skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Hyporheic Flows in Stratified Sediments: Implications on Residence Time Distributions
Abstract The fate of nutrients and contaminants in fluvial ecosystems is strongly affected by the mixing dynamics between surface water and groundwater within the hyporheic zone, depending on the combination of the sediment's hydraulic heterogeneity and dune morphology. This study examines the effects of hydraulic conductivity stratification on steady‐state, two‐dimensional, hyporheic flows and solute residence time distribution. First, we derive an integral transform‐based semi‐analytical solution for the flow field, capable of accounting for the effects of any functional shape of the vertically varying hydraulic conductivity. The solution considers the uneven distribution of pressure at the water‐sediment interface (i.e., the pumping process) dictated by the presence of dune morphology. We then simulate solute transport using particle tracking. Our modeling framework is validated against numerical and tracer data from flume experiments and used to explore the implication of hydraulic conductivity stratification on the statistics andpdfof the residence time. Finally, reduced‐order models are used to enlighten the dependence of key residence time statistics on the parameters characterizing the hydraulic conductivity stratification.  more » « less
Award ID(s):
1654009
PAR ID:
10519822
Author(s) / Creator(s):
; ;
Publisher / Repository:
AGU
Date Published:
Journal Name:
Water Resources Research
Volume:
60
Issue:
1
ISSN:
0043-1397
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; (, Water Resources Research)
    Abstract Hyporheic exchange is a crucial control of the type and rates of streambed biogeochemical processes, including metabolism, respiration, nutrient turnover, and the transformation of pollutants. Previous work has shown that increasing discharge during an individual peak flow event strengthens biogeochemical turnover by enhancing the exchange of water and dissolved solutes. However, due to the nonsteady nature of the exchange process, successive peak flow events do not exhibit proportional variations in residence time and turnover, and in some cases, can reduce the hyporheic zones' biogeochemical potential. Here, we used a process‐based model to explore the role of successive peak flow events on the flow and transport characteristics of bedform‐induced hyporheic exchange. We conducted a systematic analysis of the impacts of the events' magnitude, duration, and time between peaks in the hyporheic zone's fluxes, penetration, and residence times. The relative contribution of each event to the transport of solutes across the sediment‐water interface was inferred from transport simulations of a conservative solute. In addition to temporal variations in the hyporheic flow field, our results demonstrate that the separation between two events determines the temporal evolution of residence time and that event time lags longer than the memory of the system result in successive events that can be treated independently. This study highlights the importance of discharge variability in the dynamics of hyporheic exchange and its potential implications for biogeochemical transformations and fate of contaminants along river corridors. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, Journal of Hydrology)
    Groundwater-surface water interaction (hyporheic exchange) is critical in numerous hydrogeochemical processes; however, hyporheic exchange is difficult to characterize due to the various spatial (e.g., sedimentary architecture) and temporal (e.g., stage fluctuations) variables that influence it. This interdisciplinary study brings forth novel insights by integrating various methodologies including geophysical surveys, physical and chemical sediment characterization, and water chemistry analysis to explore the interplay of the numerous facets governing hyporheic zone processes within a compound bar deposit. The findings reveal distinct sedimentary facies and geochemical zones within the compound bar, driven by the sedimentary architecture. Cross-bar channel fills are identified as critical structures influencing hydrogeochemical dynamics, acting as baffles to groundwater flow and modulating nutrient transformations. Geophysical imaging and hydrogeochemical analyses highlight the complex interplay between sediment characteristics and subsurface hydraulic connectivity, emphasizing the role of sediment heterogeneity in controlling hyporheic exchange and solute mixing. The study concludes that sediment heterogeneity, particularly the presence of cross-bar channel fills, plays a pivotal role in the hydrogeochemical dynamics of the hyporheic zone. These structures significantly influence hyporheic flow paths, solute residence times, and nutrient cycling, underscoring the necessity to consider the fine-scale sedimentary architecture in models of hyporheic exchange. The findings contribute to a deeper understanding of riverine ecosystem processes, offering insights that can inform management strategies for water quality and ecological integrity. 
