Hyporheic flow and transport processes: Mechanisms, models, and biogeochemical implications

Abstract

Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed.

River bedform inception by flow unsteadiness: A modal and nonmodal analysis

“…Research interest about these morphologies derives from their relevance in hydraulic engineering and environmental applications. River bedforms not only interfere with river navigation [1,2] and human infrastructure [3,4], they also induce differential pressure gradients that modify the flow field and consequently the overall hydraulic resistance, induce hyporheic fluxes [5,6], and affect underground flows through preferential patterns within ancient sedimentary deposits [7,8]. The present work focuses on dunes and antidunes (see Fig.…”

Fractal patterns in riverbed morphology produce fractal scaling of water storage times

“…Travel times in rivers and watersheds are very broadly distributed [Kirchner et al, 2000;Haggerty et al, 2002;Stonedahl et al, 2012;Aubeneau et al, 2014], but the mechanisms that produce travel time distributions over many orders of magnitude are not known precisely [Boano et al, 2014]. The exchange of water between surface and subsurface flows, generally termed hyporheic exchange, plays a critical role in structuring fluvial ecosystems [Boulton et al, 1998;Aubeneau et al, 2015].…”

The ecology and biogeochemistry of stream biofilms

“…As a result, the streambed and its biofilm microbiome contribute to biogeochemical fluxes 8 . Indeed, stream biofilms are now recognized as substantial contributors to global carbon fluxes by degrading organic matter and ultimately emitting an unexpectedly large amount of carbon dioxide into the atmosphere 9,10 .…”

“…may even be considered to have undergone a 'co evolutionary' relationship, as biofilms adapt and evolve in response to the physical and chemical structure of the streambed environment, and simultaneously modify this environment by changing its hydrodynamics 6,64,65 and establishing chemical gradients 8 . These interactions between the biofilm and the sediment regulate not only physical patterns of the porous space but also the ecology of the biofilms therein.…”