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    Rights statement: © 2015 The Authors. Hydrological Processes Published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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Diffusive equilibrium in thin films provides evidence of suppression of hyporheic exchange and large-scale nitrate transformation in a groundwater-fed river

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Diffusive equilibrium in thin films provides evidence of suppression of hyporheic exchange and large-scale nitrate transformation in a groundwater-fed river. / Byrne, Patrick; Zhang, Hao; Ullah, Sami; Binley, Andrew; Heathwaite, Louise; Heppell, C.M.; Lansdown, K.; Trimmer, Mark.

In: Hydrological Processes, Vol. 29, No. 6, 15.03.2015, p. 1385-1396.

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@article{cdadf960a95b42c5ac2e500b93887f22,
title = "Diffusive equilibrium in thin films provides evidence of suppression of hyporheic exchange and large-scale nitrate transformation in a groundwater-fed river",
abstract = "The hyporheic zone of riverbed sediments has the potential to attenuate nitrate from upwelling, polluted groundwater. However, the coarse-scale (5–10 cm) measurement of nitrogen biogeochemistry in the hyporheic zone can often mask fine-scale (<1 cm) biogeochemical patterns, especially in near-surface sediments, leading to incomplete or inaccurate representation of the capacity of the hyporheic zone to transform upwelling NO3−. In this study, we utilised diffusive equilibrium in thin-films samplers to capture high resolution (cm-scale) vertical concentration profiles of NO3−, SO42−, Fe and Mn in the upper 15 cm of armoured and permeable riverbed sediments. The goal was to test whether nitrate attenuation was occurring in a sub-reach characterised by strong vertical (upwelling) water fluxes. The vertical concentration profiles obtained from diffusive equilibrium in thin-films samplers indicate considerable cm-scale variability in NO3− (4.4 ± 2.9 mg N/L), SO42− (9.9 ± 3.1 mg/l) and dissolved Fe (1.6 ± 2.1 mg/l) and Mn (0.2 ± 0.2 mg/l). However, the overall trend suggests the absence of substantial net chemical transformations and surface-subsurface water mixing in the shallow sediments of our sub-reach under baseflow conditions. The significance of this is that upwelling NO3−-rich groundwater does not appear to be attenuated in the riverbed sediments at <15 cm depth as might occur where hyporheic exchange flows deliver organic matter to the sediments for metabolic processes. It would appear that the chemical patterns observed in the shallow sediments of our sub-reach are not controlled exclusively by redox processes and/or hyporheic exchange flows. Deeper-seated groundwater fluxes and hydro-stratigraphy may be additional important drivers of chemical patterns in the shallow sediments of our study sub-reach. Copyright {\textcopyright} 2014 John Wiley & Sons, Ltd.",
keywords = "Nitrate Cycling, riverbed sediment, water quality, pollution, hyporheic zone, groundwater, pore water, DET",
author = "Patrick Byrne and Hao Zhang and Sami Ullah and Andrew Binley and Louise Heathwaite and C.M. Heppell and K. Lansdown and Mark Trimmer",
note = "{\textcopyright} 2015 The Authors. Hydrological Processes Published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. ",
year = "2015",
month = mar
day = "15",
doi = "10.1002/hyp.10269",
language = "English",
volume = "29",
pages = "1385--1396",
journal = "Hydrological Processes",
issn = "0885-6087",
publisher = "John Wiley and Sons Ltd",
number = "6",

}

RIS

TY - JOUR

T1 - Diffusive equilibrium in thin films provides evidence of suppression of hyporheic exchange and large-scale nitrate transformation in a groundwater-fed river

AU - Byrne, Patrick

AU - Zhang, Hao

AU - Ullah, Sami

AU - Binley, Andrew

AU - Heathwaite, Louise

AU - Heppell, C.M.

AU - Lansdown, K.

