Browsing by Author "Gomez-Velez, Jesus D."

Now showing 1 - 10 of 10
  • Thumbnail Image
    Can Common Pool Resource Theory Catalyze Stakeholder-Driven Solutions to the Freshwater Salinization Syndrome?
    Grant, Stanley B.; Rippy, Megan A.; Birkland, Thomas A.; Schenk, Todd; Rowles, Kristin; Misra, Shalini; Aminpour, Payam; Kaushal, Sujay; Vikesland, Peter J.; Berglund, Emily; Gomez-Velez, Jesus D.; Hotchkiss, Erin R.; Perez, Gabriel; Zhang, Harry X.; Armstrong, Kingston; Bhide, Shantanu V.; Krauss, Lauren; Maas, Carly; Mendoza, Kent; Shipman, Caitlin; Zhang, Yadong; Zhong, Yinman (American Chemical Society, 2022-09-14)
    Freshwater salinity is rising across many regions of the United States as well as globally, a phenomenon called the freshwater salinization syndrome (FSS). The FSS mobilizes organic carbon, nutrients, heavy metals, and other contaminants sequestered in soils and freshwater sediments, alters the structures and functions of soils, streams, and riparian ecosystems, threatens drinking water supplies, and undermines progress toward many of the United Nations Sustainable Development Goals. There is an urgent need to leverage the current understanding of salinization's causes and consequences?in partnership with engineers, social scientists, policymakers, and other stakeholders?into locally tailored approaches for balancing our nation's salt budget. In this feature, we propose that the FSS can be understood as a common pool resource problem and explore Nobel Laureate Elinor Ostrom's social-ecological systems framework as an approach for identifying the conditions under which local actors may work collectively to manage the FSS in the absence of top-down regulatory controls. We adopt as a case study rising sodium concentrations in the Occoquan Reservoir, a critical water supply for up to one million residents in Northern Virginia (USA), to illustrate emerging impacts, underlying causes, possible solutions, and critical research needs.
  • Thumbnail Image
    Floodplain inundation spectrum across the United States
    Scott, Durelle T.; Gomez-Velez, Jesus D.; Jones, C. Nathan; Harvey, Judson W. (2019-11-15)
    Floodplain inundation poses both risks and benefits to society. In this study, we characterize floodplain inundation across the United States using 5800 stream gages. We find that between 4% and 12.6% of a river's annual flow moves through its floodplains. Flood duration and magnitude is greater in large rivers, whereas the frequency of events is greater in small streams. However, the relative exchange of floodwater between the channel and floodplain is similar across small streams and large rivers, with the exception of the water-limited arid river basins. When summed up across the entire river network, 90% of that exchange occurs in small streams on an annual basis. Our detailed characterization of inundation hydrology provides a unique perspective that the regulatory, management, and research communities can use to help balance both the risks and benefits associated with flooding.
  • Thumbnail Image
    How Hydrologic Connectivity Regulates Water Quality in River Corridors
    Harvey, Jud; Gomez-Velez, Jesus D.; Schmadel, Noah M.; Scott, Durelle T.; Boyer, Elizabeth W.; Alexander, Richard B.; Eng, Ken; Golden, Heather; Kettner, Albert; Konrad, Chris; Moore, Richard; Pizzuto, Jim; Schwarz, Greg; Soulsby, Chris; Choi, Jay (2019-04)
    Downstream flow in rivers is repeatedly delayed by hydrologic exchange with off-channel storage zones where biogeochemical processing occurs. We present a dimensionless metric that quantifies river connectivity as the balance between downstream flow and the exchange of water with the bed, banks, and floodplains. The degree of connectivity directly influences downstream water quality - too little connectivity limits the amount of river water exchanged and leads to biogeochemically inactive water storage, while too much connectivity limits the contact time with sediments for reactions to proceed. Using a metric of reaction significance based on river connectivity, we provide evidence that intermediate levels of connectivity, rather than the highest or lowest levels, are the most efficient in removing nitrogen from Northeastern United States' rivers. Intermediate connectivity balances the frequency, residence time, and contact volume with reactive sediments, which can maximize the reactive processing of dissolved contaminants and the protection of downstream water quality. Our simulations suggest denitrification dominantly occurs in riverbed hyporheic zones of streams and small rivers, whereas vertical turbulent mixing in contact with sediments dominates in mid-size to large rivers. The metrics of connectivity and reaction significance presented here can facilitate scientifically based prioritizations of river management strategies to protect the values and functions of river corridors.
