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.

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

Winter is a key driver of individual performance, community composition, and ecological interactions in terrestrial habitats. Although climate change research tends to focus on performance in the growing season, climate change is also modifying winter conditions rapidly. Changes to winter temperatures, the variability of winter conditions, and winter snow cover can interact to induce cold injury, alter energy and water balance, advance or retard phenology, and modify community interactions. Species vary in their susceptibility to these winter drivers, hampering efforts to predict biological responses to climate change. Existing frameworks for predicting the impacts of climate change do not incorporate the complexity of organismal responses to winter. Here, we synthesise organismal responses to winter climate change, and use this synthesis to build a framework to predict exposure and sensitivity to negative impacts. This framework can be used to estimate the vulnerability of species to winter climate change. We describe the importance of relationships between winter conditions and performance during the growing season in determining fitness, and demonstrate how summer and winter processes are linked. Incorporating winter into current models will require concerted effort from theoreticians and empiricists, and the expansion of current growing-season studies to incorporate winter.

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Cold truths: how winter drives responses of terrestrial organisms to climate change.

[1] This work reviews the use of heat as a tracer of shallow groundwater movement and describes current temperature-based approaches for estimating streambed water exchanges. Four common hydrologic conditions in stream channels are graphically depicted with the expected underlying streambed thermal responses, and techniques are discussed for installing and monitoring temperature and stage equipment for a range of hydrological environments. These techniques are divided into direct-measurement techniques in streams and streambeds, groundwater techniques relying on traditional observation wells, and remote sensing and other large-scale advanced temperature-acquisition techniques. A review of relevant literature suggests researchers often graphically visualize temperature data to enhance conceptual models of heat and water flow in the near-stream environment and to determine site-specific approaches of data analysis. Common visualizations of stream and streambed temperature patterns include thermographs, temperature envelopes, and one-, two-, and three-dimensional temperature contour plots. Heat and water transport governing equations are presented for the case of transport in streambeds, followed by methods of streambed data analysis, including simple heat-pulse arrival time and heat-loss procedures, analytical and time series solutions, and heat and water transport simulation models. A series of applications of these methods are presented for a variety of stream settings ranging from arid to continental climates. Progressive successes to quantify both streambed fluxes and the spatial extent of streambeds indicate heat-tracing tools help define the streambed as a spatially distinct field (analogous to soil science), rather than simply the lower boundary in stream research or an amorphous zone beneath the stream channel.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008WR006996

Heat as a tracer to determine streambed water exchanges

River restoration is one of the most prominent areas of applied water-resources science. From an initial focus on enhancing fish habitat or river appearance, primarily through structural modification of channel form, restoration has expanded to incorporate a wide variety of management activities designed to enhance river process and form. Restoration is conducted on headwater streams, large lowland rivers, and entire river networks in urban, agricultural, and less intensively human-altered environments. We critically examine how contemporary practitioners approach river restoration and challenges for implementing restoration, which include clearly identified objectives, holistic understanding of rivers as ecosystems, and the role of restoration as a social process. We also examine challenges for scientific understanding in river restoration. These include: how physical complexity supports biogeochemical function, stream metabolism, and stream ecosystem productivity; characterizing response curves of different river components; understanding sediment dynamics; and increasing appreciation of the importance of incorporating climate change considerations and resiliency into restoration planning. Finally, we examine changes in river restoration within the past decade, such as increasing use of stream mitigation banking; development of new tools and technologies; different types of process-based restoration; growing recognition of the importance of biological-physical feedbacks in rivers; increasing expectations of water quality improvements from restoration; and more effective communication between practitioners and river scientists.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2014WR016874

The science and practice of river restoration

http://ira.lib.polyu.edu.hk/bitstream/10397/5259/1/EAAI7.pdf

Artificial neural network simulation of hourly groundwater levels in a coastal aquifer system of the Venice lagoon

Modeling surface and ground water mixing in the hyporheic zone using MODFLOW and MT3D

