The ecological significance of exchange processes between rivers and groundwater

Abstract

S U M M A R Y1. This review focuses on the connectivity between river and groundwater ecosystems, viewing them as linked components of a hydrological continuum. Ecological processes that maintain the integrity of both systems and those that are mediated by their ecotones are evaluated. 2. The hyporheic zone, as the connecting ecotone, shows diverse gradients. Thus it can be characterized by hydrological, chemical, zoological and metabolic criteria. However, the characteristics of the hyporheic zone tend to vary widely in space and time as well as from system to system. The exact limits are difficult to designate and the construction of static concepts is inadequate for the representation of ecological processes. The hyporheic interstices are functionally a part of both the fluvial and groundwater ecosystems. 3. The permeability of the ecotone depends on the hydraulic conductivity of the sediment layers which, because of their heterogeneity, form many flowpath connections between the stream and the catchment, from the small scale of a single microhabitat to the large scale of an entire alluvial aquifer. Local up-and downwellings are determined by geomorphologic features such as streambed topography, whereas large-scale exchange processes are determined mainly by the geological properties of the catchment. Colmation-clogging of the top layer of the channel sediments-includes all processes leading to a reduction of pore volume, consolidation of the sediment matrix, and decreased permeability of the stream bed. Consequently, colmation can hinder exchange processes between surface water and groundwater. 4. Physicochemical gradients in the interstices result from several processes: (i) hyporheic flow pattern and the different properties of surface and groundwaters; (ii) retention, caused by the filtering effect of pore size and lithologic sorption as well as the transient storage of solutes caused by diminished water velocities; (iii) biogeochemical transformations in conjunction with local residence time. Each physicochemical parameter may develop its own vertical dynamics laterally from the active channel into the banks as well as longitudinally because of geomorphologic changes. 5. The river-groundwater interface can act as a source or sink for dissolved organic matter, depending on the volume and direction of flow, dissolved organic carbon concentrations and biotic activity. Interstitial storage of particulate organic matter is influenced mainly by grain size distribution and by spates involving bedload movement that may import or release matter, depending on the season. After initial transient and abiotic storage, hyporheic organic matter is mobilized and transformed by the biota. 2 M. Brunke and T. GonserMicro-organisms account for over 90% of the community respiration. In subterranean waters most bacteria are attached to surfaces and remain in a biofilm. 6. Hyporheic interstices are functionally significant for phreatic and riverine metazoans because they act as a refuge against adverse conditions. The net flo...

Groundwater and Surface Water Interaction at the Regional-scale – A Review with Focus on Regional Integrated Models

“…Winter and Rosenberry (1995) and Winter (1999) take a similar approach, focusing particularly on the hydraulic conditions related to various types of surface waters. Brunke and Gonser (1997) and Hayashi and Rosenberry (2002) provide a comprehensive overview with special emphasis on the ecology of surface waters. Rosenberry and LaBaugh (2008) as well as Kalbus et al (2006) give overviews of field techniques for estimating fluxes between groundwater and surface water at different scales.…”

Buffered, lagged, or cooled? Disentangling hyporheic influences on temperature cycles in stream channels

“…However, in alluvial rivers and streams, the prevalence of bidirectional water flux between the river channel and alluvial aquifer (''hyporheic exchange'') is well established [Stanford and Ward, 1988;Findlay, 1995;Brunke and Gonser, 1997;Malard et al, 1999], and researchers have recognized tight coupling between the thermal dynamics of river channels and their underlying hyporheic zones.…”

Review: Microbial biocenoses in pristine aquifers and an assessment of investigative methods

“…The hyporheic zone provides living space for a variety of organisms, including fish larvae. Biological activity in this zone contributes to the natural attenuation of contaminated surface waters infiltrating into the aquifer (Boulton et al 1998;Brunke and Gonser 1997;Gayraud et al 2002;Malard et al 2002;Ward and Palmer 1994). Karst aquifers are characterised by solutionally enlarged fissures and caves.…”