AU - Trimmer, Mark

N1 - © 2015 The Authors. Hydrological Processes Published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

PY - 2015/3/15

Y1 - 2015/3/15

N2 - The hyporheic zone of riverbed sediments has the potential to attenuate nitrate from upwelling, polluted groundwater. However, the coarse-scale (5–10 cm) measurement of nitrogen biogeochemistry in the hyporheic zone can often mask fine-scale (<1 cm) biogeochemical patterns, especially in near-surface sediments, leading to incomplete or inaccurate representation of the capacity of the hyporheic zone to transform upwelling NO3−. In this study, we utilised diffusive equilibrium in thin-films samplers to capture high resolution (cm-scale) vertical concentration profiles of NO3−, SO42−, Fe and Mn in the upper 15 cm of armoured and permeable riverbed sediments. The goal was to test whether nitrate attenuation was occurring in a sub-reach characterised by strong vertical (upwelling) water fluxes. The vertical concentration profiles obtained from diffusive equilibrium in thin-films samplers indicate considerable cm-scale variability in NO3− (4.4 ± 2.9 mg N/L), SO42− (9.9 ± 3.1 mg/l) and dissolved Fe (1.6 ± 2.1 mg/l) and Mn (0.2 ± 0.2 mg/l). However, the overall trend suggests the absence of substantial net chemical transformations and surface-subsurface water mixing in the shallow sediments of our sub-reach under baseflow conditions. The significance of this is that upwelling NO3−-rich groundwater does not appear to be attenuated in the riverbed sediments at <15 cm depth as might occur where hyporheic exchange flows deliver organic matter to the sediments for metabolic processes. It would appear that the chemical patterns observed in the shallow sediments of our sub-reach are not controlled exclusively by redox processes and/or hyporheic exchange flows. Deeper-seated groundwater fluxes and hydro-stratigraphy may be additional important drivers of chemical patterns in the shallow sediments of our study sub-reach. Copyright © 2014 John Wiley & Sons, Ltd.

AB - The hyporheic zone of riverbed sediments has the potential to attenuate nitrate from upwelling, polluted groundwater. However, the coarse-scale (5–10 cm) measurement of nitrogen biogeochemistry in the hyporheic zone can often mask fine-scale (<1 cm) biogeochemical patterns, especially in near-surface sediments, leading to incomplete or inaccurate representation of the capacity of the hyporheic zone to transform upwelling NO3−. In this study, we utilised diffusive equilibrium in thin-films samplers to capture high resolution (cm-scale) vertical concentration profiles of NO3−, SO42−, Fe and Mn in the upper 15 cm of armoured and permeable riverbed sediments. The goal was to test whether nitrate attenuation was occurring in a sub-reach characterised by strong vertical (upwelling) water fluxes. The vertical concentration profiles obtained from diffusive equilibrium in thin-films samplers indicate considerable cm-scale variability in NO3− (4.4 ± 2.9 mg N/L), SO42− (9.9 ± 3.1 mg/l) and dissolved Fe (1.6 ± 2.1 mg/l) and Mn (0.2 ± 0.2 mg/l). However, the overall trend suggests the absence of substantial net chemical transformations and surface-subsurface water mixing in the shallow sediments of our sub-reach under baseflow conditions. The significance of this is that upwelling NO3−-rich groundwater does not appear to be attenuated in the riverbed sediments at <15 cm depth as might occur where hyporheic exchange flows deliver organic matter to the sediments for metabolic processes. It would appear that the chemical patterns observed in the shallow sediments of our sub-reach are not controlled exclusively by redox processes and/or hyporheic exchange flows. Deeper-seated groundwater fluxes and hydro-stratigraphy may be additional important drivers of chemical patterns in the shallow sediments of our study sub-reach. Copyright © 2014 John Wiley & Sons, Ltd.

KW - Nitrate Cycling

KW - riverbed sediment

KW - water quality

KW - pollution

KW - hyporheic zone

KW - groundwater

KW - pore water

KW - DET

U2 - 10.1002/hyp.10269

DO - 10.1002/hyp.10269

M3 - Journal article

VL - 29

SP - 1385

EP - 1396

JO - Hydrological Processes

JF - Hydrological Processes

SN - 0885-6087

IS - 6

ER -