Interstitial pore‐water temperature dynamics across a pool‐riffle‐pool sequence

Abstract

AbstractHyporheic habitat conditions are controlled strongly by spatial and temporal dynamics of physicochemical processes at the aquifer–river interface. In particular, heat transport between groundwater and surface water has a great impact on streambed habitats. This study uses high resolution observations of vertical hydraulic gradients (VHGs) and interstitial pore‐water temperatures to investigate space‐time patterns of groundwater–surface water (GW–SW) exchange fluxes and streambed thermal conditions of a pool‐riffle‐pool sequence of a UK lowland river. The results indicate that, although groundwater is dominantly upwelling in the research area, exchange flow patterns are strongly influenced by the streambed geomorphology. Advective heat flux caused by groundwater upwelling is shown to have a moderating impact on interstitial temperature patterns and partly compensates the impact of conduction of diurnal surface water temperature fluctuations into the streambed. Consequently, diurnal temperature oscillations, which are clearly pronounced in the top 10 cm of the streambed (up to 2 °C) are reduced by > 90% at depths below 20 cm. This study provides evidence that even in groundwater upwelling conditions, the spatially variable impact of heat conduction from the streambed surface may cause a spatially heterogeneous interstitial habitat structure with thermal conditions differing significantly in a vertical (3 °C temperature gradient at a length scale of 0·4 m) as well as longitudinal (0·75 °C at 16 m) domain. These results not only enhance the understanding of thermal patterns in lowland rivers but also have implications for interstitial habitat ecohydrology, community structures and stability. Copyright © 2011 John Wiley & Sons, Ltd.