[1] Hyporheic flow can be extremely variable in space and time, and our understanding of complicated flow systems, such as exchange around small dams, has generally been limited to reach-averaged parameters or discrete point measurements Emerging techniques are starting to fill the void between these disparate scales, increasing the utility of hyporheic research When ambient diurnal temperature patterns are collected at high spatial resolution across vertical profiles in the streambed, the data can be applied to one-dimensional conduction-advection-dispersion models to quantitatively describe the vertical component of hyporheic flux at the same high spatial resolution We have built on recent work by constructing custom fiber-optic distributed temperature sensors with 0014 m spatial resolution that are robust enough to be installed by hand into the streambed, maintain high signal strength, and permit several sensors to be run in series off a single distributed temperature sensing unit Data were collected continuously for 1 month above two beaver dams in a Wyoming stream to determine the spatial and temporal nature of vertical flux induced by the dams Flux was organized by streambed morphology with strong, variable gradients with depth indicating a transition to horizontal flow across a spectrum of hyporheic flow paths Several profiles showed contrasting temporal trends as discharge decreased by 45% The high-resolution thermal sensors, combined with powerful analytical techniques, allowed a distributed quantitative description of the morphology-driven hyporheic system not previously possible

/pdf/using-high-resolution-distributed-temperature-sensing-to-jn446zbm2y.pdf

Using high-resolution distributed temperature sensing to quantify spatial and temporal variability in vertical hyporheic flux

https://eps.mcgill.ca/~mckenzie/reprint/Gordon_et_al_2011.pdf

Automated calculation of vertical pore-water flux from field temperature time series using the VFLUX method and computer program

Rapid exchange of stream water and groundwater in streambeds creates hotspots of biogeochemical cycling of redox-sensitive solutes. Although stream–groundwater interaction can be increased through stream restoration, there are few detailed studies of the increased heterogeneity of water and solute fluxes through the streambed and associated patterns of biogeochemical processes around stream restoration structures. In this study, we examined the seasonal patterns of water and solute fluxes through the streambed around a stream restoration structure to relate patterns of water flux through the streambed to morphology of the channel and biogeochemical processes occurring in the bed. We characterized different biogeochemical zones in the streambed using principal component analysis (PCA) and examined the change in spatial patterns of these zones during different seasons. The PCA results show that two principal components summarized 83% of the variance in the original data set. Streambed pore water was characterized as oxic (indicating production of nitrate), anoxic (indicating sulfate, iron and manganese reduction), or stream-like (indicating there was minimal change in the stream water chemistry in the bed). Regardless of season of the year, anoxic zones were predominantly located upstream of the structure, in a low-velocity pool, and oxic zones were predominantly located downstream of the structure, in a turbulent riffle. We expect structures that span the full channel, are impermeable, and permanent, such as those installed in natural channel design restoration will similarly impact biogeochemical processing in the streambed. The installation of these types of restoration structures may be a way to increase the degree of biogeochemical cycling in stream ecosystems.

Seasonal biogeochemical hotspots in the streambed around restoration structures

[1] Analytical solutions to the 1-D heat transport equation can be used to quantify surface-groundwater interactions directly from temperature time series data in streams and their streambeds. The solutions rely on three assumptions: purely vertical flow, no thermal gradient with depth in the streambed and sinusoidal temperature signals. Here numerical models of heat transport in streambeds are used to generate synthetic time series data under conditions that violate the aforementioned assumptions. These synthetic records are used to evaluate the impact of violations of model assumptions on vertical water velocity estimates. Analytical methods using the amplitude ratio to derive flux are less prone to error than methods that use lag time under nonideal field conditions. The greatest source of error is nonvertical flow in the streambed. Errors from analytical solutions for flux are comparable to or smaller than errors inherent to Darcy-based flux estimates and therefore the use of temperature data to quantify flux across the streambed is a promising alternative to more commonly used approaches, such as Darcy flux calculations.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009WR007917

Laura K. Lautz

Papers

Modeling surface and ground water mixing in the hyporheic zone using MODFLOW and MT3D

Using high-resolution distributed temperature sensing to quantify spatial and temporal variability in vertical hyporheic flux

Automated calculation of vertical pore-water flux from field temperature time series using the VFLUX method and computer program

Seasonal biogeochemical hotspots in the streambed around restoration structures

Impacts of nonideal field conditions on vertical water velocity estimates from streambed temperature time series