  • Thumbnail Image
    Low threshold for nitrogen concentration saturation in headwaters increases regional and coastal delivery
    Schmadel, Noah M.; Harvey, Judson W.; Alexander, Richard B.; Boyer, Elizabeth W.; Schwarz, Gregory E.; Gomez-Velez, Jesus D.; Scott, Durelle T.; Konrad, Christopher P. (2020-04)
    River corridors store, convey, and process nutrients from terrestrial and upstream sources, regulating delivery from headwaters to estuaries. A consequence of chronic excess nitrogen loading, as supported by theory and field studies in specific watersheds, is saturation of the biogeochemically-mediated nitrogen removal processes that weakens the capacity of the river corridor to remove nitrogen. Regional nitrogen models typically assume that removal capacity exhibits first-order behavior, scaling positively and linearly with increasing concentration, which may bias the estimation of where and at what rate nitrogen is removed by river corridors. Here we estimate the nitrogen concentration saturation threshold and its effects on annual nitrogen export from the Northeastern United States, revealing an average 42% concentration-induced reduction in headwater removal capacity. The weakened capacity caused an average 10% increase in the predicted delivery of riverine nitrogen from urban and agricultural watersheds compared to estimates using first-order process assumptions. Our results suggest that nitrogen removal may fall below a first-order rate process as riverine concentration increases above a threshold of 0.5 mg N l(-1). Threshold behavior indicates that even modest mitigation of nitrogen concentration in river corridors above the threshold can cause a self-reinforcing boost to nitrogen removal.
  • Thumbnail Image
    Modeling the Effects of Turbulence on Hyporheic Exchange and Local-to-Global Nutrient Processing in Streams
    Grant, Stanley B.; Gomez-Velez, Jesus D.; Ghisalberti, Marco (2018-09)
    New experimental techniques are allowing, for the first time, direct visualization of mass and momentum transport across the sediment-water interface in streams. These experimental insights are catalyzing a renaissance in our understanding of the role stream turbulence plays in a host of critical ecosystem services, including nutrient cycling. In this commentary, we briefly review the nature of stream turbulence and its role in hyporheic exchange and nutrient cycling in streams. A simple process-based model, borrowed from biochemical engineering, provides the link between empirical relationships for grain-scale turbulent mixing and nutrient processing at reach, catchment, continental, and global scales.
  • Thumbnail Image
    A One-Dimensional Model for Turbulent Mixing in the Benthic Biolayer of Stream and Coastal Sediments
    Grant, Stanley B.; Gomez-Velez, Jesus D.; Ghisalberti, Marco; Guymer, Ian; Boano, Fulvio; Roche, Kevin; Harvey, Judson (2020-12)
    In this paper, we develop and validate a rigorous modeling framework, based on Duhamel's Theorem, for the unsteady one-dimensional vertical transport of a solute across a flat sediment-water interface (SWI) and through the benthic biolayer of a turbulent stream. The modeling framework is novel in capturing the two-way coupling between evolving solute concentrations above and below the SWI and in allowing for a depth-varying diffusivity. Three diffusivity profiles within the sediment (constant, exponentially decaying, and a hybrid model) are evaluated against an extensive set of previously published laboratory measurements of turbulent mass transfer across the SWI. The exponential diffusivity profile best represents experimental observations and its reference diffusivity scales with the permeability Reynolds number, a dimensionless measure of turbulence at the SWI. The depth over which turbulence-enhanced diffusivity decays is of the order of centimeters and comparable to the thickness of the benthic biolayer. Thus, turbulent mixing across the SWI may serve as a universal transport mechanism, supplying the nutrient and energy fluxes needed to sustain microbial growth, and nutrient processing, in the benthic biolayer of stream and coastal sediments.
  • Thumbnail Image
    The sanitary sewer unit hydrograph model: A comprehensive tool for wastewater flow modeling and inflow-infiltration simulations
    Perez, Gabriel; Gomez-Velez, Jesus D.; Grant, Stanley B. (Elsevier, 2023-12-08)
    Sanitary sewer systems are critical urban water infrastructure that protect both human and environmental health. Their design, operation, and monitoring require novel modeling techniques that capture dominant processes while allowing for computationally efficient simulations. Open water flow in sewers and rivers are intrinsically similar processes. With this in mind, we formulated a new parsimonious model inspired by the Width Function Instantaneous Unit Hydrograph (WFIUH) approach, widely used to predict rainfall-runoff relationships in watersheds, to a sanitary sewer system consisting of nearly 10,000 sewer conduits and 120,000 residential and commercial sewage connections in Northern Virginia, U.S.A. Model predictions for the three primary components of sanitary flow, including Base Wastewater Flow (BWF), Groundwater Infiltration (GWI), and Runoff Derived Infiltration and Inflow (RDII), compare favorably with the more computationally demanding industry-standard Storm Water Management Model (SWMM). This novel application of the WFIUH modeling framework should support a number of critical water quality endpoints, including (i) sewer hydrograph separation through the quantification of BWF, GWI, and RDII outflows, (ii) evaluation of the impact of new urban developments on sewage flow dynamics, (iii) monitoring and mitigation of sanitary sewer overflows, and (iv) design and interpretation of wastewater surveillance studies.
