Multiscale geomorphic drivers of groundwater flow paths: subsurface hydrologic dynamics and hyporheic habitat diversity
G.C. Poole, J.A. Stanford, S.W. Running, and C.A. Frissell. Journal of the North American Benthological Society. 25(2): 288-303. 2006.
Application of a hydrogeologic computer model underscored the
importance of geomorphic controls on groundwater and surface-water flow
dynamics the Nyack Floodplain, a montane alluvial floodplain in
Montana, USA. The model represented the floodplain as a hierarchy of
geomorphic patches, which facilitated analysis of model results using
independent (predictor) variables at multiple scales. The analyses
revealed that geomorphic structures at various spatial scales interact
with the flow regime to influence the direction, magnitude, and
stability of hyporheic flow within individual floodplain patches.
Specifically: 1) the hydrologic flow network within the hyporheic zone
is more responsive to seasonal changes in river discharge if floodplain
topography is complex and aquifer properties are heterogeneous, 2)
simplification of internal patch structure across the floodplain
eliminates the influence of fine-scale geomorphic structures on the
stability of groundwater flow paths, although the influence of patch
context remains, and 3) incremental changes in river discharge can
abruptly and substantially restructure the relationship between river
discharge and groundwater flow patterns when events such as inundation
of previously dry flood channels occur on the floodplain. We believe
that ecological theories of biodiversity can be used to understand
interactions among geomorphic variation, hydrologic dynamics, and the
maintenance of biodiversity in the hyporheic zone if the abrupt
reorganization and other variations in groundwater flow paths act as
disturbances to hyporheic communities. From this perspective, we used
model results to develop 4 hypotheses describing the potential for
causal linkages among floodplain geomorphology, hyporheic flow-path
variation, hyporheic habitat diversity/stability, and hyporheic
community diversity.
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