INTRODUCTION  How have the fields of ecology and hydrogeology attempted to delineate the hyporheic zone?  It is hard to define something we cannot immediately see.  Different definitions of the hyporheic zone (HZ) exist, based upon the field of science concerned  Importance within hydrology?

HYPO = UNDER/ BENEATH RHEO = TO FLOW MEANWHILE IN GREECE…

FAUNAL HABITAT  A distinct habitat was detected and named the ‘hyporheic biotope’.  This habitat was identified within the interface between surface and groundwater (Orghidan, 1959).  Identification of a large and diverse collection of fauna (Danielopo, 1989).

A REFUGE  Biocenosis between organisms (Sabater and Vila, 1990).  A temporary refuge for organisms in times of physical and biological adversity (Stanford and Ward, 1988).  An ‘ecotone’ (Williams, 2010)

DELINEATION ATTEMPTS  In-situ microbe calculations (Hynes, 1974) and correlation with concentrations of DO.  The ‘hyporheic corridor’ concept (Stanford and Ward, 1993).  Slower level of biological processes then that of the surface (Gibert et al, 1994)  Complex and temporally variable distribution of ecology within the hyporheic zone.

DEFINING THE HYPORHEIC ZONE  Combining the factors of groundwater flow/exchange with populations of hyporheic invertebrates (Stanley and Boulton, 1993).

THE GROUNDWATER SYSTEM  The hyporheic zone represents an area with increased mixing of surface and groundwater.  Dynamic and interesting zone  An important site of solute retention, metabolism and mineralization (Bencala, 1993).  Considers geomorphological and sedimentological structure

DELINEATION ATTEMPTS  Quantification within hydrogeology has been attempted through identification of hyporheic depth or length of flow path.  But also, in a more detailed manner, through consideration of the amount of water present through the surface and groundwater components (Triska et al).

METHODS OF DELINEATION  Examined at a wide range of scales; from riffles to whole drainage basins.  Delineated through exchange processes that occur.

INTERCONNECTIVITY Hyporheic Zone Ecology Faunal Assemblage Residence Times Hydrogeology Groundwater- Surface Interactions Interconnected Processes Physical Properties

CONCLUSIONS  Inter-system connectivity, used to be considered as distinct entities.  Heterogeneity; varied spatially and temporally  The characteristics of running water are controlled by the interaction with their surroundings.

A WORKING DEFINITION  The zone below and adjacent to a streambed in which water from the open channel exchanges with interstitial water in the bed sediments (White, 1993). It is the zone around a stream in which fauna characteristic of the hyporheic zone are distributed and live (Danielopo, 1989). It is a zone in which groundwater and surface water mix (Orghidan, 1959, Triska et al, 1993). The boundaries of the hyporheic zone vary in time and space

REFERENCES  Bencala, K. E., 1993, A perspective on stream-catchment connections; Journal of the North American Benthological Society, p  Danielopo D.L.,1989,Groundwater fauna associated with riverine aquifers: Journal of North. American Benthological Society, v.8, p  Gibert J, Danielopo D.L and Stanford J.A. (eds),1994, Groundwater Ecology: San Diego, Academic  Orghidan, 1959, Ein neur Leben-sraum des unterirdischen Wassers: der hyporheische Biotop: Arch. Hydrobiology; v. 55, p  Sabater F. and Vila P.B., 1991, The Hyporheic Zone considered as an ecotone: Oecologia Aquatica, v.10, p  Stanford J.A. and Ward J.V., 1993, An ecosystem perspective of alluvial rivers: connectivity and the hyporheic corridor, Journal. North. American. Benthological Society, v. 12, p  Stanley, E. H., and Boulton, A. J.,1993, Hydrology and the distribution of hyporheos: perspectives from a mesic river and a desert stream: Journal of the North American Benthological Society, p  Triska F.J, Duff, J.H, and Avanzino R.J., 1993, The role of water exchange between a stream channel and its hyporheic zone in nitrogen cycling at the terrestrial-aquatic interface: Hydrobiologia, v. 251, p  Ward, J. V.,1989, The four-dimensional nature of lotic ecosystems: Journal of the North American Benthological Society, v.8, p.2-8.  White D.S., 1993, Perspectives on defining and delineating hyporheic zones: Journal of the North American Benthological Society v. 12, p  Williams D.D, Febria C.M, and Wong J.C.Y., 2010, Ecotonal and other properties of the Hyporheic Zone: Fundamentals. Applied. Limnology., Arch. Hydrobiol. v.176-4, p. 349–364