    more » « less
  3. ; ; ; ; (, Journal of Geophysical Research: Biogeosciences)
    Abstract Assessments of riverine ecosystem health and water quality require knowledge of how headwater streams transport and transform nutrients. Estimates of nutrient demand at the watershed scale are commonly inferred from reach‐scale solute injections, which are typically reported as uptake velocities (vf). Multiple interacting processes controlvf, making it challenging to predict howvfresponds to physical changes in the stream. In this study, we linkvfto a continuous time random walk model to quantify howvfis controlled by in‐stream (velocity, dispersion, and benthic reaction) and hyporheic processes (exchange rate, residence times, and hyporheic reaction). We fit the model to conservative (NaCl) and nitrate (NO3−‐N) pulse tracer injections in unshaded replicate streams at the Notre Dame Linked Experimental Ecosystem Facility, which differed only in substrate size and distribution. Experiments were conducted over the first 25 days of biofilm colonization to examine how the interaction between substrate type and biofilm growth influenced modeled processes andvf. Model fits of benthic reaction rates were ∼8× greater than hyporheic reaction rates for all experiments and did not vary with substrate type or over time. High benthic reactivity was associated with filamentous green algae coverage on the streambed, which dominated total algal biomass. Finally,vfwas most sensitive to benthic reaction rate and stream velocity, and sensitivity varied with stream conditions due to its nonlinear dependence on all modeled processes. Together, these results demonstrate how reach‐scale nutrient demand reflects the relative contributions of biotic and abiotic processes in the benthic layer and the hyporheic zone. 
    more » « less
  4. ; ; ; ; ; (, Water Resources Research)
    Abstract Coupled groundwater flow and heat transport within hyporheic zones extensively affect water, energy, and solute exchange with surrounding sediments. The local and cumulative implications of this tightly coupled process strongly depend on characteristics of drivers (i.e., discharge and temperature of the water column) and modulators (i.e., hydraulic and thermal properties of the sediment). With this in mind, we perform a systematic numerical analysis of hyporheic responses to understand how the temporal variability of river discharge and temperature affect flow and heat transport within hyporheic zones. We identify typical time series of river discharge and temperature from gauging stations along the headwater region of Mississippi River Basin, which are characterized by different degrees of flow alteration, to drive a physics‐based model of the hyporheic exchange process. Our modeling results indicate that coupled groundwater flow and heat transport significantly affects the dynamic response of hyporheic zones, resulting in substantial differences in exchange rates and characteristic time scales of hyporheic exchange processes. We also find that the hyporheic zone dampens river temperature fluctuations increasingly with higher frequency of temperature fluctuations. This dampening effect depends on the system transport time scale and characteristics of river discharge and temperature variability. Furthermore, our results reveal that the flow alteration reduces the potential of hyporheic zones to act as a temperature buffer and hinders denitrification within hyporheic zones. These results have significant implications for understanding the drivers of local variability in hyporheic exchange and the implications for the development of thermal refugia and ecosystem functioning in hyporheic zones. 
    more » « less
  5. ; ; ; ; (, Water Resources Research)
    Abstract Logjams in a stream create backwater conditions and locally force water to flow through the streambed, creating zones of transient storage within the surface and subsurface of a stream. We investigate the relative importance of logjam distribution density, logjam permeability, and discharge on transient storage in a simplified experimental channel. We use physical flume experiments in which we inject a salt tracer, monitor fluid conductivity breakthrough curves in surface water, and determine breakthrough‐curve skewness to characterize transient storage. We then develop a companion numerical model in HydroGeoSphere to reveal flow paths through the subsurface (or hyporheic zone) that contribute to some of the longest transient‐storage timescales. In both the flume experiments and numerical simulations, we observe backwater formation and an increase in hyporheic exchange at logjams. Observed complexities in transient storage behavior depend largely on surface water flow in the backwater zone. As expected, multiple successive logjams provide more pervasive hyporheic exchange by distributing the head drop at each jam, leading to distributed but shallow flow paths. Decreasing the permeability of a logjam or increasing the discharge both facilitate greater surface water storage and volumetric rate of hyporheic exchange. Understanding how logjam characteristics affect solute transport through both the channel and hyporheic zone has important management implications for rivers in forested, or historically forested, environments. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email