram et al, ) and streams (Hare et al, ; Krause et al, ; Lowry et al, ). However, it had not yet been determined how the temperature signal propagates from the sediment–water interface through the water column up to the water surface–atmosphere interface and how the signal is affected by environmental parameters such as weather conditions (clear vs. overcast) and the diurnal cycle of net radiation.…”