Separation of river network–scale nitrogen removal among the main channel and two transient storage compartments

Stewart, Robert; Wollheim, W. M.; Gooseff, M. N.; Briggs, Martin A.; Jacobs, Jennifer M.; Peterson, Bruce J.; Hopkinson, Charles S.

doi:10.1029/2010wr009896

Cited by 78 publications

(99 citation statements)

References 83 publications

(159 reference statements)

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“…Finally, removal rates calculated by Protocol 2 are zeroth order with respect to NO 3 − concentration, meaning the rate is flat regardless of inflowing concentration. By contrast, our approach was first order with respect to NO 3 − concentration, which is more in line with approaches typically taken in the scientific literature (Boyer et al, 2006;Stewart et al, 2011;Harvey et al, 2013;Zarnetske et al, 2015). This may mean that Protocol 2 may overestimate N removal at some concentrations and underestimate it at others.…”

Section: Comparison With Chesapeake Bay Guidancementioning

confidence: 52%

“…For example, we assumed first-order removal of NO 3 − from the hyporheic zone based on prior work (Boyer et al, 2006;Stewart et al, 2011;Harvey et al, 2013;Zarnetske et al, 2015). As discussed earlier, this was a reasonable approximation given our relatively low NO 3 − concentrations.…”

Section: Model Limitationsmentioning

confidence: 99%

“…We simulated hyporheic zone NO 3 − removal via denitrification by assigning a first-order decay rate to the groundwater component of the model. While hyporheic zone denitrification can be simulated following Michaelis-Menten kinetics (Cardenas et al, 2008;Marzadri et al, 2011;Kessler et al, 2015), models using first-order kinetics have been successfully calibrated to field data (Boyer et al, 2006;Stewart et al, 2011;Harvey et al, 2013;Zarnetske et al, 2015), and it is considered reasonable to simulate it as a first order process when NO 3 − concentrations are low (Sheibley et al, 2003;Marzadri et al, 2011;Gu et al, 2012), which they are in this case. We varied this parameter in our sensitivity analysis using a range of literature values (Section 2.2.4, Table 1).…”

Section: Hydraulic Parameters and Boundary Conditionsmentioning

confidence: 99%

“…MIKE SHE solves the advection-dispersion equation using the QUICKEST method (Leonard, 1979), an explicit scheme that applies upstream and central differencing for the advection and dispersion terms, respectively (DHI, 2011). Denitrification in hyporheic zone models is often simulated as Michaelis-Menten (Monod) kinetics (Gu et al, 2007, Zarnetske et al, 2012, however first-order kinetics are justified when the NO 3 − concentration is less than the reaction halfsaturation constant of 1.64 mg/L NO 3 − N (Boyer et al, 2006;Stewart et al, 2011;Zarnetske et al, 2012Zarnetske et al, , 2015Harvey et al, 2013). We used a base case NO 3 − concentration of 1.0 mg/L NO 3 − N, thus we were below this threshold during most of our model runs.…”

Section: Model Governing Equationsmentioning

confidence: 99%

“…reaction or removal rate) (Stewart et al, 2011), such that ultimately one of these factors will limit the rate of N removal. Identification of this limiting factor on a strategyspecific and even site-specific basis will help to quantify the cost of achieving meaningful water quality improvements through stream restoration.…”

Section: Hydraulic Connection and Residence Time In Storage Zonesmentioning

confidence: 99%

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Effects of inset floodplains and hyporheic exchange induced by in-stream structures on nitrate removal in a headwater stream

