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Proglacial groundwater-fed features, such as seeps, substantially impact proglacial geomorphology, hydrology, and ecology. However, there is a paucity of research on the impacts of climate change and glacial retreat on

This study presents the first application of fibre‐optic distributed temperature sensing (FO‐DTS) for analysing the impact of spatially heterogeneous vegetation patterns on the thermal conditions of an ecosystem. It analyses the spatial patterns and temporal dynamics of canopy and ground temperatures at unprecedented spatial and temporal resolution to showcase the potential as well as limitations of the FO‐DTS technology for ecohydrological applications. By using the partial rhododendron coverage of a deciduous UK woodland as a model system, FO‐DTS surveys were carried out to demonstrate the detection of different dynamic thermal patterns in the presence/absence of rhododendron (Rhododendron ponticum L). The high‐resolution temperature measurements of this study provide strong evidence for the moderating impact of rhododendron coverage on air, ground and soil temperatures in forest ecosystems, which has important implications for ecological and biogeochemical process dynamics. The results successfully demonstrate the significant potential of FO‐DTS for high‐resolution, spatially detailed, transient temperature monitoring in forest environments. The survey performance and its very efficient signal‐to‐noise ratio proves the capability of FO‐DTS networks to provide highly accurate information on temporal dynamics in spatial temperature patterns with great prospect for substantially improving spatial coverage and sensitivity of temperature observations in a range of ecological applications. Copyright © 2012 John Wiley & Sons, Ltd.

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.

Hyporheic zones are increasingly thought of as natural bioreactors, capable of transforming and attenuating groundwater pollutants present in diffuse baseflow. An underappreciated scenario in the understanding of contaminant fate hyporheic zones is the interaction between point-source trichloroethene (TCE) plumes and ubiquitous, non-point source pollutants such as nitrate. This study aims to conceptualise critical biogeochemical gradients in the hyporheic zone which govern the export potential of these redox-sensitive pollutants from carbon-poor, oxic aquifers. Within the TCE plume discharge zone, discrete vertical profiling of the upper 100 cm of sediment pore water chemistry revealed an 80% increase in dissolved organic carbon (DOC) concentrations and 20-60 cm thick hypoxic zones (<2 mg O2 L-1) within which most reactive transport was observed. A 33% reduction of nitrate concentrations coincided with elevated pore water nitrous oxide concentrations as well as the appearance of manganese and the TCE metabolite cis-1,2-dichloroethene (cDCE). Elevated groundwater nitrate concentrations (>50 mg L-1) create a large stoichiometric demand for bioavailable DOC in discharging groundwater. With the benefit of a high-resolution grid of pore water samplers investigating the shallowest 30 cm of hypoxic groundwater flow paths, we identified DOC-rich hotspots associated with submerged vegetation (Ranunculus spp.), where lowenergy metabolic processes such as mineral dissolution/reduction, methanogenesis and ammonification dominate. Using a chlorine index metric, we show that enhanced TCE to cDCE transformation takes place within these biogeochemical hotspots, highlighting their relevance for natural plume attenuation.