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Heat Transmission in the Hyporheic Zone. Jennifer Goshorn. Outline. Defining the hyporheic zone Importance of the hyporheic zone Heat transport mechanisms Temporal fluctuations Hydrology Biogeochemistry Ecology Concluding remarks. Defining the Hyporheic Zone.
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Heat Transmission in the Hyporheic Zone • Jennifer Goshorn
Outline • Defining the hyporheic zone • Importance of the hyporheic zone • Heat transport mechanisms • Temporal fluctuations • Hydrology • Biogeochemistry • Ecology • Concluding remarks
Defining the Hyporheic Zone Conceptual models reflecting the aims of different disciplines • Ecologist - active ecotone between surface and groundwater in which fauna characteristic of the hyporheos are distributed and live. (Boulton et al., 1998) • Hydrologist - part of the sub-surface in which both surface and groundwater are present, but surface water exceeds 10%of the total volume. (Triksa et al., 1989) • Hydrogeologist - water beneath the surface of the ground in the saturation zone in direct contact with the subsoil. (Smith, 2005) Buss et al., 2009
Importance of the Hyporheic Zone • controls the flux and location of water exchange between stream and subsurface • provides a habitat for benthic and interstitial organisms • provides a spawning ground and refuge for certain species of fish • provides a rooting zone for aquatic plants • provides an important zone for the cycling of carbon, energy and nutrients • provides a natural attenuation zone for pollutants by biodegradation, sorption and mixing • moderates river water temperature • provides a sink/source of sediment within a river channel.
Heat Transport in the Hyporheic Zone • Advection transports heat via fluid flow • Conduction transports heat between sediment and hyporheic water • Dispersion and conduction occur as groundwater/surface water and hyporheic water interact • Solar radiation indirectly warms water via conduction and transfer of latent and sensible heat Conceptual diagram showing the different processes that influence hyporheic water temperatures Burkholder et al., 2008
Temporal Heat Fluctuations in the Hyporheic Zone Temperature vs. Depth curve • Temperature as a tracer for infiltration of stream water by interpreting time shifts in temperature signals as retarded travel times • Time-series profiles document changes in water flux into and out of a stream • Maximum and minimum temps during a complete cycle form a ‘temperature envelope’ within which all measured temperatures reside. Bounds of envelope (Jan & July, dawn & afternoon) • When groundwater is flowing into a gaining stream, the annual/daily envelope collapses toward the streambed surface. Upwelling groundwater is buffered from temperature fluctuations – constant temp • When the stream is losingwater to underlying sediments, the envelope expands downward. Water is heated at the surface and carried down. (Constantz et al., 2003)
Thermal Effects on Hydrology in the Hyporheic Zone • Permeability depends of the hydraulic conductivity of the sediment layers • Viscosity and density of water are temperature dependent • Dramatic increases in stream temperature fluctuations reflect fluctuations in hydraulic gradients • Delayed response of subsurface temperatures earlier in the season Stream and streambed temperatures and hydraulic gradients from a stream piezometer in Indiana Constantz, 2008
Thermal Effects on Biogeochemistry in the Hyporheic Zone • The hyporheic zone is characterized by steep physio-chemical gradients, which are controlled by heat and water flux between the GW/SW interface. • Temperature controls the rate of the chemical reactions • As temperature increases less oxygen is dissolved in water • Emission of nitrogen gases increases with temperature Microbial activity and chemical transformations in the Hyporheic Zone (Winter et. al, 1998)
Thermal Effects on Hydroecology in the Hyporheic Zone • During cold weather, up-welling groundwater prevents freezing of rivers and provides temperature moderation during the hot summer. • Predictive models have been developed to relate temperature to embryo development and timing of hatching and emergence under saturated dissolved oxygen conditions (Crisp, 1988 and 1990) Smith, 2005
Conclusions • Temperature plays a vital role in the hyporheic zone and surrounding environments • Heat as a tracer to model the direction and velocity of flow • Controls chemical reactions • Biological dependency • New research due to advancements in modeling technology • Cooperative work between different fields • The full potential of thermal data within the hyporheic zone is still unrecognized
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