Hester

Hammond

Scott

2016

Ecological Engineering

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a b s t r a c tStream restoration efforts in the United States are increasingly aimed towards water quality improvement, yet little process-based guidance exists to compare pollutant removals from different restoration techniques for variable site conditions. Excess nitrate (NO 3 − ) is a frequent pollutant of concern due to eutrophication in downstream waterbodies such as the Chesapeake Bay. We used MIKE SHE to simulate hydraulics and NO 3 − removal in a 90 m restored reach of Stroubles Creek, a second-order stream in Blacksburg, Virginia. Site specific geomorphic, hydrologic, and hydraulic data were used to calibrate the model. We evaluated in-stream structures that induce hyporheic zone denitrification during baseflow and inset floodplains that remove NO 3 − during storm flows. We varied hydraulic conditions (winter baseflow, summer baseflow, storm flow), biogeochemical parameters (literature hyporheic zone denitrification rates and newly available inset floodplain removal rates) and boundary conditions (upstream NO 3 − concentration), sediment conditions (hydraulic conductivity), and stream restoration design parameters (inset floodplain length). Our results indicate that NO 3 − removal rates within the 90 m reach were minimal. Structure-induced hyporheic zone denitrification did not exceed 3.1% of mass flowing in from the upstream channel, was achieved only during favorable background groundwater hydraulic conditions (i.e. summer baseflow), and was transport-limited such that non-trivial removal rates were achieved only when the streambed hydraulic conductivity (K) was at least 10 −4 m/s. Inset floodplain nitrogen removal was limited by floodplain residence time and NO 3 − removal rate, and did not exceed 1% of inflowing mass. Summing these removals for both restoration practices over the course of the year based on the frequency of storm and summer baseflow conditions yielded ∼2.1% annual removal. Achieving 30% NO 3 − removal required increasing the length of stream reach restored to 0.9 km-819 km (depending on hydraulic conductivity) and 3.8-46 km (depending on inset floodplain length and nitrogen removal rate) for in-stream structures during baseflow and inset floodplains during storm flow, respectively. In one of the first comparisons of process-based modeling to the Chesapeake Bay Program stream restoration guidance, we found that the guidance overestimated hyporheic NO 3 − removal for our modeled reach, but correctly estimated inset floodplain removal. Overall, our results indicate that in-stream structures and inset floodplains can improve water quality, but overall required level of effort may be high to achieve desired results.

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Section: Comparison With Chesapeake Bay Guidancementioning

confidence: 52%

Section: Model Limitationsmentioning

confidence: 99%

Section: Hydraulic Parameters and Boundary Conditionsmentioning

confidence: 99%

Section: Model Governing Equationsmentioning

confidence: 99%

Section: Hydraulic Connection and Residence Time In Storage Zonesmentioning

confidence: 99%

See 3 more Smart Citations

Effects of inset floodplains and hyporheic exchange induced by in-stream structures on nitrate removal in a headwater stream

Hester

Hammond

Scott

2016

Ecological Engineering

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Prolonged river water pollution due to variable‐density flow and solute transport in the riverbed

Jin

Tang

et al. 2015

Water Resources Research

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A laboratory experiment and numerical modeling were used to examine effects of density gradients on hyporheic flow and solute transport under the condition of a solute pulse input to a river with regular bed forms. Relatively low-density gradients due to an initial salt pulse concentration of 1.55 kg m 23 applied in the experiment were found to modulate significantly the pore-water flow and solute transport in the riverbed. Such density gradients increased downward flow and solute transport in the riverbed by factors up to 1.6. This resulted in a 12.2% increase in the total salt transfer from the water column to the riverbed over the salt pulse period. As the solute pulse passed, the effect of the density gradients reversed, slowing down the release of the solute back to the river water by a factor of 3.7. Numerical modeling indicated that these density effects intensified as salt concentrations in the water column increased. Simulations further showed that the density gradients might even lead to unstable flow and result in solute fingers in the bed of large bed forms. The slow release of solute from the bed back to the river led to a long tail of solute concentration in the river water. These findings have implications for assessment of impact of pollution events on river systems, in particular, long-term effects on both the river water and riverbed due to the hyporheic exchange.

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Removal of terrestrial DOC in aquatic ecosystems of a temperate river network

Wollheim

Stewart

Aiken

et al. 2015

Geophysical Research Letters

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Surface waters play a potentially important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the fate of DOC in aquatic systems is poorly constrained. We used a unique combination of spatially distributed sampling of three DOC fractions throughout a river network and modeling to quantify the net removal of terrestrial DOC during a summer base flow period. We found that aquatic reactivity of terrestrial DOC leading to net loss is low, closer to conservative chloride than to reactive nitrogen. Net removal occurred mainly from the hydrophobic organic acid fraction, while hydrophilic and transphilic acids showed no net change, indicating that partitioning of bulk DOC into different fractions is critical for understanding terrestrial DOC removal. These findings suggest that river systems may have only a modest ability to alter the amounts of terrestrial DOC delivered to coastal zones.

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Separation of river network–scale nitrogen removal among the main channel and two transient storage compartments

Cited by 78 publications

References 83 publications

Effects of inset floodplains and hyporheic exchange induced by in-stream structures on nitrate removal in a headwater stream

Effects of inset floodplains and hyporheic exchange induced by in-stream structures on nitrate removal in a headwater stream

Prolonged river water pollution due to variable‐density flow and solute transport in the riverbed

Removal of terrestrial DOC in aquatic ecosystems of a temperate river network

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