Use of remote sensing to identify areas of groundwater upwelling on active glacial floodplains: Their frequency, extent and significance on a landscape scale

Abstract

On active glacial floodplains, streams sourced from upwelling groundwater are characterised by significantly higher biodiversity than surface-fed streams. However the ecological significance of these habitats at a landscape scale has not yet been determined. A remote-sensing model was developed to identify the frequency and distribution of groundwater upwellings in remote Arctic and alpine areas, using freely available satellite imagery. Field research has established that groundwater upwellings provide stable environments (reduced variability in flow and temperature regimes, and reduced channel slope and bed movement), with high water tables, supporting vegetation growth on otherwise barren glacial floodplains. Upwellings are therefore associated with characteristic isolated patches of dense vegetation. The model uses this characteristic profiling of groundwater upwellings in a four-step process; 1) removing temporal variance from the images; 2) identifying and isolating glacial floodplains from the satellite data, 3) removing snow and ice 4) identifying vegetation density (associated with sites of groundwater upwelling) within the floodplains. The model was calibrated in Denali National Park, and validated in Wrangell St. Elias National Park; the extent of groundwater-fed areas was calculated and compared between sites for the first time. Model accuracy during calibration was 94%, and was marginally lower during validation (88%). The high accuracy of the model supports the wider applicability of site-specific relationships determined thus far. In each region, groundwater upwellings contributed to ~40% of the total riverine habitat within glacial floodplains; in combination with their high biodiversity this suggests they are ecologically significant. This model facilitates study site location, and represents a significant development in macroscale studies of groundwater upwellings in glacierised catchments.