  • Thumbnail Image
    Small Ponds in Headwater Catchments Are a Dominant Influence on Regional Nutrient and Sediment Budgets
    Schmadel, Noah M.; Harvey, Judson W.; Schwarz, Gregory E.; Alexander, Richard B.; Gomez-Velez, Jesus D.; Scott, Durelle T.; Ator, Scott W. (2019-08-28)
    Small ponds-farm ponds, detention ponds, or impoundments below 0.01 km(2)-serve important human needs throughout most large river basins. Yet the role of small ponds in regional nutrient and sediment budgets is essentially unknown, currently making it impossible to evaluate their management potential to achieve water quality objectives. Here we used new hydrography data sets and found that small ponds, depending on their spatial position within both their local catchments and the larger river network, can dominate the retention of nitrogen, phosphorus, and sediment compared to rivers, lakes, and reservoirs. Over 300,000 small ponds are collectively responsible for 34%, 69%, and 12% of the mean annual retention of nitrogen, phosphorus, and sediment in the Northeastern United States, respectively, with a dominant influence in headwater catchments (54%, 85%, and 50%, respectively). Small ponds play a critical role among the many aquatic features in long-term nutrient and sediment loading to downstream waters. Plain Language Summary Reservoirs created by river damming have extensive impacts on downstream water quality but are not necessarily the most important elements of a diverse aquatic landscape. Many more small ponds have been constructed to serve important human needs ranging from farm irrigation in agricultural areas to flood control and trapping of nutrients and fine sediment in urban areas. The number of human-influenced small ponds is projected to rise worldwide, yet their role in the delivery of nutrients and sediment from headwaters to oceans is currently unresolved. Here we used new data sets and found that small ponds are collectively responsible for trapping a substantial amount of the nutrients and sediment that are exported annually from headwaters. These findings support the need to jointly consider features such as urban detention ponds, farm ponds, and beaver ponds in managing headwaters to decrease long-term nutrient and sediment loading to downstream waters and sensitive coastal areas.
  • Thumbnail Image
    Thresholds of lake and reservoir connectivity in river networks control nitrogen removal
    Schmadel, Noah M.; Harvey, Judson W.; Alexander, Richard B.; Schwarz, Gregory E.; Moore, Richard B.; Eng, Ken; Gomez-Velez, Jesus D.; Boyer, Elizabeth W.; Scott, Durelle T. (Springer Nature, 2018-07-17)
    Lakes, reservoirs, and other ponded waters are ubiquitous features of the aquatic landscape, yet their cumulative role in nitrogen removal in large river basins is often unclear. Here we use predictive modeling, together with comprehensive river water quality, land use, and hydrography datasets, to examine and explain the influences of more than 18,000 ponded waters on nitrogen removal through river networks of the Northeastern United States. Thresholds in pond density where ponded waters become important features to regional nitrogen removal are identified and shown to vary according to a ponded waters’ relative size, network position, and degree of connectivity to the river network, which suggests worldwide importance of these new metrics. Consideration of the interacting physical and biological factors, along with thresholds in connectivity, reveal where, why, and how much ponded waters function differently than streams in removing nitrogen, what regional water quality outcomes may result, and in what capacity management strategies could most effectively achieve desired nitrogen loading reduction.
  • Thumbnail Image
    Unifying Advective and Diffusive Descriptions of Bedform Pumping in the Benthic Biolayer of Streams
    Grant, Stanley B.; Monofy, Ahmed; Boano, Fulvio; Gomez-Velez, Jesus D.; Guymer, Ian; Harvey, Judson; Ghisalberti, Marco (2020-09-01)
    Many water quality and ecosystem functions performed by streams occur in the benthic biolayer, the biologically active upper (similar to 5 cm) layer of the streambed. Solute transport through the benthic biolayer is facilitated by bedform pumping, a physical process in which dynamic and static pressure variations over the surface of stationary bedforms (e.g., ripples and dunes) drive flow across the sediment-water interface. In this paper we derive two predictive modeling frameworks, one advective and the other diffusive, for solute transport through the benthic biolayer by bedform pumping. Both frameworks closely reproduce patterns and rates of bedform pumping previously measured in the laboratory, provided that the diffusion model's dispersion coefficient declines exponentially with depth. They are also functionally equivalent, such that parameter sets inferred from the 2D advective model can be applied to the 1D diffusive model, and vice versa. The functional equivalence and complementary strengths of these two models expand the range of questions that can be answered, for example, by adopting the 2D advective model to study the effects of geomorphic processes (such as bedform adjustments to land use change) on flow-dependent processes and the 1D diffusive model to study problems where multiple transport mechanisms combine (such as bedform pumping and turbulent diffusion). By unifying 2D advective and 1D diffusive descriptions of bedform pumping, our analytical results provide a straightforward and computationally efficient approach for predicting, and better understanding, solute transport in the benthic biolayer of streams and coastal sediments.